[pure-silver] Re: duplicate info
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 24 Jun 2005 13:57:18 -0700
----- Original Message -----
From: "Nick Zentena" <zentena@xxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, June 24, 2005 9:28 AM
Subject: [pure-silver] Re: duplicate info
On Friday 24 June 2005 12:24, Chuck . wrote:
get the image he needs with little distortion. The WA
has the advantage of
being a closer focusing lens than other lenses of longer
focal length...
The problem is he'll have to focus closer with the short
lens. No? To get the
same size image on the negative the camera will need to
be closer with the
55mm.
Or should I go for lunch?-))
Nick
The problem with a wide angle lens is the light fall off
away from the center of the image. Also, most wide angle
lenses are more sensitive to object distance as far as loss
of correction. A normal or somewhat long lens is better.
I also disagree with the idea of using diffuse light. For
copying photos one needs cross lighting at about a 20 to 45
degree angle. A polarizing filter on the camera is helpful
in suppressing reflections from the surface of the print.
The position of the lights will depend on the nature of the
surface of the photo to be copied. The best copies will be
from glossy surface paper. Suppressing the texture of
textured surfaces will requrire some experimentation. If you
can obtain sheets of polarizing material large enough to
cover the lights they can be used in conjuction with a
polarizer on the camera to reduce the effect of texture.
Other choices will depend on what equipment is available.
A sheet film camera is desirable but not necessary. Where
they can be adapted to the camera enlarging lenses are ideal
for copying.
A note on distortion: Most camera and enlarging lenses
are rectininear, that means that a flat surface with squares
on it will be reproduced exactly regardless of the focal
length or distance. The "distortion" seen in photos taken
with wide angle lenses (but not fisheyes) is from viewing
the picture from the wrong distance. The effect does not
appear when copying. Most reasonably modern lenses are
designed for a flat field although enlarging lenses and
process lenses are probably better than average camera
lenses for this. Also, slow lenses are less affected by loss
of correction when the object is a different distance than
the designe optimum, which is infinity for the usual camera
lens.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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