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fp L ISO 6 testshot

Started Oct 4, 2021 | Discussions thread
xpatUSA
xpatUSA Forum Pro • Posts: 23,016
Re: fp L ISO 6 testshot

Tom Schum wrote:

With Kipon Iberit 75mm F2.4 lens set to F8 or F11 (I forgot which).

Downsized to 30mp.

19mb download for 30mp image

Tom, I often wonder what trickery is involved with the fp's 6 ISO. The reason I say that in this is because your scene looks about hazy sunlight - about 14Ev according to here .

Taking say f/11, your 2 sec exposure, and an EC of plus 0.7EV, none of the equations or tables come out as 6 ISO.

For example, the given equation according to ISO for normal metering is N^2/t = LS/K where K is a metering constant, commonly 12.5 for cameras, so we can say:

S = N^2/t*12.5/L where L = the daylight luminance of 2048 cd/m^2 (14Ev) and ignoring EC for now.

Therefore S = 11^2/2*12.5/2048 = 0.314 ISO.

Now plus 0.7 EC = 2^0.7 = 1.625 so the ISO accounting for that = 0.51 ISO, not 6.

Another chart for 100 ISO gives about 1/77 sec for f/11 plus 0.7EV. At 6 ISO that would be 1/77*100/6 = 0.217 sec, not 2 sec.

What's going on?!

Anybody?

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Just interested in the technology.

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