How to distinguish the lens height of SLR camera? I usually see some parameters such as 18-55, 18, 135, 55-250, 18-200.

The first two layers are not very accurate.

For a lens, the most valuable thing is the pile of glass!

The larger the glass plate, the more difficult the manufacturing process, the lower the output and the higher the cost.

It is the aperture value that indicates the size of the lens glass sheet.

The larger the aperture (the smaller the aperture value), the larger the aperture of the lens, the more luminous flux per unit time, the greater the possibility of taking clear photos in low light environment, and the greater the degree of background blur ... Same as above, the more expensive the better.

Take Canon's 50mm standard lens as an example:

EF 50mm f/ 1.8 780 yuan

EF 50mm f/ 1.4 2600 yuan

EF 50mm f/ 1.2 10400 yuan.

In the middle, f 1.8, f 1.4 and f 1.2 differ by half an aperture.

Therefore, the usual lenses, not to mention the collection and some special lenses, such as shift axis, macro, soft focus, super telephoto, special materials and so on.

The level of the lens is distinguished by the aperture size.

Not divided by the focal length, not divided by the zoom factor.

The aperture of low-grade zoom lens is mostly around f/3.5~5.6, f/4-5.6 and f/4.5-5.6.

The aperture of a medium-distance zoom lens does not change with the change of focal length, that is, it is a constant aperture, such as 24- 120mm f/4.

The aperture of high-grade zoom lens is not only constant, but also larger, such as 24-70mm f/2.8.

Generally, manufacturers of high-end lenses have some special marking methods, such as Canon's red circle, L.

Nikon's golden circle, ED.

Sigma is also a golden circle, marked EX.

Longteng's SP and so on.