Suggestions on a smaller guide scope? For use with SVBONY 305 PRO

[Cumbrianwolf]

I have currently been using a lump of a guide scope that is 80 mm and weighing in at nearly 1.5Kg on a mount that is near or on its limit, so I am looking at a 60 mm guide scope.

So what suggestions do you have to match an F/4 1016 mm 254 mm Newtonian?

[TerryMcK]

This guide may help https://agenaastro.com/articles/guides/selecting-a-guide-scope-and-autoguiding-camera-for-astrophotography.html#aperture

 

Essentially it states “When guiding with a camera a focal length ratio down to 1/10 of the imaging scope is ok” So you could use something like the William Optics UniGuide 50 (which I have) mated with the Svbony which has a focal length of 200mm which is just 1/5 of your Newtonian.

The scope is only 460 grams and will fit in a mini shoe. Alternatively you can use the WO guide 50 without mountings and then mount it in some guide scope rings.

 

There may be other scopes indeed I use a modified dirt cheap Skywatcher finder scope on one of my scopes to great effect. Again another light weight guider system.

[Cumbrianwolf]

1 minute ago, TerryMcK said:

This guide may help https://agenaastro.com/articles/guides/selecting-a-guide-scope-and-autoguiding-camera-for-astrophotography.html#aperture

 

Essentially it states “When guiding with a camera a focal length ratio down to 1/10 of the imaging scope is ok” So you could use something like the William Optics UniGuide 50 (which I have) mated with the Svbony which has a focal length of 200mm which is just 1/5 of your Newtonian.

The scope is only 460 grams and will fit in a mini shoe. Alternatively you can use the WO guide 50 without mountings and then mount it in some guide scope rings.

 

There may be other scopes indeed I use a modified Skywatcher finder scope on one of my scopes to great effect.

Thank you, I tried to modify the finder scope I have, but the back focus was an issue. This 80 mm refractor is a lump of a thing and the focuser decided to lose a vital screw on my last outing and I cannot find a replacement, and now I need to work out a method of repair, but the extra cash would be better spent elsewhere on a more apt guide scope. 

[AstronomyUkraine]

14 hours ago, Cumbrianwolf said:

Thank you, I tried to modify the finder scope I have, but the back focus was an issue. This 80 mm refractor is a lump of a thing and the focuser decided to lose a vital screw on my last outing and I cannot find a replacement, and now I need to work out a method of repair, but the extra cash would be better spent elsewhere on a more apt guide scope. 

You could always take the guidescope out of the loop altogether by using an OAG.

[Cumbrianwolf]

1 minute ago, AstronomyUkraine said:

You could always take the guidescope out of the loop altogether by using an OAG.

You know, that might be a better option after all, and I will look up the price of an OAG. This would drop the total weight a little more and the guiding would be direct as the telescope sees, so in theory more accurate?

[AstronomyUkraine]

Just now, Cumbrianwolf said:

You know, that might be a better option after all, and I will look up the price of an OAG. This would drop the total weight a little more and the guiding would be direct as the telescope sees, so in theory more accurate?

Definitely with a Newt. I used one on my refractor, and it takes any potential flexing out of the OTA. The prices vary from just over £100 to £280, more or less the same price as a good guidescope.

[Cumbrianwolf]

Any suggestions on what I am looking for as in adjustable prism, large prism and other facets of an OAG as it seems one size does not fit all?

[AstronomyUkraine]

10 minutes ago, Cumbrianwolf said:

Any suggestions on what I am looking for as in adjustable prism, large prism and other facets of an OAG as it seems one size does not fit all?

First you need to determine the thread size of your coma corrector to make sure you get an OAG that will fit. Also the thickness of an OAG will determine any spacers you need to keep your backfocus at 55mm.

Edited January 28, 2022 by AstronomyUkraine

[Cumbrianwolf]

3 minutes ago, AstronomyUkraine said:

First you need to determine the thread size of your coma corrector to make sure you get an OAG that will fit. Also the thickness of an OAG will determine any spacers you need to keep your backfocus at 55mm.

My coma corrector is one that fits into an 2" focuser, not sure if is has any threads on it, I shall take a look.

[AstronomyUkraine]

2 minutes ago, Cumbrianwolf said:

My coma corrector is one that fits into an 2" focuser, not sure if is has any threads on it, I shall take a look.

The coma corrector will have threads on the camera side of it. Most prisms in OAG's are 8 or 9mm, so no real differences there.

[Cumbrianwolf]

M48 x 0.75 pitch, I had forgotten that I can take the EOS mount off it.

[AstronomyUkraine]

11 minutes ago, Cumbrianwolf said:

M48 x 0.75 pitch, I had forgotten that I can take the EOS mount off it.

So you will need a OAG that will connect to your EOS connector and your coma corrector. I belive both would be 48mm.

[Cumbrianwolf]

2 minutes ago, AstronomyUkraine said:

So you will need a OAG that will connect to your EOS connector and your coma corrector. I belive both would be 48mm.

Off to do some research on what I need, thanks for the advice.

[Cumbrianwolf]

One OAG has now been purchased, and I will do away with the guide scope. Thank you all for the advice. 

Edited January 28, 2022 by Cumbrianwolf
Wrong scope input.