Cheap & dirty bag bellows: elastic "necks"

[walter23]

I'm wondering what you camera-construction experts think about the following proposition. I've got the following partially completed camera based around my 12-shot bag magazine:

The boxes are built so that the front one (left side) nests around the rear box (right side (middle, really)). A slide-in ground glass is in the works, and the bag mag (far right) just slips into grooves in the camera back.

My original plan was to have multiple front-boxes of different lengths (the one pictured for ultra-wide pinhole shooting, another one for a 90mm, and one more for 150mm), but then I decided to complicate things and move away from the simple box camera design and towards something more like a real field camera. I will be adding some kind of rail and a bag bellows that will let me focus my 150mm lens to a few feet.

However, the attachment for the bellows isn't quite worked out. I'm not going to attach it inside the frame, as this would interfere with ultra-wide pinholes when the boxes are nested (it would bunch up inside the light path). A regular bellows is possible, but again I think it would interfere with ultrawide. My best plan so far is to attach it to the outside, and the design allows some room to affix the bellows underneath strips of wood, however I was wondering if there might be a better way.

What do you guys think of having ridges running around each of the two boxes (front standard and rear standard, if you will), which could be used as stops to hold an elastic bag bellows, held in place and sealed up something like the arm holes in a changing bag?

Would this let too much light in? It seems to work for handling loose sheets of film in the aforementioned changing bags. And it would make transport and setup of this camera pretty easy.

 

[jolefler]

FWIW, I built a few bag bellows that allowed the cameras to collapse to their mechanical limits, but still allowed focussing to about 1 meter with a 135mm lens. For one camera I made a lensboard extension that allowed macro work with the same bellows.

Just thinking that permanently afixing the bellows may save some aggravation while shooting, should your elasic system be bumped off the retaining ridges or similar mishap.

Jo

 

[walter23]

I was hoping to do my 8x10 bellows this weekend, but a last minute change of plans (different liner material to avoid flare) stymied that plan. So I tackled this little camera instead. (Yeah yeah, I'm going out shooting tomorrow, it's not all build projects though it seems like it at the moment).

Yesterday I tried to design an elaborate 4-piece bag bellows and realized there were too many annoying technical problems (related to getting good, solid, light-tight seams, avoiding light leaks at the frame attachment points, etc. Today I realized I could simplify the bag bellows construction as two big squares of material taped together around the edges, with holes cut in the center of each square for the front and rear standards. Like two big square flat doughnuts attached together at their edges and mounted to the camera pieces at their holes. I could actually make it ellipsoidal or octagonal or something to avoid those big corners, but I want the corners to tug on to make sure the bellows inside isn't in the light path.

Here's a prototype, made out of ilford light-tight printing-paper bag material & duct tape. The camera will give me extensions from 40mm (pinhole or maybe medium format if I add a roll back) up to 170mm. I plan to use it for pinhole, 90mm, and 150mm, so this is exactly what I want. This was just to test extension, compression, clearance (if this horrid thing clears my proposed rail, flexible cloth will be no problem), and attachment points.

Looks pretty ghetto, but the real thing is going to be all-black (or red vinyl) cloth, nicely attached with wooden strips. When it's all done I'll stain and varnish the whole camera or something. The lens board is going to be recessed in the front standard by one inch, and I have a cover that will clip in place over top to protect it.

Having the bellows mounted on the outside may expose them to damage, but I couldn't figure any other way to accomodate the really short minimum extension I want without them falling into the light path.

 

[grahamp]

The paper is likely stiffer than light-tight cloth. One way you might be able to handle droop is to use black elastic cord inside the bag and connected to the front and rear standard. That would allow extension, but provide some support for the cloth if it falls towards the light path.

 

[walter23]

The paper is likely stiffer than light-tight cloth. One way you might be able to handle droop is to use black elastic cord inside the bag and connected to the front and rear standard. That would allow extension, but provide some support for the cloth if it falls towards the light path.

I've been considering that problem and thought I would put some kind of bungee between the midpoint of the bellows and the rear standard (on the outside), but that doesn't sound ideal - I'd still be manually yanking the bellows back over the rear frame to keep it from drooping. Your idea is really good - I think I might just try that - one elastic in the middle of each side (or corners, or both). I also thought of something similar (elastics hemmed into the corners of a cloth tube) but figured it would bunch up too much; your idea is way better. I'd have to make sure the tension wasn't too high, just enough to hold up the cloth. Hmm.

It all depends on what I decide for the final bellows construction though; I have two options, one a single or double layer of porter's darkroom blackout cloth, the other a layer of the blackout cloth as a lightproof liner and red vinyl (like a barbecue cover) for the outside layer. The latter arrangement would be stiff enough (but possibly too stiff) and thus far my glue tests on the vinyl have been pretty abysmal: 3M super 77, contact cement, and cyanoacrylate super glue all just peel off. I probably need something like PVC pipe solvent-adhesive.

 

[Colin Graham]

They sell vinyl mend kits that pretty much weld the vinyls together, but the tubes are pretty small and it's very fast acting. I've tried pvc plumbing-type solvent cements with no luck. I must have tried every vinyl the local fabric store had when I first started trying to make a bellows.

 

[walter23]

This is a pretty simple construction and I don't need much of it, so that vinyl mending stuff sounds perfect. Fast acting is fine, the construction is just two squares that get cemented at the edges. Thanks. Do you find the stuff at fabric stores?

 

[Colin Graham]

I think I got it at a local hardware store, it was in the display with all the other glues and epoxies iirc. It does work surprisingly well.

 

[tim k]

Walter, your prototype is much like the Bender bag bellows I just put together, except the Bender is round. It does not droop at all. I used contact cement, and it holds pretty darned good.
Tim K

 

[walter23]

Walter, your prototype is much like the Bender bag bellows I just put together, except the Bender is round. It does not droop at all. I used contact cement, and it holds pretty darned good.
Tim K

Yeah, I based it on the bender idea (which I read about in an archived thread here or on lfinfo) once I got sick of messing with four panels to try to reproduce the design of my shen hao 4x5 bag bellows. The shen hao design just means the sort of natural, unstressed state of the bellows is like two truncated pyramids end to end (ie, a multi-faced 3D shape). The bender design means the unstressed state is when it's fully compressed and flat.

The shen hao version is more elegant, but who needs elegance when it turns everything into a way bigger pain in the ass than you would expect. I figured out all the measurements and cut patterns and then realized the seams at the edges would screw up mounting and light-tightness, not to mention look kind of ugly with my crude seam-making methods (I want to glue, not sew, to avoid puncturing).

I'd use the shen hao 4-panel design if I was attaching it internally to a regular bellows frame, and had a neat and tidy way to make internal seams.