G1X Image Quality Comparison: FSAIQ vs Acuity for a range of compacts

Started Sep 25, 2012 | Discussions thread
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FauxMho OP
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Re: G1X Image Quality Comparison: FSAIQ vs Acuity for a range of compacts
In reply to howardroark, Sep 25, 2012

My general philosophy on this graph is to show best case - because nothing you are going to do is going to take you to better FSAIQ or greater acuity.

So yes, for each zoom position I'm using maximum aperture (minimum f/#) and assuming diffraction limited performance. Increasing f/# from that minimum will move you on the graph down (fast) and to the left (slower): acuity goes as focal length / (f/#) and FSAIQ goes as 1/(f/#)^2. Increasing ISO leaves acuity unchanged but drops FSAIQ slowly - as the square root of the number of stops. So going from base ISO (say 100) to 4x base (so 400 ISO) will halve the FSAIQ. I have a spreadsheet on my iPad that can take ISO, f/# offset from minimum, and scene luminosity/EV into account to show when I'll get an "excellent" or "acceptable" IQ, including whether I can hand-hold it or not. Very handy and not too massive an undertaking, but trying to put that into a graphical form is, as you say, impenetrable to most people.

Jumping off point - I like that term. Again, any next-order considerations like lens quality, sensor noise reduction, ISO will only make IQ and acuity worse. So pick a good starting point and see where various compromises (size, weight, cost) get you. If you like the IQ where you end up - be happy with the camera you choose, right!

You are spot-on regarding the 17-85: I wanted a more common lens to pair with the 7D to so a more typical comparison with the compacts. I also have numbers worked up for full-frames like the 5DMIII and soon the D600 and 6D, medium formats, and on up to large-aperture imagers like the recently declassified Gambit/Hexagon spy satellites. But price is a very rapidly increasing factor on all those. "FSAIQ per dollar" and "FSAIQ per pound" are interesting metrics, with the G1X being an excellent sweet spots on both.

Thanks for your thoughts and comments.

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