What's the difference between 50 sets and 85 sets of SLR lenses?

50mm and 85mm SLR lenses are a threshold of background blur. The background blur in the 50mm stage can only be said to be ok, although it is equivalent to 75mm (Nikon) ~80mm (Canon) on the APS-C frame. However, the physical focal length has not changed. In the background blur formula, the physical focal length is the influencing factor rather than the "equivalent focal length".

When the distance of 50mm is close to the subject (less than 3 meters), blurring is not bad, but this distance of 50mm can only shoot a bust. If you want to shoot the whole body, you must retreat to about 5 meters. At this time you will find that the blur of 50mm is very limited. Even if you turn the aperture to F 1.4, the background is still not blurred enough.

85mm is not the best focal length for blurring, because blurring of 135mm and 200mm is more feminine, but it is the best focal length for balancing depth of field and communication distance.

SLR is the most popular viewfinder system, which is adopted by most 35mm cameras. In this system, the unique design of the mirror and prism enables the photographer to directly observe the image passing through the lens from the viewfinder.

Therefore, you can accurately see the same image that the film is about to "see". The core of the system is a movable mirror (as shown in the light blue part), which is placed in front of the film plane at an angle of 45. The light entering the lens (as shown by the red light path) is reflected upward by the mirror to a piece of ground glass.