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how can i calculate subject distance?

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Offline mantra

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how can i calculate subject distance?
« on: 30 / May / 2010, 13:09:33 »
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hi to all

first i hope it's the right place , i mean in the forum ,to open this topic

how can i calculate subject distance ?

i'm going crazy for it

well i used exiftool and i can NOT find subject distance

i find with exiftool focusdistanceUpper and focusdistanceLower
focusdistanceUpper=2.33
focusdistanceLower=1.94


weird adobe bridge cs5 tells me 2.1m

how can interpretate such numbers ? :o

ps for example the canon 350,XT doesn't have in exif focusdistanceUpper and focusdistanceLower ::)


thanks a lot
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Offline fudgey

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Re: how can i calculate subject distance?
« Reply #1 on: 31 / May / 2010, 12:48:21 »
I really don't know, but your cs5 number appears to be the average of upper & lower distances, which may or may not equal to subject distance but at least it's most definitely in focus (assuming those two distances from exif are) and as such probably pretty close.

If you wish to dig in deep and see how CHDK calculates it's subject distance OSD, you'll need to study core/gui_osd.c function void gui_osd_calc_dof(). Note that CHDK DoF calculator might not be accurate either, at least some of its output has been discussed before, you could find a thread about it using the search.
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