Choosing between two methods of guiding

[Alex Yas]

Let's say we have a main scope with D=200-300 mm F/8-F/10 and a guidescope with D=50-70 mm F/4-F/5.
Which method of guiding with PHD2  is preferable: 

1.using a guidescope 

2.off-axis guiding on the main scope?
We assume  

1. a typical seeing of 1.5-2 arc seconds

2. the guiding cameras in both cases have the same pixel scale and

3. do not take into account possible bending when using a guidescope.

[Brian Valente]

Hi Alex,

the short answer is it depends.Both approaches have benefits and drawbacks, some of which relates to how well the equipment is mounted and configured, considering differential flexure, as well as your own rolerance for precision.

I would probably start with the guidescope and see how it goes. Guiding at f/8-f/10 sounds like an sct? So that also means there will be vignetting around the periphery where an oag would be, so you will lose additional light there. 

I hope the guidescope is well attached, not via a stalk or rings w/ thumbscrews

I would consider differential flexure (assuming that's what you mean by bending?), one of the main drawbacks of guiding with a separate guidescope. not sure why you would rule that out

Brian

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Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/