Luminous watch dials and changing bags

[chrism]

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I recently sent my watch in for a service, and I happened to think when I put my arms into a changing bag to load a film onto a reel last night that I was wearing a different, non-luminous watch. I realised that I had never considered whether the luminosity of the watch's hands would be enough to have a slight fogging effect. I'll be scanning last night's film tomorrow evening, but since I had never read any warning about this I thought I would ask: has anyone any idea whether there would be enough light from the watch to make a discernible difference to the film?

 

Chris

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[giordano]

I always took my watch off before using a changing bag, though this was as much to reduce wear and tear on the elasticated cuffs.

 

There are too many variables to allow any general statement about luminous watches in changing bags except "Don't!": brightness, film speed, what you're doing in the bag, which way round you wear the watch, how long it all takes... But in general, if something puts out enough photons to affect your retina it can also affect film, though not necessarily enough to cause visible fogging.

[Doug A]

I occasionally forget to take off my watch when I load film in the changing bag. I can't say that I've seen any fogging as a result, but I agree that it's better not to introduce another potential problem into the process.

[Messsucherkamera]

In theory, the light emitted by a luminous watch dial could cause film fogging - although it seems like it would be slight fogging rather than wiping out a section of the roll.

 

I always take my watch off when working in my changing bag in the interest of being able to get my hands in and out of the bag without getting the watch hung up in the elastic cuffs.

[adan]

There exist luminous-dial darkroom thermometers, so obviously a faintly glowing dial is not absolutely unsafe.

 

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But the odds are that in a changing bag, the film may get in closer proximity to a dial than in a wide-open darkroom environment - and since light intensity falls off as the square of the distance, if you are twice as close, you risk 4x the exposure.

[StS]

Personally, I take the wristwatch off, before using a changing bag, I find it somewhat difficult to read the time under these conditions.

 

Adding some sophistic points () - most watches these days should simply use phosphorescence hands, where only the light could fog the film. There are some watches, where the dial indices and hands are coated with radioactive materials.

 

Decades ago, Radium-salts were used; for some planes in the Deutsche Museum in Munich the cockpit has barrier tape; I heard during a tour, that very high radiation levels were accepted in fighter planes, reasoning, that the pilots would be exposed there only for hours. One can assume, that the attitude towards radiation was a bit more relaxed in the 1940s and that the profession of a pilot back then bore more immediate risks...

 

These days, Tritium salts should be used, which are beta-radiators; this radiation should not penetrate the watch-glass. It should not enter the metabolism, so one should not dissolve the watch to be swallowed then...

 

Another topic for study - is the probability increasing, that the phone is ringing, when one has both hands in the changing bag and the film is just exposed? Variation of Murphy's law...

 

Stefan

[chris_livsey]

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Tritium is indeed used in this application and as a Leica owner you are most likely to have a watch using this high end technology.

Persistent luminescence is more likely to be the mechanism that the majority of makers are using. This is where the material "glows" for a limited time after being "charged" by daylight.

I know this is nit picking and I do feel sad, as both process emit photons and this will fog if present close enough and long enough.

Perhaps you are sufficiently curious to run a small experiment with your watch and some unexposed film and report back ? Unfortunately the watches I own don't have this feature.

[chrism]

A good idea, and one I might try when I finally get my watch back. I hope it will have finished its travels when I next go to Toronto in October at which time I shall pick it up from my jeweller.

 

Chris

[chris_livsey]

We can wait, we aren't digital :D

[chrism]

Having spent the morning developing film, all I can say is:

 

Chris

[Archiver]

There exist luminous-dial darkroom thermometers, so obviously a faintly glowing dial is not absolutely unsafe.

 

"...obviously a faintly glowing dial is not absolutely unsafe" - I'm going to remember that the next time someone disagrees with me.

 

I'll say, 'what you're saying is obviously not absolutely untrue,' which will make their head spin just long enough for me to change the topic to something else.