[LargeFormat] Trouble with calculating F-stop

[Les Newcomer]

Guy

Those aren't F stops,  those are stops on the Unified System or US stops

There's a complicated mathatical formula to convert, but us photographers 
just use  "f16 and US 16 are the same"  You'll notice that on your scale 
there is no f11 f22,  they double every stop, fstops double every other.

so   4   8   16   32  64   128
is    8   11  16  22  32    45

so your calculations seem to be correct.  f45=Us128
On Sunday, October 27, 2002, at 06:47 AM, Guy Glorieux wrote:

> Greetings colleagues,
>
> I've been away for a while from the list but I'm back now and apologize
> for cutting into an interesting discussion on photography as art.
>
> I'm running into a frustrating problem with determining the actual
> F-stop aperture on  the lenses for my 11x14 camera.
>
> One lens is an old Wollensack 18.5" triple convertible, with the F-stop
> running from F 4.0 to F-256 at the 18.5" focal.  However, when I try to
> use the indicated F-stop with my meter, I get an image that is way
> over-exposed.  In fact, if I calculate the diameter of the aperture at
> 18.5" focal at, say F-128, it gives me F-45 instead of F-128.  On the
> other hand, if I use the exposure reading for F-45 from my meter and set
> the lens at F-128 (as indicated on the lens), I get a perfect picture.
> (The meter is not the source of the problem.)
>
> I have exactly the same problem with another lens, an 19" apochromat
> Atar F11.
>
> Anybody can explain to me what is happening?
>
> Thanks in advance,
>
> Guy Glorieux
>
>
>
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