Choosing a guide scope

It's a guide scope, they are all the same and for what it is worth get the cheapest you can get.

If your stars are round in your images - don't change anything.

Hi,

I have been using the same ZWO 30/120 guide scope. I have guided with it a 350mm refractor and the error was 2", I have guided with it a 1500mm Maksutov and the error was 0.5". All the difference was in the mounts.

I think sometimes we are forgetting that guiding (at least with an equatorial mount) isn't really supposed to be doing much. Its job is to correct tiny deviations from ideal tracking, once every few seconds, IF needed. If you somehow had perfect PA and perfect tracking, guiding would not be necessary, at all. If your rig deviates too much from that ideal, it is probably a mount problem (or a wind problem), not a guide scope problem.

If everything else stays the same, changing the guide scope for a bigger one in an attempt to comply with the "1/3rd effective focal length rule" (or was it a 1/2nd rule) can arguably cause more bad than good because of the added weight, torque and increased sensitivity to seeing which results in incorrect star position calculations. Don't do that unless your stars are not round and you are certain guding (and the guide scope in particular) is to blame.

Cheers,
Dimitris

@dkamen @Tim Ray @Alex Nicholas @Tony Gondola @andrea tasselli 

Thank you everyone for some good advice. I am still relatively new to all this and appreciate your wisdoms. 

Cheers,
Irwin

One noob to another.... If it ain't broke don't fix it

I really don't like my zwo f4 guide scope, but it guides my sw gti under 0.9" so I leave it alone

My 0.2 cents:

I'm currently using the cheapest autoguiding system I could find: the Svbony 30mm f/4 scope + SV905 camera combo (u$130 for the whole kit). The camera isn't even monochrome, as recommended everywhere. Paired with an AM3 and PHD2, I'm getting typical RMS error of under 0.7" with good streaks of 0.4"-ish and bumps of up to 1.1" in windy conditions:

I feel that these guiding figures would be more than enough for any system that could ride on top of the AM3.

Franco Grimoldi:
My 0.2 cents:

I'm currently using the cheapest autoguiding system I could find: the Svbony 30mm f/4 scope + SV905 camera combo (u$130 for the whole kit). The camera isn't even monochrome, as recommended everywhere. Paired with an AM3 and PHD2, I'm getting typical RMS error of under 0.7" with good streaks of 0.4"-ish and bumps of up to 1.1" in windy conditions:

I feel that these guiding figures would be more than enough for any system that could ride on top of the AM3.

Excellent indeed. Thanks.

Right now it's winter up here and we don't usually get too many nights with clear skies. When we do, I'll get out and do some testing. For the immediate future, I'll stick with my existing set up of WO Uniguide 32/Askar 107PHQ and will reevaluate in the spring. Thanks again everyone  for all the help. 

Cheers,
Irwin

I totally disagree with the theory that guide scopes don't matter.  I had a little 30F4 ZWO thing that was very poor in performance.  

I was using it in combination with my Takahashi FSQ-106 and it was bad.  terrible focus.  I upgraded it to an EVOGUIDE 50 ED and was impressed how much better the Doublet EvoGuide was in respect to focus particularly, and Star HFD as well. the EvoGuide 50ED gave much tighter guide stars, and generally overall better guiding.

I am now using a Stellarvue 80mm Doublet as a guidescope for my 10 inch RC, and whilst some people assure me that an OAG would be better, I have found the Stellarvue works splendidly, and I have no intention of moving to an OAG in the near future.

I would always choose a Doublet as a minimum for a guidescope, for the obvious reasons of Doublet performance verses Achromat.

David Russell:
I would always choose a Doublet as a minimum for a guidescope, for the obvious reasons of Doublet performance verses Achromat.

Achromats ARE doublets, and most guide-scope/finders are specifically cemented achromat doublets. And some are better than other. Russian ones being top performers in my experience. But they are air-spaced, not cemented.

andrea tasselli:

TiffsAndAstro:
My stars all look like a dot with a big cloud around each

*Because you don't use filters. If you did, and are picky about focus then they'll be all dots.

i am thinking of trying a cheap red filter, see if it makes any difference

David Russell:
I totally disagree with the theory that guide scopes don't matter.  I had a little 30F4 ZWO thing that was very poor in performance.  

I was using it in combination with my Takahashi FSQ-106 and it was bad.  terrible focus.  I upgraded it to an EVOGUIDE 50 ED and was impressed how much better the Doublet EvoGuide was in respect to focus particularly, and Star HFD as well. the EvoGuide 50ED gave much tighter guide stars, and generally overall better guiding.

I am now using a Stellarvue 80mm Doublet as a guidescope for my 10 inch RC, and whilst some people assure me that an OAG would be better, I have found the Stellarvue works splendidly, and I have no intention of moving to an OAG in the near future.

I would always choose a Doublet as a minimum for a guidescope, for the obvious reasons of Doublet performance verses Achromat.

An Achromat is a doublet. You mean an ED doublet...

My own experience is that adding a 25A red filter to my guide scope improved my average RMS numbers considerably. The guide scope is an 80mm F/5 achromat.