Pentax 645N light leak

MattKing · Sep 9, 2024

pentaxuser said:
What seems strange to me about the answer being a light leak through the insert and the accompanying diagram showing it, is why in the OP's case the leak isn't casting a shadow line across every frame when the light leak through the insert hits every negative as it is wound on to the receiving spool

pentaxuser

This often varies depending on how the ambient light strikes the exterior of the camera.
Sometimes the light leak is only obvious if the camera spent some time in the direct sun.

pentaxuser · Sep 9, 2024

MattKing said:
This often varies depending on how the ambient light strikes the exterior of the camera.
Sometimes the light leak is only obvious if the camera spent some time in the direct sun.

Maybe, Matt, but in the time it takes for a film to be run through the insert with 16 shots taken and thus for the insert to be exposed to ambient light, I'd have thought any leak point in the seal would have had the time to leak some light on more than the 4 frames of 1,3,7 and 9 and with that kind of straight-edge ruler effect

Still, we'll only know the cause when and if the OP takes action to attempt to cure it and then let's us "sleuths" know what it was

Unfortunately the OP on PentaxForums never did tell what the solution was which may have helped our OP a great deal. Always a pity when they don't report back but I have a feeling I have said this before and been told off about it

Still "c'est la vie" as the French speaking "Newfies" say

pentaxuser

OAPOli · Sep 9, 2024

The leak is likely very faint. The ambient light is variable, and so is the amount of time the film stays in view of the leak.

pentaxuser · Sep 9, 2024

OAPOli said:
The leak is likely very faint. The ambient light is variable, and so is the amount of time the film stays in view of the leak.

Maybe but it is that straight line in both the OP's example and that of the Pentax Forum example all those years ago that puzzles me

Doesn't the light leak have to penetrate the backing paper How long does this take? If it a tiny leak is it a thin ray of light as it a tiny hole in a back box that hits a limited area of the negative and only when it is intensely sunny so it spreads out along a thin line only because the hole in the seal is so close to the film that it doesn't spread out? However it that were the case then does a thin ray of intense light form a small intense circle and not a line?

I don't know enough about the science of intense light through small holes to say if a line like the OP's is likely but the OP's example reminds me of a negative where half was exposed at say 1/250th of a sec and the other half at a different speed

To my mind this seems to be more in keeping with a stutter in the shutter speed which affects the curtain

However I throw these counter arguments out simply to provoke discussion into a process of elimination of causes if possible and arrival at the most likely cause

Wasn't it Socrates that the education board sacked as it was alleged that instead of telling his class the "facts" he kept on asking them questions and inviting constant discussions on those questions

pentaxuser

MattKing · Sep 9, 2024

pentaxuser said:
Doesn't the light leak have to penetrate the backing paper

No. The light comes in from a gap somewhere, and either strikes the emulsion directly, or bounces off something in the camera and strikes the emulsion.
The film is protected (mostly) while it is wound on the spool, but when the emulsion is at or near the film gate that part is exposed to any light that shouldn't be where it is.
Alternatively, if the shutter is sticking open, it comes in from there.
From the manual - where you see the red arrows pointing, it is the emulsion side of the film:

photogear · Sep 9, 2024

OAPOli said:
Most likely a leak in the film holder frame. Inspect and replace the foam seals there.

Lines On 645N Negatives - PentaxForums.com

Hi, Does anyone have ideas as to what could be causing lines to appear on my P645N negatives? (These were home developed and scanned with an Epson

www.pentaxforums.com

it looks like the film holder frame needs its foam to be replaced. I could download a picture of it if you want. Moreover the foam seems too firm (by touching with a small stick) and shriken.

pentaxuser · Sep 10, 2024

photogear said:
it looks like the film holder frame needs its foam to be replaced. I could download a picture of it if you want. Moreover the foam seems too firm (by touching with a small stick) and shriken.

I have had another look at my seal under a magnifying glass and strong light and it does appear to be very dense, almost imprenetable foam which of course it should be if it is doing its job .

The only e-bay advert I can find is from uscamera which I assume is U.S. based it shows 4 pieces of foam instead of one continuous piece in the shape of a square which mine appears to be and that is presumably placed into the insert but separate pieces may be fine is they touch/overlap at the corners

I'd have a closer look at the seal under the conditions above with a magnifying glass to see if there is any wear or breaks in it. If there isn't any wear or breaks I'd be inclined to have the insert examined by an expert to 100% eliminate the likelihood of a problem with the seal. If an expert says its OK then the shutter curtain might have a stutter when causes the line you see

On the other hand the seals are not very expensive and if you are adept at taking out the old seal and fitting the new pieces then it won't have cost you much to eliminate the seals as the problem or confirm that the problems lies elsewhere

I hope this helps

pentaxuser

ant! · Sep 10, 2024

Changing the seals isn't very complicated, I've done it a few times on 35mm cameras. Foam seals age not very well. If you want to be sure, as mentioned above: Just use some black tape around the frame holder (easy since it is just a rectangular box) with your next film, either it is fixed and you should change the foam for a long-term fix, or it is still there, then probably you need a shutter service...

photogear · Sep 13, 2024

pentaxuser said:
What seems strange to me about the answer being a light leak through the insert and the accompanying diagram showing it, is why in the OP's case the leak isn't casting a shadow line across every frame when the light leak through the insert hits every negative as it is wound on to the receiving spool

pentaxuser

it makes sense
so what else could explain an intermittent light leak?

pentaxuser · Sep 13, 2024

photogear said:
it makes sense
so what else could explain an intermittent light leak?

A sticky shutter curtain that only sticks occasionally i.e. the curtain sticks momentarily at a specific point across the frame then moves almost instantly. This would explain the absolute straight line in your example and also why it does not appear on every frame

By all means uses light proof tape around the insert each time you load film and then see what happens. If there is no lines then it might be the shutter curtain but if there aren't any lines then to be sure it isn't the curtain you may have to put on tape when reloading on several occasions to be sure that it isn't a problem occurring at a low frequency

pentaxuser

abruzzi · Sep 13, 2024

pentaxuser said:
A sticky shutter curtain that only sticks occasionally i.e. the curtain sticks momentarily at a specific point across the frame then moves almost instantly. This would explain the absolute straight line in your example and also why it does not appear on every frame

By all means uses light proof tape around the insert each time you load film and then see what happens. If there is no lines then it might be the shutter curtain but if there aren't any lines then to be sure it isn't the curtain you may have to put on tape when reloading on several occasions to be sure that it isn't a problem occurring at a low frequency

pentaxuser

But according to another post by the OP the light leak stretched the entire width of the film, not just the image area--"the line is going across the picture and the whole negative altogether." Because the shutter is forward of the film gate a sticky shutter won't let light into the rebate area*, which takes us back to light seals.

* The exception is if you have a very bright object (sun for example)right at the edge, its possible for the light in frame might bloom into the rebact, but if that strong line is consistantall the way agross the film, then anything in the rebate is most likely the back seals.

grain elevator · Sep 13, 2024

photogear said:
it makes sense
so what else could explain an intermittent light leak?

Differences in brightness in the environment, how long it's sitting around before being wound on, and perhaps the back has a little wiggle room and might simply shift around a bit so sometimes it's light tighter than at other times.

pentaxuser · Sep 13, 2024

abruzzi said:
But according to another post by the OP the light leak stretched the entire width of the film, not just the image area--"the line is going across the picture and the whole negative altogether." Because the shutter is forward of the film gate a sticky shutter won't let light into the rebate area*, which takes us back to light seals.

You are right and this sentence had not registered with me. It was an additíon to what he said and showed originally. I take it that "picture and whole negative" means the rebate as well. Pity that his only picture doesn't show the rebate and a pity that we haven't seen the pic of the whole frame since I I assume from what he said above that this line continues in the same straíght line in the negative and that there ís the same shade difference as in the picture part of the frame

In which case the tape test on the insert is certainly called for before he can make any progress in ascertaining what is the cause

As I asked in #29 can anybody say what kind of a light leak from withing the insert causes such a clearly demarcated line but is of such a short duration that it does not create a black line but instead a line that is of the kind that resembles a frame that was exposed correctly for half its area and a second half that was exposed for a small fraction of a second longer or shorter to produce two halves that differ in light exposure by very little?

I am also assuming that each of the other affected frame are virtually identical and if they are not then that too might helps us but we have only seen one frame

pentaxuser

photogear · Oct 28, 2024

For your information, ironically (should I say), after talking to a tech, I was told not to bother with the camera - Pentax 645N - taking into consideration the complexity of the problem (intermittent light leak). So I was better off return it all to the seller. After a short negociation, we agreed to cancel the transaction, so I got a refund. I just had to pay for shipping back the camera and the lens. Considering the cost of the repair, that was the only reasonable solution.
Close case.

Pentax 645N light leak

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Lines On 645N Negatives - PentaxForums.com

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