16x20 Camera, Round Dos

[zeesme]

So I am on my second round of 16 20 camera building, numero uno was an overweight dimmwitted bastard.

A few problems I would like to resolve. Sorry if its a bit much for one thread...

1. Ground glass problems: I would like to salvage the expensive GG, it was 1/4" double sandblasted, but I could hardly see more than a coke can of light anywhere on the glass at f9... Is this the nature of such a large camera, or crappy GG? I think scotch tape may have seemed brighter in the testing stages...

2. Hardware: I used none, all wood and a few wing nuts, what would you advise for a focusing system gears and such wise? The last camera had two tripods, one for each standard, I would like to try and make this folding, or like a crown graphic, but light!

3. Filmbacks: I had a single frame holder, I would like to go double but am scared of it being brittle. My big problem was the darkslide material, most standard material met its limits and began to bow when pushed to 16", I settled for 1/4" steel, heavy as !@#!. I just read about Garolite but would love to know if it can hold up without bowing..

4. She was so heavy! my lens is quite a bit, but the frame (2"x1" pine) n bellows (untapered vinyl with mat board ribs and black cloth tape inside) weighed a ton. How can I lighten this up?


Any advice would be muy apreciado!

-Zev

[Erik Larsen]

Maybe try acrylic for the ground glass, much lighter I would think. 1/4 steel? No wonder you complained about weight. Garolite will work Ok I think. You can also use 030" or so aluminum for the dark slide. You can get gears at mcmaster carr for just about anything you need for the focusing track. Good luck with the build and let know the results, it should be interesting.
regards
erik

[Nathan Smith]

1. Ground glass problems: I would like to salvage the expensive GG, it was 1/4" double sandblasted,...

That's pretty thick glass ... and what is "double sandblasted" - hopefully this means it was sandblasted twice as much as usual but both times on the same side.

Most of the ground glass I've used was relatively thin, though I have not see the GG on such a large camera.

I assume you were composing with the aperture wide open and then stopping down for the shot? oh, I see now - f9. No, you probably didn't see a lot stopped down.

[zeesme]

I tried alum for my first darkslide, but at this scale it simply warped crazily, when using acrylic for gg, does that mean just totally scratching up a piece of plexi?

One of my primary concerns is still being able to see the entirety of the gg, has anyone seen a properly functioning 16x20, does it uh.. work like a smaller camera? perhaps a plastic fresnel would be needed...

any known folding camera blueprints would be wonderful too!

thanks for the speedy replies guys!

[evan clarke]

My 11x14 is dimmer using the same lenses I use on my 8x10, probably incrementaly worse on 16x20...EC

[jeffm2009]

I just joined the forum after reading this thread. I'm really interested in following along with this project, so please do keep us updated! :)

[thart2009]

I tried alum for my first darkslide, but at this scale it simply warped crazily, when using acrylic for gg, does that mean just totally scratching up a piece of plexi?

One of my primary concerns is still being able to see the entirety of the gg, has anyone seen a properly functioning 16x20, does it uh.. work like a smaller camera? perhaps a plastic fresnel would be needed...

any known folding camera blueprints would be wonderful too!

thanks for the speedy replies guys!

There is some interesting info here: http://www.raymentkirbycameras.co.uk/index.html

Also, I was working with some black formica for my darkroom table tops and it seems quite stiff. Would be even more so if two pieces were cemented together back to back..

[Michael Roberts]

Zev,
search DIY ULF for a lightweight alternative. I used plexi and self-adhesive window film for the gg. Works fine. There's info about hardware there too.
-Michael

[Michael Roberts]

Also, for the bellows, you can lose the mat board ribs and the black cloth. The easiest (and lightest) solution I've found (on this forum) is to start with plain brown craft paper. Paint one side flat black, the black side is the inside of your bellows. Draw out your folds on the nonpainted side; fold; weight and leave overnight. Next day, unfold, cover the outside with self-adhesive vinyl. You might need to apply an additional adhesive. I've read spray-on auto head-liner adhesive works well; also, paint a strip of contact cement along the seam to be extra secure. Then fold the bellows back up; weight again overnight. Next day attach to bellows frames. I've used this method on a rectangular bellows for a 12x20 expansion back for my 11x14. 16x20 is only a little bigger than 12x20....

[jp]

I can see how aluminum sheet would be flimsy (like aluminum used for flashing, patching, gutters, normal hardware store material.

Some aluminum plate would be much less flimsy and weight a lot less than steel. Most metal fab shops should be able to supply this. It should not need to be very thick. I have some round pizza pans made of this stuff and they are not flimsy at all. Sometimes lensboards are made of this stuff too.

[Jack Dahlgren]

I can see how aluminum sheet would be flimsy (like aluminum used for flashing, patching, gutters, normal hardware store material.

Some aluminum plate would be much less flimsy and weight a lot less than steel. Most metal fab shops should be able to supply this. It should not need to be very thick. I have some round pizza pans made of this stuff and they are not flimsy at all. Sometimes lensboards are made of this stuff too.

I agree, 1/8" aluminum sheet is probably more than stiff enough. But remember, it is the frame around the holder that has the most influence on stiffness.

1/4" steel is complete overkill unless you are parking your car on the camera.

[Jack Dahlgren]

Dark slides are paper impregnated with phenol-formaldehyde, formica is usually similar but with melamine resin instead. I think that the phenolic material is stiffer and perhaps stronger, but it depends on a number of things, including the matrix material (could be paper, linen, canvas etc.)

Garolite is a trade name for phenolic sheet. You can look up the properties if you are interested.