OAG help.

[oldfruit]

I am looking at the possibility of using an OAG for guiding as opposed to the finder guider I am currently using. Is there an OAG that would be suitable to use with either my ED80 or with my 8 inch Newtonian scope? I would like to have one I could use for both.

The reason being that whilst the finder guider seems be doing its job when I am imaging with the ED80, if I wanted to image with my 8 inch newt I think the focal length difference between the newt (1000mm) and the finder guider (200mm?) would be too great to make the guiding effective?

 

Correct me if I am barking up the wrong tree. Any advice appreciated.

 

 

Thanks,

 

Mark

[Guest Kheldar]

You should be fine with the finder guider on the 200P, many do this - I believe it's the focal ratio that's important, not so much the focal length (unless we are talking 2000mm plus like an SCT or RC)

If you're using a DSLR then the TS 9mm OAG is the only one which will provide correct spacing to use the SW flattener or a coma corrector on the 200P

Edited May 1, 2014 by Kheldar

[oldfruit]

Thanks Stephen, maybe I will try the finder guider and see how I get on.

[red dwalf]

i`m fairly sure it`s the longer focal length scopes, i.e. 8" sct and longer where the advamtage of using a oag comes in, although i`ve guided my 8" sct with the st80 i have on a dual mount bar with good success

[oldfruit]

Thanks for that Rob. My inexperience in these matters is evident.

[+RonC]

I have an OAG I could bring on Saturday to BF if you want? 

[oldfruit]

Thanks Ron, is it one you are looking at selling or you just bringing it for me to have a look at?

[+RonC]

To look at, I have not used it in anger yet as the finder/guider works well on the MN190. Might try it on the ED80 at some point?

Will bring it anyway 

(+focuser)

[oldfruit]

Thanks Ron.

[fwm891]

Finder guider should be fine at 1000mm - the other benefit is that you will haver lots more guide stars to work with. I use an OAG (@1600mm) but there are times when guide stars are few or very dim.

You could go for a 'bigger' finder guider set-up there are 60 and 80mm guider set-ups which would probably mean a set of guide rings on both ota's and just move the finder between as required.