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Splotch on Darks

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#1 ParagPA

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Posted 30 June 2020 - 11:18 AM

Hello,

 

I'm seeing a splotch on my darks, and I'm not sure what's causing it. This is a modified T3i. 

 

The darks are at ISO 1600, and 180 seconds. 

 

I took my darks during the day, outdoors, under a covered patio, with the camera attached to the telescope and the (metallic) telescope cover on. 

 

What's strange is the effect gets worse over the entire sequence. 

 

I've attached a sample image from the middle of the sequence, and an image of the entire sequence, showing how the noise increases substantially over time. 

 

Is this normal due to the camera body heating up from continuous image acquisition? 

 

Dark 1 s.jpg

 

Sequence 1.jpg



#2 endlessky

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Posted 30 June 2020 - 11:28 AM

I would say it's due to increase of temperature of the camera.

 

I think that, due to the fact that you cannot control the temperature of DSLRs, taking darks might actually make things worse, rather than help.


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#3 mmalik

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Posted 30 June 2020 - 11:30 AM

Is this normal due to the camera body heating up from continuous image acquisition?

Could be Amp Glow.... Take another sequence with camera in a dark room and lens cap on, preferably even in a dark desk drawer. Note: External light can seep/leak in as well if darks are taken under light conditions (...not recommended). Regards


Edited by mmalik, 30 June 2020 - 11:31 AM.

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#4 ParagPA

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Posted 30 June 2020 - 11:31 AM

I would say it's due to increase of temperature of the camera.

 

I think that, due to the fact that you cannot control the temperature of DSLRs, taking darks might actually make things worse, rather than help.

Interesting - I haven't heard that in the past. I'll also try stacking without darks and see what looks better.

 

I did go back and look at some ISO 800 darks I've captured in the past, and don't see this. This is my first time at ISO1600 and I wonder if that's substantially increasing the noise. 



#5 endlessky

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Posted 30 June 2020 - 12:29 PM

From my understanding, noise increases very rapidly with temperature and if you don't match within a few degrees the temperature of the lights with the temperature of the darks (pretty much impossible without a cooled, temperature controlled camera), the calibration can actually hurt the final result, instead of making it better, since the noise levels of the lights and the darks will not be the same.


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#6 Bill G.

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Posted 01 July 2020 - 06:34 PM

FWIW, when I was using a camera that had high amp glow, I would put a 90s cool down time in between exposures. It seem to allow the camera to stabilize rather than getting hotter and hotter. There's an argument to be made that the loss in imaging time was worse than the amp glow... but not in the case of my old Canon 300D. Amp glow would get pretty significant. In any case, seemed to help for me.

Bill G.


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