M645 Short edges of my 120 film overexposed

[CharlesBirks]

Hello, I'm hoping someone can tell me what problem will cause the short edges of my films to be overexposed. I visited Joshua Tree National Park and shot 5 rolls of 120 film using my Mamiya M645- 3 rolls of 100 and 2 rolls of 400. Once developed I found that many shots had the shorter 4.5 cm edges overexposed.

The result is a vertical strip with soft edges (in landscape or normal orientation) that is much lighter in appearance than the rest of the shot. Sometimes it appears on both edges equally, and sometimes on only one edge. It also appears that the right center side of the film gets less exposure on occasion as well, inboard of the lighter stripe.

It is not consistent on every exposure, and seems to be present on some shots on virtually every roll. It isn't always at the beginning or end of the roll. I was using a 55mm lens with a yellow filter, and generally trying to err on the side of underexposure in setting shutter speeds and F stops.

I also have noted that the effect is much more pronounced on darker exposures, but seems equally apparent across high-lights and shadow areas

I use a tank developing process, single roll. I'm almost sure I made no mistakes in reel loading or tank closing. In processing I prefill with distilled water, empty, then add the developer using a funnel to insure I fill the tank through the center tube from the bottom up.

The only thing I can think of is the back light seals, but expect that would result in fogging as opposed to over-exposure, but then I'm new to the 645 and no expert. I've uploaded a sample shot to my gallery that shows the problem.

Any advice? (there was a url link here which no longer exists)

 

[CharlesBirks]

Further to the saga...

Upon some reflection and further investigation I believe I have located the source of the light stripes problem as well as the gradient from left light to right dark. Two completely unrelated problems.

It has been a real learning experience for me digging into this issue, so thought I'd share..

After posting this question, I set about investigating a different problem I had in the field while taking these photos. I shot 5 rolls of TMAX, 3 of 100 and 2 of 400.

The problem.........

I was in areas hiking that had beautiful scenes with rick textures in both the near and far fields. In attempting to "get it all", and because it was a bright sunny day with big fluffy clouds, I tried to shoot with small apertures and adjust the shutter speeds down to compensate. The camera was tripod mounted, and to minimize shake I elevated the mirror before some shots and used a cable release. I noted that some of the times that I did this the mirror didn't return down unless I pressed the red release button or toggled the mirror lever.

 

[CharlesBirks]

The investigation.......

I took the front cover off of the empty camera and placed the shutter mode control lever into "multiple" so that I could see what was going on in the camera with the mirror. When triggering the shutter with the shutter release, everything worked just fine, over and over.

I next tried lifting the mirror with the external lever to see if it was hanging on anything visible. The first time it went up normally. The second time I raised it, it hung up about halfway up. Going back to the lifting lever, dropping the mirror was easy. The next time it hung up, the following attempt went off without a hitch. Obviously the mechanism needs some attention.

I also tried tripping the shutter when the mirror was at half mast. No problems there.. the shutter worked fine and a quick check of the discernible speeds showed to be timing just fine. I was not able to test the high speeds, but remember that I was shooting at low speeds in the desert.

Back to the light edges.......

After examining the entire lot of 6 rolls of film and looking at how I took the shots, I realized that ALL of the shots with the stripes were taken with the mirror raised. It was actually easier to tell the ones where I hadn't because they were taken "hand-held" and were therefore taken with large apertures and high shutter speeds.

I remembered my optics course of 40 years ago and realized that even with the mirror half up, I would still expose the entire backplane, albeit at a lower exposure, with some variation top to bottom. Additionally, the mirror is a trapezoid, narrower at the bottom than at the top. When the mirror is stuck halfway up it forms a slot along the sides that starts out wide and narrows as your approach the top of the camera, Just as light gets to the backplane from only a half lens exposed by the mirror, so light also gets to the back plane from the side slots. Being narrow, these slots only pass light pretty much going straight towards the backplane at a 90 degree angle or normal to the plane. The side stripes!

 

[CharlesBirks]

The second problem...

After accounting for the stripes yesterday I spent the evening processing prints until the wee hours. It took some doing to deal with the gradients, but managed to achieve satisfactory results.. not great but better than I expected. I went to bed with the gradient on my mind, trying to think of a camera related scenario where I would consistently get the gradient.

I woke thinking about the gradient this morning.

Shutters not synched? Nope, that would be a vertical gradient based upon the vertical shutter curtain movement.

Sticky mirror? Probably not, the gradient would be a Gaussian curve, flatter at the bottom due to the trapezoidal mirror, but basically centered on the frame.

Iris issues? That would result in a wrong exposure but not the gradient.

This camera doesn't do anything left to right or right to left. That leaves processing. In the developing can the process is vertical, which means side to side on a roll of film in the reel.

I started re-examining the negatives... all 5 rolls. I also checked some older ones too.

A file sheet at a time I was holding them up to the light and not seeing anything obvious. As I accumulated a stack of sheets on my desk I happened to look down at them and noticed a distinct purple strip where a couple of sheets lined up. Grabbing a piece of white paper as a background I re-examined every page. I was surprised to see a very faint purple gradient on some of the negatives, but only on a couple of rolls. The stripe even covered the spaces between frames. Both ISO-400!

I took a strip of film with shots I felt I could afford to lose and placed it back in the fixer bath from printing last night. About 5 minutes in the bath with agitation and the purple area faded noticeably. Fearful of burning the negatives I removed them after 5 minutes and rinsed them with an archival rinsing additive or "hypo clear" for 5 minutes, again with agitation. The purple disappeared. I let the first strip dry and re-scanned it for comparison to the original scan.. the left to right gradient is gone. Better still, the negative still looks as good as it had before in terms of contrast and detail.

Now I know that the problem was likely either fixing or rinsing. My fixing should be uniform.. I use the tanks built in agitator. Thinking about the rinsing I realized that I have been rinsing from the bottom up by funneling water down through the center of the reel holder post. This has always worked for me in the past using ISO-100 film. I guess I need to find a new method.

So, is there a difference in the amount of fixing or rinsing required for 100 vs. 400 film?

I'd love to hear from anyone on the best way to rinse film in a tank on a reel.