Film rollers in folders, how much does their integrity and trueness matter?

[Helge]

I never really paid much attention to the rollers on the sides of the film gate, almost all 120 folders have.
The other day I happened to tinker around a bit with one of my Ikontas, and noticed that the roller nearest the clear film roll seemed to run a bit crooked. And true enough, It wobbles a tiny bit when rotated. Both detectable by touch and careful observation. It can at the very most be half a millimeter, probably less.
It's hard to detect if it's the actual rod that has a curve, or if the issue is in the two hubs.

Naturally I got an urge to see if I could bend it back carefully. Testing it very carefully with slight pressure it's becomes clear that it's actually quite flexible to light pressure and good at returning to shape afterwards.
It would have taken a pretty good amount of pressure to actually bend it in the first place. More than for example a kink in bunched up backing paper, or careless handling would have been able to do.

My question is: How much do these rollers matter to film flatness, and is it something I should think about trying to fix (if even possible)?

The film gate on folders and its exact workings, seem not quite documented/understood. At least not in the resourced I could find online. Specifically it's uncertain where there plane of focus really is. What is actually keeping the film flat?

 

[AgX]

I got a similar issue and just took an apt roller from a junk camera...

But yes, rollers vary and one must be lucky to have an apt one at hand.


A bent roller in the worst case will not turn at all and result in friction at some heights of the film strip, one being within the image area.
But films survived even cameras designed without rails and rollers...

 

[Helge]

I got a similar issue and just took an apt roller from a junk camera...

But yes, rollers vary and one must be lucky to have an apt one at hand.


A bent roller in the worst case will not turn at all and result in friction at some heights of the film strip, one being within the image area.
But films survived even cameras designed without rails and rollers...

How did you get the roller out?
I have a junker for parts luckily.

I don't think the crooked roller is in any way restricting the free and smooth motion of the film.
Remember, it is a very small amount of off centering. It's not even detectable by putting a credit card edge on, on the roller in backlight (that is if it is a curve and not the hubs)
My main concern is if it could result in problematic film curving and/or alignment?
Otherwise why bother doing anything?

 

[AgX]

If I remember well I just had to twist a bit a latch in both cases which made the bearing.


You will have some bulging anyway, unless you have a suction plate. I do not expect an off-center roll to be of significant effect. And designs of film gates and pressure plates (if so) even vary.

 

[Dan Daniel]

I've had rollers which are canted (?)- one end is higher than the other. It led to film traveling a bit skewed. So the image on the full film was off-kilter, the rectangle or square was tilted a degree or two.

This has been on folders, TLRs, and Medalists.

But it never seemed to throw the whole roll off... oh wait, yes, on a Medalist if it is far out of true the film will slowly travel further and further to one side and end up crumpled against a spool.

Run a test roll to see if it spools ok. If so, assume that even the slight tilt will be easily corrected. Most of the film position is coming from the pressure plate.

 

[AgX]

I've had rollers which are canted (?)- one end is higher than the other. It led to film traveling a bit skewed. So the image on the full film was off-kilter, the rectangle or square was tilted a degree or two.

But unless you mount slides, what is the issue with a tilted frame?

 

[Helge]

I've had rollers which are canted (?)- one end is higher than the other. It led to film traveling a bit skewed. So the image on the full film was off-kilter, the rectangle or square was tilted a degree or two.

This has been on folders, TLRs, and Medalists.

But it never seemed to throw the whole roll off... oh wait, yes, on a Medalist if it is far out of true the film will slowly travel further and further to one side and end up crumpled against a spool.

Run a test roll to see if it spools ok. If so, assume that even the slight tilt will be easily corrected. Most of the film position is coming from the pressure plate.

I've run several rolls through and never detected anything off. Of course I weren't looking. And I might have been lucky with hitting the right spot on the roller or having the problematic part in an out of focus part.
My main concern is not X,Y position and rotation. it's curvature, concave and convex put into the film by the roller.
Of course that will only really matter at low apertures and up close. But those kinds of photos are not uncommon.
It's not quite clear from looking, what role the rollers play in flattering the film, if at all.

 

[jay moussy]

What about slight roller corrosion?

I have some, on a couple of folders yet to be tested, apparently rolling smoothly.
I should address the surface defect, but not sure how to proceed cleanly.

 

[bernard_L]

My main concern is not X,Y position and rotation. it's curvature, concave and convex put into the film by the roller.

At least on my super-Ikonta A, the pressure plate rests on outer rails, outside the width of the film, and with sizeable gap w.r.t. the inner rails; so, the film is not positively pressed against the inner rails. I believe the design intent is to have the film's natural curvature press it against the pressure plate, together with the rollers. The rollers being outside the image area, they can be a small distance from the pressure plate and still help achieve a flat film where it matters. See this related thread:
https://www.photrio.com/forum/threa...stment-focus-calibration.126327/#post-1670203
Back to your point about curvature: I am in the habit of advancing the film just before taking the picture (once I have decided I want to take that one). That is to benefit from the natural curvature the film inherits from the supply spool, to keep if flat against the pressure plate (pushed at both ends by the rollers).

 

[Helge]

At least on my super-Ikonta A, the pressure plate rests on outer rails, outside the width of the film, and with sizeable gap w.r.t. the inner rails; so, the film is not positively pressed against the inner rails. I believe the design intent is to have the film's natural curvature press it against the pressure plate, together with the rollers. The rollers being outside the image area, they can be a small distance from the pressure plate and still help achieve a flat film where it matters. See this related thread:
https://www.photrio.com/forum/threa...stment-focus-calibration.126327/#post-1670203
Back to your point about curvature: I am in the habit of advancing the film just before taking the picture (once I have decided I want to take that one). That is to benefit from the natural curvature the film inherits from the supply spool, to keep if flat against the pressure plate (pushed at both ends by the rollers).

That’s a very good point I never thought of.
I always thought the main advantage was tautness and the memory function.

I’m still curious about whether someone knows how the film “rests” in the gate.

 

[grat]

On my Bessa I, it appears the rollers are primarily to give a non-binding surface for the film to pass over on it's way into the gates/pressure plate, and then out again. While sketching out a design for a 3D printed 6x12, one of the issues I ran into was how to keep the emulsion side of the film from dragging across raw plastic. A small metal (or smooth plastic) roller solves the problem neatly.