An SLR is a camera that uses a mirror to display the scene in the viewfinder (as opposed to cameras that have a special viewfinder for the viewfinder, or display the scene electronically). Today, almost all film SLRs have been replaced by digital SLRs.
Single-lens reflex camera
Nowadays, a single-lens reflex camera is usually understood as a single-lens reflex camera (in English SLR - Single-lens reflex), which has a folding mirror, and one lens is thus used both for exposure and for the viewfinder, in which the real image can always be seen. This allows the use of interchangeable lenses, filters and attachments, without impairing the ability to accurately preview the resulting photo.
A single-lens reflex camera also solves the problem of parallax, caused by different positions of the viewfinder and lens in other designs. In normal photography, the difference is negligible, but in macro photography, where a shift of a few centimeters means a completely different image, it is a great advantage.
Compared to "regular" digital cameras, digital SLRs have two disadvantages, resulting from their design:
By default, you cannot take pictures "on the display" - when not exposed, the mirror is folded down, so no light hits the sensor, and therefore there is nothing to show on the display. Most newer models solve this problem by providing a live view feature. In this mode, the mirror remains raised so that the light from the lens can fall straight onto the sensor. The preview can then be viewed on the rear display, but not in the viewfinder. In this mode, the camera usually focuses much more slowly, in poorly lit scenes and in strong sunlight, the image on the display is unreadable. Because of these disadvantages, a classic viewfinder is used for photography in most cases. The use of live view on the display has its justification for scenes shot from a tripod and when shooting from an extreme low or high angle.
Until recently, it was not possible to record video sequences - the problem again arises from the nature of the SLR camera. Most modern SLR cameras, however, have the function of creating multiple images in a row. High-end models handle a frequency exceeding eight frames per second. The new models also offer video recording in UltraHD resolution. When recording video, SLR cameras have the mirror raised and the preview can only be viewed on the rear display. Compared to classic digital cameras, SLRs have the advantage of a larger sensor, thanks to which they have a larger dynamic range, a smaller minimum depth of field and a lower noise level. In addition to this advantage, they offer the possibility of changing lenses (with better drawing, higher brightness). However, they have a shape ergonomically more suitable for photography than for video recording. Controlling all the necessary parameters is not a rule, the control elements are also not ideally located and in sufficient quantity.
Unlike single-lens reflex cameras, twin-lens reflex cameras (TLR - Twin Lens Reflex) have two lenses, with the upper one used for viewing in the viewfinder and the lower one for exposure. The layout was used in the past and was printed by classic viewfinder cameras, with which they share many problems.
In Czechoslovakia, binoculars were produced under the Flexaret brand and were very popular.
Fake SLR camera
False SLRs (SLR-like, sometimes also referred to as EVF or electronic SLRs) are digital cameras that display a real image from the lens on the viewfinder, but not optically, but electronically. They do not have a mirror, so they are not SLRs in the true sense of the word. The designation is originally marketing - it was intended to indicate that the mentioned digital cameras provide the same image quality and comfort of use as SLR cameras.
There is a sensor chip directly behind the lens of the fake SLR camera, the image of which is transmitted to a miniature display in the viewfinder. This solves the problem of parallax and the use of pre-set lenses. The disadvantage is the limited resolution of the display (it is not possible to focus "by eye") and the slow refresh of the image when the electronics of the camera "can't keep up" (for example, if it is processing the currently exposed image). Although this is possible in principle, fake SLRs do not have interchangeable lenses.