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Posted by Doug Clifford on July 09, 1999 at 20:37:01:
In Reply to: Help - slide image problem posted by Len Kology on July 09, 1999 at 18:46:35:
: Can anyone identify the source of this problem. I have used print film for years but this is the first time with slide film.
: Some of the images have dark corners. I used Kodak Ektachrome film and had it processed at a "good" lab. The lens is a Tamron 28-80 with a polarizer.
Hello Len,
The answer is simple. You bought dark cornered slide film - I'm joking, of course. :-)
Actually, what you are describing is called vignetting; what is happening is the film is "seeing" either the polarizing filter or a lens shade you may have on the camera. This is most likely to occur when the lens is at the wide angle setting. The reason you probably can't see it when taking a picture is many 35mm camera viewfinders do not show the whole frame. The reason you haven't seen it before when taking color prints is the machine responsible for processing the film at the lab is cropping off the outside edges of the film frame when making prints, even so-called "full frame" 4x6 prints. When you shoot slides, what you shoot is what you get because the slide frame crops off very little of the frame. It becomes more noticeable. The effect is also more pronounced when using the lens at wide open apertures like f/3.5 or f/4.
In the broadest sense, all lenses vignette to some extent. All lenses have some light loss or "fall-off" from the center of the lens to the outside edge. Most of the time, we don't notice it.
For more information in vignetting than you'll ever want to
know, read the lengthy discussion at
http://www.archiphoto.com/personal%20pages/Vignetting.html (the
link is below.)
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