The Front Standard

I am kind of going by intuition here, so if anyone sees me going completely off track, let me know.

I finished taping up the joints on the front standard and devised a pocket for the pinholes to slide into (also with gaffer's tape). I generally use gaffer's tape to "mount" the pinholes which I got from Earl over at f295.org. The holes come as 3mm disks with the hole in the center, so I tape around them. You can see better below than I can explain here.

So I started with the standard with a big-ish hole so that the edges of the foam core don't interfere with the light transmission to the outer edges of the image. I folded a piece of gaffer's tape in half and punched a hole in it using a regular paper hole punch. That got taped over the hole in the front of the standard. This pic is blurry, but I think you can make out what is going on there.

I made a flap where the pinholes slide into the pocket so that I don't get light leaks behind the pinhole.

The pinhole is mounted in a 'standard' (for me) square of gaffer's tape, so that all of my pinholes look the same except that the diameter is written on the tape. So these now slide behind the smaller hole piece.

So this is what it looks like with the pinhole inserted. The flap sticks out a bit, so it might even make a small rudimentary lens hood for mid-day shots!

Going For It

Ok, enough thought and practice. I am going to make the 8x10 pinhole that I want, not the one I think I can build in a weekend. This is going to have interchangeable pinholes and adjustable focal lengths. It will use a bag bellows with incorporated 'sleeves' for changing film (like a changing bag).

Here is step one. The front standard.
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It is 4"x4"x2" (10x10x5cm). Stay tuned for step 2!

Flawed Mod

If you were fortunate enough to read my scintillating previous post about the pinhole camera, you probably finished it scratching your head, thinking... "Why would he shorten the focal length to get more coverage on his film?" The truth is that I was doing the same thing. It didn't make sense intuitively. If the pinhole is closer to the film, that should just make the image smaller. How would that effect the area of coverage? The answer is this... it actually doesn't make the image smaller, but it does change the magnification. It is the same effect of changing from a 50mm lens on your 35mm SLR to a 28mm lens. Things get smaller but the image stays the same size (36x24mm). This is done through the magic of optics. The glass lens elements manipulate the light path so that you can change focal length and aperture and not change the size of the projected image circle. I don't have any glass lens elements on this camera though. So changing from 115mm focal length to 81mm focal length has the effect of reducing the magnification of the scene, and if the image circle of the pinhole is big enough to cover the size of film you are using, all is copacetic. However, in my case I also changed the size of the pinhole from 0.5mm to 0.4mm, a gigantic 20% decrease! Guess what. When you reduce the size of the pinhole, you reduce the size of your image circle! So now I have an 8x10 pinhole that has an image circle big enough to cover a 4x5 piece of film. Seriously, I kept thinking to myself, "you shouldn't cut that camera down... just make another back for it." and now that is what I will be doing. I will need to calculate the right distance to cover my curved 8x10 (~126°).

For your viewing pleasure, here is a crappy still life I took after cutting down the camera. Back to the drawing board.

New 8x10 Design

So, the last foamcore pinhole camera was a lesson in light leaks. I tried a number of things, but the fact is that hand-cut foamcore is never going to form a light-tight butt joint. So the way I designed the two parts of the box did not have enough overlap all the way around to keep the light out. The other thing I learned was that I did not really need anything to keep the film in a curved plane. The dimensions of the box were such that the film naturally lay in a curved shape.

So I decided to make another 8x10 pinhole camera with these things in mind. This first picture is just for the youngsters out there (like my oldest son) who think, "I'm never going to use geometry in real life! Why do I have to take it in school!??". I probably thought that same thing in high school, but here I am in my mid 40's with a hobby that demands the use of math on an almost daily basis. I couldn't have predicted that I would ever want to build a curved plane camera, but had I not been diligent in my math classes, I couldn't; 1.) build this camera, or 2.) help said son with his math assignments. Stick with the math people. It is an investment that will pay dividends later.
Here is my Moleskine with design calculations.

The construction is simple, so I won't spend a lot of time explaining cutting, gluing and taping foamcore other than to say that you should use a 'fresh' x-acto blade when you start. The foamcore will shred if the blade is not razor sharp, making joinery difficult.

Here is the inside of the 'back' of the camera. Note the "lugs" and the flap of gaffer's tape.

The film sits under the lugs, keeping it in place and centered and curved to the right arc.

The flap of tape allows me to pull the edge of the film away from the side of the camera. Otherwise, it is difficult to get the film out of the camera without scratching the emulsion.

The front of the camera is simpler. Just a box 2" deep that fits over the opening of the camera back. It fits snugly, so no need for more light sealing. The shutter is again a simple 'drain plug' type since exposures are consistently in the >10s range. The focal length (I know it isn't the right term, but everyone knows what I mean) is 115mm, the pinhole is 0.5mm, the effective aperture is f/230 and the field of view is about 109°.

Here is the first shot with this camera. The field of view doesn't quite cover the film, so I cropped it square. This can be remedied by shortening the focal length to about 82mm which should be pretty easy to do. I probably would also need to change to a .4mm pinhole in that case. This picture was made by wedging the camera into a tree. This pointed the pinhole to the sky which is a problem for this x-ray film (blown highlights) it also caught the sun, which I couldn't really tell since the camera was above my head. That accounts for the characteristic pinhole flare. BUT! there are no light leaks that I can see and so I think that this camera with a little modification will be a nice addition to the toolbox. I may even take it to the wedding I am shooting next month. Leave your questions or comments here or on the forum that brought you here. I am glad to answer.

New 8x10 Pinhole

So I decided to make another pinhole camera. For this one I had contact printing in mind. That meant BIGGER NEGATIVES! So I have a box of 8x10 sheets of Kodak CSG x-ray film in the freezer that I have been cutting down to 4x5 for the Speed Graphic. Why not burn through some of that cheap stuff and have some fun along the way? I also happened to have some left over black foam core from my previous 6x12cm pinhole camera. So I went to the drawing board (literally) and sketched out some ideas. I like the curved film plane, but this time I thought I would keep a constant distance to the pinhole instead of the constant f-stop of the 6x12cm. I went and downloaded Pinhole Designer to do the calculations for me. That is a really great program and I highly recommend it to anyone interested in making a pinhole camera. I found the optimal pinhole size and it also gave me the right angle of view so that I could make the curved plane the right radius. I came up with a 115mm film distance with a 0.5mm pinhole. That makes an f/230 camera with a field of view around 109°. Here are some crappy phone digipics of the camera as it is today.
This is the back where the film sits. There are four stand-offs in the corners to make it curve upward on the ends. You can see too that I put some camera flocking material in the back since x-ray film doesn't have an anti-halation layer and the foam core is not perfectly flat black.



Here is the same piece with a sheet of film in it.



Here is the front of the camera. There are two stand-offs that hold the center of the film's long edges down against the back of the camera, keeping the curve 'curvy'. The other pieces on the short ends are light traps that just slide down inside of the back. They also create friction that keeps the whole thing together without rubber bands.



And here it is going together.



Finally, I just used a 'drain plug' style of shutter. The exposures for this f/230 camera are long enough, especially with iso 80 x-ray film, that I don't need anything mechanical or spring loaded.



Here is my first 'successful' 8x10 image from this camera. Obviously, I need to put something in that will keep the film centered and I also have some light leaks to deal with. But for a first image from a basically cardboard camera, it's not too bad.