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Here's an open question: How many times have you seen amp glow in your Pentax astro-images? When you had it, which camera, what were the ambient temperature conditions, how long were your subs and how long was your session? All of those factors could contribute to amp glow.

I ask because a poster in another forum (he might be in this one too!) posted an image taken with a K-1 that might be exhibiting it. I only recall here one post, I think it was from Pete_XL, that mentioned seeing it but he was using fairly long exposures (five minutes IIRC?) on a very warm, summer night.

This is a highly stretched image from last night. First time I tried 4 min exposures. There seems to be a little something at the bottom of the frame that could be amp glow. It was totally invisible in the raw files. It's a stack of five of those 4 min exposures after a full hour of data on Orion. So the K-70 was as hot as could be. Outside temp was -2°C.

I've never recognized it in any of my K-5 or K-7 shots.

I've never seen it in my K-5 - with exposures up to 8 minutes but it was cold, maybe a little above freezing on a spring evening. I saw a fair amount in a 20 min exposure on a K-3 in summer. Probably all these were around ISO 800.

That’s only 20 minutes of total exposure? Impressive!

Wow, you did a single 20 minute exposure? I haven’t done one anywhere near that long since my film days when I used to go up to an hour. Can I ask why a single exposure in that instance?

I've not seen it but then I am still shooting with out an intervalometer when on an equatorial or using astrotracer so mostly shots in the 10s to 3m range. A while back I poked around with a massive pile of bias frames and with my K-3 it looked like amp glow wasn't much of a problem (I believe that is one of the things corrected by bias frames). From what I recall it one need to really push the noise floor down to be able to start to see the pattern and really push the bias frames up. Now to see if I can find that thread where I wandered off into that discussion.

Hi Lew Dite, my goad is to do a single long exposure at native ISO/gain. Partly I wanted this since not having good stacking software (macOS) but now with APP, I don't mind stacking. There is actually a club that is the single exposure club... saw them on Facebook somewhere. The main issue is guiding and dark current. With a cooled camera and good guiding it should give good results - I'm looking for as much dynamic range as possible because my second reason is I want to avoid overexposing the stars too. My friend gets good guiding with his Orion Atlas so I kind of egged him on to shoot for 20 mins :-P Its was good but the long exposure noise (dark current, amp glow) was evident in his K-3.

Clear skies!

Thanks! 20 min at f/2.0 is like 2 hours at f/5 though.

Here is my masterbias frame for my K-1, comprised of over 300 separate exposures. As clean as you think your sensor is, the onboard electronics will always induce a signature. - Jack

K-1 Masterbias frame - Pentax User Photo Gallery

That's a curious set of linear regions you have in there. My master bias frames for the K-3II have some stuff but not those linear features, as far as I can tell. Regardless, bias frames don't reveal thermal problems, which is the most common cause of amp glow, although if there is an IR source in the camera that can be a source of amp glow that does show up in bias frames. (Some Sony cameras have that problem, especially after modification.)

PixInsight CMOS sensor users such as myself have moved away from using a masterbias. Instead, it is better to create a masterdark which does not have the bias subtracted out. Using such a masterdark with a masterflat gives a better calibration. The only limitation doing this is that the masterdark must be temperature-aligned with the lights, so it is necessary to create a "library" of masterdarks taken at different temperatures.

Sure, anyone using a master dark would only use a master bias to subtract from a master flat before applying the latter.

But why is it better to subtract a master dark from the master flat rather than a master bias? I can see it if the flat frames used a significant exposure time (say, a few seconds) but if the flats are short exposure, I don't see the advantage.

The masterbias is still subtracted out of the flats before integrating into a masterflat. The difference is that instead of using a separate masterbias and subtracting that from the darks, you just integrate the darks into a masterdark. But if going this route, you need to turn off scaling of the masterdark which is why you need to temperature match them with the lights.