Using a guide scope/finder scope as a small telescope

[Richard_B]

Hi all. I was wondering whether is would be sensible to use a guidescope (or finderscope with 1.25" eyepieces) as a small grab and go telescope. I have basic 90 and 45 degree erecting diagonals and a load of eyepieces. I would like to use a photographic tripod or monopod with it so would need some way of mounting it to a quick release plate

Regards

Richard

[Mr niall]

Generally the biggest problem is that they aren't very well corrected at the edges due to the short focal length so you get a lot of fuzziness and coma from at least 50% out. I toyed with this a few times too but in the end decided that a pair of binoculars worked out better all round in most circumstances

[Richard_B]

25 minutes ago, Mr niall said:

Generally the biggest problem is that they aren't very well corrected at the edges due to the short focal length so you get a lot of fuzziness and coma from at least 50% out. I toyed with this a few times too but in the end decided that a pair of binoculars worked out better all round in most circumstances

Thanks for the reply. I have seen some imaging done with just a basic guidescope and it was OK. If it will work in principle I may give it a go. Plus I could useit as a better findertscope for my main telescope 🙂

[Mr niall]

1 hour ago, Richard_B said:

Thanks for the reply. I have seen some imaging done with just a basic guidescope and it was OK. If it will work in principle I may give it a go. Plus I could useit as a better findertscope for my main telescope 🙂

Sure. I know some people tried imaging with the ED50 but really struggled. If you used a heavy crop it may be ok. But everyone has different tolerances  when they look through the eyepiece I guess. I use a 9x50 with a filter for spotting sunspots so that’s kind of visual only I guess.

[Louis D]

I have a 60mm finderscope made from the front end of a 60mm pair of binos.  The rear end is a machined Delrin adapter for 1.25" diagonals.  I think it was made by Russell Optics in the 90s.  It's mounted in 50mm finderscope rings toward the back end.  I use a Celestron 90 degree erect image prism diagonal focused by slipping it forward and back.  It pairs quite nicely with a 127 Mak to bring in the widefield views impossible with the Mak.  It's a bit heavy, so it's  CG has to be mounted inline with the altitude axis pivot point to prevent the alt-az mount from flopping about at differing altitudes.  I use a 24mm APM UFF in it to cope with the ~f/4 speed of the objective.

I also modified a 70x300 cheapie telescope from ebay to take a 2" diagonal and eyepieces to really max out the possible widefield.  So far, it doesn't work as well as the 60mm bino conversion, so it's a WIP.  It needs flocked and the PVC bits need to be centered better.  So far, I've got less than $30 in it, so I'm not complaining.  It would be different if I didn't have so many spare parts from previous projects laying about.

[Cosmic Geoff]

I have the Astro Essentials 50mm finder/guidescope, which comes with a proper focuser, takes 1.25" eyepieces (or T2 cameras), and comes with a two-ring mount on a dovetail bar that fits in a standard Synta finder shoe. (the mount rings alone might cost the asking price elsewhere.) I thought I could make it plate-solve with suitable attachments, but unfortunately it does not do this well under Bortle 6 when pointed at a random sample of sky.

So what else is it good for? Guiding, I suppose.  There does not seem to be enough focal depth to fit any sort of diagonal.  It might do as a high-powered finder for planetary imaging (so long as the planet is not at too high an altitude).

Edited January 24, 2022 by Cosmic Geoff

[Richard_B]

Thanks everyone. I don't think it will work for me as I won't be able to get enough focus extension - worth asking 🙂

[Louis D]

3 hours ago, Cosmic Geoff said:

There does not seem to be enough focal depth to fit any sort of diagonal.

Exactly.  I don't know why they don't offer a visual version with a shorter main tube to accommodate a diagonal.  They could use a longer focuser drawtube to support straight through usage as well.