Vignettinggreenspun.com : LUSENET : Large format photography : One Thread
Vignetting in a negative (i.e. extreme light fall off in the corners) seemingly can be caused by a variety of things - insufficient coverage of the lens for the movements used, the edges of a lens shade protruding into the negative area, or a filter on the lens. With 4x5, I never had a serious problem with vignetting because I use modern lenses with tons of coverage. However, I recently started using an 8x10 camera and some lenses, with more limited coverage than I'm used to. The problem of vignetting is driving me crazy. I'd guess that I get some degree of vignetting in the corners of about a third of all the negatives (about 100) I've made so far. I discovered (too late) that I can't use a polarizing filter and step up ring at all with one of my lenses - even when stopped down to F 64 and the bellows extended well beyond infinity, I stil get vignetting with this lens and filter. Since I contact print 8x10, any significant vignetting in the corners means that the negative is a complete waste (occasionally the problem can be cured by burning in the corners but usually not).
My question is: how do others deal with vignetting problems caused by either insufficient coverage or use of a filter (I don't use a lens shade)? I've read as much as I have been able to find about the problem and it seems to be dismissed by authors saying things like "look through the corners of the ground glass - if you see anything protruding in the lens aperture, you're going to have a problem" or other things like that. The implication is that it's very easy, just kind of glance through the ground glass and any vigneting will be very obvious.
My problem is that the corners of my ground glass are cut out and I have difficulty seeing anything when looking through them. In particular, it's hard to see the relatively subtle difference between the corners of the image on the ground glass and the rest of the image. The method that has come closest to working for me has been to remove the ground glass frame from the camera back and look at the aperture through the bellows, with my head placed at each corner of the back. Sometimes I can see that I'm going to get vignetting, but the problem is that I don't know exactly where to put my eyes when looking at each corner. It seems that if you get your eyes at a sufficiently extreme angle to the corners of the back, it always looks like there will be a vignetting problem even when there really isn't one. However, if you get your eyes too close to the center of the back then everything always looks fine.
Also, you need to know what you're looking for and most authors never deal with that subject. Stroebel's book has some pictures of what a vignetted aperture will look like (kind of like a lemon shape) so that's been the best thing I've found but vignetting caused by different things can apparently can cause the aperture to look different (i.e. the vignetting caused by a lens shade doesn't necessarily look like the vignetting caused by insufficient coverage).
Anyhow, I hope all of this is comprehensible. It's obvious that I could use some help here. Any suggestions?
-- Brian Ellis (email@example.com), April 01, 2001
No sweat. Just declare it fine art, and sign your prints "Atget."
-- Bill (firstname.lastname@example.org), April 01, 2001.
Well, except for something someone else mentioned, it sounds like you've got the bases covered. Look through the corners, take the back off AND you could try turning things around by looking through the lens at the ground glass corners. Take the dark cloth off and bring it around front with you. When you take the back off, you need to keep your eye/head about where the corners of the ground glass would be. I always close one eye when I check.
If the aperture looks like anything other than an aperture - i.e. nice and round, or with the small flat edges of the iris blades showing - you're going to get vignetting. To make it a little easier on yourself, open the aperture all the way up as you check and then close it down slowly as you watch the corners from whichever end works best for you. Close it down until it's round.
There is debate about this. i.e. it'll introduce astigmatism, etc. but try using your filters on the rear of the lens.
Even Adams, the technician supreme, got vignetting from time to time.
-- Sean yates (email@example.com), April 01, 2001.
You missed at least one potential cause of vignetting that I used to get from time to time: bellows sag. This drove me nuts too when I first started at 8 X 10. The answer really is looking in thru the cutout corners. In my experience, this truly works 100%. It sounds like the problem you're having is that the cutout of the corner isn't generous enough to see thru. If you can't easily see the lens aperture, obviously the cutout is useless. If this is the problem, I would (and did) have my GG modified with a slightly larger cutout. As you say, if you can see any bellows, anything other than a round aperture, or the edge of your filter/compendium bellows, you will get vignetting. I think if you have a large enough cutout, you will find this method foolproof. Some don't want the corners cut too large for fear of not being able to focus in the corner. My answer: which looks worse, a slightly soft image in the corner, where you generally won't be looking, and won't notice in a contact print, or a big black ring in the corner that draws your eye away from the subject? It was a no-brainer for me, and I've never had a problem since getting the cutout done, after having about 25% vignetting previously.
-- Nathan Congdon (firstname.lastname@example.org), April 01, 2001.
Except that you may have to stand on something, it's much easier to check from the front, looking back through the lens after stopping it down. If you can see the corners, or cut-outs, of the groundglass in the full circle of the aperture, you're ok. Don't try to judge vignetting by looking for fall off on the ground glass image. When you look from the back through the cut-out corners, you don't try to see what's on the groundglass, you purely want to see whether the corner of the glass has 'a clear view' to the aperture. With a short lens you can do an experiment by introducing a strong front rise, and then stopping the lens down with one hand while looking through the corner of the ground glass: the bright spot of the lens will start out football shaped. As the aperture gets smaller, you'll see the round aperture opening as football shaped, and then finally it will look round when you can see the whole thing, and at that point you've got coverage.
If the vignette is caused by something like a lens hood or too-small filter, when you look from the corner of the groundglass you'll see the full circle of the aperture, but beyond it instead of a bright view you'll see the dark shape of whatever is cutting off the coverage. If you've fully exceeded the coverage of the lens, then you may see the full circle of the aperture but even at f/64, you'll be looking at the inside of the lens barrel instead of the outside world. Bellows cut-off will also show clearly because the bellows will block your view to the front of the camera from one o
-- Carl Weese (email@example.com), April 01, 2001.
Brian: You need to lood at the aperature at the stop you intend to use. Many lenses increase coverage when stopped down. What lenses are you using on the 8x10? I really think you are making the whole process more complicated than it is. If you keep your eyes a few inches away from the ground glass and look through the cutoff corner, you should be able to see the aperature nice and round. Do that at each corner. Do check for bellows sag, which is not uncommon on 8x10. There are usually rings on the bellows where you can pull it tight to the front and avoid sag. Also, you can use a piece of cardboard folded into a tent to place under the bellows. A sagging bellows and front rise can get you in trouble in a hurry. As for filters, Sean gave you good advice about using a rear filter. There are many adapters out there that slip onto the front or rear of the lens and allow you to use square filters. The eliminate vinetting due to the filter rings. Practice a little and give everything a good checkover. You should be able to solve the cutoff problem without a lot of effort. Incidentally, some of the 305mm (12) lenses for the 8x10 had very little coverage, especially the tessar type design.
-- Doug Paramore (firstname.lastname@example.org), April 01, 2001.
Thanks to all who responded. Fortunately I don't have a problem with bellows sag. Unfortunately, my most used filter is a polarizer and I don't think there's a way to use one on the rear of the lens. I don't try to look at the corners of the ground glass. The two methods I've mostly tried have been looking through the corners and removing the ground glass frame and looking through the bellows to the aperture. I'll try again, keeping some of the suggestions at hand. Thanks again, this is a terrific forum.
-- Brian Ellis (email@example.com), April 01, 2001.
Brian, if you feel its the polarizer thats the cause of the vignetting then have you considered the B+W Special Pol Filter which is designed for extreme wide angle lenses and has an extended filter mount or use a step-up ring with a regular polarizer. Good luck,
-- Trevor Crone (firstname.lastname@example.org), April 02, 2001.
Another cause, although not true vignetting, is bellows sag (or, more properly, bellows fold) with bag bellows. Personally I always use polaroids before taking the shot and this takes care of the problem. I would mention though that vignetting is not always a bad thing. Most of my work is studio still-life, and I often deliberately introduce vignetting when using extreme movements. It can be a very useful tool for fading the background to black.
-- Garry Edwards (email@example.com), April 03, 2001.
This is a follow up to my original question. After reading these messages I hauled out the 8x10 Deardorf and discovered three things. First, in my original message I said that when I looked through the cut out corners in the ground glass I couldn't see anything. When I looked again after reading these messages, I discovered that I actually could see through the corners to the aperture, I just had to scrunch down and look upwards when looking through the bottom corners and stand on my tip toes and look down when looking through the top corners. So this was a big help. Secondly, someone's description of the aperture as looking like a football when covereage was insufficient, and looking through the corners while stopping down, to see when it started looking like a normal aperture, was also a big help. Finally, I discovered that I had been making a major operating error with this camera, an 8x10 Deardorff that I acquired a couple months ago. I realized in playing around with all this that I had been placing the lens board panel at what amounted to the absolute bottom of the fall position instead of having it centered on the film. That obviously was contributing to my vignetting problems. In any event, after trying some of the suggestions offered here, I now feel reasonably confident that I will be able to predict when vignetting is going to occur. Thanks again for the help.
-- Brian Ellis (firstname.lastname@example.org), April 03, 2001.