Which OAG or stick with guide scope?

[Jonny_H]

Hi all,

I am debating getting an OAG to add to my set-up (Esprit 100ED with ZWO 2600MC as main camera and ZWO 120MM Mini as guide camera).

That said I have to main questions:

1) would you recommend an OAG over a guide scope for my set-up? My current guide scope albeit a tad ott is an Evoguide 50ED.

2) if yes to the above, I am torn between the ZWO OAG and the OAG-L. The latter seems to give a much larger prism and aperture but seems more 'complex' to actually fit it to my scope and camera. The former is very simple but has a much smaller prism and aperture. Just not sure which would be best, if any (see question 1 )

Any help or guidance would be appreciated.

Thanks,

Jon

[wuthton]

If it's to pair with your Esprit, I doubt you'll find any advantage of an OAG over your guidescope apart from it being more compact. At over a metre of focal length is where OAGs start to shine and they become worth the faff of setting them up. 

[Xsubmariner]

I concours with Matts response, the added embuggerance of setup and finding guide stars out ways any benefit to guiding setups less than 1000mm. You don’t mention if you are experiencing problems with your current guidescope arrangement. 

[michael8554]

+3, an OAG is not going to make much difference, unless your current guidecam and guidescope scope setup is particularly wobbly (Differential Flexture)

Regarding an OAG, the ASI 120 Mini has a 4.8um x 3.6um sensor, so a  8mm x 8mm prism is large enough.

Michael

[Jonny_H]

Thanks for the comments @wuthton @Xsubmariner @michael8554

I do not really have any issues with my current set-up (as such).  Although I am trying to get to the bottom of a recent issue where by all of my stars across the entire field where slightly elongated in the same direction. I haven't had a chance to go back out yet though to test if it was just bad PA etc...

The idea behind the OAG was to make the set-up more compact and to free-up the top of the scope to potentially place other equipment, such as a Pegasus PB etc.... that's not to say I can't fit things elsewhere and work around the guidescope.

Edited January 24, 2022 by Jonny_H

[michael8554]

1 minute ago, Jonny_H said:

all of my stars across the entire field where slightly elongated in the same direction.

If the RA and Dec guide error figures are similar, then you should have round stars eg RA = 0.90arcsecs, Dec = 0.85arcsecs

Then any elongation will be due to a wobbly guidescope (differential flexture).

Post your PHD2 GuideLog.

Michael

[Jonny_H]

7 minutes ago, michael8554 said:

If the RA and Dec guide error figures are similar, then you should have round stars eg RA = 0.90arcsecs, Dec = 0.85arcsecs

Then any elongation will be due to a wobbly guidescope (differential flexture).

Post your PHD2 GuideLog.

Michael

Hi @michael8554

I posted these up a few days back albeit under another thread. My logs are from an ASIAir Pro but believe these are no different to those produced by the 'actual' PHD2 utility.

The graph produced by the app which Scotty advised me to use were based on the longer of the guiding sessions.

 

 

[Laurin Dave]

Plus one for staying with a guide scope and OAG would just make life more difficult... what was it that made you consider one?   the blips looks like they correspond with the worm cycle of the mount which is about 8 minutes  - although I'm not sure what you can do about it 

[Jonny_H]

Thanks @Laurin Dave

I do have dithering spikes in that graph to.....but at least I am aware what those ones are! just not sure on the other ones but hoping that someone can help.

[michael8554]

ASIAir produces a basic PHD2 style GuideLog that can be read by PHDLogView

Michael

[Jonny_H]

1 hour ago, michael8554 said:

ASIAir produces a basic PHD2 style GuideLog that can be read by PHDLogView

Michael

Thanks @michael8554

I think that is what I was advised to use to view the graphs which I posted on the other thread (link to other thread posted above earlier)?