Interesting rethink of ISO and Imaging

[ngc2403]

Welcome,

i have some uneasy news for all DSLR astronomy imagers

''The proper reason to expose to the right comes from figure 12 on page 2, showing the rise in signal-to-noise ratio with increasing exposure. By increasing the number of photons captured, the S/N ratio improves, and the image quality improves directly in proportion to that improved S/N ratio. For instance, that ISO 1600 shot above, has one stop more highlight headroom than the corresponding ISO 3200 shot, and (assuming the shooting conditions allow) opening up the aperture by one stop or slowing the shutter speed by half will improve the S/N ratio while pushing the histogram one stop to the right. Shooting at lower and lower ISO continues to provide more highlight headroom, and thus higher and higher absolute exposure is possible, allowing higher and higher S/N ratio. The end result is that exposing to the right at the lowest possible ISO provides the highest image quality, but not for the reason usually given.''

is a quote from a very detailed paper on DLSR's and there noise properties in general. Written by a photographer, his work is all about getting the best images and i think that i makes the subject of exposure lengths, SNR, ISO and the rest much easier to think about plus it contains some interesting points about imaging in general.

full website covering three pages

Noise, Dynamic Range and Bit Depth in Digital SLRs

I don't know about the rest of you but i think i will be trying some of this stuff when i finish my exams. I don't often suffer from planes etc going through subs and i would like to get some detail in the cores of galaxies so i think it's going to be ISO 100 and long >10 mins subs maybe 30 see how it goes.

ally

[Aza]

I have not read that paper yet, and to be honest, most of this stuff is above my head.

However from what has been said on this forum recently, it seems that going over 5-10 minute subs with a DSLR is not advised, as you start to increase noise faster than signal, so it is actually detrimental to your images.

I had previously been shooting 20 minute subs, but I am now going down to 6 minutes, but as yet not had any results to confirm this.

[ngc2403]

I have not read that paper yet, and to be honest, most of this stuff is above my head.

ok but that is probably the reason why you seem to think that noise increases faster than signal.....

i think maybe you should have a wee read through it as it is a nice math and equation light review