Hi All, I have a Sony A9, which I have been using for Aurora photography. The last time I went out, I shot at 6400iso, 2s exposures, and nearly all of the photos I got have a ton of “stuck” pixels. See the video, skip halfway in, and look at the rocks in the bottom right.
I have had a play with the the camera with the lens cap on, and at low isos, there are no stuck pixels, it’s only once I go past 640 (the second iso range) that the issue appears. Has anyone seen this kind of thing before? Is it repairable? I’m guessing most of you shoot at iso100, but for aurora it was nice to get the shorter shutter speeds.
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Hot pixels! Best way to deal with them is taking dark frames: a bunch of exposures with the exact same settings as your light/main frames, but with the lens cap on so it just captures the noise. Also important that your camera is roughly the same temperature as when you took the light frames, since this type of noise is very temperature dependent. Once you have your dark frames, you can stack them to make a master dark, and use this to subtract the hot pixels from your lights using a deep sky stacking program of your choice.
Side note: for most consumer cameras, using a higher ISO will actually lower noise, at the cost of dynamic range
It’s a crazy amount of hot pixels though, doesn’t seem normal? Pixel remapping doesn’t get rid of them either.
That seems like a fairly typical amount to me (certainly a lot less than my old canon 600d)
Okay, I’ll take your word for it, but compared to my a5100 at the same settings, it’s an insane amount.
I do have a dark frame from later that evening, so I guess I’ll have to try the subtraction. Do you know of any software that can do the dark frame subtraction in batches? I have a few thousand shots I’d like to clean up :(
Siril should be able to. I’ll admit I’ve never used it myself (I use pixinsight for all my processing), but I know it’s a fairly popular free processing option. Also you’ll definitely want to try and take more dark frames than just one. Generally you’ll stack the darks together, and then subtract that from your lights (this should remove most of the noise thats not the fixed hot pixels)
For the future, I’ll try the additional dark frames, but the hot pixels are so high SNR that hopefully 1 will do.
I didn’t even know I was getting these hot pixels on the night, last time I went out I didn’t have this issue at all, which is part of my concern, it’s like my camera has gone from 0 obvious hot pixels to thousands overnight.
Thanks for the advice though, much appreciated.
