[LargeFormat] Goerz Artars

[Guy Glorieux]

Michael, Ken,

Thanks for the information.  I should be getting the lens in the not too
distant future and will be reporting on what I get.

Michael, you had a formula for working out coverage, but I didn't quite
understand.  What is the "theta" of a lens?  Is this information easy to
find for any lens?  Then in the formual D = 2 f tan (theta / 2), is it a
straight multiplication of all factors?

Also, why would the coverage increase with stopping down the lens.  I
seem to recall having read this somewhere, but I don't quite understand
how this would work.

Finall, why would the coverage increase when shooting on a 1:1 ratio,
versus landscape?

Thanks for helping me in my education.

Guy

P.S.  Interesting reference you make to pinhole, Michael.  There is a
rule of thumb in pinhole photography that the useful coverage is about
3.5 times the Focal.  This is due to light falling out as the focal
increases on a flat film plane as the distance increase away from the
center of the image - the effective aperture thus closes down.  There is
also the fact that the shape of the pinhole turns into an oval as it is
considered from the edges and, finally, there is loss of light too due
to the thickness of the material in which the pinhole is cut.  Not
terribly scientific, I'm afraid, but useful to know.

----- Original Message -----
From: "Michael Briggs" <MichaelBriggs@Earthlink.net>
To: <largeformat@f32.net>
Sent: Saturday, May 25, 2002 5:23 PM
Subject: Re: [LargeFormat] Goerz Artars


>
> On 25-May-02 Michael Briggs wrote:
> >
> > The diagonal of 11x14 is 17.8 inches, so the lens probably won't
fully cover.
>
> My calculation is based on the coverage typically cited by
manufacturers' of
> this lens design.  Since you are probably making contact prints, your
needs for
> resolution may not be the same as in the original application of the
lenses,
> and the coverage may be somewhat larger by stopping down.
>
> --Michael
>
>
> P.S.  If one stops down far enough, the lens design hardly comes into
play and
> one has a pinhole camera.