f-number equivalent between m43 and FF

Started Mar 25, 2014 | Discussions thread
xpatUSA
xpatUSA Forum Pro • Posts: 10,525
Re: That "explanation" is so wrong...

bobn2 wrote:

xpatUSA wrote:

xpatUSA wrote:

OK, I used your method same as before but there was a problem or two. A normal scene shows a change of metering when zooming. So I shot a letter-size piece of white paper instead. Then, because it's a Foveon, each pixel is 3 photo-sites so I exported only the green channel from RawDigger to ImageJ.

Image size: 1134x756px (SD9 LO res RAW)

Histogram area selected: 670x552px

35mm zoom: mean 67.185, s.dev 8.551, min 32, max 104

70mm zoom: mean 77.853, s.dev 16.98, min 32, max 140

Numbers above are 16-bit grayscale levels.

Curves were classically bell-shaped.

Oops, the focal lengths were typed back-asswards, should be:

70mm zoom: mean 67.185, s.dev 8.551, min 32, max 104

35mm zoom: mean 77.853, s.dev 16.98, min 32, max 140

. . . making the wider-angle shot the noisier.

Confirmed by a test I just did at HI res (avoids binning obfuscation):

70mm: mean 49.7, s.dev 11.9

36mm: mean 48.4, s.dev 24.4

These last figures straight from RawDigger, whole image, no exporting involved. Numbers are un-scaled raw data values. Much mo' simple!

-- hide signature --

Cheers,
Ted

I'm still not clear what it is you're doing.

May I make quite clear that this not my idea. I'm following a suggestion made by Great Bustard but with an absolute minimum of processing.

What you need to be doing is:

I'm not going to be following alternative suggestions by anyone else, sorry.

-- hide signature --

Cheers,
Ted

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