[LargeFormat] Process lenses... which one should I get?

[Richard Knoppow]

----- Original Message -----
From: "Jim Hemenway" <jim@hemenway.com>
To: "Large Format Group" <largeformat@f32.net>
Sent: Friday, March 14, 2003 12:44 PM
Subject: [LargeFormat] Process lenses... which one should I
get?


> Gents:
>
> I need your collective help/advice.
>
> I have a pick of one of two process lenses from the same
man who gave me
> the Rodenstock APO-Ronar CL 420mm... the one with great
coverage for the
> 8x10, but so-so for the 11x14 because of its small angle
of view at
> infinity... it covers 11x14 well at 1:1.
>
> The lenses offered are 600mm and 890mm and are from the
same process
> camera.  I haven't checked my bellows to see if it will
extend to 890mm.
>
> He's offering me only one of them... which one will give
me the best
> coverage?
>
> --
> Jim - http://www.hemenway.com
>
>
  If the lenses are of the same type of course the longer FL
will have the larger image circle.
  For process lenses of the Dialyte type (like Apo Artars)
its safe to assume the maximum image circle for pictorial
use (at infinity focus) is about equal in diameter to the
focal length. This is larger than predicted by the
manufacturer's image angle specifications because the image
quality at the margins doesn't have to be as good as for
process work.
  The coverage of Dialyte type lenses does not get larger
when stopped down, the above assumes the normal stops used
in pictorial work, say f/22.
  The main effect of operating at infinity instead of 1:1 is
to pick up some coma. Coma is proportional to the stop so is
pretty much gone when the lens is stopped down perhaps two
stops from maximum aperture.
  The diagonal of an 11x14 is about 18". These two have
focal lengths of approximately 24 and 35 inches, so should
have plenty of coverage.
  What the dickens is he going to do with the _other_ lens?
Can you talk him out of both?
  Also, check your bellows draw, you will need a minimum of
a little more than the focal length for infinity focus. You
don't want to work with the bellows fully extended all the
time. You may need to build an extension of some sort. About
the only cameras I know of with sufficient bellows extension
are the monster studio cameras. The 8x10's generally had 50
inches. I don't know the limit on the 11x14 Deardorf but it
must have been around 72 inches. Not exactly field cameras.
  Andreas Feninger, who wrote some pretty good books on
photography, made some famous LF photographs of Manhattan
using a very long focus lens. He built a long wooden
exetender supported by a fourth tripod leg.