Optical or electronic viewfinder?
The optical viewfinder is good because it transmits the picture “as is” – without any embellishment, delay, flicker, etc. Since it is just a system of mirrors and lenses, it does not consume electricity, thereby extending the camera’s battery life. On the other hand, the mirror viewfinder has its drawbacks. In most cameras, it has a coverage of not 100% of the frame, but a little less – 95-98%. Because of this, unnecessary objects at the edges of the frame may fall into the frame and you will have to additionally crop the picture, slightly losing its resolution. The mirror viewfinder reflects a minimum of “service” information – shutter speed, aperture, ISO, exposure compensation. It is impossible to make him show, say, a live histogram, white balance or electronic level. Because of this, there is an increased likelihood of a defective image due to an incorrect exposure level, white balance, horizon obstruction. To finally assess the correctness of the settings and framing, you need to take a test shot, tear yourself away from the viewfinder, look at the screen and, in case of an error, make adjustments to the settings. This takes extra time, but with proper experience the number of such takes is minimized.
The main advantage of the electronic viewfinder (EVI) is that it displays information taken from the matrix with the camera settings already applied and makes it possible to evaluate the result even before the shutter is released. The viewfinder completely duplicates the contents of the camera screen when shooting and viewing. In addition to the picture itself, EVI can display a lot of necessary information – in addition to shutter speed and aperture, you can display a live histogram, electronic level, highlight overexposed and underexposed areas, frame objects that are sharpened, frame the picture using the selected image style, white balance. This helps a lot when shooting and allows you to minimize the number of “sighting” takes. That is, you can shoot without taking your eyes off the viewfinder – time is saved, less interesting moments are missed. You have to pay for this with additional energy consumption, which occurs when the matrix and viewfinder are working. In older cameras, the electronic viewfinder displayed a picture with a slight delay, this made it difficult to shoot in motion, however, in modern cameras, the delay in display, if any, is very slight. Not all system cameras have an electronic viewfinder. Simpler and cheaper models are deprived of this option and the screen is used for shooting. In principle, there is nothing terrible except for filming in bright sunny weather, when the screen may look pale. Although for a full-fledged work, it is better to prefer a camera with a viewfinder.
The second difference between a DSLR and a system camera is autofocus.
Autofocus in the SLR camera is carried out by phase sensors. A distinctive feature of this mechanism is that if the object is out of focus, the camera “knows” in which direction the focusing mechanism should be rotated, which generally accelerates focusing. On the other hand, the focus sensors are not located in the plane of the frame (matrix surface), but in a separate block located perpendicular to it. Because of this, a mismatch may occur – the sensors seem to be sharpened (the dots in the viewfinder are highlighted), and the object was blurry in the photo. This phenomenon is called “front focus” and “back focus” (depending on which direction the autofocus misses). It is treated by aligning the camera and lens in a service center. Especially often, the focus is blurry when using fast lenses on inexpensive carcasses.
Modern SLR cameras have a “live view” mode – Live View, in which the mirror rises and focuses according to the contrasting method, like mirrorless cameras. He will speak dumb below.
System cameras use a predominantly contrasting focusing method in which the matrix itself acts as an autofocus sensor. Information from the matrix is read and processed in real time. A special algorithm determines whether the subject in the focus area is sharp enough. If the sharpness is insufficient, a command is given to the lens to shift the focusing group of lenses, which will occur until the maximum contrast of the edges of the object is ensured. In this case, the initial focusing direction can be determined incorrectly and autofocus for some time “creeps” back and forth, and the worse the illumination, the longer the focusing takes. The contrast method is inferior to the phase method in speed, but superior to focusing accuracy – such things as “front focus” and “back focus” are unknown to mirrorless ones. In modern system cameras, the loss in focus speed of SLR cameras is minimal, or even completely absent.