advice on telescopes wanted

[flintboy]

Hi was I’m really looking at getting my first scope and was after some advice on weather a (Celestron 5 SE) that I believe is a 5" Schmidt Newtonian scope ,would have a greater light gathering ability than a (6" or 8" lxd mead) that I believe is only a Newtonian telescope? I’m kind of lost and would appreciate any help thanks

[aurora]

Look through the messages in the telescope and equipment thread here, there are lots of answers to similar questions, with many links to helpful information.

Short answer, the larger the mirror the more light is gathered.

Maybe a mod will move this to the appropriate forum.

[Tim Thompson]

A 6 or 8 inch aperture will always gather more light than a 5 inch, unless they have ridiculously large secondary mirrors. Also, I would personally advise a Newtonian on a Dobson type mount, over a Schmidt-Cass, as a first telescope. The Newtonian will perform better in Eyeball viewing, compared to a Schmidt-Cass of the same aperture. On the other hand, the Schmiidt-Cass is a better camera lens, and so is better if you are going to do CCD imaging or astrophotography. As an example, we are happy with our 4.5-inch SkyQuest Dobsonian as a telescope we can let the kids play with. You would want a larger version, and you would probably want digital setting circles as well.

And don't overlook the value of a good pair of binoculars. Their wide field of view can show star fields and clusters, like the Pleiades, that you are unlikely ever to see in a telescope.

[dcl]

Setting circles with a Dobsonian? Please explain.

[Tim Thompson]

Setting circles with a Dobsonian? Please explain.

Dobsonian mounts are alt-az, just like an LX-200 without the wedge. So, you align the digital setting circles on the Dob the same as you do an LX-200, by pointing at 2 or 3 known stars. Then you can move the telescope by hand to the desired (RA, DEC). There are lots of digital options for Dobs like that. The Orion Intelliscope series are SkyQuest Dobs with digital setting circles. You can also turn the Dob into an equatorial, in a manner of speaking, with a split ring mount; they are not much harder to make than a regular Dob mount.

[dcl]

Tim Thompson: Thanks for educating me on implementation of setting circles on Dobsonian mountings. It never occurred to me that it might be done by automating computation of equatorial-to-alt-azimuth coordinate conversion and installing alt-azimuth setting circles. I'd still think it would be annoying to have to track in both altitude and azimuth to follow an objecte that's not on the meridian.

[Nick Theodorakis]

Tim Thompson: Thanks for educating me on implementation of setting circles on Dobsonian mountings. It never occurred to me that it might be done by automating computation of equatorial-to-alt-azimuth coordinate conversion and installing alt-azimuth setting circles. I'd still think it would be annoying to have to track in both altitude and azimuth to follow an objecte that's not on the meridian.

I don't really track with a Dob. If I want a longer look, I put the object off to one side of the field of view, then let it drift across as I watch, then give the scope another nudge.

Nick

[Tim Thompson]

Well, you could put drive motors on a Dob, but I don't know anyone who actually has. Generally the folks who want motorized tracking build a split-ring. The digital setting circles on a Dob make it easier to point the telescope by hand while reading out the coordinates, so finding things goes faster.

[aurora]

I have seen dob's with motors.

But I put my dob on an equatorial platform, for tracking.

But I used it for years just tracking objects manually. You want your scope set up so that the amount of friction in azimuth is about the same as the friction in altitude, and so that there is no stiction and no drifting.

Works really well once you get used to it.