DIY light-tight material for bellows

[DDrake]

Hello all,

New here. Building my first 4x5 camera, following (mostly) Grepstad's design, with standards based on an old Burke and James design. Completed front and rear frames, plus ground glass holder and spring back, and bought a used Cambo bellows and Fujinon 135mm f/5.6 lens. Bellows turns out to have some pinholes, so I've started thinking about making my own.

Searching forums here and elsewhere, it looks like light-tight material is hard to come by, with the curtains from Thorlo labs being about all that is available. So I decided to experiment with easy-to-find (and not-so-easy-to-find) alternatives.

The not-so-easy-to-find stuff is some aluminized cuben fiber I had lying around (cuben fiber is an ultralight, ultra-tough fabric developed for racing sails that's been widely adopted by the ultralight backpacking community). The easy-to-find stuff is aluminized mylar (polyester) space blanket. Neither is light-tight on its own--both are very dimly translucent. I gave both materials a coat of flat black paint (Krylon Dual Superbond, claimed to stick to plastics), which seems to block all light. After an hour dry time, the paint appears well-bonded to substrates.

Next, I used 3M General Purpose 45 spray glue to bond black cotton broadcloth to the painted sides. Testing by crumpling and creasing and holding against a strong light showed light leaks. I made another pair of samples, this time painting both sides of the substrate, gluing broadcloth to one side and 1.1 oz calendared ripstop nylon to the other. Use of nylon was inspired by Intrepid Camera bellows. This time, the assembly remained light-tight, even after creasing and folding back and forth multiple times.

For both substrates, the thickness of the whole assembly is about 0.015" or 0.4mm. Adding cardstock stiffeners brings the thickness to about 0.03" or 0.8mm. This is a bit thinner than the Cambo bellows, and should be lighter as well.

Next step is to build a complete bellows and test it--I'll post pics here when I do.

My ultimate goal, once I finish the first camera, is build another weighing less than 2 lb (900g) not including lens and lens holder. Monorail, full movements, frames made from 2mm carbon fiber panels, with 20mmx20mm carbon fiber square tube for rail.

Any advice or suggestions is more than welcome--I'm a fairly experienced maker of things, with access to a CNC mill and full shop, and have some experience in 35mm and digital photography, but first experience with LF will be when I finish building a camera and start figuring out how to use it.

[BetterSense]

I agree that bellows fabric is the single largest unsolved problem in large format photography. Congratulations on your results.

I have medium format folding cameras with bellows that use fabric 0.007" thick. I have never found anything that thin. I have been hunting sub-0.010" light-tight fabric for years now.

[Willie]

Library book binding tape overlapped on the stiffeners?

[DDrake]

Hi BetterSense,

Thanks for the response. 0.007" seems crazy thin.

FWIW, thickness of the space blanket I'm using doesn't register with my calipers (Mitutoyo, displays to half a thousandth). With paint on one side, thickness is 0.0025". The aluminized cuben is 0.0020" without paint, 0.00035" with. The cotton broadcloth alone is 0.0070" and 1.1 oz ripstop is 0.0020". Using thinner fabric for inner liner (silk?), maybe something like 7D nylon for outer layer, and careful management of paint and glue thickness, maybe 0.0040" is possible for the whole assembly, minus stiffening ribs. I measure 20# copy paper at 0.0035". Would that be stiff enough to make a difference as a rib? If so, maybe 0.0075" for the whole thing.

It would be an interesting experiment. Seems Cuben or mylar without aluminum would be thinner, but I'm assuming the aluminum helps block IR.

[Bernard_L]

Just by chance I found some material in a wholesale fabric store. Thin, black fabric, rubberized on one side. Store attendant told me it's used for the inner lining of purses, etc. In French it's called caroline fabric, but can't help with English nomenclature.

[BetterSense]

I have used regular copy paper for ribs with good results. No need for card stock or heavy paper for smaller cameras.

[Peter De Smidt]

The worry is whether the material will stay light proof over use.

[LabRat]

All materials will have some "stumbling block" when used alone (holds/does not hold a fold, has some slight leaking pores, stress points will leak from fatigue after multiple folding, does not hold a form well, too thick/thin, etc), so think about composite layered materials where the other materials will counteract the other materials weaknesses...

With mylar over a thin card stock, it would be good if you can bond the materials together well, but do multiple stress tests of the folded mylar to see if it does not fatigue over time into leaks and will bond well to the base stock...

Go to a very good art store's paper department and see if you can find some suitable stock... For a mylar/paper laminate, you might be able to cold mount mylar to black seamless background paper and rib the inside for bellows...

Test, test, test (before you fold your bellows)...

Good luck, and happy hunting!!!

Steve K

[Barry Kirsten]

I too have agonised over the question of bellows material. Curtain blockout fabric is light-tight but too thick IMO for small bellows (4x5 or smaller). Rip stop nylon is thin, strong, but not completely opaque. I like the idea of plastic spray enamel as a means of making it totally light tight. But just the other day when I was using my changing bag I got the idea of that material being ideal for bellows. It's rubberised nylon, which I know is also difficult to obtain, but I may well canibalise an old changing bag in future.

Next thought to consider: which of the several published methods do you propose to use to construct your bellows? I recently mad a 5x7 bellows using the online .pdf by JB Harlin. It seemed great; well illustrated, easy to follow, but the result wasn't what I wanted. I wanted a tapered bellows that fitted square frames, but ended up with one end rectangular. Depending on how the fold is started, one end will end up rectangular. Very frustrating! There are other methods around, but I don't feel comfortable with them. Good luck with yours.

[DDrake]

Thanks for the comments so far. I drew up rib patterns for straight and tapered bellows today, and laser cut the parts from 180 lb gray card stock--apx. 0.015 thickness. Also found some flat black 'poster board' at Michael's craft store for $0.99 per 20"x28" piece which is a bit thinner--apx. 0.010"--I'll try that next. Pics of the ribs below. Note the little tabs between ribs to hold them together. In the Intrepid Camera video of bellows assembly, this appears to be how they do it, and it looks like it will work well.

I mostly followed the JB Harlin instructions for making the tapered ribs--for whatever reason, these look like they'll fold about perfectly square.

Laser cutting saves a lot of labor, and most of the other materials are either inexpensive or stuff I had on hand. So I'm not too worried if the first iteration or two fails.

More pics as the assembly continues, hopefully later this week...