Basic SLR lens knowledge

Generally, the quality of the lens is usually determined by whether the aperture is constant or the focal point is reasonable.

I. focal length,
The focal length changes the diagonal angle of view. The shorter the focal length, the wider the angle of view, the longer the focal length, and the narrower the angle of view.
If a lens has only one fixed focal length, such as EF 50mm f/1.8, It is the fixed focal length.
The shorter the focal length, the better. formula: Large zoom <small zoom <fixed focus
Fish Eye 14mm big scene, special creation, shot out deformation is very powerful, fish eyes look at things the same.
Ultra Wide angle 16mm-28mm landscape photography, scenes, and creation purposes are somewhat distorted, with a wide range of images
Wide Angle 28mm-50mm landscape photography, scenes, portrait exterior scenes, small creation special deformation, 50 sections without deformation, the picture covers a wide range
Focus on 50mm-80mm landscape photography, scenes, portraits, and large static objects, dedicated for creation, with a small range of images
Telefocus 80mm-200mm portraits, static objects, special for creation, can capture objects relatively far
More than 400mm of the Focal Points are used for sports photography, wild animals, and creations. The objects that can be captured are far away.
Conclusion: wide-angle shoot scenery, Zhong Jiao shoot portraits, and telejiao shoot birds or sports occasions
2. Optical circle value,
The larger the aperture, the better. A single constant aperture is better than a non-constant aperture. the aperture size determines the camera's light intake and the shutter speed in a dark environment,
For example, if you take a photo in the room in the evening, the shutter speed of the F/4-5.6 aperture must be slower than that of F/2.8, so it is easier to take a picture.
The thicker the aperture of the lens, the better the lens, because the large aperture must be large.
3. Other parameters,
Refer to details on the lens ID of a digital SLR camera