[LargeFormat] Trouble with calculating F-stop

[Guy Glorieux]

Thanks for both your replies, Les.

I'm just a bit perplexed by your comment on the Atar being symetrical
and the implications for the focal length and the aperture.
I will come back to you on this since I'm really squeezed for time the
next three days.  But there are features of the Atar that I did not
expect to find when I bought it this past spring which you may be aware
of (e.g. the opening on the side for waterhouse stops, as it seems).

Thanks again and I'll be back around the middle of the week.

Guy


----- Original Message -----
From: "Les Newcomer" <lnphoto@twmi.rr.com>
To: <largeformat@f32.net>
Sent: Sunday, October 27, 2002 10:37 AM
Subject: Re: [LargeFormat] Trouble with calculating F-stop


>
> On Sunday, October 27, 2002, at 07:21 AM, Les Newcomer 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.
>
> >> I have exactly the same problem with another lens, an 19"
apochromat
> >> Atar F11.
> Now it's a different problem with the Artar since at f11 it can't be
in US
> stops (US doens't have a US11)
> I'm not sure what to tell you on this one.  Is it all there?  Since
the
> Artar is symetrical, you can use half of it. This gains you a 1.75x
focal
> increase and a decrease of about 2 stops.  there should be cells
(glass)
> both front and back.
>
> Les
> >>
> >> _______________________________________________
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> >>
> >
> >
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