What's causing the band across the bottom on my 4x5's?

Discussion in 'Pinhole Photography' started by picker77, Jan 8, 2011.

  1. picker77

    picker77 Subscriber

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    First light on my new wooden 4x5, using FP4+. Getting a slash of light across the bottom of the negatives, but only when using the camera in vertical (portrait) mode. Since it happens with all film holders, and doesn't happen in landscape mode, I'm ruling out film holder problems, and suspect some sort of inside reflection. I'm new to pinholing, would appreciate any ideas. Please ignore the poor exposures, I'm still figuring this stuff out.
     

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  2. DWThomas

    DWThomas Subscriber

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    Seems like it might be a light leak between the body and the film holder. Is this a manufactured camera or homemade? Do you rotate the camera 90º for vertical vs horizontal or do you load the film or film holder differently?

    I occasionally use a 4x5 with a rotating back for pinhole shots. If I saw that I would suspect a leaking seal in the back rotation mechanism.
     
  3. phaedrus

    phaedrus Member

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    Bellows not properly attached to the rear standard?
     
  4. erikg

    erikg Member

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    is this a homemade camera? it looks like the the holder isn't quite tight to the back in vertical mode, or you are pulling the holder slightly away from the camera when you are pulling the dark slide. A light leak at the bottom of the picture is happening at the top of the camera. I'd also look for light leak, it may be very small and hard to see.
     
  5. picker77

    picker77 Subscriber

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    It's made by another gentleman, consists of a simple but nicely crafted solid walnut box using dovetailed joints. 79mm focal length, 0.020 pinhole @ about f/158. Has tripod mounts for vertical and horizontal. The shutter is my fingertip. I have many film holders, and it's doing it with any of them--but only in the portrait position. FH's are held by large flat plastic "nut" on a stud, one on each side of the camera back. The light seals are sticky-back felt, so maybe I'm tightening the hold-downs too tight and warping the plastic body of the film holders causing them to pull away a little on the dark slide end. Still doesn't make sense to me that it doesn't happen in the landscape position, though, since I don't do anything different other than change the camera's position to horizontal and use the other tripod socket. I'll try a couple of heavy rubber bands at the top and bottom of the film holder and just lightly tighten the hold-down screws, and see if that helps.
     

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  6. tokengirl

    tokengirl Member

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    This does not look like any light leak I've ever seen.

    Since you are getting a dark band at the bottom of the photo, this means that portion of the negative is receiving less exposure than the rest of the film. That portion of the film is at the top of the camera during exposure. Since this band is pretty clearly defined, it looks like *something* is casting a shadow on the top portion of the film plane when you rotate the camera to a vertical position.

    Could gravity be at work here? When you rotate the camera to a vertical position, is *something* moving down to cause this obstruction that is casting the shadow?

    Another question: which direction are you rotating the camera when you go vertical? In other words, are you pulling the dark slide from the top, or the bottom? And, if you are pulling it from the top, are you removing it completely, or just pulling it up? If you are just pulling it up, perhaps gravity is pulling it back down ever so slightly, just enough to cast a shadow?
     
  7. Konical

    Konical Subscriber

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    Good Morning, Picker77,

    I agree with the previous posters. There's an easy to way to check: When you pull the dark slide, be sure that your focusing hood is thoroughly shading the camera; likewise when replacing it after the esposure. If that doesn't resolve the matter, you'll have to look for other camera leaks.

    Konical
     
  8. Ian C

    Ian C Member

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    I think that the problem is a light leak, most likely due to the fit between the holder and the body.

    In the 3 vertical shots, the “band” looks approximately normal and the rest of the scene is fogged.

    The fogged area is strongest on the lower left side of the picture. With the camera in vertical orientation, that corresponds to the upper right. That is where I suspect that the light leak is coming from.

    In horizontal orientation the leak will be on the bottom edge to the right. With the leak along the bottom edge, the amount of light reflected by the ground is likely considerably less than when the camera is in vertical orientation with the gap able to “see” the sky to the upper right.

    You can verify the leak by attaching the holder in a relatively darkened room, removing the dark slide, covering the back of the camera and holder with a dark cloth, making the vertical format exposure, and returning to the darkened room to replace the slide.

    If the film shows no light leak then you’ll know that you’ve found the problem.

    You may want to re-engineer the way the camera seals against the holder.
     
  9. Sirius Glass

    Sirius Glass Subscriber

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    As Ian C stated, you have a light leak on the top right of the camera body. There are other problems, but find the cause of this one and the others will be easier to figure out.

    Steve
     
  10. picker77

    picker77 Subscriber

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    Thanks, Gentlemen. Sensible advice.

    There can't be anything loose inside, it's a simple wooden box. When I shoot in vertical format with it, I pull the dark slides out from the top. In horizontal mode, I pull the dark slides out to the right.

    I think for starters I'll try sealing a freshly loaded film holder to the camera body around its entire perimeter with black photo tape, and make a test exposure. If the problem goes away (and it almost has to) then I can start narrowing down the suspect area, although the upper right side of the body, as stated by some, is more likely the culprit. I'll get it sorted out, I'm sure, with a little careful testing. Will post the results here, and thanks to all.

    Never been able to get excited about small/med format pinholing, but doing this with LF is kind of fun! Now I'm thinking about 8x10 contact prints one of these days. :laugh:
     
  11. Joe VanCleave

    Joe VanCleave Member

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    I have some experience with this sort of thing, as I've made a 4x5 wooden pinhole camera. It appears to me that the rear walls of the box around the sides of the film holder are too shallow, permitting too much light to leak into the camera. This is evident in the light leak along the bottom of the portrait-oriented image corresponding to the top of the camera (images in cameras are inverted at the film plane), where you'd expect sunlight most easily to strike that portion of the camera. In my camera design I made a deeper flange, with walls that extended beyond the rear of the film holder, helping to protect the light trap against leaks.

    As a fix, you could make L-shaped pieces from thick black scrap book paper, taped together with black gaffer's tape, secured along the edges of the camera so as to fold down behind the film holder. Holes in two sides would permit the knobs to still be attached to the camera.

    Also, I've gotten into the habit of using a dark cloth (or old black shirt) over the camera when pulling the dark slide, as an added insurance.

    For the third image from the left, it appears the darkening of the sky may be from improper agitation (or too much agitation in too small of a developing tray?)

    And the last image shows mottling in the sky that could be from either improper agitation or too short of a developing time.

    Keep at it, I look forward to more images as you make progress. This can be fun, and addictive.

    ~Joe
     
  12. picker77

    picker77 Subscriber

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    Thanks, Joe. True, the rabbet cut in the inside edge of the rear of the body is only about 1/4" deep, which is about half the thickness of the film holder, and therein may lie the problem. I have a decently equipped shop, and could easily cut it deeper with a small router to allow the film holder to fit approximately flush with the back of the camera body. That would reduce the focal length from 79mm to around 72mm, which should be of little consequence since it would just make it a bit wider angle camera than it is now.

    However, since the current focal length is a little too wide for my taste anyway, I might just build a simple extension (maybe 75mm) for the back that would fit tightly in place of the film holder, a la the Zero Images 4x5. That would give me the option of either 72mm or 150mm, and narrow the field of view more to my liking. At 150mm I should be at around f/295 with the camera's current 0.020" pinhole. Even with Plus-X that would still keep most exposures below 2 minutes, and I suppose I also could go to 400 film if necessary for lower light situations.
     
  13. picker77

    picker77 Subscriber

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    Well, I think I've met the enemy, and as usual it is me. I dropped a small high-intensity LED lamp inside the camera, inserted a film holder, turned out the darkroom lights and took a careful look. I should have done this when I first received the camera, but of course I was in a hurry to try it out. The (or at least a) problem was immediately apparent, namely operator error. I've been inserting the FH in all the way until it bottoms out, then tightening down the hold-down nuts. That seemed like the right way to ensure a solid fit and repeatable framing. But not so fast, my friend... That method caused the plastic ridge across the top of the FH (which is supposed to act as a locating ridge and fit exactly into a narrow groove across the top) to go PAST its mating groove by about 1/8". Since the locating ridge on the FH wasn't dropping into the groove for it, the ridge was actually holding the FH slightly away from a light-tight fit at the top.

    After further careful inspection I also found that one of the plastic FH's I had set aside to use for this camera to be slightly warped. Not much, just a few thousandths, but then it doesn't take much. I don't think that was THE problem because the light leak happened with several different film holders, but since I have plenty of FH's that one has been trashed.

    Will shoot and develop a few today and with luck will report the problem's been solved.

    ====================================

    Ok, test complete, before and after images attached. I made no mods to the camera, just properly seated the film holder this time. I see I also managed to get my shadow in the foreground, too. Sorry to have taken up bandwidth with this silly problem, but I do appreciate the thoughts and help on solving it.
     

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    Last edited by a moderator: Jan 12, 2011
  14. Sirius Glass

    Sirius Glass Subscriber

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    Ah, the old Operator Assisted Failure [OAF]. As in the oaf did this or the oaf did that. :D

    Steve
     
  15. DWThomas

    DWThomas Subscriber

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    Glad you got it sorted out, and that you reported back. It's always good to see these diagnoses confirmed.
     
  16. picker77

    picker77 Subscriber

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    Yeah, can't understand it... that's the first time in 50 years of fooling around with cameras that I've had an operator error. Not!