How do film cameras actually sense the beginning of film?

[Jim Andrada]

I have a Mamiya C330 and it works well, but occasionally it's not "sensing" the beginning of the film. Does anyone know how the camera actually senses the start of film and whether this would be a big deal to have repaired?

 

[MattKing]

The C330 doesn't sense the film.
You just line up the start mark on the backing paper, close the back and start winding. The camera winds a set number of rotations to advance the film as required to the first frame.
One thing that you may be encountering has to do with the flex of the back door. If you don't ensure that the back door is fully latched - press both top corners in fully - the camera will sometimes think the door hasn't been closed and will therefore continue winding without stopping.

 

[Jim Andrada]

Thanks. I always wondered if it was just a number of turns or if they somehow had a little finger that was pushed by the leading edge of the film. I remembered seeing something in the manual that said some take up spools wouldn't trigger the camera to advance the film when the handle was turned.

 

[summicron1]

Thanks. I always wondered if it was just a number of turns or if they somehow had a little finger that was pushed by the leading edge of the film. I remembered seeing something in the manual that said some take up spools wouldn't trigger the camera to advance the film when the handle was turned.

The only exception I know of to the camera mechanically measuring the paper backing/film and stopping at the right point (this is why you line up the arrows with the red dot -- the placement of those arrows is a universally-agreed to standard) is the Rolleiflex Automat series.

With the automat, you don't line up anything -- you feed the film backing through a couple of rollers which clamp down on the backing when you close the camera. As you advance the film those rollers can feel when it gets fatter because the film is starting there -- and it sets the film counter mechanism in motion.

Obviously, it is a precision mechanism to feel such a thin difference when the film starts. It works very well, but was expensive which is why -- and someone correct me if i am wrong -- the less expensive "T" models didn't include it, and the most recent very expensive models did not.

Too bad. The automat is one of the main reasons to use one of those -- it makes loading so much easier, and when you are in a hurry, that counts.

 

[shutterfinger]

Backing paper is .004 inch thick. Arista EDU/Foma is .003 inch thick, Fuji is .0035 inch thick, Kodak and Ilford are .0045 inch thick.
Film + backing paper is 7 mil to 8.5 mil thick. An intermediate gear in the film advance is held in a disengaged state until the extra thickness of the film pushes the outer roller up releasing the intermediate gear allowing it to engage with the wind crank gear and the film counter gear in Rolleiflex Autoload mechanical system. In electronic sensor systems a pinpoint infrared sensor is blocked when the film lead edge passes over the sensor.

 

[Jim Andrada]

I was wondering if something similar was going on in the C330 because there's a spring loaded wheel that bears on the film. So I thought they might be measuring the total thickness of the film/paper rolled up on the take up spool. And there was some mention in the manual about the system not working reliably with some take up spools. Oh well...

Does anyone have a recommendation for someone who could do a good CLA on the C330?

 

[jvo]

it's not done by the tiny camara elves inside every film camera? Is santa real?

 

[mrosenlof]

I was wondering if something similar was going on in the C330 because there's a spring loaded wheel that bears on the film. So I thought they might be measuring the total thickness of the film/paper rolled up on the take up spool. And there was some mention in the manual about the system not working reliably with some take up spools. Oh well...

Does anyone have a recommendation for someone who could do a good CLA on the C330?

That wheel you mention is what measures how much backing paper has passed under the wheel. It's what measures the Arrow-to-first-frame distance and the spacing between frames. When the right distance has passed under the wheel (either loading to first frame, or advance to a next frame, the wind disengages and lets you finish the crank rotation to its stopping point. It doesn't sense the difference in thickness like the Rollei mechanism does.

For a CLA I'm not aware of any Mamiya TLR specialists. These cameras are not super complex and have been around for a long time. Any competent camera repair should be able to handle them.

 

[Jim Andrada]

That makes sense. On my Kodak medalist there's a little sharp toothed wheel that contacts the film very close to the edge and it's on the film side so pretty non-slip.

On the Mamiya the wheel is on the end of a spring loaded movable shaft and it bears on the paper side, so if it were to slip or stick it could be the culprit. And come to think of it the first time this happened the counter didn't move at all and I spun the crank around a few times after the film was completely wound up and suddenly the counter started to move.

Now I'm starting to wonder if maybe the "multi" switch works by just disengaging the rotating wheel.

I think it must be powered by elves.

 

[Sirius Glass]

Some 35mm cameras can sense that the take up spool does not have tension and therefore the film did not load correctly.

 

[MattKing]

That makes sense. On my Kodak medalist there's a little sharp toothed wheel that contacts the film very close to the edge and it's on the film side so pretty non-slip.

On the Mamiya the wheel is on the end of a spring loaded movable shaft and it bears on the paper side, so if it were to slip or stick it could be the culprit. And come to think of it the first time this happened the counter didn't move at all and I spun the crank around a few times after the film was completely wound up and suddenly the counter started to move.

Now I'm starting to wonder if maybe the "multi" switch works by just disengaging the rotating wheel.

I think it must be powered by elves.

As I posted earlier, this is usually due to the back not being fully latched - use both thumbs to press!
Don't ask me how I know

 

[Jim Andrada]

Thanks. That all starts to fall in place now. Next time I load film I'll see if I can figure out exactly how the degree of closure (or non-closure as the case may be) interacts with how the wheel does or doesn't engage the film.

I just like to actually figure these mechanical things out.

 

[MattKing]

Thanks. That all starts to fall in place now. Next time I load film I'll see if I can figure out exactly how the degree of closure (or non-closure as the case may be) interacts with how the wheel does or doesn't engage the film.

I just like to actually figure these mechanical things out.

It is a simple dichotomy.
When the door isn't fully latched, the wheel doesn't engage the film, so the camera thinks you aren't winding any film.
I expect it happens more to people like me who use their left hand to close the door. With the top right corner unlatched, the wheel underneath doesn't do its job.
There is a very distinct double-sided click when the door is fully latched
Ironically, if you have the camera CLA'd and the foam updated, the door requires a firmer push to latch, and the problem is more likely to arise until you get used to the change.
It is the downside of that long straight film path and large, robust pressure plate.

 

[sixby45]

Hi Matt - I second what you mention about pushing down both sides of the film door firmly - I've forgotten and just used my left thumb to click it shut, and it was not locked at all - messed up a few rolls, until reminding myself how it has to go. Thanks!