TLR, Twin-Lens Reflex Digital Camera

Reflex Lens Digital cameras are an excellent compromise of simplicity and exactitude when framing, since it combines the screen viewfinder with a very simple design, similar to direct viewfinder cameras. The camera has two lenses: the working lens, with a shutter and diaphragm, and a supplementary lens of exactly the same focal distance that projects an image on a focal screen. The lens of the viewfinder is situated directly over the one used for the image, and the focusing mechanism affects both equally. Therefore the likeliness to the frame is almost perfect. The viewfinder's lens image is reflected upwards with a mirror, because the focal plane is on the top of the camera. With this reflection we substitute the vertical inversion of the image for a lateral inversion: in the viewfinder, what appears on the right is on the left and vice versa. This viewfinder system is almost exclusive for square formats, typically 6 x 6 and is falling out of use.

Single-Lens Reflex Camera, SLR

With a much more mechanically complex design which requires remarkable precision, the SLR allows an image captured by the lens to be formed on a focal screen situated on a plane perpendicular to the film. With the film protected from light by the shutter and a moving mirror which reflects the image upwards, we can frame and focus the image which will be formed on the film during exposure with the viewfinder. When shooting, the mirror moves upward and lets the light through. The focal plane can be seen directly from above (with a viewfinder similar to the TLR) or, the more frequent, through a multiple prism reflection ( penta-prism ) which allows seeing the amplified image, without inversions and isolated from exterior light. The SLR is used in small and medium format, from the APS to the 6 x 7 and also in digital cameras. With this system we control everything that is included in the image, including the effect of the filters and accessories. The measurement of light is made on the screen (through the lens measuring, TTL), with complete precision.