PDA

View Full Version : Unreasonable test of bellow light-tightness?



Steve Goldstein
23-Jan-2017, 05:06
The bellows on one of my cameras was taped by the previous owner to repair some light leaks. It's a good taping job, actually, very neatly done and seemingly effective in my experience. Yesterday I was doing stuff around the house so I set the camera up in bright roomlight (not direct sunlight), loaded a holder with a sheet of TMY-2, pulled the darkslide, and let is sit that way for an hour. The only protective measures I took were to shield the dark-slide opening in the holder and to leave both caps on the lens. The film came out uniformly light grey, guessing maybe 0.3 by comparison with a 0.45 center filter. Developer was HC-110, Dilution B, time per F-4043.

Was my test excessive? How many of you guys leave a camera set up with the slide pulled for this length of time during the day?

Now I'm wondering if I should replace the bellows...

Bob Salomon
23-Jan-2017, 05:14
First, you don't need to shade the slot. You just learn how far to pull the slide out so the film is fully uncovered and the slide is still in the slot. Draw a line on that point so you always know how far to withdraw the slide.
Next, you need to find out what the minimum amount of time is for your camera to develop base fog. It shouldn't at any length of time.

jp
23-Jan-2017, 08:04
Can you see the shadows of the film holder edges You could pull the darkslide half way and see how light interferes with that obstacle to get an idea of where light is coming in.

Steve Goldstein
23-Jan-2017, 09:42
I can see clear film rebate all the way around.

Jim Noel
23-Jan-2017, 10:36
The bellows on one of my cameras was taped by the previous owner to repair some light leaks. It's a good taping job, actually, very neatly done and seemingly effective in my experience. Yesterday I was doing stuff around the house so I set the camera up in bright roomlight (not direct sunlight), loaded a holder with a sheet of TMY-2, pulled the darkslide, and let is sit that way for an hour. The only protective measures I took were to shield the dark-slide opening in the holder and to leave both caps on the lens. The film came out uniformly light grey, guessing maybe 0.3 by comparison with a 0.45 center filter. Developer was HC-110, Dilution B, time per F-4043.

Was my test excessive? How many of you guys leave a camera set up with the slide pulled for this length of time during the day?

Now I'm wondering if I should replace the bellows...

Short answer - YES.

Ted R
23-Jan-2017, 10:38
In my opinion that was an unreasonable test.

But if you are the obsessive type :-) before replacing the bellows make a careful check of the light-tightness of the joint between the back and the camera body and between the lens panel and the camera body, don't assume the leakage is in the bellows it may be elsewhere.

Jim Jones
23-Jan-2017, 10:52
Lens caps are more for lens protection than for completely blocking the full spectrum of light. This test may be more informative with metal lens caps or a blank metal lens board.

Bob Salomon
23-Jan-2017, 10:55
In my opinion that was an unreasonable test.

But if you are the obsessive type :-) before replacing the bellows make a careful check of the light-tightness of the joint between the back and the camera body and between the lens panel and the camera body, don't assume the leakage is in the bellows it may be elsewhere.
Or it could be a problem with where the bellows attaches to the camera.

Steve Goldstein
23-Jan-2017, 11:27
Jim, the caps were on the lens more to protect it against me than to block the light - the shutter was closed.

The flashlight test hasn't shown any light leaks yet, but now that you guys mention it, I didn't test where the bellows attaches to the standards, or where the back mounts. Into the darkroom tonight!

tgtaylor
23-Jan-2017, 11:33
My guess is that the bellows is not UV tight.

Thomas

Kevin Crisp
23-Jan-2017, 11:34
If you like tests that resemble actual conditions, then yes, this is NOT a reasonable test. How long in the field are you actually going to have the darkslide pulled? Most people pull it slowly and in some cases wait a minute or two if worried about film popping. So let's say 3 minutes? If it is longer than that you are probably making a very long exposure and the surrounding light is not very bright.

I have never had a bright flashlight test miss a significant light leak. Do it in the dark, let your eyes adjust first, turn the camera around and view from all angles.

I have a NFS 5x7 Deardorff with the original paper-ish bellows that probably predates WWII. With a repeating strobe inside the camera for a light test, I can make out the faintest diffuse 'glow' of the flash penetrating the bellows. It is very, very faint. Negatives are fine though.

Fr. Mark
24-Jan-2017, 09:41
UV? Most proteins (leather) has strongly UV ansorbing amino acids making it up. Many paints and plastics too. In fact, it can be a challenge to develop UV transparent items for general use. Glass is to some degree. It's easier for me to believe it's not IR opaque. But is the film IR sensitive? Probably not in a normal exposure, but what you did, maybe. Do you know the film doesn't have some base fog?

Alternatively, my recollection is that the Sinar shutter manual says not to do a test like you described as the shutter is not guaranteed opaque for long periods of time.

Jac@stafford.net
24-Jan-2017, 10:29
Lens caps are more for lens protection than for completely blocking the full spectrum of light. This test may be more informative with metal lens caps or a blank metal lens board.

Jim is so correct. I put a plastic/rubber composite lens caps over my IR night goggles and it saw right through them. UV is another issue, but so few common materials are significantly transparent to it, especially for the duration of film exposures.

IanG
24-Jan-2017, 10:31
Sometimes finding bellows light leaks can be very difficult. I had a camera on loan to examine 3 or 4 years ago, it was an MPP MicroPress and I wanted to see how much of it was made by Graflex, the owner said there was a light leak and he couldn't find it, could I look. The films were being fogged slightly.

The flash light (torch in English) in a darkroom wasn't enough and didn't show it so instead instead I placed a small flashgun inside the camera, this showed it wasn't the bellows but a minute gap where the rear of the bellows were attached to the body.

Ian

Kevin Crisp
24-Jan-2017, 11:26
I have a small repeating strobe that I think was originally made to attaching to life vests. I put that in the camera, put a filmholder in the back and a lens with a closed shutter on the front. I think it works better than the flashlight technique.

IanG
24-Jan-2017, 11:33
I have a small repeating strobe that I think was originally made to attaching to life vests. I put that in the camera, put a filmholder in the back and a lens with a closed shutter on the front. I think it works better than the flashlight technique.

Strobes (short for Stroboscopes) are all repeating, except in the US :D Actually what you describe sounds ideal.

Ian

Jim Noel
24-Jan-2017, 13:43
My guess is that the bellows is not UV tight.

Thomas

Or even more likely, not Infra-red tight.

Liquid Artist
24-Jan-2017, 22:06
If I was planning on doing one hour exposures then I would consider it as a reasonable test. Otherwise a little overkill.

I've had light leaks past a lens board, so that's another place to look.

Willie
24-Jan-2017, 23:09
Your test isn't unreasonable. If you are still worried set it up in bright sunlight outside and leave the film holder in for 5 minutes or so. Reasonable to do this as often we sit waiting for a light breeze to quiet before tripping teh shutter.

Steve Goldstein
29-Jan-2017, 09:04
IanG and Kevin, your comments got me to thinking, and this morning I did some further tests with a very bright small flashlight since I don't own a strobe. During my earlier torch-tests I'd only examined the bellows, this time I looked at the front and rear of the camera as well with a film-holder in place. Eureka! I've got a leak along one edge of the lensboard. Now to work out a fix.

Once again the Forum's collective wisdom comes through. Thanks guys!