Best DSLR or ILC for Night Sky Imaging?

Started Nov 8, 2017 | Questions thread
rnclark Senior Member • Posts: 3,755
Re: Best DSLR or ILC for Night Sky Imaging?

landscaper1 wrote:

rnclark wrote:

A significant factor you need to consider in comparing cameras on review sites like dpreview is to put the two cameras on equal footing. Equal ISO is not equal footing. Equal footing is to put them on the same absolute range in photons. If the gains between the two cameras are different, then the signal and noise levels between the cameras can't be compared. For example, does that noise spike you see might in one camera indicate 3 electrons or 15 electrons, translating to 3 or 15 photon noise? Knowing that is the key to understanding which camera has better sensitivity.

Gains are set by the manufacturer, but to first order scale with pixel area. So in the case of a Sony A7s with 8.4 micron pixels versus 5D4 with 5.35 micron pixels, ISO 6400 on the 5D4 digitizes the same scale as ISO 6400 * (8.4/5.35)^2 = 15,800, so best would be the closest (e.g. 12,800 on the A7s) in dpreview's comparison except that they change exposure time with iso, so one can't make a real comparison. So you just have to note that the noise would appear higher in the large pixel camera than in the smaller pixel camera. Then also remember noise in an astrophoto will not be the noise you see in such review sites, but noise from the sky.

Roger, I'm sure you know what you're talking about, but I have my doubts that I do. So, if you could make it simple for me, "Am I or am I not correct in my judgment that the A7s is only marginally better than the 5Div?"

You might be right in your assessment, but if the data are not scaled to the same signal level, one can't really tell, and it might actually go the other way.  But again, these kinds of comparisons are pretty much irrelevant as they do not represent night sky photography conditions.  You do much better by selecting good lenses than obsessing over sensors.

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