Photographers must learn! How to focus accurately manually?

For some old photographers, autofocus is like something in science fiction when they first come into contact with film photography. After all, autofocus technology began to mature in the 1990s. Before that, old cameras basically had to focus manually.

Although digital cameras now have powerful focusing functions, it does not mean that manual focusing is unnecessary. The advantage of autofocus is that it is fast, but it is often not the most accurate. In some cases, deviations are easy to occur. Relatively speaking, manual focusing will be more accurate.

So when do you need to use manual focusing?

Use a film camera.

Needless to say, most film cameras need manual focusing.

When playing with old lenses with a digital camera.

Like film cameras, old lenses need to be focused manually.

In low light environment or when the contrast of the subject is small.

The autofocus system of a digital camera depends on the light and contrast. When the contrast of an object in a low light environment (such as a smooth wall) is small, the efficiency of the autofocus system will be very low or will not work at all. At this time, it is necessary to lock the focus and re-compose or simply focus manually.

Shoot fast-moving objects.

When shooting a high-speed moving object, the camera will try to change the focal length with distance. If you use autofocus, sometimes the focusing speed can't keep up with the moving speed of the object, so you need to use manual focusing.

When taking macro photos.

For autofocus, shooting macro is a very difficult job. In the case of shallow depth of field, the camera can't judge where to focus. If you want to master the control of focusing, you must use manual focusing.

When you want to shoot through glass.

The reflection on the glass will interfere with the autofocus system. It is better to focus manually at this time. This will also happen when shooting reflections on the water.

Shooting portraits.

When shooting portraits, accurate focusing is particularly important. Portrait photographers tend to focus on their eyes, and many portrait photographers like to use the effect of large aperture and shallow depth of field, so AF system is often difficult to judge.

Composition.

Sometimes there is no focus reference in the center of the composition. Although you can lock the focus on the side and move the camera to shoot at this time, these are not as convenient and fast as direct manual focusing.

Make HDR photos.

To take a perfect HDR photo, you must ensure that every photo has the same focus. If autofocus is used at this time, the focus of each picture will inevitably change slightly.

Before learning manual focusing, we need to know what aperture is, because aperture directly affects your shutter speed and depth of field.

Aperture is a part of the camera, which is used to control the aperture size of the lens, the depth of field, the imaging quality of the lens, and the amount of light entering with the shutter. Sometimes it is also the concept of aperture value.

The expression of aperture size is expressed by f value. For the manufactured lens, the diameter of the lens cannot be changed at will, but the luminous flux of the lens can be controlled by adding a polygon or circular aperture grating with variable area inside the lens. This device is called aperture, and the f value of aperture = focal length/aperture diameter of lens.

Influence of aperture on photos: The larger the aperture, the greater the light input, the smaller the depth of field and the smaller the F value.

When the aperture value is large (to the left), the lens aperture becomes larger, more light enters, and the depth of field decreases; When the aperture value decreases (to the right), the aperture of the lens decreases, the amount of light entering decreases and the depth of field increases.

When the light allows the use of a small aperture, timely focusing is not completely accurate, but because of the large depth of field, the image will remain clear, because a large range of scenes are within the focus range.

However, when using a small aperture, it is necessary to ensure sufficient light input to ensure a safe shutter speed.

The above explanation is simply summed up in two sentences (knock on the blackboard! ! ! Recite! ! ! ):

Large aperture, small value, more light, deep scenery and large blur;

Small aperture, large value, less light, deep scenery and small blur.

The so-called focusing, in simple terms, is actually to adjust the position between the lens and the focal plane, so that the subject falls on the focal plane accurately. This process of adjusting the lens position is focusing.

So, how to use manual focusing quickly? What's the trick here?

Of course there is!

This is the "pan-focus" technology widely used in the era of manual cameras, which is usually called hyperfocal distance photography.

As we said when we introduced the aperture above:

Under the same focal length, the larger the aperture, the shallower the depth of field; Conversely, the smaller the aperture, the deeper the depth of field.

It is absolutely important to understand the concept of depth of field ruler if you want to control the zoom range of photos more finely, make the desired special photo effect, and more importantly, know the focus range more accurately.

Most old lenses are engraved with a depth of field scale, which converts the depth of field according to the focal length and aperture value.

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.

Take this Summitar f = 5cm 1:2 lens in the hands of Fei Linjun as an example (please take the initiative to ignore Fei Linjun's dust camera).

When the aperture is f/4 and your subject is 6 feet away, the distance from 5.5 feet to 6.4 feet (about) is within the clear depth of field.

When the aperture is f/8 and your subject is 7 feet away, the distance from 5.8 feet (about) to 9 feet (about) is within the clear depth of field.

The same is true for SLR lenses. Take S-M-C Takumar 135mm f/2.5 as an example (please also ignore the fighter color automatically).

When the aperture is selected at f/ 16 and your subject is 5m away, the distance from 4.5m (about) to 6m (about) is within the clear depth of field.

With this description, everyone has a very intuitive concept of depth of field ruler.

The depth of field ruler of different brands is almost the same in length, which is generally two layers, one layer shows the focused strokes, and the other layer shows the depth of field. Mastering the depth of field ruler is the basis of fast manual focusing, as shown in the figure below.

Knowing this concept, we not only clearly understand the scope of the blurred area of the lens, but also understand that no matter how the object moves in the depth of field, it does not need to be refocused.

For friends who use manual focusing, can you get twice the result with half the effort?

hyperfocal distance

When we pull down the infinity symbol at one end of the depth of field ruler, we will find that there are no numbers on one side of the depth of field ruler, and the corresponding aperture and distance on the other side are outside this distance range. No matter how far you run, you don't need to focus any more. As long as you travel infinitely, you will be able to focus. This is hyperfocal distance.

When the aperture is f/8, it is in the depth of field range from 25 feet to infinity.

When the aperture is selected as f/ 16, it is in the focus range of about 30m to infinity.

When the aperture is f/ 1 1, you can focus from 8.5m to infinity.

How's it going? It's simple.

Mastering the depth of field ruler and hyperfocal distance skillfully can not only make us omit the action of focusing in street shooting, but also capture the moment quickly. When taking landscape photos, we can also make use of hyperfocal distance's concept to take clear pictures from the farthest to the nearest.

However, again, no amount of professional knowledge can compare with hands-on practice. If you want to focus manually faster and more accurately, you still need to practice getting familiar with your camera.

Of course, when using a digital camera, don't forget to convert the equivalent focal length of each frame.

There are three kinds of people in this world: born in the era of autofocus; Know manual focusing but completely ignore the depth of field ruler; Fully understand the depth of field ruler and use it skillfully.

What kind of person are you?