Beautiful widefield - I'd almost convinced myself I need the 14-24mm f2.8 lens, but the 24-70mm is a much more practical thing to own, and that's really sharp for such a lens at full throttle.
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Originally Posted by gregbradley
As noise is the square root of the signal, a stronger signal means the noise is a smaller component of the image allowing higher ISOs (amplification).
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Hi Greg - can you elaborate on this a little? Other than the root N improvement in signal to noise you obtain by stacking N frames, I had never heard of this relationship.
Noise is going to be a sum of the thermal noise, skyglow and light pollution, as well as the abberations and diffraction peculiar to the optics, and completely independent of what you're trying to photograph. Amplification (higher ISO) will boost noise and signal identically, whereas the time variant nature of the noise means a longer integration will average out some of the noise (with a limit imposed by the average noise power) while increasing the signal.
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Hehehe, thanks Mike. I have been spooked early on in astroimaging by low lying stars that appear to move and if you look at them long enough they start to appear to be moving towards you!
Greg.
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I've seen exactly this effect late on an all-nighter and drawn the attention of my observing partners to it. Only when I grabbed my binoculars did I realise those stars were completely staionary and my mind was playing tricks. I wonder how many UFO sightings are due to this?
Cheers,
Andrew.