Photography Lens: What is the header?

In digital SLR (also known as digital SLR or DSLR) lenses, there are many specific terms, such as "travel lens" specifically refers to a large zoom lens, and "portrait lens" specifically refers to a large aperture , a large-aperture fixed-focus lens with a focal length of 85mm or 135mm, etc. So, what does the "header" that is highly mentioned in digital SLR lenses mean?

The so-called "header". ?, specifically refers to a fixed-focus lens with a focal length of 50mm. This is because when a 50mm lens is used on a film SLR or a full-frame digital SLR, its angle of view is relatively similar to that of the human eye. The head picture is similar to what the human eye actually sees, rather than a much wider angle of view than the human eye like a super wide-angle lens.

It is for this reason that the 50mm fixed-focus lens is praised by people. Another reason for the name "header" is that the optical structure of the 50mm lens is the most mature. The heads of various brands are very similar in structure, and their structure has almost been "standardized". This is also the 50mm lens. One reason why the lens is called a "header"

Why should we emphasize that the angle of view of a 50mm lens is similar to that of the human eye when used on a film SLR or full-frame digital SLR? This is because most DSLRs are not full-frame DSLRs.

The actual focal length needs to be multiplied by a factor (1.5 for Nikon, Sony and Pentax, and 1.6 for Canon). So, 50mm? When used on a non-full-frame digital SLR, the actual viewing angle is equivalent to 75mm or 80mm, which is somewhat different from the viewing angle of the human eye.

However, we usually call the 50mm lens "head". For Olympus's digital SLR, since its focal length conversion coefficient is 2, the focal length of Olympus's "head" is 25mm. .

Since the angle of view presented by the masthead is similar to that of the human eye, the pictures taken tend to be relatively flat (because the human eye is accustomed to this feeling), unlike those of ultra-wide-angle or macro lenses. , can take pictures with strong visual impact, so it is not easy to use the header well. However, on the other hand, it is also a "universal lens", for example, we often use it. It is said that "masters' mastheads rule the world", so the masthead still occupies a very important position in many people's equipment arsenal.