History of TLRs
While twin lens cameras have been around since the late 1800s, the spark of 6x6 twin reflex cameras as we know them quite possibly started in 1929 when the first 6x6 Rolleiflex was released. From here a large number of Rollei clones sprung up left and right over the years. While there have been a few manufactures that have taken their designs from scratch, a number of them still stay true to the original Rollei design.
A Twin Lens Reflex camera is pretty much what it sounds like. A TLR uses two lenses; a viewing lens, and a taking lens. The lens on the top is the one viewed thru, and the one on the bottom captures the actual exposure.
Like most medium format cameras the TLRs have a view screen that you look down into, allowing you to see the image with both eyes. This can often result in better composition as it's almost like seeing the final image on a flat surface. Also a twin lens setup allows for less complicated design of the camera. Meaning it does not have to take in consideration how to switch the exposure from the viewfinder to the film plane.
Most TLR use leaf shutters in their lens. Unlike focal plane shutters, leaf-style shutters do not open vertically or horizontally, but rather opening from the center of the lens and closing back to the center. They are constructed of blades that spiral inward much like the aperture bladed used on most lens modern or traditional. These kinds of shutters are usually limited in speed; normally not exceeding 1/500th of a second. However due to the way the film plane is exposed using this kind of shutter, it means that when using an electronic flash there is no maximum flash sync speed. Even at 1/500th of a second, the camera will sync with an electronic flash. Certainly gives it an advantage over most SLR cameras even top end digital SLRs. But they are overall slower than most focal plane shutters.
There are two main downsides to using a TLR design. The first downside is obviously that you cannot see through the actual taking lens. Therefore if there is something wrong with the taking lens, or the focus is not perfectly lined up with the viewing lens, you will not find out until after the negatives are developed. The other issue is parallax. That is to say the closer your subject is to the camera, the more the actual image and what you see gets shifted. This is why most TLR cannot focus closer than 4 to 6 foot. Any closer the final image may be further down in the frame than what you actually seen while focusing.
