I just started using my ASI290MC camera with an old film-era 55mm focal length lens at f/2.4. When first connecting to the camera SharpCap Pro had a message saying it might be best to change from 8-bit Raws to 16-bit. So I changed even though the camera is only 12-bit. The histogram looked normal for a while. But was time went by in the stack there started to be other bumps to the left of the main histogram peak. By the end of the one hour stack there were 10 extra bumps to the left of the main peak.
What is the cause of this weird histogram? Should I have left it at 8-bit RAW?
Thanks for your help.
Russ
EAA Live Stacking Strange Histogram
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Russ Milton
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EAA Live Stacking Strange Histogram
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Re: EAA Live Stacking Strange Histogram
Hi Russ,
yes, the message is a little generic and doesn't pick up that your camera might only be 12 (or 14 bit), but you got to the right mode so that part worked OK
The most likely cause for the bumps you are seeing is if you have drift or rotation going on as you stack - you will see this in the image as a dark border building up on one or two sides of the image (possibly rotated). The minor bumps to the left are coming from that darker area of the image, which is not quite black. Nothing to worry about really, except that you might want to look into improving your tracking or use guiding or the recentering option in live stacking to limit the drift.
cheers,
Robin
yes, the message is a little generic and doesn't pick up that your camera might only be 12 (or 14 bit), but you got to the right mode so that part worked OK
The most likely cause for the bumps you are seeing is if you have drift or rotation going on as you stack - you will see this in the image as a dark border building up on one or two sides of the image (possibly rotated). The minor bumps to the left are coming from that darker area of the image, which is not quite black. Nothing to worry about really, except that you might want to look into improving your tracking or use guiding or the recentering option in live stacking to limit the drift.
cheers,
Robin
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Russ Milton
- Posts: 2
- Joined: Wed Jan 21, 2026 9:59 pm
Re: EAA Live Stacking Strange Histogram
Thanks Robin for the insight. So using 16 bit Raws is OK for my 12-bit camera.
My polar alignment is quite good with less than 10 arc-minutes offset from pole. But the 10 extra humps in a 60 minute exposure gives a suspicious 6 minutes per hump. I'm guessing it comes from periodic error in the worm-drive. I'll train the Losmandy G-11 mount to correct for that periodic error which should greatly reduce that effect.
Best Regards,
Russ
My polar alignment is quite good with less than 10 arc-minutes offset from pole. But the 10 extra humps in a 60 minute exposure gives a suspicious 6 minutes per hump. I'm guessing it comes from periodic error in the worm-drive. I'll train the Losmandy G-11 mount to correct for that periodic error which should greatly reduce that effect.
Best Regards,
Russ
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admin
- Site Admin
- Posts: 17382
- Joined: Sat Feb 11, 2017 3:52 pm
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Re: EAA Live Stacking Strange Histogram
Hi Russ,
yes, it could be something like that where the image is oscillating a bit and each time it moves to one side then you get a darker region added on the other side. Add that to a bit of general drift and you could easily get the pattern you are seeing.
If I'm right about the cause then you won't see those spikes in the live stacking histogram graph - that's because the live stacking one deliberately excludes the edges of the image from the measurement (about 10% of the image on each side I think). That keeps the sort of effect you are seeing out of the live stacking histogram unless the drift/rotation becomes extreme.
cheers,
Robin
yes, it could be something like that where the image is oscillating a bit and each time it moves to one side then you get a darker region added on the other side. Add that to a bit of general drift and you could easily get the pattern you are seeing.
If I'm right about the cause then you won't see those spikes in the live stacking histogram graph - that's because the live stacking one deliberately excludes the edges of the image from the measurement (about 10% of the image on each side I think). That keeps the sort of effect you are seeing out of the live stacking histogram unless the drift/rotation becomes extreme.
cheers,
Robin