OAG + QHY5L-II M setup help/hints?

[bugeater (Marty)]

So I picked up a TS 9mm OAG in the classifieds and have set it all up with my QHY5L-II. This camera worked fine with a little 50mm f/3.25 guidescope, but I want to eliminate as many guiding issues as possible, including differential flexure.

Took me a lot of messing around to get everything joined properly - why on earth can't Baader produce a proper instruction manual for their MPCC? I couldn't attach the MPCC to the OAG without an adapter and then the backfocus difference was all wrong. Only after a lot of messing around did I work out that an inner set of threads could be unscrewed from the whole thing to get the backfocus right, but none of Baader's material indicated this was possible. I even found posts where people were machining these threads off because they were fouling on the prism in the OAG.

Anyway, after all this I got it outside and have found it tricky to get working particularly well. I guess I'm used to the pinpoint stars of the guidescope, but they look large and bloated at best in the OAG. This is normal right? My setup has a focal length of 1000mm, so I guess the magnification is greater. I've tried to see how good the focus can get with just the main focuser, and I think I'm close to parfocal with the main camera.

Also the guide image is pretty flaky. Does anyone have some QHY5L-II settings that work for them? If there is a brightish star in the image, then everything seems okay, but if there are only faint stars the image becomes really noisy and it's impossible to do any guiding. I'm also lucky if there is one star to chose from. I guess the light pollution filter won't help, but I can't see how that can be moved.

I really want to use this thing, but so far it's been difficult. Any hints or tips to help me on this journey would be appreciated.

[rustigsmed (Russell)]

hi marty,

I used to use the TSOAG9 and with the MPCC, yes I probably went through the exactly same steps as you! but it did get it working well in the end. as for the image quality of the stars, don't worry if they aren't perfect its not that important. I've guided on some dim shapes that hardly look stellar at all.

The main thing to do is to concentrate on getting the focal position as close as possible as that may be your problem as that camera is really sensitive you should be able to get a guide star all the time. also consider extending the exposure above a second or taking darks. I use a lodestar which I believe is similar in sensitivity and can pretty much leave it on 1 second exposure and not worry about darks (although I don't recall what your scope is, mine is f4).

Hope that helps.

Russ

[bugeater (Marty)]

I've got a 200mm f/5 newtonian. I've tried to get it as close to parfocal as I can, but it's tricky since even at best the stars are still quite blurry. I have been trying longer than 1 second exposures, but that's only helped a bit. I think I need to get the camera settings right (gain, 12 bit mode?, 2x2 binning?). Maybe I've got the prism too far to one side too?

[rustigsmed (Russell)]

you can check the prism position during the day time, but moving it as close to the edge (away from primary camera's sensor) and looking through the stalk till an image appears. Once you have that position tighten it up, its a matter of then moving the camera only up and down the stalk till you get focus, a small movement makes a big difference so make sure to take your time on getting it right.

[Amaranthus (Barry)]

A little blurry is fine - it makes it easier for the guiding software to estimate the centroid location, statistically. Obviously it can't be way out of focus, but slight defocussing is arguably preferable. In short, get the OAG focus about right, and then move on.