double image when making long exposuresgreenspun.com : LUSENET : Large format photography : One Thread
Hi again friends. I'm still having the double-image problem when making long exposures, and have eliminated the possibility that it's a bellows or pinhole issue. Others have mentioned having the same problem, suggesting that the film may be "popping" during my long exposures, due to being exposed to the air after being inside the film holder.
I have another theory that I thought I'd run by you to see if it has any merit (any film manufacturing experts out there??). I've only had this problem when making long exposures, in dim light, with small apertures. So, what I'm wondering is, if there is some kind of internal reflection going on inside the film, that only becomes visible on the film when the light levels inside the camera are extremely low? What I'm thinking is that the image might be reflecting off one of the emulsion layers, or the back of the film. The double image is always just slightly offset from the "correct" image-- maybe 0.5 mm or so, and when using front rise it becomes more pronounced toward the bottom of the film (i.e., the image area that's furthest from the center of the lens, and the most susceptible to such a reflection).
The reason I've come up with this is, my film is frequently exactly the same temperature as the ambient air because I backpack with my camera, so the "popping" issue likely doesn't apply. One morning I found what would have been an all-time killer image in the rainforest, and just to make dang sure I got one good original, I shot all of my film on the same image-- 16 sheets, and EVERY SINGLE ONE had the identical double image problem. My lens, bellows, lensboard, aperture, etc., are all pristine, and I always tap the film holder several times to lodge the film in place. I can't think of any other thing that it could be.
Thoughts, similar teeth-gnashing experiences?
-- chris jordan (email@example.com), April 12, 2001
It seems to me that if every sheet has the same double image, there is some problem inherent in the camera or lens. I won't speculate as to what. Have you tried borrowing another lens to use? Or borrowing another camera to use with your lens? That may be the only way you'll figure it out.
-- Ed Buffaloe (firstname.lastname@example.org), April 12, 2001.
Not sure my logic is right here but I'll toss this out anyway. It would seem like if reflections are the problem that they would also be a problem on bright days when using short exposures. I seldom see this problem with 4x5 but often with 8x10. Never have seen it with 2 1/4 x 3 1/4 sheet film. Mostly on hot humid days with long exposure times. I've blamed it on the film shifting during exposure. The double image is usually near the edges. Maybe I should let the camera sit for a time after I pull the dark slide. Then again maybe there is something about reflections in low light vs. bright light that I'm not seeing. Chuck
-- Chuck (email@example.com), April 12, 2001.
Chris, I can empathize. I have certainly been there. It is not only the temperature that is causing the film to buckle during exposure it is humidity. A partial solution is the open the dark slide and let the film sit there (in contact with the more humid air) for 15 minutes. I find that 2-3 minutes is just not enough. The real solution is the Schneider vacuum back but I have not sprung for that yet. Next time instead of exposing 16 sheets, draw the dark slide and just sit there and wait. It will be time well spent. One last thing, before you put the holder into the back, give a light rap on the forearm. This seats the film so that it does not "drop" in the holder during the long exposure.
-- Pat Raymore (firstname.lastname@example.org), April 12, 2001.
The popping issue may not have to do with temperature, but humidity. Were these pictures made in misty or foggy conditions? I've run into this repeatedly with my oversize cameras on foggy days. I think that it is the bellows-full of humid air that the film from the plastic-wrapped holder is suddenly exposed to when the darkslide is drawn. The sudden absorbtion of humidity may pop the film position. The only solution I've come up with for working with sheet film and long exposures in humid conditions is to pull the slide and wait a minute or more before beginning the exposure. I have done this a few times successfully but don't know if it will be a permanent answer to the problem. Obviously, if your popped negs were from the Mojave desert this analysis would not apply, but since you mention a rain
-- Carl Weese (email@example.com), April 12, 2001.
hey guys, the vast majority of my shooting is in very humid conditions (i do live in seattle after all) and my exposures are all very long-- almost always longer than 10 minutes and frequently in the 1-3 hour range, shot either at night or in the rain on those famous seattle dark dreary drizzle days when cars have their headlights on at noon. so, i'll bet the humid-popping thing is the answer. thanks so much for your responses-- the humidity issue is not something i ever would have thought of, and it's never been mentioned in any of the literature i've read. i appreciate you guys taking the time.
p.s.: if you're interested to see what Velvia does under long exposure conditions in the above-described lighting, check out my website: chrisjordanphoto.com.
-- chris jordan (firstname.lastname@example.org), April 12, 2001.
Is the 0.5mm offset of the image always along a vertical axis? If it is, I would suspect that the film crawled. That means that the film moved in the holder during exposure. I always avoid that possibility by tapping the holder in the palm of my hand before inserting it into the camera to make sure that the film is moved to the lower edge of the holder.
-- Ken Burns (email@example.com), April 12, 2001.
Chris, I would also suspect that your problem is the humidity (the emulsion absorbs moisture making it pop outwards). Leaving the slide open for a while will probably solve this. However, the fact that it happened to all 16 sheets of film, in exactly the same way is a bit concerning. Does this happen only with long exposures, or do you see this with short ones as well? Because maybe your lense is projecting a second image onto the film.
I can't see it being internal reflections as they are not focussed back onto the film. Reflections would result in general flare and loss of contrast.
-- Dave Anton (firstname.lastname@example.org), April 12, 2001.
I have to believe this problem is due to some optical abnormality. The film can't be moving as you have proven this to be just about impossible. Let me ask a few questions. What lens are you using? Are you using a filter? What kind of filter is it? Is it on the front or rear of the lens? You say the problem seems to become alinear when you employ rise. If the offset grows larger the closer the projected image gets to the outer limits of the image circle, might this indicate something amiss inside the lens? Has the lens ever been worked on? I'm just throwing out some things to consider for the purpose of getting everyone to think about every possible oddity that could be at the root of your problem. I don't believe it could be related to light reflecting off the film or inside the camera as this reflection would be totally diffused and not result in a focused image back on to the film.
-- Robert A. Zeichner (email@example.com), April 12, 2001.
Chris: Try this. Put a piece of double-sided tape in the center of a film holder and tape the center of the film to the holder. It will push the film outward a bit, but that won't matter. Then make an exposure as you do when you get the double image. That should let you know if the film is popping. I still think you have a camer or lens problem. I don't live in Seattle, but I live on the south side of Alabama and most of the time our air is moist enough to drink. I have never had the problem you are experiencing while I am shooting 4x5. I would try, as another poster suggested, to borrow an identical lens or try your lens on another camera. These type problems can make us want to take up golf, but I think you can find the solution if you try keep up the search.
-- Doug Paramore (firstname.lastname@example.org), April 12, 2001.
I was going to ask what Robert did - what lens are you using? I'm thinking the lens might have ghosts that for some reason become more apparent when the reciprocity fails.
I'm having a difficult time believing that the film is sliding in the holder almost exactly the same way every time.
-- John H. Henderson (email@example.com), April 13, 2001.
Film movement in the holder is actually a very common problem, especially when you are working with long exposures. Anyone who has very much studio experience working with the long exposure times dictated when working with hot lights is well aware of the problem. Those who are knowledgeable are well aware that it is almost mandatory to tap the film holder lightly in the palm of your hand before inserting it into the camera in order to make sure that the film has fallen to the bottom (which side of the holder that is the bottom depends on whether one is shooting a horizontal or vertical composition). Doing so will prevent the gravity-induced movement.
If you will hold the film holder in a horizontal plane parallel to the ground, you can hear the film move around inside the holder if you quickly move it back and forth from side to side.
Robert Mapplethorpe has a "famous" portrait of a princess from somewhere in Europe that has the double image you will get if the film moves during exposure. If your double image is similar to one he got, then you problem is definitely film movement in the holder during a long exposure.
-- Ken Burns (firstname.lastname@example.org), April 13, 2001.
I would tend to blame your lens. If you shot 16 sheets and EVERY SINGLE ONE had it, I think the "popping film" is less likely. Borrow a second lens and next expedition shoot the same picture with each lens - - mount your lens, shoot picture, mount second lens, shoot picture. Does this happen when you are shooting into a light source? That has happened to me -- a lit lamp image was double -- perhaps reflections from wet plants, etc., are causing the problem.
Are you using filters and shooting into a light source or bright reflection? That, too, caused a double image once in a picture a friend took -- all the film he shot with the filter in place had a double image, the film he shot without the filter did not. Go figure. Get rid of the filter or try mounting it behind the lens.
-- william blake (email@example.com), April 15, 2001.
I can't think of a lens-based problem which will get stronger merely because the light is weak. I suppose the back of your aperture blades could be shiney with wear, but you'd see that straight away.
Try mounting the lens with the lensboard rotated through 90°. If the ghost image doesn't rotate it's highly unlikely that your lens is at fault. If it does rotate, bulging film can't be the issue.
-- Struan Gray (firstname.lastname@example.org), April 16, 2001.
One last option: your lensboard is loose, or the lens is loosely mounted to it, or the front standard wobbles. Think in terms of a wobbly table with one leg too long so that there are two stable positions. The double image arises when the lens rocks or moves during the exposure under the (random) influence of vibrations or wind.
-- Struan Gray (email@example.com), April 16, 2001.
There is one more cause for your double images that I have experienced that you should probably check out. A tripod leg that is slipping slightly during the exposure. I have experienced this in two ways. One was in soft sand, and another occurred when the plastic sleeves the joints of my Gitzo tripods became so wore that they began to slip.
-- Pat Raymore (firstname.lastname@example.org), April 16, 2001.