Tips for improving focusing speed and accuracy

First of all, it should be pointed out that the manual focusing of digital SLR is completed by rotating the focusing ring of the lens, that is, the convenience of manual focusing has nothing to do with the body of digital SLR, but only with the lens.

Full time manual focus (hereinafter referred to as FMF) is an important advantage of ultrasonic motor lens, but for most people, ultrasonic motor focusing is fast enough, so FMF seems dispensable. In fact, FMF is very useful, especially in macro photography, which requires high focusing accuracy. The key is that you should be able to use it, Let's explain it in detail.

1、 What is full-time manual focus?

Full time manual focusing is to keep the shutter half pressed after focusing in AF single focusing mode, and directly manually adjust the focusing ring. Its main function is to fine tune the focus. When using full-time manual, you must half press the shutter AF without releasing your fingers (there is another better method, which will be introduced later), otherwise the meaning of full-time manual will be lost.

2、 How to judge whether the lens has full-time manual function?

If the lens adopts USM (Canon), SSM (Sony) and other ultrasonic motors, or the lens has a distance window, most of these lenses generally support full-time manual focusing. Of course, the safest way is to look at the instructions of the lens.

3、 What are the main disadvantages of a part-time manual focus lens?

For the lens with part-time manual focusing, the focusing mode must be set to "manual focusing" before it can be rotated. Otherwise, the focusing ring of the lens is locked and cannot be rotated, which is very inconvenient to use.

4、 What are the uses of full-time manual focusing?

（1） Focus fast fine tuning

The AF of the camera itself may not be reliable in cases requiring extremely high precision focusing such as macro. Before FMF technology, users have to use MF for fine focusing. For most cheap lenses, Since the distance required from the nearest focus to the infinite focus is very short (generally, the whole focusing distance can be completed by rotating 45 degrees. Please tell me if there is an exceptional cheap lens. Anyway, I haven't found it yet), we still don't realize the benefits of FMF. However, for advanced telephoto lens or macro lens, it generally needs to rotate 90 degrees or even more than 180 degrees, In order to complete the focusing distance in the whole process (in fact, I like to use this kind of lens, macro photography focusing. In many cases, the focus will deviate at the moment of breathing, and the lens with long focusing stroke is very conducive to fine focusing). In this case, FMF can play a great role, The user can use the ultrasonic motor to quickly aim at the part with large contrast on the target object (for example, when shooting a panda, you can focus on the ear first. Because the contrast between the ear and the background is large, this is generally the case. If you have to pick a scene with small contrast between the ear and the background, I have nothing to say), and then use FMF to correct it manually, Focus the final focus with small contrast (the eyes, panda eyes and orbit are black, and the contrast is very small). Because the switching between AF / MF is saved, the focusing speed and focusing accuracy can be greatly improved, and satisfactory photos can be taken. It should be noted that the mechanism of FMF determines that manual correction focusing must be carried out after AF is completed, so continuous focusing and FMF cannot be used at the same time.

（2） Cancel half pressing the shutter to start AF

To give full play to the true power of FMF, users had better cancel half pressing the shutter to start AF in camera settings. Generally, the default setting in the camera is to start AF by half pressing the shutter. Therefore, FMF must also be half pressed before it can be used. Therefore, users can not really realize the benefits of FMF. Most SLRs can cancel half pressing the shutter to start AF by setting, Start AF with af-on or AE lock key instead (there are too many small DCS. I haven't tried to change the setting like this. Welcome to add). After the settings were changed, FMF began to reflect its power.

1. Selective start AF

If the default setting of the camera is adopted (i.e. half pressing the shutter for focusing), generally, AF will still be performed again when the shutter is pressed again after shooting a picture. During macro shooting, AF may not be focused again. If you do it again, it will delay time. Use af-on or AE lock to start AF, We can selectively start AF (that is, we won't start AF when half pressing the shutter). As long as we don't actively start AF, the lens is a full MF operation.

2. Selective interrupt AF

In an environment where AF locking is difficult, the lens is easy to lose focus (the focusing ring rotates between the shortest focusing distance and infinity). Start AF with af-on or AE lock key instead. In the middle of AF, even if the focus is not closed, AF will stop in real time as long as the af-on / AE lock key is released. In other words, even if you fall into the defocus state, you can interrupt AF at will and use MF to correct it. As long as AF can be aligned near the main body, at least the angle required to twist the focusing ring can be saved.

5、 Can continuous auto focus and full-time manual be used at the same time?

In general, continuous auto focus and full-time manual cannot be used at the same time, but after canceling half pressing the shutter to start AF and changing to af-on / AE lock to start continuous focus, AF can be stopped at will as long as you let go. In this way, the limit that half press will continue to use continuous focus does not exist. What are the benefits of this operation? Take macro shooting as an example. If you use single focusing and half press the shutter almost every time, the focusing ring is likely to rotate many times, which is a waste of time. After continuous focusing is adopted, we first aim at a far distance to start continuous focusing, and then gradually approach the main body. Since the focusing speed is generally fast from a far distance, only slight correction can be made after stopping continuous focusing (because AF continues to aim near the main body).

6、 How to maximize the potential of focusing system?

After using FMF, canceling half press shutter AF, continuous focusing and focusing locking (there is a special focusing locking button on the advanced lens), you will find that the focusing system we have been using has such great potential. At this time, users will fully realize the benefits of supporting full-time manual focusing lens.

7、 What is the difference between FMF and DMF?

Sony also provides a function called DMF (direct manual focus), which is similar to FMF. MF correction can be used after AF is completed. However, there are some differences between the two. Sony's DMF actually allows the fuselage to disconnect the contact of the driving lens so that the lens can be MF. The advantage of this design is that all AF lenses driven by the fuselage can be corrected with DMF after AF is completed. However, in this way, it can not support continuous focus and full-time manual hybrid applications like FMF.