Photography strategy-lens-basic knowledge

This article should be placed at the beginning of the lens article, but due to personal negligence and typographical errors, the basic knowledge of this lens is placed at the end of the lens article. I'm really sorry!

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Put up a wallpaper to make amends!

Get down to business!

It seems that some previous articles have been scattered. Forget it, sum up this article.

Because Quan Huafu is the mainstream at present, the following pictures are all carried out according to Quan Huafu's standards, and half of APS-C pictures need to be converted into equivalent focal lengths.

The conversion coefficients of all Sony micro-cameras and Nikon non-full-frame digital SLR cameras (APS-C format) are 1.5.

Canon's EOS digital SLR (APS-C format) is 1.6 and (APS-H format) is 1.3.

Panasonic, Olympus 4/3 system, conversion factor is 2.

The conversion coefficient of a full-frame camera is 1 (that is, no conversion is required).

Simply put, it is easy to understand that the focal length of a non-full-frame camera is converted into the focal length of a full-frame camera based on the standard of a full-frame camera.

Schematic diagram of scene changes from different perspectives

Perspective relationship during shooting

The relationship between focal length and viewing angle of camera lens is shown in the above picture. The wider the focal length, the wider the viewing angle. When using a 35mm full-frame camera, the viewing angle of 14mm lens can reach 1 14 degrees. On the contrary, the viewing angle of a 300mm lens is only 8 degrees 15 minutes, which is very narrow, but it can enlarge and image a part of the subject.

In order to give you a better understanding, I found some more pictures.

visual angle

focal distance

Little knowledge-infinity on the lens

Let's have a rest.

The amount of light passing through the lens is represented by the f value. F value is the value obtained by dividing the focal length by the aperture diameter of the lens, which can be expressed as F2.8, F4, F5.6, etc. The smaller the F value, the more the lens luminous flux, and the greater the F value, the less the lens luminous flux. When the f value is small, it has the advantages of faster shutter speed, blurred effect and easier observation in the viewfinder.

Aperture f value = lens focal length/lens aperture diameter

The above formula shows that to achieve the same aperture f value, the aperture of a long focal length lens is larger than that of a short focal length lens, and the translation is-the longer the focal length, the larger the volume! The shorter the focal length, the smaller the aperture value that can be made under the same volume (theoretically)

What are the advantages of a large aperture? Isn't this question just a bunch of answers? ...

Summarized it. That's about it.

1, it is easier to blur the background-the subject foreground and background blur, highlighting the theme. Large aperture can significantly highlight the blur effect of the theme (there must also be a telephoto end-because blur is also proportional-to sum up, the longer the focal length, the smaller the aperture, the better the blur. )

2. The shutter speed can be relatively reduced-the shutter speed can be increased to achieve a safe shutter and make up for the jitter caused by the slow shutter speed. Under the condition of low light, the shutter speed can be avoided from being too slow, and high-quality photos can be obtained without greatly improving the sensitivity.

3, easy to shoot in low light. be the same as the above

4, improve the focusing speed-but this is relative, the aperture is fully open, the amount of light is relatively large, and it is easy to focus in low light at night, but under normal illumination, because the large aperture brings better blur, it also brings extremely shallow depth of field, which will interfere with focusing! If there is no anti-shake, it is easy to lose focus. (telephoto end-large aperture)

Like this, (I know it's a painting, but the situation is the same anyway), it's because you accidentally shook your hand and lost focus.

Little knowledge-T value/lens hidden value

After changing the focal length of the lens, the object in front of you seems to be farther or closer to the background. This visual effect is called spatial depth (perspective). For example, under a wide-angle lens, the background looks far and wide, and the distance between the subject and the background is exaggerated. Under telephoto lens, if the focal length becomes longer, the background will feel closer and closer to the subject, and the perspective will be weakened. Using this effect, when we want to include the periphery of the subject in the painting, we can choose a wide-angle lens, and when we only need to highlight the subject, we can choose a telephoto lens.

Put two pictures to illustrate the depth of the space.

Figure 1: the extension of wide angle and the depth of space.

Fig. 2 The compressed background of telephoto highlights the theme.

This should be easy to understand.

Let's move on to the next part.

Depth of field (DOF) refers to the relatively clear imaging range before and after the camera focuses. In optics, especially in video recording or photography, it is the distance range that can be clearly imaged in space. Although the lens can only focus the light to a fixed distance, it will gradually blur away from this point, but within a certain distance, the degree of image blur is imperceptible to the naked eye, which is called depth of field. When the focus is set in hyperfocal distance, the depth of field will extend from half of hyperfocal distance to infinity, which is the maximum depth of field with a fixed aperture.

Depth of field is usually determined by object distance, lens focal length and lens aperture value (aperture size relative to focal length). Generally speaking, except for close range, the depth of field is determined by the magnification of the object and the aperture value of the lens. When the aperture value is fixed, increasing the magnification, whether it is closer to the subject or using a lens with a long focal length, will reduce the distance of depth of field; When the magnification decreases, the depth of field will increase. If the magnification is fixed, increasing the aperture value (reducing the aperture) will increase the depth of field; Reducing the aperture value (increasing the aperture) will reduce the depth of field.

For some images, such as landscape photos, it is more appropriate to use a larger depth of field. However, in portrait photography, small depth of field is often used for composition, resulting in the so-called background blur effect. Because of the progress of digital images, the sharpness of images can be changed by computer post-processing, so can the depth of field.

Under the condition of the same equivalent focal length, equivalent aperture and focal length, the depth of field of photosensitive elements of different sizes remains unchanged. Among them, the conversion between focal length and equivalent focal length, aperture and equivalent aperture is generally based on 135 sensor.

Don't understand?

it doesn't matter

There is a depth of field scale on the lens.

The depth of field ruler uses two units: feet and meters; When a certain distance value is aimed at the white mark, the object at that distance is imaged on the focal plane. On both sides of the white crosshair below the Jing Shenbiao, there are numerical values indicating the aperture value. When the aperture value of the lens is set to a certain value, the depth of field is two numerical ranges on the distance scale where the aperture value reticle is aligned.

We generally don't have to bother now, because the camera can help us with these calculations. We just need to look at it. If the lens has no depth of field scale, there is nothing to care about, because we may have a chance to use it for a long time.

These two pictures illustrate the depth of field in detail.

Shallow depth of field

depth of field

The distance from front to back when focusing clearly is called depth of field. The scene of the photo is divided into-foreground-middle scene-background.

I believe that my friends will not think about it. ...

But in line with the principle of popular science, I still post it, and try to be as detailed as possible!

The smaller the aperture (the larger the F value), the farther the focus, the shorter the focal length and the greater the depth of field.

The larger the aperture (the smaller the F value), the closer the focus, the longer the focal length and the smaller the depth of field.

For any aperture, the depth of field behind the focus is about twice that before the focus.

Well, there are 3500 words at the end of this chapter, both short and long.

This chapter talks about the following points.

Angle of view and focal length

F value-aperture

Spatial depth (perspective)

depth of field

We will use these four points when shooting, but we don't have to memorize these theoretical knowledge when we start shooting. We just need to know this knowledge. It is best to learn to shoot with feelings and give everything to the camera in the early stage, so that we can do whatever we want when shooting! Of course, in the future advanced photography, the author will explain in detail how to use these points.

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