OAG and focuser size

[Datalord]

I tried out my G3-16200 tonight and with a bit of starting hardship, it worked out. Except I couldn't get my OAG camera to get any stars at all. It's my first time using an OAG, so I might be asking a stupid quesion:

Will this OAG simply not get any light from the WO71 2" focuser? Or is the ZWO-ASI120C just not sensitive enough to guide on this? I did make a BPM and darks, but actually getting a usable picture in PHD2 was beyond me.

[Davey-T]

I'd have thought you should be able to get stars on the OAG, I can using QSI683 with built in OAG and Loadstar on the Star71, colour camera won't help though.

I'd ignore the main camera and try to get Jupiter to focus with in the OAG as it's nice and bright so should show up even if it's miles out of focus, just to make sure it works, if so it's a case of getting both cameras in focus at the same time by moving towards focus on the main camera and fiddling with the guide camera to keep it focused as you go.

Dave

[Dr_Ju_ju]

I have a 120mm, & PHD2 has no problems, picking stars & guiding.

I set up mine during the day, when you could easily see what is happening. I used an aerial stack on top of a tower block, that is approx. 2k away. I first set focus for the main camera, lock main focuser, then adjust the OAG, so that it is as close to focus as can be.

Note that it doesn't have to be pin sharp focus, PHD2 works better if it isn't, and as the OAG, just picks off a small portion of what's coming in, and due to parallax offset, what is centred on the main camera, may not even show on the OAG, so you will need to manually slew to compensate.

[Datalord]

8 hours ago, Davey-T said:

I'd have thought you should be able to get stars on the OAG, I can using QSI683 with built in OAG and Loadstar on the Star71, colour camera won't help though.

I'd ignore the main camera and try to get Jupiter to focus with in the OAG as it's nice and bright so should show up even if it's miles out of focus, just to make sure it works, if so it's a case of getting both cameras in focus at the same time by moving towards focus on the main camera and fiddling with the guide camera to keep it focused as you go.

Dave

Blunder, it is not a colour. 

1 hour ago, Dr_Ju_ju said:

I have a 120mm, & PHD2 has no problems, picking stars & guiding.

I set up mine during the day, when you could easily see what is happening. I used an aerial stack on top of a tower block, that is approx. 2k away. I first set focus for the main camera, lock main focuser, then adjust the OAG, so that it is as close to focus as can be.

Note that it doesn't have to be pin sharp focus, PHD2 works better if it isn't, and as the OAG, just picks off a small portion of what's coming in, and due to parallax offset, what is centred on the main camera, may not even show on the OAG, so you will need to manually slew to compensate.

I'll try the daylight version today to see if it is simply blocked off, which is my suspicion. I had to use a converter from T68 to T54 which suspiciously looked as if it sås going to block off the oag. 

[Davey-T]

If the prism is on the long side of the sensor you should be able to drop it down a fair way in to the light path without interfering with the image'

If you take flats you can start with the prism too low and gradually raise it so that it doesn't show in the image although this is easier to do with some OAG designs than others.

Dave

[Datalord]

Ok, tested it. The adapter to M54 simply obstructed the OAG mirror. I have to use my good old guidescope instead in this setup. A bit of a bummer as I was hoping to test it out, but that must wait till the RC comes.

[Stub Mandrel]

I use an ASI120MC for guiding with a 50 x 163 guidescope (so it's rather fast at f3.5), so far I have never failed to find a choice of guide stars (on m13 the other evening even the cluster itself was obvious at just 1s exposures).

What I have noticed is that with short exposures and short focal length focusing is very fussy, focusing accurately on a bright star is big help as then all the tiny ones appear as if by magic!

[Datalord]

1 hour ago, Stub Mandrel said:

I use an ASI120MC for guiding with a 50 x 163 guidescope (so it's rather fast at f3.5), so far I have never failed to find a choice of guide stars (on m13 the other evening even the cluster itself was obvious at just 1s exposures).

What I have noticed is that with short exposures and short focal length focusing is very fussy, focusing accurately on a bright star is big help as then all the tiny ones appear as if by magic!

I've used it with a guidescope for well over a year, so that's not an issue. I only have a problem with the combination of OAG, M68 to M54 converter and the WO71 scope. I'm going back to guidescope for the time being.