What is the lens aperture?
Since the aperture can be small or small, how much time the lens of the best quality imaging? According to the above figure, the minimum aperture F22 when the aperture with the pinhole almost, the digital camera has become a pinhole camera, said before the pinhole imaging is not good; aperture when the hole has become the largest hole, imaging is also poor. Therefore, according to the Chinese national tradition of the doctrine of the mean, please bear in mind:
The lens is best in the medium aperture (the picture is most clear).
We call the best aperture for the best aperture.
If it is 135 digital SLR, medium aperture is F8 or F11. Small digital DC depends on the specific model, if the optional aperture value between F2.5 to F8, the middle of the F4.6 for the best aperture.
If the time is like water, the lens aperture is the faucet, it controls the size of the water (into the light). For the lens of course, we hope that the aperture of the bigger the better, it is like the taps at home, although we usually wash your teeth never wash it open the largest, but if one day home fire, we will immediately screw the maximum, and Hate why did not have a big point of the faucet. A lens is the largest aperture imaging is not good, usually we generally use the largest aperture; but in the special low light and not allowed to use the tripod case, such as the night of the street documentary capture, we will not hesitate to use the maximum aperture, And regret why did not buy a large aperture lens.
But the price of a large aperture lens is very expensive, the weight is amazing. For example, there are two versions of Canon70-200mm, aperture F4 price of 4,000 yuan, weighing 700 grams; aperture for the F2.8 that a price of more than 8,000 yuan, weighing 1500 grams. This is because the aperture level, the lens is much larger, processing difficult. It is worth the first-class aperture to pay twice the money and weight of the sweat, this is a matter of opinion.
Into the amount of light to solve. But sometimes the problem is coming: we do not need a big hole at all times. Such as the summer sun on the beach, four flowers, in order to distinguish in the end is human or white sand, we need to carefully observe the squinting. The camera is the camera's eyes, this time the camera also need to narrow his eyes. Obviously, in order to cope with different light intensity, we also need to put the lens to adjust the size of the hole to the device in order to narrow the pinhole when the light, low light when the big hole. This device is the aperture. Aperture English name for Aperture. A group of convex lens coupled with the aperture on the birth of a complete lens.
Definition: Aperture is the lens to adjust the size of the device into the light hole.
The common aperture values ??are as follows: F1, F1.4, F2, F2.8, F4, F5.6, F8, F11, F16, F22, F32, F44, F64. Each second block adjacent aperture value between the amount of light into the difference of one times. For example, the aperture from F4 adjusted to F2.8, the amount of light will be more than doubled; from F2.8 to F2 more than doubled. Perhaps you have seen, the aperture value and the actual size of the aperture is the opposite, the maximum amount of light when the aperture for the F1, the minimum for the F64. For 135 cameras, the minimum aperture for most lenses is F22.
No one intended to spend a few hours to take a vague picture, we have to find ways to increase the amount of light. Is there any way to make this hole open and produce a clear image? People immediately thought of the condenser lens condenser function. The glass convex lens installed on the big hole, the problem is not resolved?
Really so. Camera lens is so born. Today, a variety of digital camera lens is a combination of a few pieces of convex lens, and then outside with a package of plastic or metal. With the lens, the aperture of the hole in the hole - that is, the aperture below - is no longer pinhole, and it becomes a hole.
All cameras are based on the principle of small hole imaging: take a sealed box, in any side drilling a small hole, and then the hole facing the window, the window of the scene, such as a tree or something, The wall of the box produces a reflection of the tree. If we painted the inner wall with a photosensitive material (loaded with film or CCD / CMOS), this hole in the box is a complete camera. This is the pinhole camera.
Since a camera can not need a lens, why now the front of the camera is not a small round hole but a few pieces of glass? And these pieces of glass (lens) also sold so expensive! This is because the hole to be imaged, the hole must be very small, which is the origin of the pinhole camera name. If the hole is as big as the door, the hole will not be like. So we do not have a door image. Hole small into the light amount is small, so play pinhole photography is very patient training, a photo exposure a few minutes to a few hours are common. Moreover, due to the diffraction interference of light, pinhole camera pictures are not clear enough, such as smoke and mirrors in general.
