vignetting problemsgreenspun.com : LUSENET : Large format photography : One Thread
Hi, I have a vignetting problem and was wondering if anyone could help me out. I am using a Toyo 45AX with a Caltar II 65mm f/8 lens in a recessed board and trying to use it on a regular basis with a Wista 6X9 holder. I am getting vignetting around the edges of the 6X9 frame, and yet the lens does cover up to 4X5. I have the one 4X5 image taken with this lens to proove it. I can't figure out why the 6X9 is getting cropped though. I am using no hood, or filter and very little, if any, movements. My usual shooting aperture is between f/32 and f/45 with exposure times ranging from 1/8 to 45 seconds. What adds to the mystery more is that a few of the 6X9s with this lens have come out o.k. What am I doing wrong? Can anyone help me? Thanks for an
-- Brent Flint (firstname.lastname@example.org), June 12, 2001
Brent: I would cut a cardboard mask with a 6x9 opening to fit on the grond glass and then look through it and the lens to see if there is something blocking the image path. It might be that the recessed board is coming into view under some circumstances. With the mask, you should be able to see if there is an obstruction to the light path, either by looking through from the back or from the front. Put a light behind the camera and look through the lens to see if you can see all four corners at infinity focus.
-- Doug Paramore (email@example.com), June 12, 2001.
Brent: You say that the vignetting is around the edges. By that, do you mean that the vignetting is along the sides and ends of the frame? If so, is it along all four sides of the frame at the same time? If not along all four, along which side does the vignetting occur? The reason I ask is that most of the optical vignetting problems we encounter are usually in the corners of the frame. If the problem isn't confined to the corners, I would suspect that the problem is somehow related to the film holder.
I'm not familiar with the Wista holder, but I would suggest examining that holder to determine if there is something about it that might be causing the problem. How far is the film opening recessed back into the holder? Is it far enough that some vignetting along an edge could result from any rise or fall movements? Do you totally remove the dark slide when exposing? Check those things out and let us know what you find.
-- Ken Burns (firstname.lastname@example.org), June 12, 2001.
The more I experiment, the more I suspect it is an image circle problem. Is it possible that the lens just doesn't have the covering power at infinity at such a small aperture? Is there a way of correcting for this? I was thinking that I could focus closer, then stop down, but that doesn't seem right. I don't think it's the holder - everything there seems to check out o.k. I'll run a test roll through and try different focus points and f-stop combinations and take notes. Thanks, Brent
-- Brent Flint (email@example.com), June 13, 2001.