Light barrier for film holders

Lukas Werth · Jul 16, 2007

Last night, I pondered on the possibility to construct curved filmholders for a new pinhole camera I have in mind to make. The one substantial obstacle I see is the light barrier any filmholder must have when the dark slide is taken out for exposure.
Any proposals of how to make?

One more question, maybe: does anyone have a clue from where to get this completely light-tight black paper placed between sheet films in the boxes of some brands? Getting some larger sheets of this would be quite helpful for the filmholder design I have in mind.

Ray Heath · Jul 16, 2007

g'day Lukas
the loop (furry) side of self adhesive Velcro

freygr · Jul 16, 2007

brass weather stripping into a groove? or closed cell foam weather stripping, or a cut rubber o-ring (large).

Ed Workman · Jul 17, 2007

I tok apart a wood 8x10 holder that was screwed together. I found a strip of felt, under the felt is a spring, althoough I did not remove the felt to examine it. I have run across a patent for such a spring and the action of the assembly I saw seemed to incorporate this type. That spring is strp of metal approx 8+ by 1/2 inches, folded the shortway. The upper side [just behind the felt] is cut into many fingers that are wider at the edge than at the fold so as to more nearly conform to the dark slide etc, rather than producing a continuous edge that might be stiff enough to bridge over irregularities thus allow light leaks. IIRC itthe patent described this as " an improved light valve"

Ole · Jul 17, 2007

Black velvet ribbon from your nearest fabric supply shop. That's what I used to repair the light trap on my Linhof Color.

Donald Miller · Jul 17, 2007

Most film holders use beryllium copper strip as the spring material under a very light weight velvet...I have not found velvet material light enough in any fabric store that I have checked before...perhaps it is a problem in the US only.

Beryllium copper strip can be purchased from Small Parts. They have an online catalog and you can Google them to find their site.

One word of caution...beryllium is problematic to respiratory systems if you plan on doing any grinding on the material. Shearing the metal strip and bending it should not present any problem of dust inhalation.

Dan Dozer · Jul 18, 2007

Lukas - I'm with Ole on this one. I used light weight brass with velvet ribbon from the fabric store. Here is the detail that I used and it seems to work just fine.

barryjyoung · Aug 4, 2007

Ed Workman said:
I tok apart a wood 8x10 holder that was screwed together. I found a strip of felt, under the felt is a spring, althoough I did not remove the felt to examine it. I have run across a patent for such a spring and the action of the assembly I saw seemed to incorporate this type. That spring is strp of metal approx 8+ by 1/2 inches, folded the shortway. The upper side [just behind the felt] is cut into many fingers that are wider at the edge than at the fold so as to more nearly conform to the dark slide etc, rather than producing a continuous edge that might be stiff enough to bridge over irregularities thus allow light leaks. IIRC itthe patent described this as " an improved light valve"

This material is called fingerstock and can easily be found in small quantities from companies selling RF shielding products. Google RF shielding and you will find many vendors. I use Tech Etch among others.

http://www.tech-etch.com/shield/index.html

They are helpful and friendly.

Do not grind or file Berryllium Copper, it is a bad carcinogen. If you need to cut it, use scissors. If you absolutely cannot survive without grinding it, keep it wet as in underwater and use only an open coat aluminum oxide wheel that is soft. If you have to machine it, keep it flooded with coolant and make chips no thinner than .004 inch or it will become airborne and you will have something MUCH worse than asbestos in your lungs. A little dab'l do ya!

Barry Young
Young Camera Company

ronlamarsh · Nov 15, 2010

Dan Dozer said:
Lukas - I'm with Ole on this one. I used light weight brass with velvet ribbon from the fabric store. Here is the detail that I used and it seems to work just fine.

Waht type of brass? i.e. thickness etc.

Light barrier for film holders

Lukas Werth

Ray Heath

freygr

Ed Workman

Ole

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Donald Miller

Dan Dozer

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ronlamarsh

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