Have an issue where the flat plan in ACP will not run flats with the Aluma AC4040. I have had some feedback on the ACP forum, there was a suggestion of bringing up the topic here as it might be a software of firmware issue. I will tell ACP to run dawn flats. This is BTW the same plan that I used with my STL6303E camera-worked like a champ every time. What ACP is telling me is that the ADU is about 3590, with a 25" exposure with the sun two degrees below the horizon. It shoots a 64X64 subframe. It will not shoot any flat frames at all. I can shoot garbage flats in the observatory full frame, manually. Also, when I look at Maxim in the morning after a failure, it will say in the exposure type (light, dark, bias, flat) light not flat. Attached is the ACP log file for flats and a Maxim log. Around 14:00 is when it is supposed to start flats. It shot something, didn't say it was flats. One note, it says roof closed, the roof was not closed, I have to do so manually. I have modified the ACP flat plan thus: TargetBackgroundADU 12000 ; Target flatfield mean in ADU TargetADUTolerance 8000 ; Tolerance on the above MinExposure .11 ; Minimum exposure (as short as possible) MaxExposure 25 ADUAcceleration_AM .6 ; Factors to improve exposure scaling accuracy ADUAcceleration_PM 1.10 TwilightSunLo -3 ; Low elevation of Sun for flats (morning) TwilightSunHi -2
For the AC4040, and readout mode set to High Gain, the camera will saturate at somewhere around 3600 ADU out of 4095 (as it is 12-bit). With High Gain StackPro, the camera's sub-exposure time affects the whole image time. I suspect what is going on is the exposure time is too short to use StackPro mode. eg 25 seconds won't be composed of a bunch of stacked 12-bit images. So try shorter exposure time, high gain only for your flats, and perhaps an ADU count around 2000.
Thank you Colin. OK, to be clear, High Gain Stackpro for images, but use just high gain for flats, and set the saturation limit in ACP to around 2000. I'm guessing what ACP was doing was increasing the exposure time to get to 12000 ADU. It can shoot flats from .11" to 25". I was thinking about this last night, and wondered if HGSP was doing some internal shenanigans. Also wondered if 12000 ADU was high for a CMOS detector. This couldn't be a Maxim version issue, I'm merrily working with 6.28? Another question regarding setting up HGSP. I shoot 10 minute exposures...thoughts on setting the sub exposure? There is a way to do this (forget how at the moment) it is set to the default value currently. If it ever clears up here, will give this a try.
To set the sub-exposure time: (My example is for an STC-7, but you'd pick the AC4040 in the list). So, if you've got a 30 second subexposure time, and shoot 25seconds, it's only going to have 1 sub in the frame, IIRC. So your ADU count will max out at saturation. So shorter exposure should fix it. A couple other customers indicate they get decent flats at lower ADU counts than with a CCD. (eg in your example, 12000 out of 65536 at 16bit = 750/4096 at 12bit)
Thanks Colin, will try it when the weather cooperates. I did some testing in the observatory using only the interior lighting. Also the building is flat black inside. They were garbage flats but they seemed happiest between about 2750 and 3000. I tried HGSP and HG, they were both about the same...Much more than this, they were not happy, if this makes sense. I'm not sure if this is going to hold for sky flats that have better or more even illumination, might have to play with the setting I think it is now 2500, +/- 500. So ACP was trying to get it up to 12,000 when it needed to be around 2750 or so. So it increased the exposure. Exposure range in ACP is .11" to 25". I think this is clearly the right track, might take some fiddling to tune it.
Agree, you are on the right track. In-camera stacking is really only useful for exposures on the order of minutes, not seconds. The point of it is to defeat the CMOS Active Pixel Sensor glow caused by the logic. Depending on your particular 4040 sensor, exposures of 15s to 60s can be done one-shot without a lot of glow. So we usually default it to 15s. By comparison: Code: AC4040 FSI QE 74% - broad STXL-6303 peak QE 68% - narrow 12-bit dual-gain on-chip ADC vs 16-bit off-chip ADC Full Well 79ke- vs 100kei- So the ADU count is going to be pretty different for the 6303 CCD. It may be worth loop @Bob Denny in for advice on telling ACP what to use for exposure ADUs on the sky flats, considering what you're learning from us. BTW when doing sky flats, am expecting short exposures, depending on how big the scope and the transmittivity of the filter being used.
Thank you Colin. I started this on the ACP list, Bob has been in on it. I will pass along what I learn and come up with. I am working with a 17" Planewave in a Bortle 1.5 sky (not quite a 1, but better than a 2). The filters are the LRGB ones I got from you folks for the FW7-STX filter wheel. Am at about 7450' elevation, as you might imagine the sky here is very good...and I have generally good seeing as well. Last week before the storms, had a night of 1" or less according to my Santa Barbara Scientific meter. Not bad for 50 yards from the house.
