Update: I decided to add to the instructions to make it a little more coherent and comprehensive.

A more organized set of instructions are also available on my website [link] under Tutorials - Home Made TLR Camera

HOW TO MAKE A TLR CAMERA:

In Optics class we were assigned to make from scratch a functional film camera out of whatever supplies were available in the Research and Engineering room and from home.

For my camera, I went with a twin lens reflex (TLR) design so I wouldn’t have to deal with the moving mirror component were I to have chosen a single lens reflect (SLR) design.

Unlike an SLR, a TLR uses two objective lenses at the same focal length. One lens is used for the viewfinder system (viewfinder lens) and the other is used for taking the photo (photographic lens). For more information on TLRs, see Wikipedia: [link]

I used my Tamron 90mm F2.8 lens box as the basis for the camera. The good thing about the Tamron box is that it has two layers of boxes, originally for better protection of the lens. But two layers also helps prevent light leaks. I also considered using wood to make a box for the basis of the camera. However, I was working on a time limit and figured cutting wood would take a lot longer than cutting cardboard. If you have the time, I suggest using wood for a more durable product since cardboard falls apart with prolonged use.

The entire box was painted black. The inside was painted black to prevent internal light reflections were any light to get in. The outside was painted black for aesthetic purposes.

For the lenses, I used two double convex lenses with a focal length of about 105mm. Double convex lenses can be purchased online for about $5. If you buy them online, the manufacturers will probably tell you the focal length. Old glasses should also make decent lenses. You will just have to do calculations to determine the focal length. An easy way to estimate the focal length of your lens is to hold the lens up to a window. Allow light to go through the lens and project an upside-down image of the window onto a piece of paper. Move the piece of paper until the image of the window comes into focus. When the image comes into focus, measure the distance from the paper to the lens and that will be your estimated focal length. Having a friend help is strongly suggested. If you can’t get the projected image onto the paper or if the projected image is so small you can’t tell if it’s focused, try adjusting your distance to the window.

The lenses were attached to wrapping paper rolls (like really thick toilet paper rolls). Two holes were cut in front of the Tamron box to fit the wrapping paper rolls. Simple calculations were made to determine where the holes should be cut. The holes should be cut such that the distance traveled by light entering through the viewfinder lens, bouncing off the internal mirror, and up to the viewfinder is the SAME distance as the distance traveled by light through the photographic lens to the film. See the bottom left portion of the drawing for more detail.

The wrapping paper rolls fit tightly into the holes in the Tamron box as to not allow light leaks but were still movable to allow focusing. However, both lenses were not designed to move simultaneously. This is something that should be fixed in the future.

A hole was cut out of the top of the Tamron box. Translucent wax paper covered the hole to make the viewfinder. DO NOT USE transparent plastic wrap or normal white paper. The translucent wax paper allows light to pass through diffusely such that light entering the viewfinder lens can properly project an image on to the viewfinder.

Note cards were used to surround the viewfinder on three sides to prevent reflections and get better contrast on the viewfinder.

The inside of the camera was divided into upper and lower compartments with cardboard and a lot of black tape. Light can NOT be exchanged from upper to lower compartments and vice versa. Preventing light leaks from the top compartment to the bottom compartment does take some time, trial and error but it is necessary.

In the upper compartment, an internal mirror was attached at a 45 degree angle to reflect the incoming image from the viewfinder lens to the viewfinder. Again, place the mirror such that the distance traveled by light entering through the viewfinder lens, bouncing off the internal mirror, and up to the viewfinder is the SAME distance as the distance traveled by light through the photographic lens to the film

The lower compartment housed the film which would capture the incoming image from the photographic lens. The image that appear on the viewfinder from the viewfinder lens was assumed to be negligibly close enough to the image that was captured on film from the photographic lens. (However, there are still some differences between the two images, so proper composition is fairly difficult)

A rubber-band loaded leaf shutter was made from three floppy disks, rubbed bands and black tape. The shutter was attached in front of the photographic lens with a lot of black tape. I kept the shutter on the outside since putting the shutter inside would require more cutting, potentially causing light leaks. I won’t describe how the shutter was made since you can find that general information here: [link]) (under Leaf shutters) The only difference between my design and the Wiki described leaf shutter is I used rubber bands to pull instead of springs to push the leaf blade.

And that's essentially how to make a twin lens reflex camera.

It took me about 2 weeks to design and build the camera. 2 to 3 days per week. About an hour or two per day.

------
Below are some photos taken with the camera. The shutter speed was fairly slow due to indoor conditions. People can't stand still so they turn out blurry. Focusing is difficult at times.

Photos were taken on generic 3.5x5 (5x7 cut in half) B&W sheet film. I forgot the exact brand, but you can find them at B&H: [link] . If you don't want to buy sheet film, you can use normal roll film too. You will have to cut the film into small manageable pieces in a darkroom.

After weeks of aggressive use, the camera began to fall apart and minor light leaks began to seep through, resulting in some strange effects. So black tape was smooshed on everywhere to try to prevent more light leaks.
*
*
*
*
*
<sub>under the CC license, this photo may be used on other websites as long as:
1. Attribution (credit) is given to Jean Fan, roseonthegrey, AND roseonthegrey . deviantart . com
2. A link is placed on the website linking back to the original photo
3. All other conditions under the CC license are met (photo may not be altered in any way)</sub>