Why do Leica III* cameras (all LTMs?) roll emulsion-side out on take-up spool?

[Xícara de Café]

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Hello,

I'm curious as to why Leitz chose to invert the curvature of the film as it is wound from the canister and on to the take-up spool. It's been on my mind because my usually trusty plastic Paterson developing spool had been running in to trouble when I attempt to load it with film from my Leica IIIf. It jams once i get to frame 30 or so and puts kinks into the negatives (usually 2 or 3 frames affected) and I believe this is because of added friction due to the inverted curvature. I should perhaps load the Paterson spool with the emulsion side of the film out or make sure that the film has been rewound into the canister for at least 24 hours before processing the film (not always practical). 

I suspect that the reason for the inversion was to maintain a relatively flat film once shot and processed, the film having been coerced in to both emulsion-in and emulsion-out orientations. If anyone though has any comments or tips on how to avoid problems with the developing spool, please respond!

All the best,

[TomB_tx]

By wrapping the film this way the film also wraps farther around the sprockets, keeping more holes engaged. This may lower the forces on each tooth - so there may have been concern either about tear-out of the holes, or of the film disengaging or jumping over teeth.

The majority of 35mm camera makers also kept the reverse curl method.

[Pyrogallol]

40 years ago I decided that my home rolled bulk film should be in 30 exposure lengths rather than 36 because it went easier into a Patterson spiral, and I am still rolling 30.

[TomB_tx]

I hadn't noticed the issue with plastic developing reels, as I've used only stainless reels and tanks for over 50 years - at least for 35mm film. I use a Patterson only for 127 film!

[luigi bertolotti]

21 hours ago, TomB_tx said:

By wrapping the film this way the film also wraps farther around the sprockets, keeping more holes engaged….

 I think this is indeed the real tech reason

[Xícara de Café]

1 hour ago, luigi bertolotti said:

 I think this is indeed the real tech reason

Yes, it makes a lot of sense but I'm surprised that TomB_tx said that "The majority of 35mm camera makers also kept the reverse curl method". Admittedly i don't have a large collection of cameras but those that i have (Nikons, pre and post-war Contax cameras, a Kiev 4 and a Minox 35 GT) all maintain the curvature from the canister.  

[luigi bertolotti]

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Rollei 35 uses the "reversing" like Leica (iirc… it's years I don't use mine…)

[TomB_tx]

6 hours ago, Xícara de Café said:

Yes, it makes a lot of sense but I'm surprised that TomB_tx said that "The majority of 35mm camera makers also kept the reverse curl method". Admittedly i don't have a large collection of cameras but those that i have (Nikons, pre and post-war Contax cameras, a Kiev 4 and a Minox 35 GT) all maintain the curvature from the canister.  

RIght on the Contax (and therefore Kiev), as it originally used a cassette as the takeup. The Nikon F was a reverse curl design, as was the Canonflex - also introduced in 1959. Canon changed when the introduced the "QL" (Quick Load) models in the mid '60s, I don't know about later Nikon models, as I've only had the F. Others that reversed were the common Pentax, Minolta, Mamiya Sekor SLRs.

Others that did not reverse curl are Exakta and Yashica TL.

So there were indeed a mix of straight vs. reverse curl models, but I think the reverse curl design was most common.

[Xícara de Café]

I think Nikon must have seen the light, my F2 is a non-reverser 🙂

[Xícara de Café]

On 6/4/2019 at 7:50 AM, TomB_tx said:

The majority of 35mm camera makers also kept the reverse curl method.

TomB_tx,

My apologies! The Nikon F2, like the F, does indeed reverse wind the film, I checked only now. It's strange that I've never had a problem loading the Paterson spools from film shot in this camera. It must be that I have been processing the film soon after finishing the roll. Doing some more Googling, I found that Paterson itself, recommends rewinding the film back into the canister and leaving it sit "for some hours" for these reverse-winding cameras, before loading the film onto the Paterson spool. I'll need to be more patient in future! 

[adan]

On 6/4/2019 at 4:14 AM, Xícara de Café said:

I suspect that the reason for the inversion was to maintain a relatively flat film once shot and processed, the film having been coerced in to both emulsion-in and emulsion-out orientations.

Yes, one basic reason for reverse-wound film is that it makes the film lie flatter, both from tension while in the camera, and by taking out some of the curl so that once exposed and developed, it lies flatter in the enlarger or slide projector. It stretches out the curvature that "sets" from sitting tightly rolled in the cassette, emulsion side in, for weeks or months after manufacture.

One can see this also in Hasselblad's backs, where the film comes off the factory spool, is bent backwards once around a roller to reach shooting position, and then bent backwards again to reach the takeup spool. Hasselblads were noted (or at least, promoted) for better film flatness than, say, Rolleis (except the SL66), where the film curvature was in the same sense at all times (emulsion inside), and never counteracted when passing through the camera. (It also helps make the interchangeable backs more compact - but that's just a case of "two birds with one stone." ).

Anyone who's ever needed to flatten out a curly air-dried fiber print (or anything that has been rolled up for storage: maps, etc.) understands the principle - produce tension opposite to the natural pull of the emulsion, or a curve induced by being stored as a roll.

Edited June 9, 2019 by adan

[Ambro51]

Natural spinning motions of the finger and thumb.  Never question Oskars design.

[pebbles]

It is simply to keep the film flat in the film plane. Otherwise the film would move away from the plane as the film was used.

[jankap]

Not with the Tessina. Herewith the winding of the 35mm film is the same in and out.