Praktica LB2: developed film shows strange frame spacing. How could I fix this?

El_Stino · Jul 7, 2022

Execution of exposures themselves aside, the main issue I have on this roll is this wierd spacing. The intervals between the frames becomes increasingly wider towards the end of the roll.

I suppose the winding lever keeps pulling out film a bit too much? Because of this I now have 26 frames on a 36-exposure roll.

How could I fix this?

chuck3565 · Jul 8, 2022

See my reply on Reddit.

AgX · Jul 8, 2022

In case the spacing is gradually getting wider my first though is the sprocket wheel being unlocked and the film transported instead by the the take-up spool.

El_Stino · Jul 8, 2022

chuck3565 said:
See my reply on Reddit.

Oh you are on here as well. Thanks again for you reply!

El_Stino · Jul 8, 2022

AgX said:
In case the spacing is gradually getting wider my first though is the sprocket wheel being unlocked and the film transported instead by the the take-up spool.

Thank you for your reply. Oh I see, so normally the winding lever should be turning the sprocket wheel instead of just the take-up spool, pulling more accurate amounts of film (or just stopping the take-up spool from pulling too far)?

AgX · Jul 8, 2022

El_Stino said:
Thank you for your reply. Oh I see, so normally the winding lever should be turning the sprocket wheel instead of just the take-up spool, pulling more accurate amounts of film (or just stopping the take-up spool from pulling too far)?

Yes , the idea with classic cameras is that the sprocket wheel does the actual film transporting, by the sprocket turning same, fixed amount each time.
The take-up spool is coupled to the sprocket by gears so that the corresponding winding at the take-up spool is achieved to take up the film transported by the sprocket. In case the sprocket wheel for whatever reason gets disengaged from its drive shaft the take-up spool still is turning and transporting now the film itself. As its circumference grows at each turn, at each lever stroke a larger length is transported, yielding growing inter-frame spacings.

reddesert · Jul 8, 2022

I don't know this particular camera, but generally the sprocket wheel limits the transport by counting holes. On many cameras (including most 35mm SLRs) the sprocket wheel turns along with the takeup spool when you wind the lever, and you should see this when test-winding with the back open. There are some cameras where a sprocket is turned by the film passing over it, and when the sprocket has turned the correct number of teeth, it latches and stops the film transport. (For ex, most single use cameras work that way.)

My other comment is that you have a light leak between the frames. It goes into the rebate, the edge of the film, so it is coming from behind the film rather than through the shutter. I would check the light seals at the back, especially at the ends near the hinge and the latch end.

El_Stino · Jul 9, 2022

reddesert said:
I don't know this particular camera, but generally the sprocket wheel limits the transport by counting holes. On many cameras (including most 35mm SLRs) the sprocket wheel turns along with the takeup spool when you wind the lever, and you should see this when test-winding with the back open. There are some cameras where a sprocket is turned by the film passing over it, and when the sprocket has turned the correct number of teeth, it latches and stops the film transport. (For ex, most single use cameras work that way.)

My other comment is that you have a light leak between the frames. It goes into the rebate, the edge of the film, so it is coming from behind the film rather than through the shutter. I would check the light seals at the back, especially at the ends near the hinge and the latch end.

Thanks for your reply. I'll definitely do some more testing with an already exposed, blank roll.

The light leaks are quite noticable indeed. It's curious that they only (or mostly) seems to occur between the frames. It might indeed be best to look for replacement, there's one strip of light sealing that doesn't look too good anymore.

gone · Jul 9, 2022

If the film is slipping on the sprocket teeth, wouldn't the frames be overlapping instead of being spaced out? I've never had a camera that acted like the op's.

El_Stino · Jul 9, 2022

momus said:
If the film is slipping on the sprocket teeth, wouldn't the frames be overlapping instead of being spaced out? I've never had a camera that acted like the op's.

Thank you for your reply.

That's what I have thought as well. Apparently the sprocket wheel isn't limiting the take-up spool from pulling too much film, so the thicker the roll of film on that end becomes, the more film is being pulled around the take-up spool with each push of the advance lever.

AgX · Jul 9, 2022

momus said:
If the film is slipping on the sprocket teeth, wouldn't the frames be overlapping instead of being spaced out? I've never had a camera that acted like the op's.

Yes and No.
If the sprocket wheel would be the only means of transport, you would be right. Not so, if the take-up spool takes over.

But also keep in mind you are the first to mention the film slipping on a driving sprocket wheel, as this is hard to imagine with film being transported/wound the S-way.

That is why above I had it instead on the sprocked wheel having got disengaged from its drive shaft, which is something completely different from the film slipping over the teeth.

AgX · Jul 9, 2022

What I suggested above should easily be checked on:

-) load and transport the film the standard way
-) without pushing in the disengage-button at the bottom, try to wind up more film onto the take-up spool by turning it by its serrated lower flange.
-) if this can be done, with film perforations still engaged on the teeth, the sprocket wheel got faulty disengaged from its drive shaft.

El_Stino · Jul 10, 2022

AgX said:
What I suggested above should easily be checked on:

-) load and transport the film the standard way
-) without pushing in the disengage-button at the bottom, try to wind up more film onto the take-up spool by turning it by its serrated lower flange.
-) if this can be done, with film perforations still engaged on the teeth, the sprocket wheel got faulty disengaged from its drive shaft.

Ok, thanks again for your advice! You're very helpful

El_Stino · Jul 10, 2022

El_Stino said:
Ok, thanks again for your advice! You're very helpful

Aha! I think I've found the problem. It seems like the sprocket wheel can be moved slightly down for some reason. If this happens, it doesn't lock in place after having advanced film (which normally should only happen when the allow-rewind button on the bottom is pressed).
So indeed the sprocket wheel disengages from the central axis connected to the winding lever when the film is able to accidently slightly push the sprocket wheel down. If the sprocket wheel is positioned slightly higher, against the upper "wall" of the inside of the film case (where it is supposed to be, apparently), then it DOES lock after having advanced film in sync with the advance lever push.

I suppose I could technically put a small removable piece of plastic (ring?) at or around the axis just beneath the lower pins of the sprocket wheel to keep it up. Then I would have to unload the film in the darkness of my film changing bag, since I suppose I would not be able to press the rewind button on the bottom while such a piece of plastic is still inside. I'm not sure.

El_Stino · Jul 10, 2022

El_Stino said:
Aha! I think I've found the problem. It seems like the sprocket wheel can be moved slightly down for some reason. If this happens, it doesn't lock in place after having advanced film (which normally should only happen when the allow-rewind button on the bottom is pressed).
So indeed the sprocket wheel disengages from the central axis connected to the winding lever when the film is able to accidently slightly push the sprocket wheel down. If the sprocket wheel is positioned slightly higher, against the upper "wall" of the inside of the film case (where it is supposed to be, apparently), then it DOES lock after having advanced film in sync with the advance lever push.

I suppose I could technically put a small removable piece of plastic (ring?) at or around the axis just beneath the lower pins of the sprocket wheel to keep it up. Then I would have to unload the film in the darkness of my film changing bag, since I suppose I would not be able to press the rewind button on the bottom while such a piece of plastic is still inside. I'm not sure.

Ok, after a further check: it ís possible to unengage the sprocket wheel by pushing the rewind button on the bottom while the sprocket wheel is pushed up. I also found that there is a tiny crack in the bottom of the sprocket wheel, which might have allowed it to keep slipping down the axis. I might try carefully gluing this back together, while not gluing the sprocket wheel to the advance axis inside haha.

chuck3565 · Jul 10, 2022

I would add a washer under the sprocket as mentioned on Reddit and, since the sprocket is cracked , I'd wrap a strong thread around it and cinch it tight and glue the thread plus the sprocket.

El_Stino · Jul 10, 2022

chuck3565 said:
I would add a washer under the sprocket as mentioned on Reddit and, since the sprocket is cracked , I'd wrap a strong thread around it and cinch it tight and glue the thread plus the sprocket.

Oh yes, now I fully understand what you meant. That would be idea I think, yes! A thread might indeed keep it together even better, I'll certainly give that a try.

Thanks again for your help!

RalphLambrecht · Jul 10, 2022

A good camera technician can probably do this but I would stay away from it.

Praktica LB2: developed film shows strange frame spacing. How could I fix this?

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