Digital Camera Viewfinder

When framing with any camera we use a viewfinder that allows us to see, more or less exactly, what the final aspect of the picture will be. There are two types of viewfinders: the direct viewfinder (were we get an idea of the image's limits by looking through a window), and the screen viewfinder , were we can see the image projected by the lens we use to make the image. The difference between both is noticeable: The direct viewfinder is a virtual image, seen by the eye but not projected, which approximately frames the image captured by the lens, and informs us of the focus through indirect mean (double image telemeter); on the other hand, the image on the screen is a real image, captured by the lens and projected on a plane, exactly the way it will be formed on the film or digital sensor during exposure. On the focal plane the image appears vertically inverted; on most screen viewfinders the image is straightened with a mirror (which substitutes the vertical inversion for a lateral inversion) or for a prism (which corrects both inversions). All digital cameras have a liquid crystal display in which we see the image framed by the lens.

Plate Cameras
In the first cameras, and the large format ones nowadays, the viewfinder is a emery glass focusing screen which occupies the entire back part. The image appears inverted

vertically and we have to look at it covering the environmental light with a dark cloth. Once the frame has been set we close the shutter and introduce the plate holder in the exact place it usually is on the screen.

Direct Viewfinder Cameras
The arrival of rolls of film allowed the amateur photographer to save the work of framing and loading (glass) plates one by one. With flexible film, the direct viewfinder or Galilean appeared, which approximately frames the image which will be formed on the film during exposure. This is the viewfinder of simply designed, small cameras and "compacts". These have a double image telemeter, although most actual models have an automatic focusing mechanism. In any case, we have to remember that framing with a direct viewfinder is susceptible to error, specially at short distances, since the viewfinder and lens are not in the same place.

Direct viewfinder cameras have the advantage of low sound and mechanical complexity, and with them we can still see the image through the viewfinder when shooting.