[Solved] Courious transparent leftover ampglow with Asi 294 MC Pro and APP in the integration frame

Nobody? 😐 

Hi, I use the ASI294 and yes its got an annoying ampglow. Once thing that is important is the offset setting on the 294, I use 30. This is necessary so that your noise is not clipped to black which will lead to calibration error. Check out this video by Quiv the lazy geek:

@astrogee Thanks for your reply.

My ZWO Asi 294 has offset 30 by default. In the fits header is showing offset 30. Hm.. 😞 

My darks have a strange green bar at the end of the histogram or it is clipping data, don´t know. Is this normal? Or maybe a light leak?

I do darks without telescope with a metal cap in fron of the camera.

When you took the pictures, what was the outside temperature and at what percentage of power was the camera cooling?

@minusman oh, I didn´t remember exactly, but the temps where round about I thin 13-17°+ and the cooler I thin was running at around 40-50% or something.

Okay, that's a good range for the cooling performance. With my asi 294 I can only set the cooling performance to a maximum of 50%. Otherwise I have a dark spot in the lower part of the image. But this only becomes visible when you stack a few images.

Do you also make the flat darks with the metal cover on the camera?

Posted by: @minusman

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Do you also make the flat darks with the metal cover on the camera?

Yes, I do the flat darks also with the metal cap on the camera.

@plejadshunter I think its ok, I think the colour bars in the histogram are there because your sensor has some colour pixel noise. For example, all the green dots in the dark frame.

EDIT: But can you turn off the auto white balance in your dark frame display?

EDIT: I'm also thinking that the colour noise in the dark may require a much higher offset to calibrate it out... like 5000?

Ok, here a screenshot without auto wb.

 And how I can increase the offset for darks?

@tobiasthale So there is quite a bit of noise there but I think you should use the same offset for your whole library, all your darks, flats and lights taken at the same offset, gain and temperature. I suppose some calibrations may not care but in general I have a library of darks and bias at -10c (because I know I can always reach that temperature), and I do flats and dark flats on site, and the gain and offset is always the same (30) for all.

@astrogee yes, all frames (lights, darks, flat darks and flats) are with the same temp, gain, offset.

Hi Tobias,

Here is a suggestion you might try to deal with the residual/transparent amp glow you are seeing. (I can't make it out on your attachments but their resolution on the forum is not that good. I will say that in my experience, amp glow on an ASI294MCP doesn't radiate from the middle of the left side of images as drawn by your three white areas. It radiates from toward the top as in your dark image. Could you be experiencing a light leak?).

Prepare a master dark from exposures longer than your light frames. You need to use bias frames for that. The longer exposures will capture and record more amp glow in that master for subtraction from your lights. Load that master dark for calibrating your lights. At the bottom of the Integrate tab, check to enable Scale MasterDark along with Adaptive pedestal/reduce Amp-Glow. Perhaps the algorithm APP uses to scale that longer exposure Dark can remove the leftover amp glow you are seeing.

Jeff

I have a QHY183c I use and the AMP glow is really bad. The best way to deal with bad amp glow like is do not use any bias frames, use a dark flat to calibrate the Flat frame and do not use any kind of dark optimization. Also take at least 30 darks and flats. The more you have of each the lower the noise will be in the actual calibration frames. I went through a lot of amp-glow induced calibration pain until I stopped using BIAS frames. Also make a copy of the master flat and master dark, debayer them, and stretch it and then you can compare a debayered light frame to see if everything aligns. You don't always have to debayer but it can help if the amp-glow and other issues are stronger on one of the channels.

Speaking of Bias frames, yes its better to use dark flats but APP will automatically use dark flats instead of bias frames if you load dark flats. So I sometimes just load everything I have and let APP sort it out 😛

@jhart longer darks as lihgts? But they didn´t match then!? And bias frames shouldn´t do with this imx294 sensor.

@dheyergmail-com that´s what I do all the time. I do dark flats instead bias frames, every calibration frame 30 each. But didn´t help.

@astrogee don´t know, Iload lights into lights, flats into flats, darkflats into darkflats and darks into darks. But it´s still the issue there.

Hi Tobias, APP has the ability to use a Master Dark created from longer exposure dark frames to calibrate lights taken with a shorter exposure. But you have to create that Master Dark first and then load it when you are calibrating your lights. You are right that the ASI294 sensor can act funny with bias frame (or dark flats taken at less than 2 seconds). You could create all of your Masters first. That is, load your flats, dark flats and longer exposure darks in APP. Don't load any light frames. Run APP to create your master dark, master flat and master dark flat. Reopen APP, load your lights and those masters instead of individual dark, flat, or dark flat frames. In calibrate, enable scale MasterDark along with reduce amp glow and click (re-)assign Masters to Lights. I don't know if that will solve your problem, but it is an available option to try.

This is an interesting problem... Can you post the histogram of one of your lights? And the meta data?

@astrogee you mean me?

What´s meta data? You mean the fits header?

@tobiasthale yeah fits header

@astrogee

Hi @tobiasthale

Interesting you have exactly the same settings I use (offset=30, gain=121)... but I notice that your amp glow doesn't exactly match the pattern of your finished result. The final image has an artifact in the middle of the right side whereas your light does not. So I'm thinking your darks or dark flats are from the wrong library or like @jhart says, a possible light leak in the darks. Once, when I made my darks I was getting some weird "amp glow" in some of the images so I removed the ones that did not look typical and I assume that was a light leak problem. Now I do my darks in a dark room.

Posted by: @astrogee

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but I notice that your amp glow doesn't exactly match the pattern of your finished result. The final image has an artifact in the middle of the right side whereas your light does not. oom.

Can you show me what exactly you mean with the artifact?

Can you show the fits header data from the calibration frames and the settings from the calibration tab? Also look for ROWORD "row order" in the fits header and make sure al the calibration frames and lights have the same setting. The ASI AIR should also be setting the same offset for all frames but you never know the offset setting could change.

Hi everyone, can you post a picture of the Bad Pixel Map? If you use one when calibrating.

@tobiasthale In your 2nd image. there are three radial noise patterns from the middle of the right side, which you circled. Thats what I mean by artifact because we don't really know what it is or where its coming from. But I notice its not the same as the amp glow which radiates from the top right mostly. But I think your 2nd image artifact is due to light leak in your darks. That's my best guess. Check all your darks and you may find that a few of them have a light leak resembling the artifact in your 2nd image.

@dheyergmail-com you mean the headers from master dark, master flat and so on?

Here are the settings from tab 2 calibrate