Podcaster: Shane and Chris
Title: Refracting Telescopes
Organization: Actual Astronomy
Description: The Actual Astronomy Podcast presents Refracting Telescopes. In this episode we dive into our telescope of choice, refractors, with a discussion around Achro’s, APO’s, doublets, triplets and flat field designs. We compare notes on how we were each introduced to these sleek instruments as well as our current collections of long and short instruments and conclude with how refractors actually compare with other telescope types.
Bio: Shane and Chris are amateur astronomers who enjoy teaching astronomy classes and performing outreach where they help the eyes of the public to telescope eyepieces.
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So fine. All right. Fracture episode all right. let me know when you’re ready to go all right.
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3, 2, one welcome to episode. 214 of the actual astronomy.
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Podcast through the looking glass people because Today’s episode we’re talking refractors. I’m Chris and joining me machine.
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We are amateur astronomers who love going out under the night sky in this podcast.
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Is for anyone else likes looking up on the stars. How many refractors do you own chain?
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Oh, yeah, I should account it. 1, 2, 3, 4, 5, 6 thanks.
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7 7. Oh, you win 9 I think it’s 9 there might be coming finder scopes, too, now, or what?
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No, no, these are. This is all relevant legitimate Yeah, I think it’s 9 10.
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If you want my h alpha but you know that’s that’s cheaper.
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Wow! I’ve got 6 you know 50 to 5 inches.
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Yeah, i’ve got the 50 acro that we’ve set up his ultimate wide field telescopes got my tack a hashy 60 fs i’ve got my ed 80
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or not my Eddie i’ve got i’ve got an attack hashy.
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I’ve got my 125 pentax?
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Borg: Yeah, how many sat whatever that is I think that’s 6 isn’t something like that?
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Yeah, yeah. So So i’ve got the the mini board 50 acro.
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I’ve got the board 50 fl a willie optics Xena Star, 61 ms, as I telemeter.
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That’s 63 i’ve got a very old tack, hashy ts 65 that I really should sell.
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Yeah, you said I don’t use it i’m just stepping up here.
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So then I go to a 76 tack. Dcu.
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I have a 76 Tasco, 10 te another vintage telescope, and then from there I think I jumped to the the telephone.
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Genesis, Sdf: which is 101 and then the 1 20.
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Ed: Skywatcher: Yeah. yeah, yeah. it was. It was interesting when you when you said, Hey, how about we do it?
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An episode on refractors. it’s like every episode of a refract.
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Yeah, I think part of that was going to be my first response is yeah isn’t that what we do everywhere?
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But but it’s been an oversight I think I don’t believe we’ve actually deleted into the world of refractors, and just like dedicated an episode to it.
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So. so I think this is a good choice and and I thought since it’s our birthday.
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We get to pick the episode. The actual astronomy is now 2 years old, 2 years old.
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When when there we go. Nothing screams is starting more than that long, slender tube refractor perched high upon amount.
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Do you remember your first view through one of these exquisite instruments?
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I do I was quite young I don’t know like I think, what I’ve said before on the podcast is.
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I was like 8 to 10 years old somewhere in that range, and my mom took me to the local astronomy Clubs Observatory.
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They had a public night, and in it was a 4 inch.
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Why am I drawing a blank now? it’s a vintage? brass telescope here?
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Brush here. Yes, thank you. 4 inch per year.
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I forget the focal length, but the image was saturn it’s firmly burned into my memory.
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I will never forget that, and that certain was not just like i’ve always been interested in astronomy at that point in my life. but that really like wild me as to what you could see through a telescope and
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and that really lit the fire to to pursue the hobby.
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Yeah, No, it’s yeah it’s very cool it’s just trying to look up really quick to see if we could see what was going on with that telescope.
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But that doesn’t really say what the what the focal length is of it anywhere very handy that I can find very quickly.
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But i’ve seen the telescope looks pretty long but I almost don’t want to say it’s an f 12.
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I feel like maybe it’s yeah like 10 or something like that Yeah, it would be probably in that 10 to 15 range.
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It’s quite long. Yeah, and this was made like this telescope would not.
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Well, I can’t remember remember when it was made I might be around a 100 years old now.
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Oh, it’s more than a 100 Yeah, it was it yeah it would be right around there and you know telescopes, then were certainly not mass-produced.
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So this would have been. I like a one-off that was made for the the local club, and it is now in a museum on display.
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So people can see it at the Western Development Museum in Moose Jaw, Saskatchewan.
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Yeah, I always thought it was kind of a shame that the local Astronomy Club had decided to put it in a museum.
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Might I think, feel like that’s a very odd thing but I would love to look through it one night.
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But I don’t know hopefully that happens at some point Yeah, I just I see an ad from about a dozen years ago, online just sort of cruising around, and somebody was selling one in 2,008 for fourth or for 8
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$1,000. No, they are. they are not not inexpensive Yeah, I’m trying to remember my first view through a refractor.
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Well, it was actually probably dave chapman’s I think he had like a 70 Tell of you, Ranger said what they’re called, anyway was something like that that was my first view of of anything through a refractor.
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And yeah, I was just blowing away I don’t i’d seen the ads for these things the ads for just so so gorgeous they just made you want to get one and look through it and I went to
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my first star party, and I really had wanted to look through a refractor.
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I owned an eight-inch dog at the time, and I looked through that telescope.
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And then Roy Bishop had a astrophysics starfire near 105, and I look through that.
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And then Tony Jones is 5 inch astrophysics. Think it’s a star fire as well like an F 9 or something, and I spent a long time looking through that and yeah, just just having looked through like these small
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apochromatic, or I guess the range of the Ranger was Ed, just really good little refractors, and I just was like, Oh, this is this is what I want.
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I want to get one of these these instruments. They are just so so need to look through the the star parties around here, mostly dominated by dobs and caster greens.
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They’re there definitely are refractors. but it seemed like the majority of the refractors also had cameras attached.
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So yeah, I never really looked through refractors that often until you moved here, and you brought your Borg 125. Yeah.
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And at that point I think I had my 12 inch light bridge, and you know, you and I would often be out observing at the same time, and we share views, and I just could not believe how sharp everything was through your
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refractor, and every time I walked away from your telescope I just said to myself, like man, that is such a nice view. Yeah.
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And then, as I got more and more frustrated with the hauling of a big 12 inch and the columnation, and you know, on and on, and on, finally converted over to a refractor, person I suppose I
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bought, trying to think. The first serious refractor that I bought was well, I had an 80 William Optic, that I never used too much.
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So then my my next real purchase was the 120 ed which I really loved, and I kept the light bridge, I think, for another 2 years before I ended up selling it.
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But didn’t use the light bridge anymore at all once I got the refractor.
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I just had so much fun with it. so the light bridge is no longer mine. And now I have a stable of refractors.
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Yeah. And yeah, after after viewing through a 5 inch apocr amount like I’d look through smaller ones.
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And then I really decided that was the instrument for me you know we’re talking the last episode. i’d like to get like a more permanent setup for it you know.
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And that’s really really my goal like my wife asked me just to like.
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Well, what what telescope do you want to put in like a like a small observatory?
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And I said, Well, 5 inch because that’s that’s really just such a great all-round instrument wide field awesome on planets, you know.
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And it really really can go deep. I ran it quite a bit against like a really high-end 8 inch reflectors, and you know it’s right up there.
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So it would see as deep as an eight-inch reflector, more or less, for like very very close.
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And and then you got this huge field of view, so it, you know, really could serve double duty as a telescope that can run with, you know, substantially larger instruments, as well as give this huge wide field of view
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and to me that just, you know, equates to kind of like a instrument.
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So. and just like like you, said the aesthetics of those crystal, clear and and sharp images that the that the refractor shows.
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Yeah, and you know I think we’ll probably get into some of the pros and cons of different designs.
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As we go through this episode, because not all refractors are the same, and there are some nuances to be aware of.
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If anybody is interested in making a refractor purchase.
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Yeah, I just want to run through. Is there some pretty large?
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Them famous refractors, you know and until you know the the twentieth century that the refractor was the big instrument a trace for the observatories.
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And it’s really stuck I think it in you know in the public’s mind, everybody’s mind as sort of a quintessential observatory instrument but you know that really has been the case for really for over a
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century, but some of the largest ones, like the 40 inch yurks is the largest in in operation as far as being a telescope.
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You can actually go and and look through, Though there was one in Paris for an exhibition which I think was around 1,900.
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It was slightly larger, and then there’s a giant solar one, but I think it just like casts an image.
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It’s not like tube mounted and it’s in like a special solar observatory, but as far as being like a traditionally refractor on amount the year’s 40 inches. is the largest i’ve never been there to see
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it. I went to to the Lick 36 inch, but it was closed on the night that I I went up.
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I had hoped to to look through that that’s in California in Paris.
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There’s the mud on 33 or m just outside of Paris.
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That’s another pretty famous pretty famous one there’s the us naval observatories, 26 inch, and then there’s the famous Lull observatory, 24 inch.
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Now there’s 3 and There’s lots of different large refractors to be in between all these as well, but that there’s a nice list on on Wikipedia.
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People can go through of the world’s largest refractors think they list like the largest 50 refractors in the world, or something like that.
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Yeah, and it’s just kind of neat to to take a look, and and to see through them all.
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But yeah, i’ve i’ve never been been fortunate to go and and look through any of those large ones.
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But, boy, I sure would love to look through some of the large refractors someday.
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Yeah, it would be amazing. even the the refractor that Mark Ricci was telling us about. I think it was the second episode. maybe, that he joined us.
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Yeah, I forget the observatory name. I think I have it bookmarked here.
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But yeah, he did. an episode on his refreshing use Youtube channel about it. wasn’t it like 9 inch or something like that.
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Something like that. Yeah, I can’t remember it’s decent size. And yeah, I did some imaging through it.
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And yes, it was really fun. Yeah, yeah, yeah, definitely. you know, when when my wife and I travel, we we pick destinations based on you know, history and culture and some of the excuse me, some of the things we look for nice restaurants or entertainment.
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But certainly on my list now is is observatories where I could look through big refrigerators, and you know, if I can fit that into some of our travels i’ll definitely be making that a priority Yeah, I certainly
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would would like to as well I just haven’t landed in a spot that that has any, or 2 I guess just for the sake of actually going into some my own astronomy.
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I think there’s some pretty good sized clerks in Florida, but when i’m been down there and and keen to go to some astronomy, I I you know myself in spots that were going to
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be dark and good for doing astronomy and they tend to be far away from from those locations.
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Let’s see, so there’s there’s sort of 2 main types of refractors.
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When we talk about refractors, we have acrimatic or acrimat, and fractures, or appo, or apocratic refunders.
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So so shame what what’s an acrimatic refractor.
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Maybe we’ll start there. Well, I don’t know the like the textbook definition.
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But basically an acrimatic refractor it won’t have the color correction of an appo. But it’s It’s essentially designed to limit the effects am I reading this right here.
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Yeah, the i’m reading your definition here so why don’t I just start with that.
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Yeah, just add a lens or acrimat is a lens that is designed to limit the effects of chromatic and sphere collaboration.
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The acromatic lenses are corrected to bring 2 wavelengths into focus on the same plane.
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One element is a concave element, or a negative made out of flint glass, such as f 2, which has a relatively high dispersion, and the other is a convex positive element made of crown glass such as bk 7 which has lower dispersion
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So these lens elements are mounted next to each other, often cemented together and shaped so that the chromatic aberration of one is balanced out by the other.
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Yeah. yeah, yeah, I mean, a lot of the older telescopes are acrimats, and you know the one of the one of the things to make an acromat perform.
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Better is. you have a very long focal length, you know.
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Really to an apple so like my tasco 10 te is a 76 telescope for aperture, but it’s 1,200 in focal, length, so
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it’s like almost an f 16 which is unheard of with modern telescopes for the last part.
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Yeah, So just kind of break this down a little bit basically what the acrimats are doing is there’s there’s kind of there’s kind of sorta and i’m kind of fudging this around a bit but
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there’s There’s sort of 3 wavelengths of color that the telescope is trying to draw into focus.
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There’s red, green, and blue. So and basically the acrimats are gonna bring in 2 of those really close together or overlapping.
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So you get a nice sharp focus in in 2 colors or or a very, you know, very, very close and 2 colors.
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And then there’s there’s one that that kind of is a bit of an outlier, and so what what we see, and and at least what we often see like in a really fast acrimat like an 80 f 5
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you point it out a bright star you’ll see a giant sort of purple haze around it. Okay, Yeah, yeah, it introduces some color, and and like for brighter objects.
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So this is particularly with the planets. Sometimes that color can take away your ability to like kind of see that fine detail or the contrast that’s needed to pull out subtle differences like on Jupiter or Mars yeah But the
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acrimats can be well made, you know, like these older instruments, you know, like we were talking about for more than a century ago, you know.
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They would give very sharp images, even though they would have some of the secondary color.
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But, like shame, was saying, to compensate and to bring that third color in closer to those other 2.
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They increase the focal length of the telescope of the focal ratio, and so that that does a variety of things.
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One of the things that it does is it makes the light cone less steep.
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So it’s easier to bring the colors. the colors are just naturally going to be close together.
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And then the other thing is is that the actual focus range of the telescope.
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It’s not could be tight so it’s going to be easier to hit that sweet spot, so kind of does a variety of things.
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But those are like the 2 main ones that that help out to get everything into sharp focus.
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Yeah, yeah, like my my Tasco tente is a phenomenal telescope.
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My Zeus telemeter that’s a 63 by 840 focal length. It’s also outstanding. So there there certainly are some good ones out there yeah and not
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everybody’s as sensitive to the the color correction, like you know you, you know, and, in fact, like you know honestly like I’m, not that sensitive to the color correction.
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But but I do find like that. Takahashi has the best color correction of my instruments.
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But you know I i’ve been looking at like jupiter and the moon with the the 50 acrimats that that we met up last year, and they’re pretty fast, you know f 5 so but but you
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know, Still, great great views really enjoy them. So I talked briefly, like in my notes about the elements flint glass, such as F.
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2, and then Bk: 7 and glass. So the the f 2 flink glass that’s like just pretty common glass, like, if you you know, took time machine back 20 years or 30 years and went to get glasses, and you were just getting regular
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glasses a lot of the glass that you would get. I believe, anyone or not optician or anything.
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I believe a lot of that would be like a flint glass, and then bk 7.
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That might be familiar to people, because in the less expensive binoculars, you know those binoculars that would give those almost like diamond, like eggs of people.
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Shame if you’ve been through a pair like that before. Yep. Yep, for sure that’s pk 7 glass. that’s that’s being used in those binoculars.
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But now, just because maybe in the binoculars you want Bk: 4 glass, because the bk 7 doesn’t work as well in binoculars, I believe Bk: 7 glass can work pretty good for making a decent
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acrimatic refractors. so it’s not really like a strike against the the telescope that it’s using that type of glass.
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Yeah, yeah, exactly. And and that is that is kind of a like an important part of refractors, or at least something that you may wonder about.
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If you start looking at refractors, is, what does this all mean?
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With the different glasses that are used, because it seems like every manufacturer has their own glass or mating system that they’ll use to, you know.
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Correct for you and aberrations and other things so I think we’ll get into that as we go through.
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The episode. it’s just what some of these different classes mean in terms of quality. Yeah.
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And there’s there’s a few different types of design that have become popular.
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There’s, there’s quite a few types but i’m going to kind of list sort of the the main ones as far as the the designs, and we’re not going to go into each one of these in any detail but there’s
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the franhoff for design by joseph franhofer, who’s a famous optician, created the spectrograph, and discovered, you know, the those dark bands in the spectrum.
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There’s Clark design refractors oil space designed actually chromatic refractors and stainile or stenhile. I’m.
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Probably not saying that correctly. but those are kind of like the main types of refractors like.
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If you just went and pulled a refractor off the shelf.
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It’s gonna be one of those types probably a front hofer or a stenhile.
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They’re probably going to be your your top top designs there.
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So how does color come in to play and like? How How can you know what color impacts the focal ratio of the particular acrimat you have will will impact your view.
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Well, first of all, like, you need a little bit of experience.
00:21:28.000 –> 00:21:42.000
So even if you just look through like an 80 f 5. you can pretty quickly figure out a bit of a calculation, and it’s called the Conradi standard and there’s like a bit of a
00:21:42.000 –> 00:21:52.000
sliding scale. If you look up conradi standard and graph, you’ll actually find this this chart. it’s like kind of looks like a bit of a spreadsheet.
00:21:52.000 –> 00:22:07.000
Chain, I think, is probably what it is kind of a matrix yeah and it’s pretty famous for actually describing like how much color you’ll see, or how much color you likely won’t see knowing that everybody is a little bit different
00:22:07.000 –> 00:22:20.000
the generally what you’re looking at is your objective in you know, in inches and millimeters as a ratio with with the focal ratio.
00:22:20.000 –> 00:22:33.000
So for for example, like let’s just pick something easy i’m looking for like well, like a 4 inch let’s see like a 4 inch refractor.
00:22:33.000 –> 00:22:48.000
Okay, That’s f 8 what you’re gonna divide the 8 divided by 4, gives you a boat 2, and that’s going to sort of land rate in the middle of what they call like filterable levels of chromatic
00:22:48.000 –> 00:23:05.000
aberration. Now, if it was like f 4 or f 5 that’s getting into a level that is too much chromatic operation. and then, if you’re 4 inch was like go like an f 12 that’s where
00:23:05.000 –> 00:23:13.000
a 4 inch begins to have minimal or no chromatic aberration visible for for the average person.
00:23:13.000 –> 00:23:18.000
So basically 3 times the aperture and inches.
00:23:18.000 –> 00:23:29.000
So now, if you took like a five-inch telescope, you’ve got to multiply 5 by 3, and that’s going to give you 15, so you need to get the f 15.
00:23:29.000 –> 00:23:36.000
So you can see quickly. these telescopes get longer longer and longer, almost like exponentially, but by the aperture.
00:23:36.000 –> 00:23:53.000
Well, of course they are, because you’re just you’re just increasing the longer focal length that’s needed in order to reduce that secondary color, and but like I own an 80 f 5 which puts a
00:23:53.000 –> 00:23:57.000
pretty close, but not quite over the line for unacceptable levels of Ca.
00:23:57.000 –> 00:24:08.000
And it’s fine like I enjoy, viewing with it you know there’s there’s sort of an application for these type of telescopes in for sure, and and it kind of is like you you you know you use
00:24:08.000 –> 00:24:13.000
the right tool for the right job, and with these super fast acrimats.
00:24:13.000 –> 00:24:27.000
They’re not intended to be used on the planets or bright objects like you’re looking at you know extended deep sky objects, you know, wide field that’s that’s the real purpose there, so you know as long as
00:24:27.000 –> 00:24:34.000
you’re not using high magnification on jupiter you’re probably going to be quite quite fine with that telescope.
00:24:34.000 –> 00:24:45.000
Yeah, and you’ll see like there’s a lot of a good example of this is there’s a lot of like 6 inch f 8 acrimats, and the rate on that acceptability line between filterable levels and
00:24:45.000 –> 00:24:59.000
unacceptable chromatic aberration and then you’ll see lots of 6 inch f 5 telescopes at there that are, you know, rate in well within that unacceptable level of chromatic
00:24:59.000 –> 00:25:02.000
aberration zone, but like you were saying shane the secondary color.
00:25:02.000 –> 00:25:16.000
That’s sort of purple haze that we talked about earlier that will appear around bright objects, and and maybe wash against some of that fine planetary detail doesn’t really apply as much on the deep, sky so people that are
00:25:16.000 –> 00:25:23.000
buying 6 Inch F 5 instruments they’re hopefully not buying them to look at the planets or the moon.
00:25:23.000 –> 00:25:29.000
What they’re doing with them is looking and comets for example, I knew somebody that had a 6 in J.
00:25:29.000 –> 00:25:32.000
F 5. I was sort of be cool to look at it.
00:25:32.000 –> 00:25:35.000
They brought it out one night when Comet Holmes was in having its big o purse.
00:25:35.000 –> 00:25:43.000
There all those years ago, and just had this amazing view of common homes through through the six-inch refractor.
00:25:43.000 –> 00:25:47.000
But I don’t think we can bother putting it on a planet that night.
00:25:47.000 –> 00:25:52.000
They’re deep sky machines yeah yeah that’s exactly it Yeah, Yeah, that’s where you use them.
00:25:52.000 –> 00:26:08.000
And if you stick with that again, you’ll probably be pretty happy, you know, as a side conversation to this discussion about refractors is the focal length, speed, or or a fast scope versus a slow scope the other thing, with a faster
00:26:08.000 –> 00:26:15.000
telescope is, they are a little harder on eye pieces, meaning, you know you need a better eye piece to correct the field at the edges.
00:26:15.000 –> 00:26:26.000
Particularly wider field eye pieces. So something else to keep in mind that if you go with an F 5 reference or your your’re going to require eye pieces that are well corrected.
00:26:26.000 –> 00:26:32.000
Otherwise the stars look like kind of check marks or or doves, or you know.
00:26:32.000 –> 00:26:36.000
Some people say v’s but anyway, they’re no longer pinpoints the further from center.
00:26:36.000 –> 00:26:49.000
You get Okay, all right maybe I’ll read the definition for the apocrats sure go for this, since my notes are a bit scattered, so the apocalypse they’re better corrected for
00:26:49.000 –> 00:26:56.000
chromatic appreciations aren’t going to have as much that color They’re attempting to bring in the 3 primary Rgb.
00:26:56.000 –> 00:27:15.000
Red, green, blue colors into focus at the same spot. They typically have less spherical aberration, and these lenses are using optical glasses with special dispersive properties to get those 3 colors to to commit a
00:27:15.000 –> 00:27:28.000
sharper focus. So this is a cheap using fluoro crown glasses, often referred to as fluoride, or the more modern version of that, I believe, which is Fpl.
00:27:28.000 –> 00:27:37.000
53 and they’re using abnormal flint glasses such as land, I think, like i’m gonna go and limb lanthanum.
00:27:37.000 –> 00:27:50.000
I think that’s what what you know that the text that I was reading was was referring to as abnormal and classes, and you’ll even get these these glasses being combined with some sort of optical transparent
00:27:50.000 –> 00:27:54.000
liquid in between them to to sandwich the lens together.
00:27:54.000 –> 00:27:58.000
But you know, sort of breaking it down a little bit further.
00:27:58.000 –> 00:28:10.000
We not only have acrimatic and apochromatic telescopes refactors, but there’s also the semi app but remember, they used to call them semi-appos chain.
00:28:10.000 –> 00:28:16.000
You remember that? Then they eventually just sort of had honed in on the on the E common ed telescopes.
00:28:16.000 –> 00:28:18.000
Yeah. Well, my, my tea at my Takahashi.
00:28:18.000 –> 00:28:26.000
Ts. 65, so it’s a 65 aperture, 1,000 focal length, telescope.
00:28:26.000 –> 00:28:41.000
This was, I believe, released in 1,971. it’s a triplet, meaning 3 3 objectives to form the the main lens area. But it’s labeled as a semi-apocrat.
00:28:41.000 –> 00:28:49.000
So yeah, you know It’s kind of funny, because it it really performs like an apocrypha, or at least what we consider apocalypse today.
00:28:49.000 –> 00:29:01.000
Yeah. So the semi-happy it’s a term used to to describe something, it’s a little bit better than the typical front hofer acrimatic refractor, but not quite as well corrected as the
00:29:01.000 –> 00:29:05.000
apocrats, and these are sometimes more properly called.
00:29:05.000 –> 00:29:10.000
Now Ed Telescopes, or Edie refractors.
00:29:10.000 –> 00:29:16.000
And And as with all of these type of refractors can be downright excellent, and they’re using low dispersion glass doublets.
00:29:16.000 –> 00:29:28.000
Typically, although, like you, said, yours was a was a triplet there. So there’s a lot of different varieties of these, and certainly you can find them in in a variety of different config But typically they have at least one special
00:29:28.000 –> 00:29:35.000
dispersion element to focus virtually all wavelengths of light extremely close.
00:29:35.000 –> 00:29:46.000
But they’re not quite getting there, but it results in pretty darn good in focused star images, and they’re typically doublets, and they have some sort of fancy glass.
00:29:46.000 –> 00:29:57.000
Is what it boils down to, and that the fancy glass that one of my telescopes had was, I think, it was called shot class, or 51.
00:29:57.000 –> 00:30:02.000
I feel 51, and it was it was pretty good although like when I was reading around like sometimes they’ll refer to Fpl.
00:30:02.000 –> 00:30:06.000
53 as being in this. and typically I thought Fpl.
00:30:06.000 –> 00:30:21.000
53 was more like the fluoride glasses so it just depends on like what glass is being used and the meeting elements, and that whether it’s going to be deemed as apocratic or or ed and let’s see so
00:30:21.000 –> 00:30:26.000
they’re trying to bring in 3 wavelengths of light and typically with the ed.
00:30:26.000 –> 00:30:34.000
It allows the green spectrum to drift off so and i’ve seen this as well with the with the ed scopes.
00:30:34.000 –> 00:30:50.000
Often you’ll see more like a green spurous color than then you will with the acrimats, which will have more of this purple halo, and it’s really just how much they drift away from that green you know
00:30:50.000 –> 00:31:04.000
that allows me to claim that It’s that it’s semi-appo, and I’ve seen that in particular, with especially some of the really early like Orion Ed Eightys for example, we would put it on like Cirrus or other bright
00:31:04.000 –> 00:31:18.000
stars, or the moon and you’d be able to see just this little bit of a green cast along the limit, and in fact, really, with our little 50 acrimats I find that I get more of this green cast even though they’re
00:31:18.000 –> 00:31:20.000
they’re acrimatic I think just because they’re so small.
00:31:20.000 –> 00:31:26.000
But that’s really what you’re seeing when you and you have a semi-proachment.
00:31:26.000 –> 00:31:31.000
Okay, go ahead. Yeah, I was just gonna say to 1 one nuance with fluoride.
00:31:31.000 –> 00:31:46.000
Is that it’s it’s actually crystal whereas the Fpl’s are truly glass right Now fluoride is far more expensive, because it’s harder to come by it’s harder to work, with but the
00:31:46.000 –> 00:31:51.000
real advantage, or I think there’s a number of advantages with fluoride.
00:31:51.000 –> 00:31:58.000
But one of them that I was just reading about although there’s a little bit of I don’t know if everybody’s in agreement with this, but glass.
00:31:58.000 –> 00:32:04.000
No matter what version you’re getting fpl 5153 or 55
00:32:04.000 –> 00:32:09.000
They have micro bubbles in them and that’s just the inherent nature of glass.
00:32:09.000 –> 00:32:15.000
The crystal doesn’t have those microbes in them and as such.
00:32:15.000 –> 00:32:25.000
There’s less dispersion within. the glass or within the fluoride compared to glass, although some people say it wouldn’t really be detectable by your eye hard to say.
00:32:25.000 –> 00:32:35.000
You know what I can say, for sure is that the talk the taco hashi telescope that I have with fluoride does take magnification exceptionally.
00:32:35.000 –> 00:32:41.000
Well, now, not all of that, though, is just because it has fluoride in it.
00:32:41.000 –> 00:32:49.000
The other aspect here is just the attention to detail on the polish of the of the lens, so you could have fluoride.
00:32:49.000 –> 00:33:03.000
But if it’s not polished correctly it’s going to be a terrible performer, So there’s a little bit of the manufacturing quality that goes into this as well as the quality of the glass or yeah, the quality of
00:33:03.000 –> 00:33:18.000
the objectives. and if people want to read up on on the glass, and kind of how all this stuff maybe works together, if you want to dive deeper, more deeper, than when we went to here, I the real book on this is by Greg
00:33:18.000 –> 00:33:28.000
Smith, Rogers, or Geoli and richard Barry. it’s called telescopes, I pieces and astrographs, design, analysis and performance of modern astronomical objects.
00:33:28.000 –> 00:33:43.000
Of course it of print, and but you might be able to find it through a friend, or through an astronomy library, or maybe even your your local library might be able to to track down a copy to get in for you But that’s i think
00:33:43.000 –> 00:33:47.000
that’s the sort of the definitive book not that old either Let’s see.
00:33:47.000 –> 00:33:56.000
Okay, So there’s a variety. of elements that can be used so far we’ve really talked about doublets and a little bit about triplets, and it’s it’s fairly simple isn’t.
00:33:56.000 –> 00:34:00.000
She like double It’s 2 elements triplets 3 elements and quadruplets.
00:34:00.000 –> 00:34:11.000
Guess what they have, how many elements or so let’s see the more elements, the more expensive, more or less agree.
00:34:11.000 –> 00:34:18.000
Yeah, yeah, the the more elements the more expensive because you’re just there’s more glass there.
00:34:18.000 –> 00:34:26.000
But then there’s also a lot more in the manufacturing that has to happen to make sure that all of those elements work well together.
00:34:26.000 –> 00:34:39.000
Yeah, spacing some of them have oil in them so the alignment of those lenses as well needs to be bang on, or else the telescope will not perform very well.
00:34:39.000 –> 00:34:48.000
Yeah, so it’s kind of like like you know and I was I was thinking about like the differences like, Why have 2 elements versus 3 or 3 elements instead of 4?
00:34:48.000 –> 00:34:53.000
Why bother going 4 elements? You know the the only thing I can really say about that.
00:34:53.000 –> 00:35:01.000
And having looked through a variety of triplets, is that you can get a slight bump in color correction by by going to the triplet.
00:35:01.000 –> 00:35:11.000
But really this is something I think that almost becomes something that’s visible, just sort of through images like if you’re imaging with the telescope.
00:35:11.000 –> 00:35:27.000
And then the quadruplets again, they’re They’re being created for basically wide field flat field, not necessarily planetary imaging, or having really flat, wide field of views like your U of the television Petsville design no Vixen
00:35:27.000 –> 00:35:34.000
has made some pedestals as well. But what kind of comments do you have for the doublets, triplets, and and quadrupling?
00:35:34.000 –> 00:35:40.000
Well, I really like the doublets because they cool quickly and they’re they’re relatively light.
00:35:40.000 –> 00:35:47.000
So you know, 120 doublet is far later than 120 triplet.
00:35:47.000 –> 00:35:51.000
So I am a big fan of the doublets. I do have a tell of view.
00:35:51.000 –> 00:35:55.000
Genesis, Sdf. which is a pets full.
00:35:55.000 –> 00:36:02.000
This is a very interesting design, because what it does the telescope lens that’s in that in the telescope itself.
00:36:02.000 –> 00:36:06.000
So a pets full has 2 elements at the front, and then 2 elements at the back of the tube.
00:36:06.000 –> 00:36:14.000
Essentially, and the 2 elements at the front are something like an F, 10 or an F.
00:36:14.000 –> 00:36:23.000
11 focal length. However, the telescope itself is actually like F, 5, point, 4, or something.
00:36:23.000 –> 00:36:34.000
So the 2 elements at the back one while they work in conjunction to like you, said Flatten the field, but also reduce the focal length essentially like there’s a reducer there.
00:36:34.000 –> 00:36:46.000
The so it can take a longer focal length lens and then package it into a much smaller tube. so it’s It’s a very interesting design collimation.
00:36:46.000 –> 00:36:52.000
Is exceptionally important when you have 4 lenses meaning they’re all aligned properly.
00:36:52.000 –> 00:36:58.000
But anyway, what what ends up happening is you get a very wide field telescope.
00:36:58.000 –> 00:37:09.000
That is exceptionally flat. and when we say flot we mean, then, that all of the stars in that field of view are sharp or pinpoints right to the edge.
00:37:09.000 –> 00:37:13.000
That’s a hard thing to achieve you know it’s.
00:37:13.000 –> 00:37:23.000
If anybody is in the world of like project management there’s the the pyramid or the you know the the 3 points of you know. what is it fast, cheap, and high quality?
00:37:23.000 –> 00:37:30.000
You know. Pick any 2 you can’t have all 3 you know with a pets full.
00:37:30.000 –> 00:37:38.000
You’re sort of getting everything whereas with other designs or sometimes some trade-offs that you have to consider.
00:37:38.000 –> 00:37:42.000
Yeah, I’m, i’m more a fan of the conjoined triangles of success than anyway.
00:37:42.000 –> 00:37:51.000
All right. Yeah. So there’s and there’s a couple others that have built them as well like Vixen had a 140 that was like a pencil design.
00:37:51.000 –> 00:37:56.000
And then I know the new Macro. I think they called that or the Yeah, or something.
00:37:56.000 –> 00:38:03.000
Yeah, the neo and I think there was a couple different versions of that in not quite a 6 inch size, 140
00:38:03.000 –> 00:38:16.000
And then breastser actually has, and sort of like one of those things that there has caught my attention is these breaster, and I know Astros app was supposed to come up with it for a long time a for element and I always
00:38:16.000 –> 00:38:30.000
thought those ones would be interesting i think they’re again. like you were saying like an f 10 or an f 11 that work more like an f 5 in the 6 inch size, but pretty pretty heavy scope, and longer often longer than than
00:38:30.000 –> 00:38:35.000
what that short focal ratio would maybe otherwise require.
00:38:35.000 –> 00:38:39.000
So definitely some trade-offs there, and kind of like what you were saying.
00:38:39.000 –> 00:38:41.000
You know some of these telescopes with more elements.
00:38:41.000 –> 00:38:48.000
Of course they’re going to be heavier and not as portable and therefore have They’re going to require some longer cool down time.
00:38:48.000 –> 00:38:57.000
Say absolutely yeah like like My little 50 doublet requires no cool downtime and it really doesn’t matter.
00:38:57.000 –> 00:39:05.000
The temperature swing it’s pretty much instant my 120, Ed, if it’s a big temperature swing probably 30 min.
00:39:05.000 –> 00:39:16.000
But if I had a 120 triplet it that 30 min is easily doubled, maybe even more than that, depending on the temperature swing.
00:39:16.000 –> 00:39:24.000
Yeah, it really does play a factor, and in it that that aspect of it depends kind of where you live, where you and I live.
00:39:24.000 –> 00:39:33.000
There we we can easily have you know, our houses at 20 degrees, Celsius indoors, and go outside where it’s minus 20 degrees.
00:39:33.000 –> 00:39:40.000
Celsius. Yeah, a 40 degree swing is wild and you know having a fast cooling telescope is important.
00:39:40.000 –> 00:39:58.000
Yeah, no, that’s that’s for certain and Then sort of throw through some confused into this doublets can also be quadruplets, because you can add in additional like field flattener sets of optics, like but the board systems like We have a
00:39:58.000 –> 00:40:08.000
couple of the Borgs here, and you can purchase field flatters for those which are another set of lenses that that you kind of fit in.
00:40:08.000 –> 00:40:13.000
Down towards the Ip end, and then that turns it into more like an astrograph.
00:40:13.000 –> 00:40:26.000
Not really for visual purposes, but they they tend to be, you know, wide field, flat field, well corrected instruments for for doing like deep sky photography.
00:40:26.000 –> 00:40:38.000
But I really enjoy the board. 5 inch, anyway, and and the other ones I’ve looked through are pretty neat, too, simply because you know, at reasonably fast folk ratios like F 7, or so you get that really wide field of
00:40:38.000 –> 00:40:44.000
view, and and still extremely good color correction into that apochromatic range.
00:40:44.000 –> 00:40:54.000
Absolutely. Yeah. So one thing I put in here towards the at the end of the notes is because this is one thing I was always wondering about.
00:40:54.000 –> 00:41:09.000
You often hear about how refractors punch above their weight. and I think the one thing that we’ve talked a lot about here is their ability to cool down really fast, and and you and I have both witnessed this more times we can
00:41:09.000 –> 00:41:15.000
count is, is that these small instruments they cool so fast that you can see so so much more.
00:41:15.000 –> 00:41:28.000
And whereas a lot of people, when when we’re going, observing especially like on a work night, or something, might not only be going out for for a couple hours, when you’re able to use the majority of that time for your
00:41:28.000 –> 00:41:32.000
observing, whereas some telescopes might take a couple hours to cool down.
00:41:32.000 –> 00:41:40.000
Definitely really makes these seem like magical instruments compared to larger, slower, cooling instruments. saying, Oh, yeah, yeah, they do.
00:41:40.000 –> 00:41:44.000
And and that’s something that I really enjoy just set it set it up.
00:41:44.000 –> 00:41:56.000
And you know pretty much good to observe. in a you know by the time you get your I piece in and your star charts out, You know everything’s ready to go Yeah, I remember the time I remember when I when I was pretty sure you were gonna buy
00:41:56.000 –> 00:42:10.000
a refractor. You had your 12 inch, and and I set up my 5 inch apocrat, and I was, you know, on my third or fourth or fifth object, or something, while you were doing your optical alignment, and
00:42:10.000 –> 00:42:19.000
our remember, like you were just looking at me, looking at what you were doing, and you know you were the better part of half an hour, 45 min setting up, and I was already, you know.
00:42:19.000 –> 00:42:27.000
Well into the the observing session and and that definitely has has a pretty big impact, as well like it does.
00:42:27.000 –> 00:42:34.000
Yeah, yeah, it all adds up to my preferred way of observing, I still love reflectors.
00:42:34.000 –> 00:42:39.000
I think they’re amazing. Yeah, i’ve looked through some outstanding Casa Greens.
00:42:39.000 –> 00:42:52.000
They’re also great telescopes I used to own some 5 inch back sudoves, and you know where I’ve settled for how I like to observe it really is refractors for me you typically You
00:42:52.000 –> 00:43:05.000
know, as you said you’re observing a lot faster. but you can get wider fields of view, and it really is hard to beat just how sharp the views are through a refractor.
00:43:05.000 –> 00:43:19.000
The the pinpoint stars. the the high detail on planets like what blew my mind to with reporting is, is, I had an 8 inch Dobsonian, and then a 12 inch top Sonian and when I would look at
00:43:19.000 –> 00:43:24.000
Jupiter like I would see the the 2 equatorial bands and the polar regions.
00:43:24.000 –> 00:43:40.000
But usually that was about it. when i had my 120 Ed. I’ve seen some outstanding views of Jupiter, where I can see festoons and color variations within the great red spot and like
00:43:40.000 –> 00:43:45.000
jayedness through all of the cloud bands, like some really impressive detail.
00:43:45.000 –> 00:43:49.000
On and on some nights of outstanding seeing it’s almost photographic.
00:43:49.000 –> 00:43:53.000
Yeah. and I just never saw that level of detail with my Newtonians.
00:43:53.000 –> 00:44:00.000
Now there’s other factors that could have been at play like I have better eye pieces now, and i’m a better observer.
00:44:00.000 –> 00:44:03.000
Now than I was then. So some of that all factors in.
00:44:03.000 –> 00:44:07.000
But just really enjoy the the views that they present in the ease of use.
00:44:07.000 –> 00:44:15.000
Yeah Em: We’re not trying to sell anybody on sort of the refractor reflector to debate or anything like that.
00:44:15.000 –> 00:44:27.000
And one of the one of the things that has aided me in in going down the the Refractor road is Many of my observing friends have have good size reflectors, and I and I love looking through those instruments.
00:44:27.000 –> 00:44:31.000
So people shouldn’t then I know sometimes people say Oh, like you’re a refractor guy, or whatever i’m like.
00:44:31.000 –> 00:44:47.000
Well, i’m the owner of refractors but the user of factors and reflectors, and, like I said the the only reason why my 12 inch isn’t up and running my 12 inch reflector is just that every time I want to look
00:44:47.000 –> 00:44:56.000
through a twelve-inch reflector I call mike, because he’s much better at getting it set up and aligned, and all that stuff, and and he’s really awesome at finding stuff.
00:44:56.000 –> 00:45:00.000
So you know, makes sense, and I want to look at a variety of different things in the sky.
00:45:00.000 –> 00:45:12.000
And yeah, it’s always great to just have other observers with with the big reflectors, and then set up one of my refractors next to it, and and we go back and forth and and take a look at all kinds of different stuff
00:45:12.000 –> 00:45:19.000
So yeah, just really love those sessions, the ability. Just just look through different different instruments.
00:45:19.000 –> 00:45:31.000
But I will say this because one of the questions that that i’d had, and I know a lot of observers have like what’s a comparable refractor to reflector comparison you know and you’ll see
00:45:31.000 –> 00:45:35.000
some people say like Well, they punch above their weight there’s reasons for that.
00:45:35.000 –> 00:45:39.000
We discussed the cool down time and set up time in particular.
00:45:39.000 –> 00:45:43.000
But there also are some other factors that come into pay play.
00:45:43.000 –> 00:45:58.000
One is that off 9 people won’t have the reflectors properly aligned, although typically the folks that we observe with our are aligning their options up pretty good. and then the the other is simply the the physics, of
00:45:58.000 –> 00:46:08.000
having a central obstruction, and that definitely cuts down on the light coming in as well as some of the contrasting properties of of the instrument.
00:46:08.000 –> 00:46:20.000
Say 2. Yeah, yeah, like a typical Newtonian will probably be in that 20 to 25% range for the size of the central obstruction, which is the secondary mirror.
00:46:20.000 –> 00:46:25.000
I think Casser Greens and Max are in that. like closer to 30%.
00:46:25.000 –> 00:46:36.000
Yep. So there’s that aspect that does take away. you know some of the light gathering, and then, like with a refractor, you have the spider veins that hold that secondary.
00:46:36.000 –> 00:46:40.000
Mirror that can sometimes also impact the image and it’s just different.
00:46:40.000 –> 00:46:54.000
So like a bright star through a reflector, assuming that the veins are just straight on veins like the the star sort of has like a like a cross, or like a plus sign, you know, in terms of diffraction spikes
00:46:54.000 –> 00:46:58.000
whereas a refractor, or like a to cast a green or a Mac.
00:46:58.000 –> 00:47:03.000
It’s like concentric circles around the bright object is what you get.
00:47:03.000 –> 00:47:21.000
So just a slightly different view. Yeah. So in and in the field of my comparisons in particular, using my five-inch, a Parker mount a really good one, and comparing it to friends like really well maintained sometimes vintage
00:47:21.000 –> 00:47:36.000
like 8 inch optical craftsmans or custom-built 10 inch reflectors as well as my 6 inch into 67 Russian Mike Suhov.
00:47:36.000 –> 00:47:42.000
I like. I came up with a fairly simple formula for how it all compared to me, and it’s sort of a plus or minus kind of thing here.
00:47:42.000 –> 00:47:50.000
But it’s a it’s a pretty close approximation and that’s that you simply subtract the sort of essential obstruction.
00:47:50.000 –> 00:47:54.000
Ratio by by the by, the instrument.
00:47:54.000 –> 00:48:03.000
So, for example, with with my Russian Max Suitov, which is about 150 and a 30% central destruction.
00:48:03.000 –> 00:48:11.000
Give or take that ends up being a but like a 45, or 50 size.
00:48:11.000 –> 00:48:17.000
If you took like 30% of 150. And so there for that instrument to me.
00:48:17.000 –> 00:48:29.000
Anyway, when I look at the planets, the view, like sort of the aesthetic view is very similar to what I would get through like a really good four-inch apocratic telescope?
00:48:29.000 –> 00:48:38.000
Now what what you gain with the larger instrument is an increase in resolution, but it’s harder to see that increase in resolution.
00:48:38.000 –> 00:48:55.000
But you definitely can see slightly more resolution, However, because of the obstruction and atmospheric seeing conditions central obstructions will degrade the instrument down to my opinion a level that’s equivalent to
00:48:55.000 –> 00:49:07.000
like in this instance, this example are really good for inch instrument sort of going. going back to the reflector versus refractor.
00:49:07.000 –> 00:49:20.000
We compared quite extensively, and optical craftsmen and excellent, perfect, well-maintained condition to to my 5 inch apartment.
00:49:20.000 –> 00:49:26.000
And so I think the secondary on that was about like an inch and a half, or maybe like 1.6 inches.
00:49:26.000 –> 00:49:31.000
And then the the optical craftsman wasn’t quite an eight-inch telescope.
00:49:31.000 –> 00:49:42.000
We figured out it wasn’t wasn’t quite there So when it was all said and done, we determined that the optical classroom was equivalent to like more like about a 130 or 135
00:49:42.000 –> 00:49:49.000
millimeter telescope versus my 125, 5 poker, mat, and i’ll tell you.
00:49:49.000 –> 00:50:04.000
Yeah, it would just on the best nights and we compared this over many years on the best night that optical craftsman would definitely pull ahead by just a little bit on the planets and some other stuff.
00:50:04.000 –> 00:50:16.000
But on most nights, just like you would, with 2 telescopes that are only that are, that are unobstructed, or 2 refractors that are maybe just 10 or 12 difference in size be pretty difficult to See
00:50:16.000 –> 00:50:29.000
the difference i’m most nights and that’s kind of what we found like. We felt that the 5 inch apocromat was was extremely close to the to the 8 inch reflector Yeah, that’s interesting
00:50:29.000 –> 00:50:35.000
i’ve i’ve read that before you know some some people have. I’ve never done a side-by-side test like that.
00:50:35.000 –> 00:50:45.000
But yeah, you know that aligns with a lot of what i’ve read is that they they run very close with, you know, an 8 inch usually pulling away on the nights as you indicated.
00:50:45.000 –> 00:50:51.000
Yeah, exactly. And so I think that kind of you know gets us towards the end of this.
00:50:51.000 –> 00:51:07.000
And again, the recommendation is for people to, you know, if people are looking for instruments to get into well, I think the refractors in the smaller sizes, especially in that, like you know, 80 to 100 size make
00:51:07.000 –> 00:51:17.000
a lot of sense, because you’re you’re getting a small, lightweight, easy to mounties to use instrument that pretty much is sort of in the best of that really small class.
00:51:17.000 –> 00:51:27.000
But I really think, like once you get to about that 8 in size, and the reflector, you know you’ve got to be getting a pretty big refractor.
00:51:27.000 –> 00:51:42.000
That’s difficult to mount and you know you get a lot of barriers cost to get a really good one, whereas the the reflector in an 8 inch size, a really really good 8 inch reflector it’s just
00:51:42.000 –> 00:51:56.000
not going to be as expensive as as that 6 entry fracture which which is what you need to kind of probably start to surpass the really good age reflectors, And then and then just to go up again like the pretty easy to get
00:51:56.000 –> 00:52:08.000
a really good 10 inch reflector, pretty challenging to get like an eight-inch refractor, And that’s just going to be obscenely expensive and and just logistical nightmare to mount So you know
00:52:08.000 –> 00:52:25.000
it just makes sense. Once you want instruments that are above, say inches and above to you’ve really got a look at those reflectors, and then, like you know, inexpensive reflectors like from skywatch or other brands are are downward
00:52:25.000 –> 00:52:31.000
awesome and are gonna show you stuff know that that the small refractors.
00:52:31.000 –> 00:52:44.000
Just aren’t able to pull in and that’s Why, I think it’s a really great combination to get something like a 3 or 4 inch refraction, and then get like your 8 or 10 inch dobby sony and
00:52:44.000 –> 00:52:48.000
I think. Then you have like such a beautiful combination of instruments.
00:52:48.000 –> 00:52:58.000
Yeah, that’s a great point. Yeah, variety spice of life, Spice of life don’t put spaces in your instruments, Folks that’s really bad things.
00:52:58.000 –> 00:53:02.000
No salt, no salt. I said, Okay, all right, very good.
00:53:02.000 –> 00:53:08.000
Anything else to add chain. No, that’s everything chris I think we I think we covered all we can on refractors.
00:53:08.000 –> 00:53:15.000
Yeah, again, if people want to read more they Can look into the book on, let’s still get that again.
00:53:15.000 –> 00:53:22.000
Telescopes eye pieces and astrographs design analysis and performance of modern astronomical operations.
00:53:22.000 –> 00:53:30.000
That’s just an awesome book. people can look into and Yeah, Maybe maybe we’ll do like a dedicated reflector episode soon.
00:53:30.000 –> 00:53:37.000
I think you know It’s Well, well worth it to have these and I don’t want people thinking that we have some sort of you know.
00:53:37.000 –> 00:53:41.000
Agenda here. I don’t think everybody needs to own every instrument.
00:53:41.000 –> 00:53:55.000
But it’s but it’s. great when you can observe with a group of people, and everybody has a variety of different telescopes and and tools Yeah, good stuff, all right.
End of podcast:
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