Choice of guide scopes, what I have or something else....

[Joseki]

Hi, I was wondering about guide scopes and thought I'd benefit for some advice from someone who's already been there.

I'm thinking about selling off a short fl achro I have but the only reason I hesitate is it might be handy as a guide scope when I start getting more serious about astrophotography. It's 90mm and fairly heavy. Alternatively I have a nice intes 50mm finder scope which you can swap the ep on and might make a lighter solution. Option 3 would be to ditch both and get a lighter scope like the ST80 for the extra mm over the 50mm - just a case of more stars I guess. I quite like the idea of the 50mm if it would work as I want to aim for a reasonable amount of portability in the setup (though I'd be using the HEQ5 - soon to be pro). I would probably go down the route of a stand alone autoguider btw.

Anyway, any suggestions would be very useful. Cheers

[Mkofski]

John,

I use a 50mm finder that takes a standard 1.25" diagonal as a guide scope. I'd stay with that over a heavy refractor. Of course, which was best would depend on the focal length of your imaging OTA and what mount you are using. If you are imaging with a 2000mm + SCT a 80mm f/8 refractor may be a better choice than your 50mm finder.

Mike

[orion61]

The higher the magnification the better your shots will come out.

The ST-80 is a great choice for a guide scope.  I use a Bausch & Lomb 80mm 800 FL

Schimidt Cass that is feather lite! you can find them from time to time. They came in

a kit with a correct image diagonal for Spotting, a T adapter for use as a Telephoto, and as a small telescope.

[DaveS]

The ST80 is pretty much standard issue for guiding, pair it with the gude camera of your choice and you're away. Pull the lens from the rubbish barlow supplied and use the empty tube as a focus extender.

[pete_l]

Since you already have both the finder and the 90mm you could give both a try and see which you prefer.

Guiding software uses algorithms to find the centre of the star it's guiding with, so a large pixel scale (such as the 4 - 6 arc-sec/px) you'd get with the finder and a QHY5 shouldn't be a problem.

Personally, I'd suggest that if you are using an HEQ5 Pro, then keeping the weight down would help with your guiding. But the secret is to keep your options open and see what works for you.

[Joseki]

Thanks for the advice everyone.  Plenty to think about.  I think I'd have to pick one option and go with it to begin with as I'd still need to get the mounting hardware but lightweight and fairly portable is probably what I should go for first.

[lensman57]

Hi, I was wondering about guide scopes and thought I'd benefit for some advice from someone who's already been there.

I'm thinking about selling off a short fl achro I have but the only reason I hesitate is it might be handy as a guide scope when I start getting more serious about astrophotography. It's 90mm and fairly heavy. Alternatively I have a nice intes 50mm finder scope which you can swap the ep on and might make a lighter solution. Option 3 would be to ditch both and get a lighter scope like the ST80 for the extra mm over the 50mm - just a case of more stars I guess. I quite like the idea of the 50mm if it would work as I want to aim for a reasonable amount of portability in the setup (though I'd be using the HEQ5 - soon to be pro). I would probably go down the route of a stand alone autoguider btw.

Anyway, any suggestions would be very useful. Cheers

I use a 50mm aperture  dedicated guidescope, F3.2  plus two 60mm ones, F 3.6 with helical focusers. With a guidescope and below 1500mm of FL a 50mm aperture guider is more than adequate. A guide scope must be able to provide a widefirld bright view of stars so that you have a choice of stars to guide on, it is not supposed to resolve stars. The guiding software is more than capable of calculating position of the centroid of the star and then guide on it. A while ago I conducted some calculations to this effect and with the average UK seeing even a lens of 50mm FL is adequate, that is 50mm FL not 50mm aperture. I would also be very reluctant use terms such as magnification with relation to AP. There is no magnification as such, a DSO target will always be the same size for a given Focal Length no matter what sensor is used . As for the stars even the HST can not resolve them as a disk and they will always be a point of light at best. For PHD guiding atleast the author of the sottware recommends a slightly out of focus star for better guiding and my experience supports this. I do have an ST 80 and have had the Ascension version of your 90mm F5.5 scope and found no advantage in using them with my set up. I have used the 60mm guider with my SW 127 MAK @ F11.9 with great success. See the capture of M51 in my Astrobin Sig.

Regards,

A.G