frames overlap - question

[sanmich]

I'm not 100% sure but I may have a problem with my IIIf:

I have two films were frames are badly overlapping, both at the beginning of the film.
Other than that spacing is spot on.
Now of course, I may not have been careful enough when loading them, but I am playing with the camera, and comparing with my old III, and there is a clear difference of the torque that the spool is able to develop before slipping. The IIIf is offering almost no resistance to slippage (I tried to change the spools with no effect).

I would like to ask:
I know that in principle, the spool is just collecting the film, and the sprockets are in fact responsible for the film advance, but could what I describe produce the frame overlap at the film beginning, when the film tension is still low?

In that case, is the slippage occurring between the spool and the shaft?
I don't know if it makes sense, I think that I could easily reach the shaft (just removing the lens mount screws and the shell screws and the shell should open if I remember correctly) and I could very slightly open the small metal springs along the shaft that seems responsible for the friction with the spool.

Does that make any sense?

Thanks!

 

[Mr_Flibble]

It might just be the tension of the 'slip spring' on the shaft is a little low. It's regulates the friction between the shaft and the take-up sleeve (the thing the spool fits over).

The spool in my Leica I is similarly loose (very little resistance), but I never had problems with frames overlapping. The sprockets make sure the distance advanced is always the same.


This might help identify the problem:
http://www.pentax-manuals.com/manuals/service/screw_mount_leicas.pdf


Good luck

 

[sanmich]

It might just be the tension of the 'slip spring' on the shaft is a little low. It's regulates the friction between the shaft and the take-up sleeve (the thing the spool fits over).

The spool in my Leica I is similarly loose (very little resistance), but I never had problems with frames overlapping. The sprockets make sure the distance advanced is always the same.


This might help identify the problem:
http://www.pentax-manuals.com/manuals/service/screw_mount_leicas.pdf


Good luck

Thanks Rick
I think I understand how it works.
is it easy to reach the slip spring to increase the spring tension?

 

[john neal]

Michael,

IIRC there is a screw on the end of the take-up shaft, just remove that and the end of the shaft separates so the spring can be removed, stretched / replaced, cleaned and so on. It's a while since I had to do this, so bear with me if not 😉

 

[sanmich]

Michael,

IIRC there is a screw on the end of the take-up shaft, just remove that and the end of the shaft separates so the spring can be removed, stretched / replaced, cleaned and so on. It's a while since I had to do this, so bear with me if not 😉

Hey John

no screw that I can see, but a c-shaped locker.
I think that's what is to be done: remove the casing, remove the c locker, and stretch the spring. I'll try when I have some time...
thanks for the help!

 

[sanmich]

So I opened the camera yesterday, but just before reaching for the spring, I decided that the friction didn't look that bad. I was concerned that increasing the spring tension might bring other troubles, and that maybe I just need to be more careful when loading.
I'll give it a try, and worst comes to worst, I know what to do.
Thanks for your help!

 

[maddoc]

My IIIf consistently produces to narrow frame spacings and my IIIb starts to develop the same problem. If there is a fix I would try to adjust myself.

 

[Nomad Z]

My IIIf had a similar issue when I first got it. I think that what happens is that the film isn't spooled tightly enough and doesn't pass over the sprockets as closely as it should - it bows up a little, and the sprockets jump holes.

On my camera, I used some small washers as spacers to increase the friction at the spring, and it's been fine since. To set the tension, I used the feel of the spool in my M2 as a guide.

 

[sanmich]

Gabor,

I think there are two different issues:
The sprockets are the part really responsible for the right frame spacing. If the spacing is starting to get erratic, it may be time for a service/repair.
the spool is meant to collect the film, and allow for enough tension so the film stays on the camera sprocket. If this doesn't happen, and the sprockets are not playing their role, the film advance is only due to the spool movement, and the spool, by design, slips, so the result is not a slightly uneven spacing but a total mess with frames half overlapping.

 

[sanmich]

I think that what happens is that the film isn't spooled tightly enough

do you mean in the cassette?
maybe one of the things that needs to be done is to tense the film back after loading, then check the holes positions.

 

[Nomad Z]

No, I mean around the take-up spool. The spool is supposed to have enough friction to take up the slack created by the sprockets driving the film into the chamber. If the friction is too low, the sprockets try to drive it in, but the line that the film follows isn't controlled properly - the angle of the film after it has left the sprockets can change.

Imagine taking a cassette, pulling the film out all the way, and then trying to get it back in by pushing the film into the slot rather than turning the spindle. The film is pushed out to the inner wall of the cassette rather than pulled down towards the spool. At first, it might push in okay, but it will gradually become more difficult - you're trying to make a spiral of film tighter as more film goes in, which means that all of the surfaces of the film need to slide past each other. As more and more layers build up, that sliding effect stops working and it becomes difficult to push more film in.

Something similar is happening in the camera's take-up chamber. It becomes harder and harder for the sprockets to drive the film into the chamber, and the line that the film takes is right around the outside of the chamber (worst possible line for engaging the sprockets with the film's holes). At a certain point, the teeth on the sprocket ride under the edge of the holes and the sprocket jumps.

On mine it was sort of intermittent. I had a big series of irregularly overlapped double exposures that covered about a foot or so of film, so sometimes the drive would work, sometimes it wouldn't, until it had got to the point where the drive failed completely. The overlapping exposures were in about the first 1/4 or 1/3 of the film, and the rest was blank.

 

[Nomad Z]

Actually, I think what I've described above isn't quite correct. I made a sketch and uploaded it here...

http://www.rangefinderforum.com/photopost/showphoto.php?photo=185137

This is looking from underneath, so the back of the camera is at the top.

What I forgot was that the film is wound onto the take-up spool emulsion side out, so the sprocket drives it through and creates a bow in the film between the spool and the back of the camera. At first, the film would work its way down to the other side of the spool, and maybe coil loosely. As more film is pushed through, the film can no longer coil loosely around the spool, and it starts to rise up to the back of the camera. At a certain point it loses its tension over the sprockets and the sprocket jumps a hole. Remember - there is enough room for this to happen because the film passes between the tips of the sprockets and the back of the camera during loading.

 

[sanmich]

I'm not sure about your description, Nomad Z.
What I have understood is that the spool and the sprocket advance the film, but because the radius on the spool increases, the spool would pull too much film after a while.
To avoid the problem, the spool is slipping on the shaft (or the sleeve on which the spool sits slips over the spool) allowing for the right amount of film to advance.

 

[Nomad Z]

The spool does not advance the film, it only takes up the slack created by the sprocket. The reason there is friction between it and its spindle is, as you say, to allow for the change in diameter as more film is wound on. It has to have the right amount of friction to work properly - if it becomes too tight at any point, will try to pull the film past the sprockets faster than the sprockets can feed it through. If it becomes too loose, it doesn't take up the slack and you get the effect shown in my diagram - the film bows into the cavity and the path of the film over the sprockets is disrupted.

 

[Luddite Frank]

The spool does not advance the film, it only takes up the slack created by the sprocket. The reason there is friction between it and its spindle is, as you say, to allow for the change in diameter as more film is wound on. It has to have the right amount of friction to work properly - if it becomes too tight at any point, will try to pull the film past the sprockets faster than the sprockets can feed it through. If it becomes too loose, it doesn't take up the slack and you get the effect shown in my diagram - the film bows into the cavity and the path of the film over the sprockets is disrupted.

Nomad - If the too-loose / film backing-up and buckling situation is the case, would there be some scratching of the film,parallel to its long axis, where it rubs against various parts of the body ?

Michael - how difficult is it to physically pull the take-up spool out of the camera ? Most of my Barnacks ( II. III, III-f ) require a pretty tight grip on the knurled hub of the spool to pull it over the friction spring of the camera... not a very scientific description, but if the spool pulls-out with little or no resistance, then the friction spring may indeed be loose.

Another thought - are you tensioning the rewind-knob before or after winding-on the first blank frames ? I usually tension mine after inserting the cassette and take-up spool, and tensioning the wind-on knob slightly to make sure the film is seated on the sprockets, then tension the rewind, double-check sprockets, install the bottom cover, then fire / wind-on the blank frames.

I have shot many, many rolls of film in my Barnacks and have not encountered frame spacing errors, aside from a few initial loading mishaps early-on...

Good luck !

LF

 

[Nomad Z]

Nomad - If the too-loose / film backing-up and buckling situation is the case, would there be some scratching of the film,parallel to its long axis, where it rubs against various parts of the body ?

I got some horizontal scratching on the back of the film.

The one thing I find strange with Michael's issue is that there are overlaps at first, but it's fine after that. With mine (with the one roll that went badly wrong), there was a load of overlaps near the start, followed by blank film (ie, no advance). For a few rolls before that, it seemed to be winding on okay, but I still had scratches here and there on a couple of rolls - near the end of the film. Also, after I added the washers to increate the tension, a couple more rolls have had scratching near the end, but most have been fine, and I haven't seen it recently. Maybe my tension still needs to increase a little.

Michael's is strange because, if the tension was marginal, I would expect it to have a better chance of taking up the slack near the start of the roll because the torque is being applied through a smaller radius, so the effective torque pulling on the film is relatively large. Then again, maybe they are affected slightly by things like ambient temperature. (Notably, my ruined roll happened outside on a winter's day.)