Archived posting to the Leica Users Group, 2001/02/13
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]
At 9:50 PM -0500 2/13/01, bill harting wrote:
>Norman, I have been using the summicron 35, mostly wide open, with this
>shade for only a couple of months and am not aware that it causes
>vignetting. I had been using it with a 3.5 summaron, also without this being
>a problem. could i have overlooked it? i am sure. Maybe someone has done
>some more explicit testing?
>
>bill
The following is some stuff I posted on checking for vignetting at
various times:
- ----------------------
Vignetting cannot be reliably checked through any viewfinder or on
film. The following is a procedure which does work reliably:
<snip>
In any event, if you mount your lens of concern on your camera, open
the camera back and lock your shutter open with a cable release or
whatever, hold it up to a brightly lit surface such as a window, you
can look through the front of the lens and see the film aperture
through it. Look for the corners, and stop your lens down. If you
have a 50/1.4 lens on your camera, you probably have to stop the lens
down 4 stops to f/5.6 or so before it is the aperture blades that are
cutting off the light coming from all directions, rather than part of
the lens barrel. A 105 macro lens with an aperture of f/4 might need
to be stopped down only one stop, or also to f/5.6 before the same
condition applies. Only at this aperture or smaller does physical
vignetting cease, and the only vignetting that still applies is
optical vignetting due to the cos^4 law and other design issues.
<snip>
You can also check for filter or hood vignetting this way. If the
filter or hood cuts into the light path while you can still see the
corners of the frame, it vignettes at that aperture and that
focussing distance (and that focal length, if a zoom)
- ----------------------
You can check the other way around, too, by looking through the back
from the film gate corners, and seeing whether you can still see
light through the lens, or whether the hood (or filter) cuts into the
light path.
You have to do this regularly on LF cameras when using a lot of
movements and bellows shades w/flaps; it's the only reliable way.
- --
* Henning J. Wulff
/|\ Wulff Photography & Design
/###\ mailto:henningw@archiphoto.com
|[ ]| http://www.archiphoto.com