Introduction to photography knowledge

Once for photography, for composition and then press the shutter. Looking at the excellent works I accidentally photographed, my heart is full of contempt for photography. But, but when I started taking pictures, I was confused. I am overwhelmed with all kinds of data, signs and collocations. As a former novice, I will give you a list of my shortcomings to help you make progress together.

Is there a difference between the P file and the automatic file of a digital camera?

Entry-level digital SLR, such as D40, has an AUTO file besides P file, but what's the difference between them?

Although the exposure of P file is also controlled by camera, it can give people more flexibility. For example, by turning the dial of the camera, you can choose various combinations of aperture and shutter, and you can make exposure compensation. Automatic files do not have this function. In addition, when using automatic gear, the internal flash will be automatically turned on when the light is insufficient, but P will not. To put it bluntly, automatic transmission is to completely simulate your SLR as an automatic small DC.

What is a camera's safety shutter?

Safety shutter refers to the slowest shutter speed that can basically ensure that your photos will not be weakened by hand shaking when taking pictures.

Generally speaking, the safety shutter is the reciprocal of the focal length of the lens. For example, if you shoot with a focal length of 200mm, your safety shutter is 1/200 seconds.

But we should pay attention to the following problems. First of all, because the above is just a traditional saying in the past, because there was no DX digital SLR at that time. If you use a DX camera such as D80, the focal length of the lens should be multiplied by 1.5 times due to the smaller viewing angle, then your safety shutter may have to work for 1/200 seconds, which should be 1/300 seconds. Second, if the lens you use has anti-shake function, such as VR lens, the speed of this safety shutter can be reduced a lot. Third, and most importantly, you should practice basic skills, so that you may use a slower safety shutter. If you are good at kung fu, you can make a clear film at a fraction of a second at the wide-angle end and a fraction of a second at the telephoto end.

Pay attention to the lens you use when using the built-in flash!

If you use the built-in flash, if you use a long lens like 70-300 at the same time, a semi-circular shadow is likely to appear under your photo. It's not a problem, it's just that your lens blocks the flash light.

Why is my lens installed on the fuselage, and I can only release the shutter at a certain aperture number, and everything else is displayed at a fee?

What happens is usually a D-lens, that is, a lens with an aperture ring. You must lock the aperture to the minimum position according to the instructions.

Why do some places always glow when I play back photos, especially bright places? But when I downloaded it to the computer, everything was fine?

This is because you set the playback status to highlight, so the brightest part of the photo will flash. All you have to do is press the multi-choice key to return to the normal viewing state. Here is a reminder. After buying a camera, it is necessary to read the instructions carefully first.

What's the use of range hoods? How to use it reasonably?

Some people may think this is bullshit. As the name implies, the hood is designed to block the light, especially when taking pictures with backlight or side backlight. But sometimes, you will find that although you use a hood, there are still light spots in the photo, and you don't use inferior or fake UV mirrors, or even UV at all.

This problem mainly occurs when APS-C camera uses Quan Huafu lens. Because the hood of Quan Huafu lens is designed for a full-frame camera, its maximum length is subject to the fact that there is no shadow in the photo. But if it is used in APS-C camera, such as D80, the hood will fail, or partially fail. Because you only use the imaging part in the middle of the lens, the hood is obviously not long enough. Therefore, if you want to completely solve this problem, you need another range hood.

I put on my hood as soon as I take a picture, no matter day or night. Of course, the purpose of my doing this is not entirely for shading, especially at night. My purpose is actually to protect the lens. Because I care about the image quality, in order to improve the image quality to the greatest extent, my lens basically does not use UV (except when taking pictures at the seaside and when it rains). Without ultraviolet rays, there will naturally be more risks, especially when climbing wild mountains, branches and so on will often be scraped on the camera. I installed a hood, which can protect me to some extent.

Relationship among lens focal length, viewing angle and depth of field

1. The focal length of the lens is a fixed physical size, which is as many millimeters as there are, and 100mm is 100mm, which will not become 150mm and will not change with different camera frames;

2. The lenses with the same focal length are placed on cameras with different frames. The larger the border, the larger the viewing angle, and the smaller the border, the smaller the viewing angle;

3. For the fuselage with the same frame, if the lens has a longer focal length, the depth of field is shallower (shorter), the focal length is shorter and the depth of field is larger (or deeper and longer).

Generally speaking, the focal length of a lens refers to the distance from the optical center of the lens (the center of a single lens or the imaging centers of multiple lenses) to the focal plane. The focal plane is the imaging surface or photosensitive surface in the camera. This kind of photosensitive surface has developed from dry glass plate used in the early days to film plate used in the later days, and then to CCD, super CCD or CMOS photosensitive devices used in digital cameras now. The size specification of this imaging surface is what we call a frame.

From the above definition, it is not difficult to see that the focal length of the lens is actually a distance length, a fixed length, and a physical size. Whether your 105mm lens is placed on D300 in DX format or D3 in FX Quan Huafu, this physical distance is fixed and there is no change. What changes is only the size of the focal plane (CMOS) of your camera. The larger the focal plane, the larger the viewing angle, which means that the larger the shooting scene can be accommodated, and the smaller the viewing angle, the smaller the scene can be accommodated. In other words, the same subject, using the same focal length lens, when the focal plane is Quan Huafu, the shooting area will be larger and the subject will be more comprehensive. If it is in DX format, the shooting area will be smaller, and a part of the periphery of the subject will be cut out of the picture, so the imaging will be more local.

This is seen from the fact that lenses with the same focal length are placed on cameras with different frames. Let's change the method and see what will happen if the same camera uses lenses with different focal lengths.

If we use a camera of the same frame, whether D3 or D300, we shoot with a lens of 100mm, and then shoot with a lens of 150mm at the same shooting distance. We will find that when shooting with 150mm lens, only a part of the 100mm lens can be shot. In this way, the viewing angle is smaller, just like the camera with different borders used above.

Although the two shooting conditions are different, one is Quan Huafu+150mm focal length lens and the other is DX+100mm focal length lens, the size ratio of the subject in the picture is the same because of the same viewing angle. Therefore, people invented a method to describe the use of lenses with the same focal length on cameras with different frames, that is, the word "equivalent". We can say that the last 100mm lens on D3 is 100mm, which is equivalent to the focal length (viewing angle) of 150mm after being placed on D300. Note: when I say "equivalent" here, I mean perspective effect, not lens? The focal length of 100mm becomes 150mm because people often ignore the word "angle of view" in brackets intentionally or unintentionally. A more complete and correct statement is, "100mm lens on D3? 100mm, when placed on D300, its viewing angle is equivalent to a lens with a focal length of 150 mm, which can clearly explain the essence of the problem.

What is a constant aperture lens?

First of all, the concept of constant aperture is relative to zoom lens. Some zoom lenses are very cheap, such as 70-300mm/f4.5-5.6 without anti-shake, only a few hundred yuan, and some zoom lenses need tens of thousands, such as Nikon's new 24-70mm/F2.8, the latter is expensive because the latter is a constant large aperture, so you can use the aperture of f28 no matter how large the focal length is adjusted. In terms of pattern, Canon's 24- 105/f4 lens is the same, and the aperture of f4 can be used regardless of the focal length of 24mm or105 mm.. And 70-300mm/f4.5-5.6 is not a constant aperture, so although you use the aperture in the camera first and adjust the aperture to f4.5, as long as you pull the focal length to the telephoto end, the aperture will become smaller.

Constant large aperture lens In order to keep the aperture of f2.8 constant, the lens body is generally relatively large, so the cost is high and the price naturally goes up.

What is the best aperture of the lens?

The best aperture of ordinary lens is often in the range of f5.6-f 1 1, so there is a saying that there is no dog head below f8. The best aperture of advanced lens, the so-called "bull's head", is often relatively large, even if it is fully open, it may be sharp. This is also one of the reasons why people pay high prices to buy cow heads. They entered the bull's head, not only for the sake of out-of-focus imaging, but also for the pursuit of high resolution under large aperture. Therefore, this is why I often use f5.6 when I use 17-55.