How is proper film winding achieved?

Theo Sulphate · Jun 16, 2016

I'm uncertain how single-stroke-only wind levers work in taking up film.

I've looked at the patents for knob wind and rapid wind (multi-stroke); they seem easier to understand.

Consider that in a camera such as the Kodak Retina IIa or a Voigtländer Bessamatic, you must make a single stroke of the lever to the end of its travel. You cannot multi-stroke the lever. The problem is this: for the beginning frames, the diameter of film on the take-up spool is small; for the ending frames the diameter of film on the spool is larger. In either case, the number of sprocket holes the film must advance has to be constant in order to achieve consistent frame spacing. I assume that the sprocket wheel shaft is what governs this. Otherwise, the increasing diameter of film on the take-up spool would cause later frames to be spaced further apart than earlier ones.

My assumption is that as soon as the requisite number of sprockets have been counted off by the sprocket shaft, a clutch of some sort has to disengage the take-up spool from the wind lever so that the film is not advanced further. This means that at the beginning of the film the full stroke of the wind advances to the next frame, but at the end of the film only part of the stroke is being used to advance to the next frame.

Can anyone tell me if this is correct?

ic-racer · Jun 16, 2016

Some cameras require the full winding stroke to cock a focal plane shutter for each frame. In that case there is a slipper mechanism on the take up spool and the teeth pull the film through the gate. When the slipper mechanism becomes faulty, the film can bunch up.

gone · Jun 16, 2016

I've had the top off a Retina Ia once (stripped gear shaft that advanced the film), and there was no sort of compensating mechanism that I could see. There may have been something deeper in there, but I didn't go that far.

On a Super Ikonta V, I had to wrap the take up spool w/ some tape to make it larger because the frames would start to overlap if I didn't, but that was because the film that the camera was designed to shoot when it was made was thicker than today's film. It had a mechanism of some sort that must have compensated for the film on the spool growing larger each time it was advanced. Sorry I can't be any help, as the more I think about this, the more confusing it appears to be.

My Canon FT QL has one of those slipper mechanisms, along w/ the quick load device. After you advanced the film the lever needed to go the full stroke, even though the film had already stopped advancing. The film needs to go exactly the same distance each advance, no matter what size the take up is as it gets bigger each advance.

Theo Sulphate · Jun 16, 2016

Elaborating a bit further:

Since the sprocket shaft, film, and shutter-cocking mechanisms all have to travel the same distance every time, always, the take-up spool can't be rotating the same amount at the end of the roll as it does at the beginning. If it were, it would attempt to pull more film at the end of the roll. Something must compensate for this.

gone · Jun 16, 2016

That's why I edited that from my post :[

The more I thought about it, the less I seemed to understand. I think ic-racer's explanation is a good one for some cameras.

shutterfinger · Jun 16, 2016

The two systems I'm aware of for roll film holders is a cam or a clutch. In a cam system the cam has different spaced notches in which a spring lock lever seats into and prevents further winding.
A clutch system disengages after a given length of film passes. It is probably controlled by a gear that is turned by the film edge.
A non multiple stroke lever is a ratchet that is locked by a mechanism similar to the cam system, gearing insures the proper amount of turn for the cam. The distance between gear teeth can be varied also. Many advance gears have two sets of teeth, one the input usually linear, the other the output which may have nonlinear tooth spacing.

I am not familiar with a Retina.

rwreich · Jun 17, 2016

I've noticed that the throw on the 120 back for the RB gets shorter as I move through the frames. Of course, it is disconnected from the mirror and shutter, so there's that.

tedr1 · Jun 17, 2016

The RB67 uses roll film without sprockets however the same principal applies, single stroke wind. There are some wonderfully detailed drawings of the film wind mechanism in the repair manual for the RB67 Pro S camera (body and film holder) which I have in pdf form, unfortunately I can't identify the source of the download, it was March this year and free, you may be able to locate it by searching online for Mamiya RB67 Pro S repair manual.

Peltigera · Jun 17, 2016

If you open a 35mm camera and put your thumb on the take-up spool to stop it turning, you can still move the advance lever and the sprocket shaft will still turn. It is clearly not a geared linkage.

Sirius Glass · Jun 17, 2016

Peltigera said:
If you open a 35mm camera and put your thumb on the take-up spool to stop it turning, you can still move the advance lever and the sprocket shaft will still turn. It is clearly not a geared linkage.

It depends on the camera. some free wheel the sprocket shaft [Voightlander Vito II] and some are geared [WideLux F7].

Svenedin · Jun 17, 2016

momus said:
I've had the top off a Retina Ia once (stripped gear shaft that advanced the film), and there was no sort of compensating mechanism that I could see. There may have been something deeper in there, but I didn't go that far.

On a Super Ikonta V, I had to wrap the take up spool w/ some tape to make it larger because the frames would start to overlap if I didn't, but that was because the film that the camera was designed to shoot when it was made was thicker than today's film. It had a mechanism of some sort that must have compensated for the film on the spool growing larger each time it was advanced. Sorry I can't be any help, as the more I think about this, the more confusing it appears to be.

My Canon FT QL has one of those slipper mechanisms, along w/ the quick load device. After you advanced the film the lever needed to go the full stroke, even though the film had already stopped advancing. The film needs to go exactly the same distance each advance, no matter what size the take up is as it gets bigger each advance.

I'd love to know about this Super Ikonta V. I have a Super Ikonta IV and I thought that was the last of the line. There is nothing wrong with frame spacing on my S-I IV unless I start the film in the wrong place and I have done that...

Brett Rogers · Jun 18, 2016

Theo Sulphate said:
I'm uncertain how single-stroke-only wind levers work in taking up film.

I've looked at the patents for knob wind and rapid wind (multi-stroke); they seem easier to understand.

Consider that in a camera such as the Kodak Retina IIa or a Voigtländer Bessamatic, you must make a single stroke of the lever to the end of its travel. You cannot multi-stroke the lever. The problem is this: for the beginning frames, the diameter of film on the take-up spool is small; for the ending frames the diameter of film on the spool is larger. In either case, the number of sprocket holes the film must advance has to be constant in order to achieve consistent frame spacing. I assume that the sprocket wheel shaft is what governs this. Otherwise, the increasing diameter of film on the take-up spool would cause later frames to be spaced further apart than earlier ones.

My assumption is that as soon as the requisite number of sprockets have been counted off by the sprocket shaft, a clutch of some sort has to disengage the take-up spool from the wind lever so that the film is not advanced further. This means that at the beginning of the film the full stroke of the wind advances to the next frame, but at the end of the film only part of the stroke is being used to advance to the next frame.

Can anyone tell me if this is correct?

It's pretty simple. Some wind lever systems (more rarely in older 35mm cameras, a knob) incorporate a ratchet into the wind gearing (usually, but not always, adjacent to the lever itself). This enables you to part wind the mechanism progressively. Others for various reasons do not feature this and, hence, the lever must be fully actuated in a single throw. The Bessamatic being an example of the latter. But it has other points in its favour of course.

Brett Rogers · Jun 18, 2016

Peltigera said:
If you open a 35mm camera and put your thumb on the take-up spool to stop it turning, you can still move the advance lever and the sprocket shaft will still turn. It is clearly not a geared linkage.

Well, of course it is. If it wasn't, it wouldn't rotate at all—in which case—it would be as useless as tits on the proverbial bull. Please—think about it.

What is most often the case, is that the take up spool is clutched onto its shaft, so that whilst it rotates as driven by its gearing from the take up sprocket (usually, not invariably) it may also slip, as required, to accomodate the increasing diameter of film rolled around the spool. This way, the drive sprocket may wind a constant length of film across the gate for each exposure without the exposed film jamming at the spool as its effective diameter grows.

AgX · Jun 18, 2016

Peltigera said:
If you open a 35mm camera and put your thumb on the take-up spool to stop it turning, you can still move the advance lever and the sprocket shaft will still turn. It is clearly not a geared linkage.

The take-up spool is friction-coupled to the sprocket wheel to compensate for the growing circumference and thus pull of that spool per rotation.

Peltigera · Jun 18, 2016

Brett Rogers said:
Well, of course it is. If it wasn't, it wouldn't rotate at all—in which case—it would be as useless as tits on the proverbial bull. Please—think about it.

What is most often the case, is that the take up spool is clutched onto its shaft, so that whilst it rotates as driven by its gearing from the take up sprocket (usually, not invariably) it may also slip, as required, to accomodate the increasing diameter of film rolled around the spool. This way, the drive sprocket may wind a constant length of film across the gate for each exposure without the exposed film jamming at the spool as its effective diameter grows.

What I meant was that the linkage between the advance lever was not just gears - the clutch you mentioned. It is actually quite possible (and common) to link two rotating parts so that one drives the other with no gears - with rubbers bands, for instance.

John Koehrer · Jun 18, 2016

AgX said:
The take-up spool is friction-coupled to the sprocket wheel to compensate for the growing circumference and thus pull of that spool per rotation.

Concise, AND accurate. In only one sentence, BRAVO!

Beyond that, The geared cocking train has a gear which at the end of it's stroke
will have a lever that blocks it from traveling backwards. The ability
to ratchet is a toothed gear and pawl that prevents counter rotation of that gear.

Theo Sulphate · Jun 18, 2016

AgX said:
The take-up spool is friction-coupled to the sprocket wheel to compensate for the growing circumference and thus pull of that spool per rotation.

John Koehrer said:
Concise, AND accurate. In only one sentence, BRAVO!
...

Indeed - I was going to mention that. I wish my ability in German was half as good as AgX's in English.

Thank you, everyone, for your thoughts and replies.

How is proper film winding achieved?

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