When creating Dark Frames for calibration purposes, the resulting darks always come out totally white, which leads me to the conclusion that the result is inverted before being saved to disk. This obviously caused severe problems with the subsequent calibrations.
I use a cooled ASI1600 Colour camera and, yes, I always screw the cap back on to the refractor before staring the Dark Sequence. Most of the time I set up the sequence to shoot one dark followed by a Bias frame etc. The Bias frames come up black, almost black when stretched, which is correct, but the Darks always come up white (inverted). When I manually invert the Dark frame in SGPro, the picture is black and when zooming in I can see hot pixels, so I assume that the actual photo is correct but that it is then automatically inverted whilst being saved.
Maybe I’ve changed some setting for Dark Frames, but I don’t know where I could have done this? Any ideas? How can I invert the files permanently, as the inversion in SGP is for display purposes only (I assume).
Thank you, for your reply. That is possible, but would such a saturation also occur when doing normal exposures at the same exposure length as the darks? I did 360 second exposures for both the light frames and the dark frames. Light frames had no issues. Also used the exact same camera temprature, as per dark frame creation instructions.
Hi Chris, just another thought: can a chip in fact become saturated if there are no Photons hitting the sensor of the camera? The electrons stored in the Well, which when filled to capacity, leads to saturation should not be present when the lid is on the scope and all is dark, meaning that no or very few electrons are actually hitting the sensor.
Nonetheless, I’ll do what you suggested, by successively lower the dark exposure time. Let’s see what happens.
I ran into a similar problem with a different camera. I finally diagnosed the problem by holding the telescope lens cover up to the light and discovered it had an area that was thin enough to pass light. The cap was black and looked opaque until I held it up to a bright light!
We don’t automatically invert for display purposes. You can click the “Invert” button but this is a conscious decision and not saved with the data (and also likely not what is causing the issue)
As mentioned, I would check for light leaks, especially if you’re taking dark/bias during the day. If you feel it is the frame type (unlikely) you can also do “Light” frames with the objective blocked and see what results you get to at least remove the possibility of it being the type of frame.
I’m glad you found the problem. It is amazing how little of light leak it takes to create a completely white frame. These cameras are really sensitive.
Most cameras have some sort of light leak. When I take dark frames I generally cap the camera and place it in a closet, sometimes in a cooler with the lid cracked. Then stuff a towel under the door.
I used to wrap aluminum foil around the camera but that makes it difficult to get adequate cooling (which you’ll need at the TEC is running)
