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Dark frame subtraction cannot remove cosmic rays. It removes things the camera sees in the dark at the time of dark frame capture. This is things like dead pix
by malfist 3y ago
Dark frame subtraction cannot remove cosmic rays. It removes things the camera sees in the dark at the time of dark frame capture.
This is things like dead pixels, hot pixels and amp glow.
If a cosmic ray was removed by a dark frame, two cosmic rays would have had to happen, one during dark frame and one during the actual capture. They'd have had to be the same intensity and hit the same pixels. This is probably never going to happen.
As for who this is for? You and I may benefit too with less cosmic ray noise in our photos. We still see them, though we have a lot more information in our photos. You can see them too if you take dark frames yourself. Even if you put your camera in the freezer to avoid most other noises you'll see them
- davidmurdoch 3y agoWhat's the freezer thing about?
- dekhn 3y agothere are several sources of pixel noise, some of which are temperature dependent. Making the sensor cold reduces the temperature-dependent pixel noise background.
- davidmurdoch 3y agoSo less sensor noise, but all your lenses are foggy now. Haha
- malfist 3y agoWell, for dark frames the lense cap is on. The idea is that you're taking a totally black photo. Freezer, along with being cold is also a big metal box that will help deflect some rays
- dekhn 3y agoIt's not the lens, it's the sensor that's kept cold- in practice, people taking low-noise shots would use something like this: https://amscope.com/products/mt5800-ccd https://amscope.com/products/mt5800-ccd If you put it in a freezer, you can use desiccant or other strategies to avoid moisture-fogging. Or just wait til everything reaches equilibrium?