Dark (leakage) current doubles every 10 degrees C or so, and needs no photons to generate the excess electrons resulting from the leakage.
April 2, 2023
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An example is the Sigma fp, one of which I own. Nice camera except that it is not good at flash.
Don Cox -
We all used to shoot ASA 125 film hand held. But I'm not sure the results are all critically sharp.
Don Cox
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It's an Arrhenius law thing. There's an activation energy - or rather a range of activation energies, depending on the crystal defects near your pixel. As JK said, (at temperatures around 300K) the rate doubles roughly every 10 kelvin.
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The rate is quite low, for most pixels, in most photographic conditions - or photography with these sensors would be a bit rubbish. The accumulation of "dark current" electrons has a Poisson distribution, just like regular photo-electrons. The Arrhenius law for "dark current" is why it's good to have a cold sensor when taking long exposures of dark things.
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As you know, the loss of sharpness was not due to low ISO but to the required shutter speed.
Current cameras often have either IBIS or lens VR, so base ISO usage is more frequent (unless subject motion prevents it). -
David, good source of information.
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By "Poisson distribution", do you mean frame to frame for the same photosites, or do you also mean spatially, within a single exposure?
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The former, I would assume, substituting pixels for photos. Too many outliers for the latter.
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Sorry for being unclear.
I meant that each pixel on the sensor has its own activation energy, depending on nearby crystal defects such as dislocations and out-of-lattice doping atoms.
So each pixel has its own (Arrhenius) rate constant for the accumulation of dark current electrons. This rate constant, multiplied by the exposure time, gives the mean of the Poisson distribution of the accumulation of dark current electrons for that pixel.
Every pixel has its own Poisson process.
But...
Most pixels will have very similar (low) rate constants. A small proportion will have higher rate constants. A smaller proportion will have even higher rate constants. The distribution of such rate constants is presumably studied by sensor designers, but is unknown to me.
These per-pixel rate constants aren't fixed over time. Some crystal defects fix themselves - again following an Arrhenius rate law. New defects can be created by radiation.
I guess it's possible that recording 8k video for a few hours would reduce the dark current noise in your astrophotograpy images. I have no evidence for this. 😀
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I noticed when using my A7Rii for exposures of several minutes that it didn't seem to need LENR. Shots without it seem fine despite many complaints to the contrary. Then one day I got caught photographing LE on a hot sunny day. And the camera exhibited all sorts of hot pixels. Perhaps the complaints originated from hot countries.
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I have followed this thread and others about ISO/exposure (they can be identified by their length) and find that I am more confused than I was before about how I should set ISO on my Canon R6. I am not totally thick, but under Beginners' Questions I would expect a more prescriptive answer than a discussion of Physics fundamentals, particularly when the participants appear not to agree on them and when some take an adversarial stand towards others.
What can be done to give simple answers to simple questions? I personally have had enough of the difficult answers, though I may be in a minority in this.
:) :) :)
Edit Perhaps a thread entitled Beginners' Answers would be the appropriate answer!
David
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Unfortunately the posts after the first few should have been moved to the Beginners Questions Discussion Forum where the more technical discussion is meant to be had.
Maybe if we just stick to my OP which I tried to explain noise and indirectly how that affects how to set ISO.
Is there anything in my OP that is not clear?
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You mean, apart from it being too long and involving concepts that I dont believe the average beginner is familiar with?
As I wrote above, Beginners' Answers would be more appropriate.
:)
David
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I didn't discuss any concepts that in my experience average beginners have had any significant difficulties in understanding.
Which concepts in my OP are you referring to?
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IMHO "Signal to Noise Ratio" may need an explanation, a separate article, a link, something. The article might benefit from including images to illustrate the problem and to prove the proposed solution works.
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Yes, that is a good idea but I know the likes of you, bobn2, JimKasson, Michael Fryd (not necessarily in any order) are far more qualified and experienced than me to write such an article.
To be honest, being a layman enthusiast photographer my interpretation of Signal to Noise Ratio doesn't go beyond words to the effect of "Ratio of Good Data to Bad Data".
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Signal includes noise, it's good + bad data.
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ok, ok 😊 Now you are really over complicating things. I'm sticking with just Good data to Bad data ratio for the sake of maintaining what sanity I still have at my 60+ years of age 🙂
