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Guidescope vs OAG with Edge HD 8"

ToupTek OAG Acquisition Guiding Polar Alignment Deep Sky
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OAG or Guidescope?
Multiple choice poll 52 votes
71% (37 votes)
29% (15 votes)
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Eddie Pons avatar
Eddie Pons avatar
Well, I've been trying to dial in my OAG for a while now with my edge at focal length of 1473 (with .7 reducer.)  I was getting between 1-2 arcsecond resuls. Last night, with one hour available before clouds moved in (again,)  I said the heck with it.  I used my Orion 50mm guidescope instead of the OAG, AND I GOT THIS.  Tell me again why I should go back tot he OAG, lol?!  (I should add I got an excellent polar alignment with Sharpcap and the same guidescope.) 300 sec subs were very sharp.
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James avatar
James avatar
You should be able to get better results with the OAG one dialed in.

The other benefit with an oag and a sct is that if the mirror shits a little, the oag shifts with it.  

Your screen shot is showing the guiding in pixels.  What was it in arc seconds?

What mount are you using?
Rafał Szwejkowski avatar
Rafał Szwejkowski avatar
The guiding numbers you get from the 50mm guide-scope don't reflect the whole movement of the telescope.  The flexure is hidden - it's like breaking the thermometer to get rid of the fever.
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Eddie Pons avatar
Eddie Pons avatar
EQ6-R.  Flexure is only an issue if it shows up in your stars.  Anyway the question is moot.  I just thought the poll would be funny. I’ll use the OAG once I can take everything apart and double check alignment.  But between that and getting NINA’s AF to work properly with the SCT, I’ve wasted valuable imaging time.
Nick Grundy avatar
Nick Grundy avatar
i'm still a fan of a guide scope, though you'd have to make sure your pixel scale was enough

1400FL with an ASI2600 or similar is about .55"/px. Using something like an ASI178mm you'd probably want at least a 600mm FL in the guide scope to come close the scale. Otherwise you guiding would look great, but @1400mm is could still be a mess. 

I went through this but was fortunately educated by some wise people on AB. 

Fun question though. I'm always curious if i'm the last one who actually likes a guide scope.
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Eddie Pons avatar
Eddie Pons avatar
Nick Grundy:
i'm still a fan of a guide scope, though you'd have to make sure your pixel scale was enough

1400FL with an ASI2600 or similar is about .55"/px. Using something like an ASI178mm you'd probably want at least a 600mm FL in the guide scope to come close the scale. Otherwise you guiding would look great, but @1400mm is could still be a mess. 

I went through this but was fortunately educated by some wise people on AB. 

Fun question though. I'm always curious if i'm the last one who actually likes a guide scope.

True.  I’m aware of all this.  Had an 80ed on my refractor for this very reason.  But it was fun to see such small numbers in PhD2.
Michele Campini avatar
Michele Campini avatar
It is perfectly normal that by shortening the focal length then your RMS improves.
If you put the 30mm F4 you'll do even better, but your stars will be like spaghetti.
Graeme Holyoake avatar
Graeme Holyoake avatar
Eddie Pons:
Well, I've been trying to dial in my OAG for a while now with my edge at focal length of 1473 (with .7 reducer.)  I was getting between 1-2 arcsecond resuls. Last night, with one hour available before clouds moved in (again,)  I said the heck with it.  I used my Orion 50mm guidescope instead of the OAG, AND I GOT THIS.  Tell me again why I should go back tot he OAG, lol?!  (I should add I got an excellent polar alignment with Sharpcap and the same guidescope.) 300 sec subs were very sharp.

Your screenshot appears to be giving your error values in pixels, not arcseconds, so the comparison is meaningless.
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Eddie Pons avatar
Eddie Pons avatar
I’m comparing to the same values before and after.  It’s all relative.
Graeme Holyoake avatar
Graeme Holyoake avatar
Eddie Pons:
I’m comparing to the same values before and after.  It’s all relative.

That's precisely my point.  You're comparing error in pixels from 2 vastly different scales.  I don't know what focal length your 50mm guide scope is, but let's imagine it's somewhere around 180mm.  0.15px RMS at that focal length is roughly the same as 1.2px RMS at 1473mm (assuming you're using the same guide camera in both cases).
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