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f/3.5
It's time for me to stop whoring the small details of exposure using negative film, or rounding it up to f4 for shooting slides... What exactly should F3.5 read on a Sekonic L-508 or similar as? f/2.5 + 5/10?
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hi there
this might help!
http://en.wikipedia.org/wiki/F-number
it is confusing ... 3.5 is 1 full stop beyond 2.5 
have fun !
john
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Oh god, I got lost in the numbers...
at least for f2.5 it's close enough that I can meter at f2.8 and probably not worry about it, besides my only f2.5 lens has an f2.8 click... haha.
I always thought that f3.5 was ha half stop slower than f2.8... so wouldnt it be f2.8 plus half a stop, reading as f2.8 and five tenths on the meter?
Or am i missing something.
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f/2.8 + 2/3rds, or f/4.0 - 1/3rd.
You could probably get away with calling it halfway between f/2.8 & f/4.0
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 Originally Posted by EASmithV
Oh god, I got lost in the numbers...
at least for f2.5 it's close enough that I can meter at f2.8 and probably not worry about it, besides my only f2.5 lens has an f2.8 click... haha.
I always thought that f3.5 was ha half stop slower than f2.8... so wouldnt it be f2.8 plus half a stop, reading as f2.8 and five tenths on the meter?
Or am i missing something.
on the page i linked to there are 3 tables one is labled "1/3 stop"
it has both 2.5 AND 3.8 and there are 3 third stops between them ... 3 third stops is 1 stop
they go like this ...
.07 .8 .9 1 1.1 1.2 1.4 1.6 1.8 2 2.4 2.5 2.8 3.2 3.5 4 4.5 5 5.6 ...
bold are full stops the others are 1/3 stops ... 2.5 is 1/3 less than 2.8 and 3.5 is 1/3 less than 4
they are 1 full stop relative to eachther
i have never used your meter before
but you should set it up as 2.5 + 1 ... pretty easy
you are lucky you don't have any lenses that use the stoltz or other oddball systems
yours is pretty easy as long as you don't overthink it 
Last edited by jnanian; 03-15-2012 at 12:36 PM. Click to view previous post history.
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Argh. I swear they make f3.5 lenses to annoy me.
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My Weston has 3.5 on the dial; maybe they courted Rolleiflex users.
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There are historical reasons for this, of course...
In Germany, "base 100" was common. 2.2, 3.2, 4.5, 6.3, 9, 13, 18, 25, 36, 50, 72, 100 ...
In France they tended to use "base 10": 2.5, 3.5, 5, 7, 10, 14, 20, 28, 40, 56, 80 ...
And the "modern" system is "base 1": 2, 2.8, 4, 5.6, 8, 11, 16, 22 (which is really closer to 23), 32, 45, 64 ...
The US (Unified System or something like that, not USA) was 1, 2, 4, 8, 16, 32 and so on - where US16 =f/16.
And of course the "reverse systems", which are proportional to either the diameter or the area. Stolze is one, another was called "French System".
Some lenses, especially casket sets and convertibles, have markings corresponding to the diameter of the aperture. Or the area. In whatever units seemed reasonable at the time.
Worst of all are what I call "AU", or "Arbitrary Units" - where the aperture settings are marked with 1, 2, 3, 4, 5, 6. Or 1, 2, 3, 4, 8, 10...
-- Ole Tjugen, Luddite Elitist
Norway
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Your Sekonic should show f3.5. It's measures go much further below that, and much higher. If you have set the custom functions to 1 stop, it will not show you the smaller increments. Likewise, half-stop is better, third stop better again for reversal metering.
.::Garyh
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Canon EOS1N ('Brutus', 1993—), TS-E 24mm f3.5L, 20mm f2.8, 17-40 f4L, 70-200 f2.8L
Pentax 67 ('Pentaximus', 2010—) + SMCP 45mm f4, 55mm f4 & 165mm f4LS;
Zero Image 6x9 multi-format pinhole (2008—); Sekonic L758D;
Olympus XA, Nikon Coolpix P7700
"If you're not having fun, then you're not doing it right!"
♦
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For negs I usually treat 3.5 as 4, so as to err on the side of slight overexposure. For slide, I treat 3.5 as 2.8, so as to err on the side of slight underexposure. You can of course also change the EI just a bit to compensate, as needed.
Don't sweat the petty details, and don't pet the sweaty details.
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