Dark Frame Library - help

[julian489289]

I have been building my dark library whilst the skies have been cloudy. 

I use a Canon 650D DSLR for my imaging controlled through APT.   Usually, my dark frames are black and contain a number of hot pixels.  However, over the last few nights whilst building my library a white glow has appeared to the right side of the dark frame.  I have had the camera body lens cover on and the view finder blanked off so no light can get into the camera.

I have taken a number of darks at ISO 800 varying from 120, 240, 300, 480 & 600 second exposures.  In each increase in exposure the white glow has increased.

Can anyone please advise as to what maybe causing this glow as I have never has such an effect before?? 

I have enlosed Jpeg's of the Canon CR2 RAW dark frames so you can see the issue, in order 120 sec, 240 sec,300 sec, 480 sec and 600 sec exposure.

Hope you can help me and advise.    Thanks

[Dave Lloyd]

Is this amp glow or am I completely on the wrong track?

[julian489289]

If it is Dave, what is it, how does it affect my dark and can I get rid of it?

[Bizibilder]

That's why you take darks   !  They are subtracted from your light frames thus making the amp glow disappear (as it will also be on your light frames).  They will also remove hot pixels etc.  The amp glow will become more pronounced as you increase the ISO and/or exposure time.

[gnomus]

It looks like amp glow.  I'm not sure but since your lights are likely also affected by amp glow, I'd be tempted to ignore the 'issue'. go ahead and process and see what comes out.  If you don't like the result then try processing without darks - are you dithering? 

I'm not sure there is much can be done about amp glow, but it seems odd that this is a new problem.  Have you started lengthening exposures recently?

[Edit: Apologies, cross-posted with bizibilder]

[sharkmelley]

Your experience with the 650D is more evidence that amp glow is a potential problem on the 650D/700D cameras.  It's a great shame that amp glow is once again becoming a problem.

Discussion here regarding the very similar 700D:

http://stargazerslounge.com/topic/233942-amp-glow-700d/?p=2534957

Mark

[julian489289]

Thanks Guys.  I have done 800 ISO and 480 & 600 sec exposures before yet never seen this phenomenon.  Is it an issue for 700D's and below or do the better models also suffer from this?   Yes I do dither with my lights though when I get clear skies!! 

[sharkmelley]

You are most likely to see this issue when taking darks in relatively warm conditions after the camera has been imaging for a long period of time.  If you take a sequence of long exposures over a period of, say, an hour or two you will see the heat gradually building up.

When doing a series of long exposures, keep the rear LCD switched off (the DISP button on earlier models does this) and not just blank.  Having the LCD on used to heat up the camera on earlier models - I'm not sure if this is still the case on more recent ones.

By the way, as a general point, the fact that heat builds up within the camera over an imaging session makes it difficult to perform dark matching with library darks because the thermal noise will be different in each light frame as the camera warms up.  Dark subtraction is best done by scaling the master dark so the thermal noise in the master dark matches the thermal noise in each individual light.  PixInsight does this really well (e.g. switch on "Optimise dark frames" in the Batch Preprocessing script).  I think Deep Sky Stacker has a similar option but I've never tried it out.

Mark

[julian489289]

Thanks Mark.  I am currently taking darks in the cold weather approx 4-6 degrees to match in with my lights that I am to take throughout December & January.  Typically getting darks exif temp 10 to 16 degrees at the moment.  I seem to get the amp glow all of the time though from the first dark to the last dark over a few hour session.  

On the 650 D the LCD screen folds of which I assume switches it off similar to the disp button, unless someone knows differently.

I will have to look into optimise dark frames in DSS re the dark matching.  Ahhhh, so much to affect the final result!!

[Yoddha]

Julian,

Take a look if you have configured Virtual Anti-Vibration pause. In this mode APT uses LiveView to simulate Mirror-Locking which cause amp-glow for most of the EOS models (as I know only 1100D and 1200D are free of this effect because they have no true Mirror Lock function).

[julian489289]

Thanks Ivo, where would I set and unset that?   I do have C.Fn mirror lockup automation  ticked though, would this contribute?

[Yoddha]

Antivibration is set in APT's Camera tab. Usually APT manage to change the C.Fn Mirror lock to the right value, but if this not happnes, then try to disbale it from the camera's menu

[julian489289]

Hi Ivo, sorry I'm confused.  I have C.Fn mirror lockup automation  ticked in settings but the anti vibration pause set to 0 degrees in the camera tab.  Is this correct or should I deselect mirror lockup in settings?

[Yoddha]

Please set the antivibration to 0s, then start a plan and see if C.Fn in the bottom of Camera tab is set to OFF. If this happen then you can try if there is still amp-glow.

[julian489289]

Thanks Ivo, will try when I get home

[julian489289]

Ivo, Just seen a screen shot that I took previously.  In the bottom RH corner it says C Fn ML off but I still got the amp glow

[Yoddha]

Is the Anti-vibration pause 0s too?

[Tinker1947]

Are you useing a main power supply, the battery in the camera will get hot and may not help.......

[julian489289]

Yes Ivo, anti vibration pause is 0s

[julian489289]

Thanks Tinker, I use battery power as i am not mains powered.  However, I have seen some posts who state that mains power gives more glow???

[julian489289]

I cannot see what could have caused the change to the chip to get this amp glow. 

I enclose jpegs of darks taken on 08/11/15 & 21/11/15, nothing different to the settings or how acquired and only taken a couple of weeks apart.    

8/11/15

https://www.dropbox.com/s/n244027gaq85gtt/D_2015-11-08_01-02-47_0001_ISO800_360s__15C-1.jpg?dl=0

21/11/15

https://www.dropbox.com/s/yol7mlaj3or3wgs/D_2015-11-21_23-39-26_0025_ISO800_360s__15C-1.jpg?dl=0

[The Jackal]

I shoot with a Canon 700D and after stacking my images in Pixinsight I got this results (see photo). The glow doesn't show up on any of my images but yet it is there on the image. The final image took loads of cleaning up to remove the glow which was little visible no matter what.