What kind of light leak is this?
Old 05-21-2012   #1
waileong
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What kind of light leak is this?

Excuse the grain; this is HP5+ pushed to 3200.

What kind of light leak is this? You can see clearly the image of the backing paper in the frame. You can see the frame numbers. Indeed, all the frames are similarly exposed.

I've had fogging, I've had darkroom accidents, I've even had shutters that leak light.

But I've never seen a roll of film completely and evenly exposed so that the backing paper can be clearly seen-- yet it is not fogged enough and can still render an image!

Any ideas anyone?
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Old 05-21-2012   #2
135format
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is the film properly washed, i.e. all the anti halation dyes washed off. I think HP5 has green dye on the back.
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Old 05-21-2012   #3
waileong
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Hp5+ does not have an anti-halation dye. In any case, what has that got to do with light leak?
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Old 05-21-2012   #4
135format
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or maybe faulty film without anti halation dyes on back. i.e. improperly coated.
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Old 05-21-2012   #5
135format
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Quote:
Originally Posted by waileong View Post
Hp5+ does not have an anti-halation dye. In any case, what has that got to do with light leak?
HP5 has a whole lot of dyes on it normally. Possibly sensitizing dyes as well as anti halation dyes.
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Old 05-21-2012   #6
135format
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Halation is light (mostly IR) passing through film and bouncing back from pressure plate as visible to film light. The dyes stop that from happening. But if there was any moisture/condensation on film back the marks could be made in dyes from backing paper. Thats why I asked if film is properly washed. It could possibly wash off. I'm just guessing here not saying that is definitely the problem.
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Old 05-21-2012   #7
135format
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did you develop the film
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Old 05-21-2012   #8
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Maybe the film had some issues with moisture from freezing/cooling or packing, making it possible for a transfer from the backing-paper, pre exposure?
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Old 05-21-2012   #9
waileong
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Quote:
Originally Posted by 135format View Post
HP5 has a whole lot of dyes on it normally. Possibly sensitizing dyes as well as anti halation dyes.
Don't think so. I've used a lot of hp5+ over the years.
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Old 05-21-2012   #10
135format
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Quote:
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Don't think so. I've used a lot of hp5+ over the years.
I'm thinking of 4x5 which has plenty, I assume roll film has it too but I'll stand corrected on that if you are sure.

But you are saying then that there is nothing on the back of the film and that the marks are in the emulsion.
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Old 05-21-2012   #11
Tim Gray
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What camera are you shooting on? Printing on the backing paper showing through I thought usually occurs because of crummy 'red windows' on your 120 camera.
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Old 05-21-2012   #12
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Some users of shanghai film has this issue.
http://www.flickr.com/groups/shangha...7625990033682/

Humidity seems to be the problem
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Old 05-21-2012   #13
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Quote:
Originally Posted by waileong View Post
But I've never seen a roll of film completely and evenly exposed so that the backing paper can be clearly seen-- yet it is not fogged enough and can still render an image!

Any ideas anyone?
I assume that the backing print-though occurs across all frames and out of frame areas at about similar intensity, and that the print-though numbers are offset to the edge enumeration by the length of one spool circumference.

If so, I've seen things like that, mostly on expired or overheated film, but about 20 years ago Ilford had a few bad batches of backing paper that caused similar issues even on fresh film. It is due to chemical interaction of the emulsion with the backing inscription - the ink or its decomposition products fog the film or affect the film sensitizing in some way or other.
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Old 05-21-2012   #14
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Quote:
Originally Posted by waileong View Post
Hp5+ does not have an anti-halation dye. In any case, what has that got to do with light leak?
You need to download the techinical pdf from Ilford. You'll see it does have an anti-hation backing that comes off during development. Bottom line is your wrong.
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Old 05-21-2012   #15
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Just tell folks it was a background special effects projection

I've seen examples of this happening to different films. It's the ink from the backing paper. Bummer.

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Old 05-21-2012   #16
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Doh - of course a red window leak wouldn't expose all of the ink backings. Somehow I missed that on the first look.

Maybe send an email or PM to Simon Galley over on APUG. He works for Ilford and should sort you out pretty quickly. Is it fresh film or old?
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Old 05-22-2012   #17
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Found the answer. It's expired film. Long expired film coupled with cosmic radiation. Or perhaps too many doses of supposedly film-safe x-rays.

Thanks guys!
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Old 05-22-2012   #18
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... a aluminium foil hat would help with them pesky cosmic rays
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Old 05-22-2012   #19
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Found the answer. It's expired film. Long expired film coupled with cosmic radiation. Or perhaps too many doses of supposedly film-safe x-rays.
Not unless you stored (or aircraft transported) that film unwound into a long tape - cosmic radiation and x-rays come from one direction and cannot expose film rolled up into a spool evenly.

As said, it is a issue with the backing number ink - and if the film is long expired, it might even be from the period when Ilford had a issue with these fogging their film...
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Old 05-22-2012   #20
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Not unless you stored (or aircraft transported) that film unwound into a long tape - cosmic radiation and x-rays come from one direction and cannot expose film rolled up into a spool evenly.

As said, it is a issue with the backing number ink - and if the film is long expired, it might even be from the period when Ilford had a issue with these fogging their film...
See http://forum.mflenses.com/rollei-ret...ak-t48361.html for an example.

I'm using a new Mamiya 6 too, coincidentally.
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Old 05-22-2012   #21
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... you could always worry about radon gas!! that accounts for more than 50% of the background radiation we get at ground level ...
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Old 05-22-2012   #22
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Originally Posted by waileong View Post
See http://forum.mflenses.com/rollei-ret...ak-t48361.html for an example.

I'm using a new Mamiya 6 too, coincidentally.
that would be a new one which came out before the 7 which came out before the 7II which is how long ago...
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Old 05-22-2012   #23
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That is positively an ink issue, again.
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Old 05-22-2012   #24
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That is positively an ink issue, again.
Two ink issues to hit two major manufacturers? In fact, if you search there's also another example involving kodak colour film....
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Old 05-22-2012   #25
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Two ink issues to hit two major manufacturers? In fact, if you search there's also another example involving kodak colour film....
It is perfectly common for heavily expired or overheated film to expose such a behaviour - indeed it is hard to avoid. Inks are made up of oils and high surface pigments, and once migration phenomena begin to occur, even a chemically inert printed patch will attract hydrophobic substances and complex molecules more than the surrounding bare paper, due to its surface properties.

As I said, it is practically impossible for any external source to expose a roll of film evenly from all sides and from the outer layer right to the centre of the spool - so we can categorically exclude x-rays or cosmic radiation. If any, there could be a light leak in the production or lab, occurring at a time when the film is not on its roll - but it is very hard to imagine a situation where something would manage to selectively expose the film right through the backing paper without entirely zapping its exposed front.

Oh, and wasn't the Rollei 120 spooled at Ilford? I remember something like that from a discussion on its barely legible numbers - a misfeature it shares with Ilford films...
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