Film gate on a wood camera?

[rbiemer]

I am in the early stages of making a wooden 6 x 12 pinhole camera and have most of my design sorted out.

However, the film gate and the edges of the body where the film will pass on its way from the supply spool to the take up spool are giving me a little trouble; I need to figure out what I want to do or use to minimize or eliminate scratches on the film.

I am making an inner body out of basswood and then will construct an outer shell to go over that.

Here's a photo of the initial very rough stage of this:

The two channels on each end are where the 120 film spools will go. The roughly drilled out area in the center is the film gate and the pinhole and shutter will be on the side facing away. The green rectangle on the right side is one of the edges I'm concerned about. Same for the other side.

I originally thought to chamfer the edges in the film chamber and around the gate, finely sand/polish the edges and then put some finish on that.
But, I am a bit concerned that may not be a smooth enough finish?

I can get extremely fine sanding/polishing sheets (down to as fine as 12,000 grit) but I have been thinking about maybe some velvet or felt--something like the light trap as seen in 35mm film cartridges--along those edges?

Any other suggestions, folks?

There are a few more photos of this here:
https://plus.google.com/photos/101417185126711568596/albums/5997435038650585857
And this is just the beggining of this project for me. I will be adding more photos of the build as I go along.

Thanks!
Rob
EDIT: I noticed I had typed "6 x 9" and the camera is, in fact, 6 x 12...

 

[peteography]

Glass is often used for the pressure plate. I'd suggest a plastic, metal or a roller of those two materials though. Might be time to destroy a cheap broken down folder or something similar. Possibly you could use some form of resin finely sanded?

 

[rbiemer]

Rollers aren't a bad idea, Pete. And I think I have a couple of potential donors: a while back somebody gave me on of the Kodak instant cameras and I'm pretty sure it is still in the "junk" box. Not sure if these cameras had rollers like the Polaroids do or if any would be sized appropriately for this. As well, I would then need to get any roller mounted in the body well enough to be usable...
Non-rotating glass rods might work better--or at least be a bit easier to build into the camera.
Thank you for the thoughts!
Rob

 

[02Pilot]

FWIW, the ONDU wooden pinholes use some sort of cloth tape in that spot. I didn't notice any scratches on the film when I used mine. The tape is not a secure as I would like, however.

If it were me, I think I'd create a small channel along the corner and fill it with epoxy, then sand that down to a very smooth finish. 12,000-grit should do the trick, but if you want it even smoother you can use an automotive polishing glaze - I like 3M Imperial Hand Glaze personally. Rollers would work, but I don't think there's a need for that level of complexity. Felt would be fine as long as it stayed clean.

 

[rbiemer]

FWIW, the ONDU wooden pinholes use some sort of cloth tape in that spot. I didn't notice any scratches on the film when I used mine. The tape is not a secure as I would like, however.

If it were me, I think I'd create a small channel along the corner and fill it with epoxy, then sand that down to a very smooth finish. 12,000-grit should do the trick, but if you want it even smoother you can use an automotive polishing glaze - I like 3M Imperial Hand Glaze personally. Rollers would work, but I don't think there's a need for that level of complexity. Felt would be fine as long as it stayed clean.

It was seeing some examples of scratched negs from the Ondu that started my concern about this in the first place.
And, I have been thinking about rollers and agree that that kind of complexity is more than I want to attempt.

What I think will work for me is to not create a channel at that corner but to simply bevel or round over that edge and then put a thin coat of epoxy and finely sand and polish that. If I then actually see scratches, I will try some felt.

Thanks,
Rob

 

[rbiemer]

I thought I still had a couple of rolls of 120. I didn't and I needed one to sacrifice so I can get some of the dimensions correct.
There is still one place almost near me that has some 120 in stock; the Cornell Uni. book store. 25 miles from home but I had to come to Ithaca today for something else so it wasn't a drive just for the film.

Had to get a manager to find the film...🙂 The students working didn't have any idea what I was talking about.
2 rolls of Fuji 800 for $16 and tax. :\

At least I can get the position of the film spools set and the red window for frame counting located.

Rob

 

[pvdhaar]

What makes your design vulnerable to scratches, is that it's based on a 35mm film camera layout with the film plane sitting at the back. With 120 cameras (Hasselblads, Bronicas etc..), you'll see that the film sits with the backing paper rolling over rollers, and with the film side not touching anything. It wouldn't hurt to look up some images of film inserts to see this set-up. The down side is of course that the spools stick out behind the film plane, but a 120 camera is bigger than a 35 anyway..

 

[rbiemer]

Peter,
Many thousands of box, folding, and TLR cameras have been made that wind the film similarly to what I am making. The better ones do have some kind of roller but not all of them do.
The camera(s) I had in mind as I was designing this one were the Ondu and other similar pinhole cameras I have seen--particularly the 8Banners pinhole cameras. I wanted one of the 8Banners cameras but couldn't afford one when they were being made.
And Ezzie's 6 x 24 camera is another major inspiration--see his thread here:

http://www.rangefinderforum.com/forums/showthread.php?t=140286

And, after thinking about the cameras that Ive been inspired by, I remembered that I had one of the Bessler 6 x 9 paper cameras. And I didn't get any scratches on the film with that one...I may be over thinking this.

Rob

 

[mdarnton]

It seems that since film flatness will not be an issue, your basic philosophy should be to get the film from one side to the other in the straightest, least tensioned/pressureed path possible. One way to get around corners would be having only the edges of the film be the bearing surfaces in those areas--leave the extremes of the corners that the film goes around in contact, and in the middle, image area, cut back anything that would touch the film surface. No rollers necessary, then.

 

[rbiemer]

It seems that since film flatness will not be an issue, your basic philosophy should be to get the film from one side to the other in the straightest, least tensioned/pressureed path possible. One way to get around corners would be having only the edges of the film be the bearing surfaces in those areas--leave the extremes of the corners that the film goes around in contact, and in the middle, image area, cut back anything that would touch the film surface. No rollers necessary, then.

In the week or so since you posted this suggestion, I have been cleaning up the wood body and thinking about this idea.
And it makes a lot of sense to me so I am going to do it this way I think. My only concern is that there might be some "bleeding" of the light between the frames. But I can change the film gate to correct that If I need to.
After dinner tonight, I am starting to glue and hope to have some more photos of the construction to add here--particularly how I've implemented your idea, mdarnton!!
Rob

 

[tunalegs]

It seems that since film flatness will not be an issue, your basic philosophy should be to get the film from one side to the other in the straightest, least tensioned/pressureed path possible. One way to get around corners would be having only the edges of the film be the bearing surfaces in those areas--leave the extremes of the corners that the film goes around in contact, and in the middle, image area, cut back anything that would touch the film surface. No rollers necessary, then.

This is actually the entire reason that film rails exist in 35mm film cameras. The edges of the roll of film are supported by the rails about 1mm above the actual film gate. This keeps the center of the film from dragging over the edges of the gate.

 

[rbiemer]

About half way through my build. Here's what I decided to do about the film "rails":

The next thing will be to build the outer body, then on to taking some photos!
I have a bunch of annotated photos of my progress so far here:
https://plus.google.com/photos/101417185126711568596/albums/5997435038650585857

Rob

 

[JoeV]

I was going to suggest using some thin brass tubes, of the kind made by K&S Engineering and sold in hobby shops around the US (here I'm merely assuming, as I don't know the OP's country of origin), and placing these strategically at the two corners, for the film to roll upon.

It's much less complicated than it sounds, because K&S sells these brass tubes in various sizes whereby you can purchase a set where one tube nests snuggly inside the larger set, meaning you simply drill two holes to mount the thinner tube to the camera body and the larger tube slips over the thinner one as a sleeve. Do this on each side of the film gate and Bob's yer Uncle.

~Joe