What's the difference between the aperture sizes of mobile phone cameras?

One is to increase the luminous flux.

The second is to reduce the depth of field.

Of course, there is also a hidden influence, that is, image quality, which will be discussed later.

Let's talk about luminous flux first

Because the marked f value is actually proportional to the reciprocal of the aperture radius, and the lens luminous flux is proportional to the aperture area (so complicated), it is converted into 1.4 (that is? ), the luminous flux doubles. Generally, the order of F values is as follows (in geometric series): 1, 1.4, 2, 2.8, 4, 5.6, 8,1,16, 22, 32 ... at each level above.

Now it is clear that F4 is one step larger than the aperture of F5.6, and the luminous flux per unit time is twice as large, that is, F4 can double the shutter speed of F5.6 under the premise of the same exposure ... In other words, F4,1125' = f5.61/60' looks like a large aperture. For example, when shooting a stage model, the light is insufficient. At this time, under the same focal length, the F2.4 (telephoto end) of Sony F7 17 can be about 4 times faster than the F4.8 shutter of the telephoto end of ordinary household computers, so the probability of film sticking caused by slow shutter is of course greatly reduced.

Let's talk about depth of field.

The so-called depth of field can be simply understood as the clear distance range in the photo. When taking a picture, take the focused object as the center, and everything x meters away from it is very clear. This x can be simply understood as depth of field. The greater the x, the deeper the depth of field, and vice versa. Everyone has seen those classic character films. Except the main characters are clear, the things near and far from the subject are a little vague, so you will focus on the subject at first glance. Yes, this is an example of creating a shallow depth of field with a large aperture. For the same lens, the larger the aperture, the shallower the depth of field under the condition of constant focal length. Similarly, taking F7 17 as an example, the background blur of the telephoto end F2.4 and F8 is very different. The former can "catch" you from the vast sea of people, and the latter may take half a day unless you are a beautiful woman.

Well, from what has been discussed above, a large aperture is very beneficial. Then why don't DC manufacturers make the aperture as big as possible?

First of all, we must consider the cost. If the aperture is large enough, it is necessary to enlarge the aperture of the lens in order to pursue greater transparency. Maybe the lens is a penny for a penny, and the aperture of 72mm is more expensive than that of 52 mm. Why do most telephoto machines (F3. X) is larger than the aperture of telephoto end (F4.9 or even 5. X) home machine? Because telephoto machines are cannons with huge caliber, they are naturally comparable to the small lenses of home machines. Of course, there is also a price difference.

Second, a larger aperture does not mean an improvement in image quality. Anyone who has played photography knows that the best image quality of the same lens is often not in a large aperture, but when the maximum aperture is reduced by 3-4 levels. Therefore, for most consumer DC, the image quality under large aperture is not as good as that under medium aperture.

Third, the depth of the scene is not always needed. A large aperture means that the focus must be accurate, otherwise it is easy to paste a little right or wrong subject. An extreme example is the traditional film fool machine, which uses a hyperfocal distance with a small aperture and doesn't need to focus at all (because the depth of field is very long at this time, and it is almost clear from 1.5M to infinity), which is much more convenient than the machine that needs to focus-isn't it convenient to use a home computer?

Fourthly, it is not difficult to achieve an aperture of F2.8 at the wide-angle end, but it is not easy to achieve an aperture above F3 at the telephoto end. This can be intuitively understood. Of course, the amount of light entering a long telescope can't be compared with glasses, can it? Therefore, there are very few lenses with full F2.8 aperture.

Well, based on the above considerations, at present, most digital camera manufacturers set the aperture of the triple optical zoom home machine at F2.8-F4.8 for the average between cost and performance.

Conclusion 1: Large aperture has advantages and disadvantages.

We talked about the large aperture in the interview. Let's talk about the small aperture first. What's wrong with a small aperture? In my opinion, the problem of most home computers at present is not that the maximum aperture is not large enough, but that the minimum aperture is not small enough!

First, let's see what a small aperture can do.

A small aperture, corresponding to the large aperture above, means a small amount of light and a deep scene. The depth of the scene is used to shoot people. What about the depth of the scene? Used to take pictures of the scenery. Small aperture can not only create the effect of deep depth of field, so that the landscape is all in a clear section, but also produce a transparent effect, and at the same time, it is more layered (relatively speaking, because the layering of home computers is always a weakness).

A small amount of light is also used for special purposes. Typical examples are taking waterfalls and night scenes. There are two ways to shoot waterfalls. In order to freeze the flow of the waterfall and see the water droplets clearly, it is natural to have a large aperture and a short shutter. However, if you want to create a powder-sprayed waterline flow effect, you should try to lengthen the shutter time (1/2 seconds or slower), and then you need a small aperture. Anyone who has photographed waterfalls with Canon A series knows that F8 is still too big to photograph waterfalls during the day. If the shutter speed is forced to be lowered, it will inevitably lead to overexposure. At this time, I thought it would be nice to have an aperture of F26.

Of course, this is almost a joke. The minimum aperture of consumer-grade machines is about F 1 1. Because the size of CCD is much smaller than the traditional 135 film and the corresponding aperture is much smaller, it is quite difficult to achieve F 1 1.

At present, DC is not only a consumer-grade machine, but also the smallest F8 for most semi-professional machines, which greatly limits the application of DC in night scenes and dynamic photography.

It is worth noting that the wide-angle end and telephoto end not only have different maximum aperture, but also have different minimum aperture. The most typical example is Kodak 6340. The wide-angle end of this Schneider-certified lens can have a large aperture of F2.2, but the smallest can only reach F5.6. You will know how painful it is to shoot the night scene with a tripod. .......................................................................................................................................................................

What's more, the maximum aperture at the wide-angle end of the new 7440 has shrunk to F2.8, and the advantages of the minimum aperture or F5.6 are gone, but the disadvantages are still there.

Conclusion 2: The minimum aperture is worthy of attention, especially at the wide-angle end.

Influence of large aperture on mobile phone photography

Large aperture can not only bring greater depth of field and background blur effect, but also improve the shutter speed of the camera. The security shutter of handheld mobile phone is generally around 1/30 seconds. If it is lower than this speed, blur may appear even when shooting still objects. When shooting at night, in order to ensure the lowest shutter speed, the mobile phone will automatically increase the ISO sensitivity, resulting in a lot of noise on the screen.

If the aperture of the mobile phone is large enough, the more light CMOS can get at the same shutter speed. Conversely, a higher shutter speed can be used to prevent image jitter. Therefore, when shooting moving scenes or poor ambient light, a large aperture lens has more advantages than a small aperture lens. When shooting people's still lives, the large aperture can also bring the background blur effect close to SLR.

Therefore, the camera aperture of smart phone must be as large as possible. This year's highly acclaimed Samsung S7/S7 Edge has a large aperture camera of F/ 1.7, which is also one of the biggest selling points of this machine. At present, the aperture of domestic smart phones is generally around F/2.0, and few domestic mobile phones can be lower than this value. The upcoming OPPO R9s cooperates with Sony and is equipped with IMX398 photosensitive element. While maintaining16 million pixels, the aperture is raised to F/ 1.7, which is the maximum aperture that can be achieved by smartphone cameras at present.

In addition to the super-large aperture of F/ 1.7, OPPO and Sony have jointly developed dual-core focusing technology, which makes OPPO R9s focus faster and the photos brighter and clearer. Although OPPO R9s has not been released yet, judging from the parameters released at present, the aperture value of F/ 1.7 alone is enough to make photographers look forward to it.

The large aperture is the lens of the camera, which is generally positioned at the professional or quasi-professional level, and the workmanship is much better than the general lens. In the case of the same frame, the same level of aperture (whether bull's head or dog's head) has the same luminous flux and the same depth of field under the same conditions.

The aperture itself is a real optical device, usually in the lens group, which is a part of the lens. Generally, it is composed of several rolled leaf-shaped metal sheets with an adjustable hole in the middle. The size of this hole can be adjusted by the rotation of the metal blade. This is the origin of the aperture size.

Extended content: how to use the aperture?

Large aperture is suitable for shooting portraits or still life flowers, because the larger the aperture, the shallower the depth of field, which can highlight the shooting theme. The background of many photos we see is completely blurred except for the characters, which is due to the large aperture lens.

The benefits of blurred background are obvious, especially when taking photos for girls. With the help of background blur, all the surrounding sundries can be "erased" and only the photographed characters can be highlighted. It can be said that the blurring of large aperture background is the most basic skill in portrait shooting.

On the contrary, a small aperture is more suitable for shooting scenery. The smaller the aperture, the deeper the depth of field. Every detail of the photo taken by a small aperture is very clear, which is most suitable for shooting large-scale scenery with a wide-angle lens.

In addition, when shooting light paintings, star orbits, running water and other subjects, the aperture should be as small as possible, and the exposure time should be extended with the help of a tripod. If necessary, you need to add a filter to reduce the amount of light. Of course, these belong to the category of professional photography, so I won't go into details in this article.