A Question of Mounting

[mchn88]

I'm new around here, and I made a little intro about myself in the introductory portion of the forum.

Without a long duplication, I've been chasing around the planets and various faint fuzzies with an 8" Sky-Watcher for a while, and I'm very interested in jumping into astrophotography.

One question I have concerns what type of mount to go with.

I've seen fabulous pictures around here, and around the Web, that were taken with telescopes like the Meade LX200 that come packaged with an Alt-Azimuth mount. I understand the concept of how beneficial slewing across one axis is, and I'm aware that wedges can be added to an Alt-Azimuth mount to make them function like an equatorial mount.

So, my question that I've been wondering is what is best to do...

1. A package-deal catadioptric scope on an Alt-Azimuth mount that can be modified with a wedge for photography.

2. Just go with the Alt-Azimuth mount, no wedge required (I'm just throwing that in becasue I don't know from personal experience whether one of these mounts can allow long exposures while training on two axis).

3. Buy a good equatorial mount (maybe an Orion Atlas mount?) and put whatever I want to on it.

I'm kind of thinking that 3 is the way to go. From everything I read, it seems telecope collections tend to grow. I'd like to buy a good robust mount that can train well with whatever reasonable weight I'm going to want to put on it. Maybe some nights I would have a refractor up for imaging the solar system, but other times I would have a larger aperature catadioptric tube on it for deep sky work.

If you think 3 is the way to go, maybe you could point me in the direction of a good mount. I threw out the Orion mount becasue it seems to be frequently used, and it can support a wide variety of equipment.

Welcome to any and all opinions, and I don't take any offense to someone putting me straight if I'm way off base here.

[RickJ]

The simple answer is that you can never spend too much on the mount if deep sky imaging is your quest.

Alt-azimuth only works for planetary imaging and very poor deep sky work. The problem is rotation of the field. Track on a star and such a mount will cause the camera to make a circle about it. So you must take many short exposures, derotate and stack them. Short exposures don't equal one long one. Every time you read out an image more read noise is added to the final image. Before long it can dominate so there's a limit to stacking if you want a good image. If you only want "something" then it will work but it won't be long and you'll tire of this as there aren't many objects that work very well with this method. This means you need some sort of equatorial mounting.

Dual axis poncet platforms are available for Dob's like yours. With a guiding camera and an imaging camera (needed in any case) you can get good images with the scope you now have at probably the lowest cost. Such devices will track for an hour or two then have to be reset so they can be a bit annoying to use but I imaged with a sector arm GEM and survived the resets. How much do you want to pay to avoid this is something you have to decide. For an example using a 12.5" Dob see: http://www.robertbrunck.com/

I've imaged with wedge and SCT but can't recommend it, especially starting out. Lots of problems can rear up. The long focal length of the SCT is only one of them. So while I image with a 14 LX200R it is on a Paramount rather than and LX200 fork. Yes the meridian flip is a bother but a small one compared to those I ran into with the wedge system. Gears just weren't up to it. Mount took too many unexpected jumps the guider just couldn't keep up with. Others have made this work however.

I would recommend starting with something with a rather short focal length, say a good 3" ED or APO refractor with field flattener. There are a ton of good wide field targets for such a scope that will keep you busy for several years. Put it on a mount at least equal to the Atlas you mention and you should be in good shape. This is assuming you don't want to go the dual axis poncet table with guider input with your present scope. In any case you will need to do an accurate drift alignment to avoid rotation of the field that you'll get otherwise. Work with an astrophotographer in your local club if at all possible. That can save you many nights of grief. Also read up on the subject as much as you can before diving in.

I started with a 6" f/4 before moving up to my present scope but both were on the Paramount. I'm a firm believer in spending like crazy for the mount and buying whatever scope and camera you can afford with the dregs remaining in the bank account. I fought (and often won) the battle with lesser mounts but it took a lot of the fun out of it and left me drained after an imaging night. It was work and some nights I lost the battle. Over doing the mount is about impossible and makes the imaging night much more enjoyable. At least for me.

Other needs, an off axis guider or other means of rigidly mounting a guiding system so there's no flex in either (not as easy as you might think). A guiding camera (a web cam can be used to hold cost down), an electric focuser is best but a good dual speed one also works. Your focus depth is small, 1/10th mm for an f/6 scope, so hitting focus is not an easy task. A Bahtinov mask (google it) can help here as well.

Rick

[mchn88]

Thank you very much RickJ for your response.

I think that I have the same mindset you described in that I'm looking at putting a substantial investment into a solid mount. With the mount, I'll go with the best scope I can additionally afford. From there, as things progress, I can move up on the scope in the future.

I'm tossing around numbers in my head that would equate to the Atlas EQ-G mount and an Orion EON 80mm ED Apochromatic Refractor. That would get me up and going (and on the hands-on learning track).

I'm not planning on using my current Dob for any imaging work. I've developed the mindset (after many mistakes) that it's an uphill battle to try and make any device operate in a function outside of it's design. I kind-of view the tables for Dobs in that regard. I'm satisfied that my $400 Dob has given me a lot of enjoyment (and will continue to), but I'm going to leave it as is. I'll stick with an equatorial mount for imaging and better viewing. I was a little shaky on the Alt-Azimuth mount / wedge combo for the same reason. Your experiences seem to confirm my thoughts that the best tool for imaging is a mount designed for that purpose from the onset.

Anyway, thank you very muh again for the advice, and for taking the time to share your own experience with me.

[RickJ]

A platform like the fellow used in the link I posted is very solid. Main drawback is the need to reset every so often. But you also have to reset a GEM when you cross the meridian and that inverts the image as well. Resetting the platform does introduce some rotation as well I think. Not using one I may be wrong here. Those using one can correct me if need be.

In any case an Atlas certainly will carry the scope you mention. With a chip much larger than say what's in the ST-2000 would likely require a field flattener. That's true of all scopes in this class. Only those with built in correction won't need one and those get very costly very quick, FSQ for instance.

Rick