What is the lens aperture of a camera used for?

All cameras are based on the principle of pinhole imaging: take a sealed box, drill a small round hole on both sides, and then align the punched side with the window. The scene outside the window, such as a tree, will generate a reflection of the tree on the inner wall of the box opposite the round hole. If we coat the inner wall with photosensitive materials (film or CCD/CMOS), the box with holes is a complete camera. This is a pinhole camera.

Since the camera doesn't need a lens, why isn't there a small round hole in front of the camera but a few pieces of glass now? And these glasses (lenses) are so expensive! This is because the pinhole must be very small to image, which is also the origin of the pinhole camera name. Not if the hole is as big as the door. So we don't have an imaging door. The light in Kong Xiao is very weak, so I am patient with pinhole photography. It is common for a photo to be exposed for several minutes to several hours. Moreover, due to the diffraction interference of light, the photos taken by pinhole camera are not clear enough, just like looking at flowers in the fog.

No one wants to spend hours taking a blurred photo. We should try to increase the amount of light. Is there any way to enlarge this small hole and generate a clear image? People immediately thought of the condensing function of convex mirror. Put the glass convex mirror on the big hole and the problem will be solved.

That's true. This is how the camera lens was born. Today, all kinds of lenses of digital cameras are arranged and combined with several concave-convex mirrors, and then wrapped in plastic or iron. With the lens, the pinhole imaging hole-that is, the aperture below-is no longer a pinhole, but a hole.

Solved the problem of light input. But sometimes the problem comes again: we don't need to have big holes all the time. For example, under the scorching sun on the beach in summer, there are sparkling flowers everywhere. In order to distinguish between human flesh and white sand, we need to squint carefully The lens is the eye of the camera, and the camera needs to squint at this time. Obviously, in order to cope with different light intensity, we also need to equip the lens with a device that can adjust the size of this hole, so that it can be reduced to a pinhole in strong light and a big hole in weak light. This device is the aperture. The English name of Aperture is aperture. A set of concave-convex mirrors with aperture gives birth to a complete lens.

Definition: Aperture is a device to adjust the size of the lens entrance hole.

Common aperture values are as follows: F 1, F 1.4, F2, F2.8, F4, F5.6, F8, f1,F 16, F22, F32, F44. The optical input difference between adjacent aperture values of every two blocks is twice. For example, if the aperture is adjusted from F4 to F2.8, the amount of light entering will double; From F2.8 to F2, it has doubled. Perhaps you have seen that the aperture value is opposite to the actual aperture size. The aperture is F 1 at the maximum light input and F64 at the minimum. For 135 camera, the minimum aperture of most lenses is F22.

Several Necessary Explanations of Photographic Terminology-Bob Qingyun

Since the aperture can be large or small, when is the best imaging quality of the lens? According to the above picture, the aperture is almost the same as the pinhole at the minimum aperture F22, and the digital camera becomes a pinhole camera. As I said before, pinhole imaging is not much better. When the aperture is maximum, the small hole becomes a gate again, and the imaging is poor. Therefore, according to the traditional golden mean of the Chinese nation, please remember:

The lens images best at a medium aperture (the picture is the clearest).

We call the best aperture of an image the best aperture.

If it is a 135 digital SLR, the medium aperture is F8 or F 1 1. Small digital DC depends on the specific model. If the optional aperture value is between F2.5 and F8, F4.6 in the middle is the best aperture.

Time flies, the aperture of the lens is the faucet, which controls the size of the water flow (the amount of light entering). For the lens, we certainly hope that the larger the aperture, the better. It's like a faucet at home. Although we never turn it on when brushing our teeth and washing our face, in case of a fire at home, we will turn the faucet on at once. I hate why we didn't install a bigger faucet in the first place. The maximum aperture of the lens is not conducive to imaging, and we usually use the maximum aperture less; However, when the light is particularly weak and there is no tripod, such as shooting a street documentary at night, we will definitely use the maximum aperture without hesitation and regret why we didn't buy a large aperture lens at the beginning.

But the large aperture lens is expensive and the weight is amazing. For example, Canon70-200mm versions have an aperture of F4, 4000 yuan and a weight of 700g. F2.8 has an aperture of more than 8,000 and weighs1.500g.. This is because the aperture is relatively large, the lens is much larger and the processing is difficult. Whether it is worthwhile to pay twice as much money and sweat for a large aperture is a matter of opinion.