QHY camera gives tiny images and gigantic pixel sizes

[Joe Morris]

I may be having a similar problem with a different OSC CMOS camera, the ZWO ASI2600MC. My pointing exposures are unsolvable so the plans fails from the get go. I’m using MaxIm 6.26 and the latest ZWO ASCOM driver released 1/22/2022. In MaxIm I set the gain to 0 but have no option to set the offset (which should be around 50 for this gain according to the ZWO website). I can set the offset in other image capture software using the camera’s native driver and hope that it carries over to MaxIm.
The pointing exposure appears for a millisecond on MaxIm’s screen and disappears. It’s very small like an autoguider image.
The time and location of the observatory is set correctly.

[K Michael McDowell]

Joe - Yes, it does sound like the same problem I was having. Based on my experience I would say your offset value is too high. The QHY driver that I am using allows for adjustment of the gain and offset in the driver software under settings in MaxIm's camera setup. It sounds like that may not work for you if your driver software doesn't give you access to the offset setting.
Bob and I did a series of tests with my camera just shooting dark frames. With my factory settings the "black" value was around 5000 ADU in binning 1, increased to about 16000, 44000 and 65500 in binning 2, 3, and 4 respectively. Thus, the binning 4X4 frames were totally black, no stars, would never plate solve because there is nothing there. By reducing the Offset value, I was able to get the black ADU down to about 500. The literature I have read on the subject seems to agree that you want the offset setting to result in a black level between 500 and 1000 for binning 1 images. For my camera that meant changing the factory setting from 71 to about 12.
You could take a series of dark frames with your camera with current settings at the different binning levels and check the black values. Then using your 3rd party software reset the offset value to something lower and see if it makes a difference in MaxIm.
After the changes I made I have had successful plate solves every time. So, it is definitely worth a try. Good luck!
Mike

[Dick Berg]

Hi Joe,

I have to say that those pointing images are the smallest binning 1 ones I've ever seen - 16 x 24 pixels!! The FITS header for those images have 250 mm for the focal length with a 51 mm aperture. That would be about right for a regular (DSLR-like) camera lens. Otherwise it looks like there's some factor that's been misapplied or ignored in some setting somewhere.

The log file is also instructive:

02:59:01 Calculated unbinned plate scales (arcsec/pix): H = 158.07 V = 158.07
02:59:01 Calculated field of view (arcmin): H = 16460.7 V = 11001.9

16460 arcmin is 274 degrees. So there, too, is a result that seems strange. You have to figure this out first before you can run any tests on the dark readings of your camera, which may or may not have the same issues Mike has overcome.

Check the ACP/Preferences/Telescope panel that you have input the focal length of your telescope in the correct units (millimeters). Slipping a decimal point or two here will produce the result you see in the log. Also go into MaxIm, in the Camera Control panel and make you have pressed the "X" button to expand the subframe to it's maximum. In MaxIm's Observatory panel, look at Site and Optics and make sure you have the correct focal length there, too.

These are just a few suggestions. Somewhere there must be a number or two of them that are not set correctly.

[Bob Denny]

I'll go with Dick on the tiny pointing images. In your log, this is the first hint:

02:59:01 Calculated unbinned plate scales (arcsec/pix): H = 158.07 V = 158.07
02:59:01 Calculated field of view (arcmin): H = 16460.7 V = 11001.9

Since the images themselves are so tiny, I'm going to guess that there is some camera adjustment that causes it to tell ACP that it has very few (104 x 69 pixels) gigantic pixels.

Snap3.png

Looking at the FITS header it looks OK with 3112 x 2080 frame size and 3.76 micron pixels. Reasonable. Then why the tiny FITS image? That is not controlled by ACP. This is the image that MaxIm is producing. It was taken, as logged, at bin-1.

[Joe Morris]

Thank you Mike, Dick, and Bob. I've got a lot to check and will get back on this. Strange, because after the ACP plan failed, I took 26 beautiful images using the "Autosave" tab in MaxIm.

[Bob Denny]

Now that's really strange!!!!! I might consider asking Diffraction how that is possible. They know ACP.

[Joe Morris]

I wanted to admit operator error so that anyone reading this thread would not be misled. I was so focused on the ZWO driver and problems with CMOS cameras when binned, that it took me awhile to find my problem. As Dick suggested and as Bob echoed, it was my error entering the RedCat 51 telescope focal length in ACP. I enter the focal ratio of 4.9 instead of the actual FL of 250mm. Amazingly, I entered the correct number in MaxIm.

Last night, my ACP plan ran flawlessly while collecting 25 four minute subs of the Witch Head Nebula.
Joe

[Bob Denny]

Ahhhhhh OK, thanks very much for letting us know. It takes a good person to come back and share their issue.

Thanks again,