Please help me identify the source of this light leak on my negatives.

[cirwin2010]

Problem: Most of my hp5 4x5 negatives are fogged. The side of the film with the notch codes will be darker than the other side and it forms a bit of a gradient. The fog is present in the film rebate area which is where it is most obvious. I will occasionally get a "clean" negative, but I cannot pinpoint the cause of the problem. I originally thought it was an issue with my sp-445 developing tank, but switching to a Paterson tank has not resolved the problem. See first attached image.


Equipment:
-New Chamonix 45F-2 camera
-New Toyo film holders and older Riteway & Lisco Regal holders


What I have tried to reproduce the issue (see second image):

1. Developed a negative from my box of new film to see if the box got fogged. Negative came out completely clear

2. Put a film holder into the camera, removed the dark slide, and shined a bright light on the camera to check for light leaks. Negative came out completely clear.

3. Put a film holder into the camera, removed the dark slide, and pulled the film holder slightly away from the body. This was an attempt to compare this type of light leak to what I have been getting. Negative rebates came out completely clear unlike the "bad" images.

4. Over exposed an image in camera to test if the issue is light piping or internal reflections from long exposures. Negative rebates came out completely clear.

NOTE: all above tests took place with Toyo film holders since these are what I normally use.


The above tests would lead me to believe that "bad negatives" I have been getting were a fluke. However, I went and shot more hp5 after and got more of the same results. I also exposed some fp4 in some Riteway film holders. The film rebates on those are clear. I am uncertain if the problem with my other negatives simply did not occur for those images or if the film is not sensitive enough to show the problem.


This problem is really dragging me down. I want to use my new 4x5 camera for my serious projects, but I cannot with these unreliable results. Please help me.

[sharktooth]

That's a strange one for sure.

The tests you did to see if you could reproduce the problem seem to be appropriate. There is some fogging on the notched end of the one where you pulled the holder away from the back, but it's not quite the same as on your original problem shots.

The rebate area on the overexposed test shot is clear, so that seems to indicate the problem was only with your original shots. One possible scenario is that the box of film may have been opened and accidentally exposed to light. If that happened, the top sheet (or sheets) may have been partially fogged, but the lower sheets were protected by the ones above. Stranger things have happened, but that's all I can think of at the moment

[cirwin2010]

That's a strange one for sure.

The tests you did to see if you could reproduce the problem seem to be appropriate. There is some fogging on the notched end of the one where you pulled the holder away from the back, but it's not quite the same as on your original problem shots.

The rebate area on the overexposed test shot is clear, so that seems to indicate the problem was only with your original shots. One possible scenario is that the box of film may have been opened and accidentally exposed to light. If that happened, the top sheet (or sheets) may have been partially fogged, but the lower sheets were protected by the ones above. Stranger things have happened, but that's all I can think of at the moment

I thought that too regarding the box of film. However, this issue has survived through two boxes of HP5+ and occurred once again after running these tests. The film I am using should be fine.

[sharktooth]

The tests you've done all make perfect sense, yet they didn't display any unexpected problems. This begs the next question about why the test shots all came out as you'd expect. There has to be something different in how you're setting up your regular shots compared to your test shots. Either that, or it's an intermittent issue which your tests didn't capture. Based on your description, the problem seems to be more constant than intermittent.

Since the camera is new, I'd remove the bellows and back from the camera, and then reinstall them. Maybe the bellow or back hasn't been attached correctly, so a re-installation may correct that or make any fault more apparent.

[sharktooth]

Some other things to consider:

1) How are you loading film holders? Are you using a changing bag or doing it in a darkroom. What is the potential for accidental fogging?

2) How are you handling the film to get it in the processing tank? Are you doing this in a changing bag or in a darkroom?

3) Are you being extra cautious when removing the dark slide to ensure that you're not pulling the film holder away from the camera back?

4) Is the film holder held tight to the camera back by the spring back?

5) Does the film holder orientation have any affect on the problem (horizontal/vertical)?

[cirwin2010]

The tests you've done all make perfect sense, yet they didn't display any unexpected problems. This begs the next question about why the test shots all came out as you'd expect. There has to be something different in how you're setting up your regular shots compared to your test shots. Either that, or it's an intermittent issue which your tests didn't capture. Based on your description, the problem seems to be more constant than intermittent.

Since the camera is new, I'd remove the bellows and back from the camera, and then reinstall them. Maybe the bellow or back hasn't been attached correctly, so a re-installation may correct that or make any fault more apparent.

I've checked the bellows using a bright light source in a dark room. I've also refitted them to the camera and everything seems fine. I would not think a light leak from the bellows would fog the film rebates, but who knows at this point.

[cirwin2010]

Some other things to consider:

1) How are you loading film holders? Are you using a changing bag or doing it in a darkroom. What is the potential for accidental fogging?

2) How are you handling the film to get it in the processing tank? Are you doing this in a changing bag or in a darkroom?

3) Are you being extra cautious when removing the dark slide to ensure that you're not pulling the film holder away from the camera back?

4) Is the film holder held tight to the camera back by the spring back?

5) Does the film holder orientation have any affect on the problem (horizontal/vertical)?

1) Film is loaded in my blacked out basement, at night, with all lights and light sources off in the basement and the floor above. It is the darkest place I have ever been. My test of developing the film straight from the box should also prove that this is sufficiently dark

2) Film is being loaded into my processing tanks in a dark bag. My dark bag is known to be good since I primarily use it with 120 film and I've never had a light leak issue with those.

3) I've been exercising as much caution with removing the dark slide as I think I can. I pull it straight out while gently holding the back of the camera to ensure the film holder does not move.

4) I've checked by using a bright flashlight in a dark room while looking through the bellows. My other tests should also show this is fine as well. My deliberate light leak also demonstrated that if the film hold is not properly secure to the camera, the film edges covered by the film holder would not be exposed.

5) I think I have gotten fogged verticals, but I have not checked this recently.

[sharktooth]

4) I've checked by using a bright flashlight in a dark room while looking through the bellows. My other tests should also show this is fine as well. My deliberate light leak also demonstrated that if the film hold is not properly secure to the camera, the film edges covered by the film holder would not be exposed.

That's not entirely correct. Your test shot with the film holder pulled away from the back clearly shows fog at the notched end of the film, as well as a short distance along the sides at the notched end. It doesn't look the same as your other sample shots with the problem, but it trends that way.

Light coming through the lens can't expose the rebate area of your film, but light coming from other areas certainly can.

I'd be suspicious of anything that can be changed during normal shooting. For example, if you change the film back orientation from vertical to horizontal the back may not have been seated properly, and a light leak was the result. The problem would continue until you changed the orientation again and reseated the back properly. This may explain long term intermittency.

If you're new to large format work then it might be something as simple as not inserting the film holder far enough, or too far. There is a ridge on the film holder that drops into a groove in the camera back to set the position. In some cameras it's hard to tell if the film holder has been fully inserted. It can feel like the film holder has been fully inserted, but in actuality it's sitting on that ridge and not properly seated. A light leak will definitely be possible.

[cirwin2010]

That's not entirely correct. Your test shot with the film holder pulled away from the back clearly shows fog at the notched end of the film, as well as a short distance along the sides at the notched end. It doesn't look the same as your other sample shots with the problem, but it trends that way.

Light coming through the lens can't expose the rebate area of your film, but light coming from other areas certainly can.

I'd be suspicious of anything that can be changed during normal shooting. For example, if you change the film back orientation from vertical to horizontal the back may not have been seated properly, and a light leak was the result. The problem would continue until you changed the orientation again and reseated the back properly. This may explain long term intermittency.

If you're new to large format work then it might be something as simple as not inserting the film holder far enough, or too far. There is a ridge on the film holder that drops into a groove in the camera back to set the position. In some cameras it's hard to tell if the film holder has been fully inserted. It can feel like the film holder has been fully inserted, but in actuality it's sitting on that ridge and not properly seated. A light leak will definitely be possible.

I suppose you are right about the nature of the sheet with the deliberate light leak. I wonder if I pulled the film holder away from the other edge if it would look closer to the results I am getting. Might be something to try later.

I have ensured that back assembly of the camera is properly seated. Also each time I insert a film holder, I give it a bit of a wiggles to check that the ridge is properly seated in the camera body.

[Doremus Scudder]

If I remember correctly, some Toyo holders had problems with the dark slides not being completely opaque (search here and on Photrio; there were a couple of threads about the problem).

If that is your problem, then the holders that were exposed to the most light with the dark slides in place would be the ones that exhibit the fogging. You might test yours by placing them, loaded, in bright sunlight for a time and then developing the negatives.

Hope this helps,

Doremus