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If you sufficiently swamp read noise, and even with banding, 1/4 - 1/3 histogram on most DSLRs (all modern DSLRs) these days is enough, then you shouldn't see any banding in the final result. However I suspect the histogram on.well, both of these shots, was probably very close to the left edge, well below 1/4 histogram. This is a good example of what happens if you woefully underexpose. So simple calculations do not always do the trick - the camera manufacturers have the last word!Ĭalculations will tell a lot, real life images will verify or falsify - and raise some new questions.Ħ0x1 sec expose - banding and other trouble.Ģx30 sec exposure and the image is MUCH cleaner.
Apt vs backyardeos iso#
Here is a real world answer (there are a lot of alternative answers to this question as different camera makers tune their image sensors very diffenently).īanding seems to be a function of saturation and ISO and several other factors. If you cannot get to 1/3rd histogram in 120 seconds, then that would indicate you probably don't have as much LP as an average suburban yard, and you might be able to expose for longer. In a red zone, stick to 1/3rd histogram exposures (as measured by the back of camera histogram, or by a program like BackyardEOS/BackyardNikon or APT). The general rule of thumb is to avoid exposing beyond 1/3rd histogram.
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Light pollution will also implicitly limit your exposures, regardless. It will have a small impact on your image if you use 30圆0s subs, but not enough to really care about. If you are imaging in a region of high light pollution (say the average suburban back yard, which is usually a red zone), then you don't really need to care about read noise at all. Because of both of those, which individually are usually a larger source of noise than read noise, and combined most definitely so, read noise is usually a much smaller problem. You also have dark current and light pollution to contend with. Imaging in the real world is a bit different, as we have more sources of noise than just read noise and the object signal. Ignoring dark current and any noise from light pollution, and assuming 1e-/s signal flux: It's not quite as bad as having 150e- read noise total.because noise adds "in quadrature" (that is, you add it then take the square root). On the other hand, if you stack 30圆0s subs, you will have thirty "units" of read noise factored in.
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Say read noise is 5e-, then a single 30 minute sub would have 5e- read noise. A single 30 minute sub would have one "unit" of read noise. Stacking will be similar, but not the necessarily same.