Uneven light fall-out on transparenciesgreenspun.com : LUSENET : Large format photography : One Thread
On two of my recent trips, I've noticed that some 5x7 transparencies have a kind on light fall-out on the edge. The area which is affected is always the right edge, and the light fall-out takes the form of a darker band which is approximatively vertical and about 0.5 inch (1.5cm) thick, between 1 and 2 stops. The left edge is OK, and no swing was used. The problem occurs only when using a Schneider 110XL with exposures of a fraction of a second in strong daylight (longer exposures seem OK). No lens shade was used, and I have checked for vignetting through the corners of the ground glass. Film was processed professionally. Because I have not observed the problem with longer exposures and other lenses, I suspect the shutter (prontor professional) but I don't know how to test this idea as it appears OK. Thanks for any suggestions.
-- Q.-Tuan Luong (email@example.com), January 29, 2001
I suspect you stepped down when you took those shots. That means the shutter must malfunction significatly to create that kind of effect. You should be able to see it with the naked eye.
-- Sorin Varzaru (firstname.lastname@example.org), January 29, 2001.
Mr. Luong, Maybe, you could trigger this lens on a flash and photograph the shutter right open, checking if there's something on the way. Good luck!
-- Cesar Barreto (email@example.com), January 29, 2001.
I cannot imagine a defect that might occur with a leaf shutter that would manifest itself in a linear band. Since the image is reversed on the film it would help to know which "right edge" you are speaking about.
-- Wayne DeWitt (firstname.lastname@example.org), January 29, 2001.
Before checking the shutter, check the bellows when using this lens. You might have a bellows pleat blocking part of the tranparency when shooting. I don't know how a malfunctioning shutter would make a line of underexposure, though that doesn't mean it isn't possible. You might also have one of the pleats or the back, just in front of the film holder, reflecting back some light from the edge.
Set up the lens in the same configuration as you had when the problem occured & look through with a strong flashlight & see if there is any kind of interference in the light path.
-- Dan Smith (email@example.com), January 29, 2001.
Damn, Q. I have the same trouble with 35mm trannies, and thought it was from an uneven focal plane shutter. Could it be from Polarized light?
-- Bill Mitchell (firstname.lastname@example.org), January 30, 2001.
Where do you get your 5x7 films. I am having a hard time finding any lately.
-- Matt O. (email@example.com), January 30, 2001.
Don't know if this is the same thing but I experienced something similar to what you mention. I was shooting B&W and would get negatives with lower density along one of the 4" edges of the film. This seems to correspond to what you are describing i.e., darker edge with transparency film. My first notion was light leak but then I realized fogging would increase density, not reduce it. It took a long time to figure it out. It was a light leak which was coming out the side of the bellows close to the film plane. The frame blocked this fogging light from hitting the 4" edge closest to the hole but the light sort of sprayed across the rest of te neg, increasing density theree. Of course, when I viewed the neg, it looked the correctly exposed part (i.e., the bit that was not hit by the light leak) was underexposed compared to the rest of the film that was. Proof that perceptual illusions and bugaboos afflict us way after the picture is taken...
You mention that you only get this with one lens, which seems to rule against a bellows leak (althought it might be worth checking for that too - pinholes reveal themselves and hide themselves in the field depending on the focal length used since you rack the bellows out or fold them in etc). Since this is a shorth focal length, is it possible that there is a light leak in the bellows near the lensboard which doesn't affect the film much when the bellows is racked out with a longer focal length but is visible to the film with shorter lenses?
Good luck. Hope you isolate the gremlin and toss it into outer darkness where it belongs... Cheers, DJ.
-- N Dhananjay (firstname.lastname@example.org), January 30, 2001.
Sorry, forgot to add - the strong daylight also makes me suspect pinhole i.e., it may be the beginning of a pinhole and it take strong light to get through in sufficient amounts to affect the film. Although I'm lost as to why longer exposures are unaffected. Cheers, DJ.
-- N Dhananjay (email@example.com), January 30, 2001.
Since nothing in the plane of the shutter/iris can be imaged in the film, I cannot see how that could be the source.
With the problem restricted to one lens, it would seem like the problem involves either the lensboard, or the relative postion of the front and rear standards causing a light leak.
-- Glenn C. Kroeger (firstname.lastname@example.org), January 30, 2001.
Check your lens board to see if it sits properly. I had the same problem with a warped board. Maybe try switching lens boards.
-- john (email@example.com), January 30, 2001.
Wayne, that's the right edge on the transparency, so this would be the left edge in the camera. Matt, for several years I've been cutting down 8x10 film. I'll soon have an article on the 5x7 format.
-- Q.-Tuan Luong (firstname.lastname@example.org), January 30, 2001.
The reason I asked about the orientation of the film is because I too suspected a light leak that was fogging the majority of the film except for the underexposed band. But I suspect that you would have noticed exposure anomalies on the order of 1+ f/stops. I would have suspected a poorly-fitting lensboard, since I've come across a few Linhof-type lensboards that don't seat properly (are you using the adapter on your Canham?). Maybe the processing? Have you changed processors? If you can rotate your back maybe you want to load from the left for a few frames to eliminate somr of the possibilities.
-- Wayne DeWitt (email@example.com), January 30, 2001.
Hi Q-Tuan! I've very much the same problem with a device which I myself put together for pinhole photography. I mountes a metal plate in which there was a pinhole on a self made lens board and all my negatiwes had Two! bads on two sides (one on each side) couldn't find any explaination and only now I understand from all these comments that my self styled lens board must have been allowing for leakage, I guess that yours does the same and I will mount the lens on another board believing that the problem is solved! Take care and thanks for your work on this site.
-- Andrea Milano (firstname.lastname@example.org), February 03, 2001.
Thanks for all the suggestions. I have some new data. I got back a new batch of film from the last trip.
First, this was processed by another lab, so this would eliminate the possibility of a post-exposure problem.
Second, there was one scene where I used 90,110,150, and 300 lenses to get various croppings of the same basic shot. The 90 and 110 images both suffer from the problem. On the 150 image, it's present, but extremely subtle, and totally absent on the 300 image. This eliminates the possibility that the problem would be linked to the 110.
To be more precise about the dark band, it is more like a horizontal gradient, the darker side being along the right edge. The rest of the image appears correctly exposed, and there is noticeable underexposure in the band.
Dan's explanation was what I first had in mind, but after setting up the camera, I could not find obstructions in the light path, and besides, everything looked symetrical.
-- Q.-Tuan Luong (email@example.com), February 08, 2001.
When I've had a bellows obstruction with a wide lens, the result has been a solid band, not a partial obstruction, but who knows? I couldn't really see the obstruction when composing the image either on the groundglass (because of the falloff of the wide lens) or externally. To fix it, I added some loops and cords described in this thread, for gathering the bellows toward the front standard, and I haven't had a problem since. It also makes the camera a bit more stable in the wind.
-- David Goldfarb (firstname.lastname@example.org), February 08, 2001.