Viewfinder

Viewfinder

The optical viewfinder

The viewfinder allows us to frame an image; in reflex cameras, it is very precise because, through the mirror, it receives the light from the lens and then it is able to see exactly what the sensor is seeing. In this way it does not make parallax errors. Not all optical viewfinders are the same because the best pentaprisms give a transparency, therefore a greater luminosity and provide a greater coverage of the image. In fact, if the viewfinder is able to cover only 90% of the image, it means that I will see more of the viewing area with respect what I would see in the viewfinder.

In figure 01, we can see how the mirror, in its resting position, deflects the light rays through the pentaprism. This straightens the image and displays it through the optical viewfinder. In this phase, the sensor does not receive any light, and the live view function, if present on the camera, will not work.

Advantages of the optical viewfinder

Framing the photograph through the optical viewfinder gives some advantages with respect to the live view. One of the advantages is the possibility of not being affected by external light and to not remain at the mercy of distractions. Another advantage comes from the fact that use of the optical viewfinder allows for some functions to be utilized which cannot be used in live view mode (for example, autofocus models using points or mathematical means and so on).

01 Optical viewfinder: mirror in resting position.

Pentaprism

Optical viewfinder

Internal schema of a reflex with mirror down

Light

The electronic viewfinder

The electronic viewfinder is another type of viewfinder present on some cameras while the optical viewfinder is only present on reflex cameras. The majority of compact digital cameras do not have viewfinders, only live view. Some evolved compact digital cameras, some mirrorless digital cameras and all SLT’s have an electronic viewfinder.

From the outside, the electronic viewfinder is similar to the optical one except for the fact that there is no pentaprism (and therefore, takes up less space). The typical triangular bulge on the top part of the camera is also absent.

On the inside, it is instead completely different because the image seen is reproduced on a small display.

With respect to using the live view on the principal camera display, it gives us the ability to see better in situations of intense light or low light. This type of viewfinder has a display with a lower number of pixels than the principal one. Because it is notable smaller, it is able to maintain an elevated resolution.

Unlike optical viewfinder, the electronic ones receive an image and display it. In other words, the light does not arrive at the viewfinder but at the sensor, then passes to the amplifier, then on to the processor. The image is then shown on the principal display. This system always shows 100 percent of the image because the data that is displayed is exactly what is seen by the sensor. Therefore, it is possible to see how the image will actually be in the viewfinder (and with the correct exposure).

02 Electronic viewfinder of a mirrorless camera.

Sensor

Electronic viewfinder display