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Light leak from WLF on P67 long exposures ?

Photopathe

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I am trying to figure out what hapenned on these long exposure shots (around 30 seconds). I was using the WLF, the 45mm lens (and a tripod obviouly). I think I left the WLF opened after focusing. Is this a known problem? Can the WLF cause light streaks on P67 long exposures ?
Thanks!
 

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John Wiegerink

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I'm assuming these were all shot with the MLU switch on? Take the lens off and cock the shutter and then trip the mirror lockup. Now look to see if the mirror is all the way up with no gaps. You can lightly touch the mirro in the up position to see if there is any play. Now, with the mirror still locked up, use a cable release and set the shutter to "B" bulb. When you trip the shutter release watch the mirror to make sure it stays in the total lockup position.
 
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Photopathe

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Thanks for the useful reply! I just performed the test that you suggested. There is no play (maybe half a mm movement when pushing with a q-tip, I don't think it qualifies...) and the mirror stays well put when releasing the shutter.
Again, is it a possibility that the problem comes from the waist level finder left "open". I know I left it open (as in the attached picture) while exposing. It didn't cross my mind it could cause a problem. Now I remember several models of 35mm reflex cameras do have a viewfinder blind for long exposures. That gave me the idea that maybe the open WLF could be the problem. Could it make sense ? Or do you use it this way without any trouble ?
Of course I can test it next time taking the same shot with the WLF opened and then closed.
 

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Hassasin

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WLF itself cannot cause light leaks. It's natural to bleed light onto the focusing screen by design.
 

MattKing

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Hassasin said:
WLF itself cannot cause light leaks. It's natural to bleed light onto the focusing screen by design.
Click to expand...

It occurs to me that a different finder might block light from a problem area in the body, while the WLF lets the light through to that problem area.
In that case, using the WLF merely reveals the issue.
 

John Wiegerink

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You could do the test folks use to find out if the bellows has light leaks on their folding cameras. Shine a bright LED flash light into the body with the lens off in. a dark room and look through the find and see if you see any leaking light. Then. do it into the finder and look into the body for the same leaks. Worth a try!
 

itsdoable

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If the mirror foam is incomplete or degraded, you can get some light leaking from the waist level finder into the mirror box when the mirror is up.
 
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Photopathe

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In the darkroom I removed the lens and pointed a strong flashlight inside with the mirror locked up, looking in the viewfinder. There are small light leaks through the sides. So far they had an impact only when using the WLF with long exposures, which makes sense. I attached two pictures here. One can see that the back of the mirror has the same shape as the defect in the sample images in the original post. Also one can see that there is only a tiny bit of foam in one corner. It has a clear cut and doesn't seem degraded. It looks like something to dampen the shock of the mirror, but I don't know. Is there really supposed to be foam all around ?
Also, I can see very faint light even through the "black backing" of the mirror when in up position. Is it normal? It's a strong flashlight and I place it very close to the thing.
 

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loccdor

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The easiest solution is just to close the waist level finder during long exposures. I tend to take these precautions out of habit even if I don't suspect anything wrong with the camera.
 

OAPOli

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I just did the same experiment as you. Indeed the screen leaks light on the sides of the raised mirror!

I don't know if it's because of a design flaw or from a lack of sealing material. My body was fully serviced a few years ago so maybe it's the former.

It's only a significant problem in specific situations but thanks for bringing it up!
 
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Photopathe

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My copy is in mint condition. I also am under the impression it's a design flaw. Like loccdor said, the easiest solution is just to close the waist level finder during long exposures. Just good practice anyway I guess. But I wonder if gluing a narrow band of foam all around would improve this. Then again a little voice tells me it's not wise to mingle with this...
 
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Photopathe

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You're welcome!
BTW can you confirm that there is foam just in one corner on your copy, as per my photo?
 

MattKing

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The other solution would be to put your black baseball cap over the finder during long exposures - unless you are already using it to shade the front of the lens from flare
 
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Photopathe

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OAPOli said:
Yes, rectangular piece of foam on the top right only. Mine has completely degraded.
Click to expand...
You mean to say there was foam all around (not just the piece in the corner) for sure and it degraded? You see traces of it ?

Would it be a good idea to carefully glue a narrow strip of foam all around ? I am not sure there ever was. Maybe it's a good thing to put some even if it was not originally there ?
 

OAPOli

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No I meant there is only a small rectangular piece of foam on the top right which has degraded. The metal elsewhere is clean and has never seen foam.

I don't think that adding foam all around would do any harm, apart for the mess it will become in 10 years.
 

itsdoable

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I can't remember how much foam my P67 had, but back in the day, but it was pretty standard practice to close the WLF, and put a black opaque cloth over the camera on long exposures, especially if you are using an ND filter. Especially so with prism SLRs without an eye-piece blind.

The mirror only has to block enough light out so that the amount of leakage is more than an order of magnitude less than the exposure light.
 

Taylor K Nankervis

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What is this about??

If I can shoot with either of my Pentax 67 cameras without any finder on (no TTL, no WLF, no chimney) — just to get around the crop factor, with no streaks or spoilage to speak of, there is something deeper happening with your camera.

I suggest shooting a test roll of film with no finder, at all speeds, using a 4x-8x loupé for critical focusing. Scrutinise the results. There is a possibility of light-piping elsewhere e.g. an unevenly closing back, or during loading or unloading of the roll of film in strong light.
 

OAPOli

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The P67 leaks light from the VF screen to the inside of the camera when the mirror is up. You can test it yourself by raising the mirror and shining a light at the screen.

The leak is small so this is a concern only for long exposures times AND when the screen is left exposed in a high ambient light setting. Plus if you look at the OP's pics, the leaks aren't affecting the rebate area, meaning the source is in front of the shutter. This excludes problems with the door or rolls.

PS. the folding and chimney finders show 100% of the screen.

BTW it appears this is a known issue:
 

Taylor K Nankervis

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OAPOli said:
PS. the folding and chimney finders show 100% of the screen.
Click to expand...

The folding finder, while handy, is not really favoured in my work for its stiff hinges.
The chimney finder is awkward in the portrait orientation, so easier to shoot sans-finder of any type. I think the heavy TTL finder is more suitable as a paper weight in the studio now given its lack of use! Most of my enclosed-space exposures are from 20 to 45 seconds+/variable (RVP50, EI40) and yet no evidence of light piping.
 

John Wiegerink

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Glad you found the problem and now to find the solution that makes you happy. I bet Drew's P67 doesn't leak light or we would have heard about it by now?
 
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Photopathe

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Summing it up... It happened outside in strong light with the WLF left open with relatively short long exposures (between 20 to 30 seconds) and using mirror lock up.
One can see by comparing the sample images from my original post and the picture from inside of the camera (one can see the up mirror forms a slight angle and is not perfectly parallel to the sides of the blocked area...) posted later on that the shape of the leak confirm the leak is coming from the focusing screen. Inspection with flashlight in the dark confirms it. OAPOli did the same and confirms it.
Taking the habit of closing the WLF before shooting seems like the right solution but...
From time to time I do have a shot with some subtle traces of light leaks when shooting in strong light at certain angles. I always tough it's just normal it happens sometimes but now I wonder if at least some of them were caused by this design flaw.
So I am thinking about adding foam all around the edge. Will probably do it but then again it's an expensive camera so makes me nervous. Maybe there is a reason they didn't put foam there. I suppose if something go wrong I just have to remove the foam.
 
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