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Making a camera with a focusing ground glass and full movements has a few challenges but if you know what to look for and which parts need to be the most precise you can make a fully functioning 120 camera from scratch. The great thing about 120 roll film is that it doesn't require a completely dark room for loading like other view camera films that use sheet film holders. The super wide panoramic feel to this format is what inspired me to make this camera in the first place.
The only item in this project that is not made by hand is the large format lens with a built-in shutter and aperture. In this case I built the camera suited for a 90mm or longer lens that covers a 6x17cm frame. However, This camera can be made to almost any width. Some 120 cameras go up to or even over 24cm. The maximum width really depends on the coverage of the lenses you want to use. Yes, that's right, you can change out the lens on this bad boy too. To find out that coverage of a lens you have or are thinking of buying, there are two pretty easy methods. One is to look up the information on line. Schneider optics has the information on all vintage lenses right on their website, for example. If you already have a mountable large format lens, you can simply tape a ruler to a wall adjacent to a window in a dim room. Move the lens in and out from the wall to focus the projected image and then note the measurement of what's called the "image circle". This will be the maximum diagonal width of your film frame. It is a good idea to make the maximum frame fit well within this image circle since you have a camera with lens movements.
The basic tools that I use are a router table, drill press, jig saw and band saw. The band saw is not 100% necessary but will really cut down on the amount of time this will take to complete.
To design the camera and all the parts, I used Sketchup. Although there were some parts I changed on the fly without redrawing them in Sketchup. The program is most useful to see how the overall project will fit together.
Step 1: Make the focus device.
The focus device is simply a threaded rod and a threaded furniture lug attached to a block that moves along the threaded rod when turned. The focusing board lays on top of two aluminum jig tracks cut to length. I just bought a 24" one with four mounting holes and cut it so that I didn't even have to tap new holes.
Step 2: The main body and making the locking mounts
The main body is basically a box open on the front and back. I used a simple finger joint on the top corners and a single horizontal dove tail for the bottom board since the box has legs. After that I made the locking system for the bellows and interchangeable film holder and ground glass.
The bottom board of the main body is made symmetrical in both front to back and side to side directions. One side will hold a mount for the bellows allowing the bellows to be easily removed. This is will give access to the lens for removal. The other side will accept identical mounts so that the film holder and ground glass can be exchanged.
On a router table, use a V-groove router bit to make the front and back of the ridges on the bottom board. Then clear out the wood in between the ridges with flat bit and several passes. Since it is all symmetrical it is faster to make a cut, flip the board around and make the same cut on the other side.
Then with a flat 1/8" bit make an 1/8" groove down the exact center for the center board.
The top of the bellows, film and ground glass holders are fitted with a ball and spring locking device that can be found in woodworking stores.
See the video to see how this works when exchanging the film and ground glass holders out.
Step 3: Film back and darkslide.
I had to a find a good material for making the dark slide. If the material was too thick or too flimsy it just wouldn't work out as well. I never got into model building but apparently Styrene from Evergreen is commonly used for making structures and also good for creating textures. It's a dense stiff black plastic material that comes in sheets from .01 to .08 inch and can be glued in place with quick set epoxy. I made the dark slide light tight by sandwiching it between two cutouts of the styrene. This creates a nice baffle and a smooth surface for the dark slide to slide between.
The one side of the cutouts is shown in the second picture. I made sure the cutouts extended slightly out of the top of the film holder so the dark slide could always be squeezed between the two pieces. I also beveled the tops of the cutouts to make the inserting easier too.
Step 4: Make the ground glass
Making a ground glass is relatively easy but takes over two hours to finish. Basically two pieces of glass are rubbed together with sanding grit and water in between... for two hours.
Here are some things you will need:
- 2 pieces of glass. One can be cut to the size you need or left sightly over sized. The other needs to be 3-4 inches bigger each direction.
- White Aluminum Oxide Lapping Powders, both 5 micron and 3 micron sizes. These are available at www.willbell.com.
- Glass cutter
- Developing tray. Preferably something old that isn't critical to your darkroom.
- Masking tape
- Distilled water
To set up, tape the back side of both pieces of glass just a little bit off the edge. This will keep stray lapping powder off the back. Then tape the large glass piece to the bottom of the tray. In the picture below I did not tape the bottom glass' edges. I figured it out after I took the picture, however the top piece shows how I taped it up.
-Next take a very small amount of the 5 micron powder, as shown on the spoon picture, and place it in the middle with about three or four times the distilled water. The edge of the small glass can be used to spread it out one way to get started but isn't really necessary.
-Start rubbing away gently and randomly. There should be a quiet sand sifting noise. There is no need to apply a lot of pressure. Make sure to change the edge you are pushing on and change the position and rubbing pattern every few seconds.
-Check the progress after about 15 min by washing off the powder on the small glass piece and wipe it dry. You will see any problem spots that have not taken on a frosted look yet.
-I did not have a problem with the smaller piece at all on this fist attempt. I am fairly certain my success is due to using an over sized piece of glass in the bottom of the tray. Below is a comparison of the two pieces after the first hour with the 5 micron git was completed.
-The second hour is the same process but with the 3 micron grit. Make sure to clean and dry everything between the grits. Mixing the 5 micron in with the 3 micron grit will render the 3 micron grit useless as far as a finer grit.
For the final cleanup, rinse the glass pieces with distilled water to avoid mineral deposits on your ground glass.
The results are pretty decent for the wide-angle viewing glass that I needed. The far edge of the image circle is very clear with a 90mm f/8 lens, even when looking straight on through a loop. Although, a Fresnel lens may improve the ground glass viewing angle even more. (Note: The glare in the center of the ground glass on the last picture is because there are no bellows installed)
Step 5: Make some bellows
I decided to try out some bag bellows which are made by separately sewing the inside and outside layers inside-out, gluing them together and then turning the whole thing inside out. This way you do not get one seem, that would let light through. The important thing is to use blackout fabric or something close to it. Use a tight stitch on a sewing machine. After gluing and turning the bellows inside out, fix them to the mounts for the camera body on one side and the mount for the lens board on the other. Although the bag bellows are easier to assemble than regular folded bellows, they will only work for lenses up to about 120mm. Longer lenses than that, the bag might droop into the lens' field of view.