Basic knowledge of SLR lens How many lenses do you need for wide angle?

1, the simplest photography does not need a lens, just a pinhole, and its aperture is generally below f/ 128. Early camera

Basic knowledge of SLR lens How many lenses do you need for wide angle?

1, the simplest photography does not need a lens, just a pinhole, and its aperture is generally below f/ 128. Early cameras used a single-lens lens, and the imaging could be sharper than pinhole, and the aperture was larger, which could basically be photographed by hand. The working aperture is about f/ 12. Because it was a large negative, the effect was acceptable.

2. From two lenses to three lenses, the aperture of the lens is larger and the imaging is quite sharp. Cook triplets are the best design known at present. If it is four lenses, the imaging is quite good, such as Zeiss Tessar, which has a four-piece three-group structure and two lenses are glued together to form a group. The only problem with the four-piece sky-inserted lens is that the aperture can't be made too large, otherwise the image quality will be degraded. For a 35mm camera, the ceiling of the ceiling structure is f/2.8, even if the best optical glass is used at present. If you want a larger aperture, you need more lenses.

3. Speed (i.e. maximum aperture) is not the only problem. The larger the viewing angle, the more lenses are needed. A low-speed small-angle lens, such as Leitz 560mm f/6.8 Telyt, uses only two lenses. Generally, 50mm f/ 1.4 needs 6 or 7 tablets, and 2 1mm f/4.5 Zeiss Biogon needs 8 tablets. More lenses make them bigger, heavier and more expensive.

So far, we have only considered the number of lenses needed to make a sharp, fast or wide-angle lens, but there is still a problem to worry about, and that is the actual size of the lens. When focusing at infinity, two of the above 560mm Telyt lenses must be 560mm away from the film, so the lens length is 60cm! On the contrary, the total length of 21mm biogen is 45 mm. When focusing at infinity, the optical center of the lens must be 2 1mm away from the film and basically occupied by the lens, so that the last lens is only 5mm away from the film. That's why Biogon can't be used in SLR cameras, because there is no room for mirrors!