Lead:
Aperture values are very useful, for example, the Huawei Pura70 Ultra achieves a maximum aperture of 1.6 for the lens with a 1-inch extra-large bottom sensor, which is 4% larger than the previous Xiaomi 14 Ultra, which claimed to have a maximum aperture of 1 inch (f/1.63).
The difference in aperture alone is actually very small, but Huawei has also customized the RYYB array for the one-inch sensor - which continues to bring 40% light intake gain! That is to say, Huawei's total light intake advantage has reached 44%!
Combined with Huawei's XD Motion motion engine, this lead in light intake brings an unparalleled capture experience!
1. What is aperture
Regarding aperture, the familiar Sony gives the definition shown in the figure above, and this is the simplest literal definition of aperture, and the most common aperture value on mobile phones is obtained through the following calculation relationship.
- The aperture of a mobile phone lens is defined as the focal length of the lens divided by the clear aperture: the numerator F of the aperture value represents the focal length, while the denominator number represents the clear aperture value after being divided. However, since the mobile phone uses an equivalent focal length, the equivalent coefficient must also be considered.
Equivalence coefficient method: obtained by dividing the diagonal value of 43.3 of the full-frame sensor by the diagonal value of the mobile phone sensor. So how to calculate the diagonal of the mobile phone sensor?
First, the diagonal length of sensors greater than or equal to 1/2 inch is calculated by multiplying the sensor size by 16 mm, and for those less than 1/2 inch, the diagonal length is calculated by multiplying the sensor size by 18 mm.
For example, the Nubia Z50S Pro's main camera sensor is IMX800, and the cropped frame is 1/1.56 inch when taking photos, so the diagonal length of the photo frame is 16/1.56=10.26mm, and the coefficient of the equivalent full-frame is 43.3/10.26=4.22.
As can be seen from the above data, the Nubia Z50S Pro has a main camera aperture of 5.21mm, combined with its 35mm main camera equivalent focal length, then its main camera aperture value is 35÷5.21÷4.22=F/1.59, which is the aperture value seen by users.
In summary, the larger the base of the lens sensor, the smaller the equivalent coefficient, which perfectly explains the phenomenon that the aperture becomes smaller as the sensor increases. But don't forget that there are also two factors that affect the aperture value: the focal length of the lens and the clear aperture.
Because as the focal length of the lens decreases, the aperture value will also increase, which can perfectly explain why the equivalent focal length of the main camera of the mobile phone has been reduced from 27mm in the past to 23mm now.
However, the trend of increasing the sensor is unstoppable, and the continuous shortening of the focal length of the main camera is also a problem - after all, if you shrink it again, it becomes an ultra-wide angle, so the solution of increasing the clear aperture is the most effective "miracle" route to the large aperture.
2. What is the use of a large aperture?
The most direct use of aperture is to control the amount of light intake, so in order to better compare the amount of light intake represented by various aperture values at the same lens focal length, the equivalent full-frame aperture value obtained by multiplying the aperture value by the equivalent coefficient is introduced.
For example, the official main camera aperture value of the Blue Factory X100 Pro is f/1.75, and since the base of its IMX989 sensor is 1/0.98 inch size, the equivalent coefficient is 43.3÷16×0.98=2.65, so its equivalent aperture value is F/(1.75×2.65)=F/4.64.
The Xiaomi Mi 14 Pro, which also has a 23mm main camera focal length, corresponds to an official maximum aperture value of F/1.42, an equivalent coefficient of 43.3÷16×1.3=3.52 combined with a 1/1.3-inch sensor, and an equivalent aperture value of F/(1.42×3.52)=F/5.
In other words, the Xiaomi Mi 14 Pro looks like the main camera has a larger aperture value, but in fact, when converted to an equivalent aperture value due to the sensor, it gets less light than the Blue Factory X100 Pro.
Since the amount of light entering is a two-dimensional index and the aperture value is a one-dimensional index, the aperture value is required to be squared when comparing the difference in the amount of light entering the aperture value, so that the main camera of the X100 Pro has a smaller amount of light entering the Mi 14 Pro, which is larger (5/4.64)² ×100%=16%.
The most immediate effect of this is that the shutter time can be shortened, that is, the same exposure can be achieved in a shorter time, thus solving the problem of easy blurring when shooting high-speed moving objects.
In addition, in low-light environments, the higher light intake can also be used to achieve the same exposure time at a lower ISO, resulting in a cleaner high signal-to-noise ratio imaging. This is the connection between aperture, shutter, and sensitivity, which together are called the "three elements of exposure".
- Finally, there is the relationship between aperture and depth of field, generally speaking, the larger the aperture, the shallower the depth of field - that is, the background blur effect is better (highlighting the subject is suitable for close-up).
As shown in the figure below, the depth of field of the subject is positively correlated with the depth of focus of the focal plane behind the lens. It is precisely for this reason that the depth of field is not only affected by the aperture, but also the longer the focal length of the lens or the closer the shooting distance, the shallower the depth of field.
3. What is the use of a small aperture?
It seems that the advantages of a large aperture are obvious, does this mean that the main aperture of the mobile phone can be made bigger without a brain? Unfortunately, in the end, the world still can't escape a "fish and bear's paw" trade-off, because the small aperture is also beneficial!
The simplest, since the depth of field of a large aperture is shallow, then the reverse is the depth of field of a small aperture, in other words, it has the advantage of having a clear background. For example, when taking documents and group photos, it is required that the panorama be taken clearly, and at this time, the small aperture is better used.
When it comes to shutter time, the small aperture can in turn get the "slow shutter" gameplay, such as when shooting subjects that require ultra-long exposures such as traffic and star trails, the small aperture can avoid overexposure. Incidentally, the small aperture can also bring the gameplay of shooting "starlight".
In addition, the small aperture of the lens optical design also has its unique advantages, because it allows the light to pass through the center of the lens group with better imaging quality as much as possible, so it can reduce the negative impact of off-axis light on imaging.
The negative effects of imaging mitigated by the small aperture here mainly include spherical aberration and coma, two common aberrations.
As shown in the figure below, spherical aberration refers to the aberration caused by the inability of the rays of a straight lens group to converge on a focal point, while coma refers to the aberration caused by the oblique rays passing through the lens group and not converging at the same focal point.
Of course, the aperture should not be too small, otherwise the diffraction phenomenon will be tricky, and generally speaking, when the obvious diffraction fringes exceed the size of one pixel, the output quality will be significantly reduced, which is sensitive to mobile phone sensors with small pixel sizes.
Combining the advantages and disadvantages of large and small apertures, you can adjust the gear of the variable aperture camera lens according to different shooting scenes, so as to better complete various imaging outputs.
So for mobile phones that can't adjust the aperture value of the lens, how to determine the corresponding aperture value? Combined with the evolution of the main camera aperture of mobile phone manufacturers, it is true that the upper limit value is not achieved, but the aperture is enlarged on the road to the dessert value.
4. Variable aperture double full method
The Xiaomi Mi 14's main aperture value of F/1.6 shown in the image above is the so-called "sweet spot value", and the reason why it does not reach the upper limit is that the Xiaomi Mi 14 Pro achieves the maximum variable aperture of F/1.42 with the same lens focal length and the same sensor.
In this way, the focus is on the ten-stop variable aperture technology pioneered by Huawei. Friends who are familiar with camera photography may think that Huawei has turned "block" into "gear", but in fact, Huawei's so-called "ten gears" can be understood as "ten segments", not the aperture value of the whole block.
For example, if the amount of light entering is halved from f/1.4 to f/2.0, it is called a whole stop progression, but Huawei's first gear is not a step-by-step relationship, but the four integer stops covering F/1.4 to F/4.0 are divided into ten segments.
In fact, as early as the Nokia N86 era, there was a three-stop variable aperture technology of F/2.4, F/3.2, and F/4.8, but that was introduced to match its 1/1000s mechanical shutter, and this small aperture combination can ensure that it will not be overexposed in bright light.
As for Samsung's F/1.5 and F/2.4 variable apertures, the practical application is actually very good, because the F/1.5 aperture value can ensure the low-light image quality, while the F/2.4 aperture value can ensure the backlight image quality.
However, with the introduction of the outsole sensor, the rapid development of HDR technology, the progress of the optical quality of the lens, and the squeezing of the internal space of the fuselage, the variable aperture design was abandoned. In other words, the previous variable aperture technology was only a transitional solution.
Variable aperture scheme for Samsung S9
However, Huawei's first 10-stop variable aperture technology expands the range of aperture value changes to the greatest extent.
- With a variable aperture, the main camera doesn't have to go to great lengths to choose the maximum aperture value for the dessert spot, just fill the maximum aperture value in one step!
Later, Huawei made the aperture into a circle-like (second-generation technology), so that you can get a good-looking and soft round bokeh flare.
Summary:
The larger the mobile phone sensor and the longer the lens focal length, the more difficult it is to make the aperture larger, so in the trend of the main camera sensor of the mobile phone is getting larger, the focal length of the aperture begins to shorten, but the most effective large aperture scheme is achieved by increasing the clear aperture.
Since the aperture of a mobile phone lens is calculated by the ratio of the equivalent focal length to the clear aperture, by multiplying the equivalent full-frame factor, the equivalent aperture value can be obtained to compare the actual amount of light entering the aperture and the advantages and disadvantages of the large and small apertures can be distinguished based on this.
The advantages of a large aperture are higher shutter speeds for better snapshots, lower ISO exposures for low-light image quality, and natural light background blur for shallow depth of field for portrait close-ups.
The advantages of small equivalent aperture - because it does not have the advantage of light intake, it is good for shooting slow speed works, and because it can obtain clear panoramic imaging with deep depth of field, it is good for documents and group photos, and incidentally, you can also get starlight play.
Finally, because it has the effect of constricting light, it can be significantly improved for the troublesome coma optical phenomenon caused by large apertures, and as for the spherical optical phenomenon, with the popularization of aspherical lenses, the improvement effect of small aperture is no longer obvious.
Advantages of variable aperture - the maximum aperture value can be directly reached to the upper limit supported by the lens in one step, and with a series of practical common aperture value combinations, it can take into account various corresponding scenarios suitable for large, medium and small apertures.
Quick Facts:
1. The diagonal of the full-frame sensor - can be found by its length and width "36×24" and the "Pythagorean theorem", the final value is about 43.2666, and further about 43.3mm.
2. The equivalent coefficient can be used to find the physical focal length of the lens - divide the equivalent focal length of the lens given by the mobile phone manufacturers by the equivalent coefficient to obtain the corresponding physical focal length of the lens.
Further reading:
Summary of CIS technology from Sony and Samsung - CMOS sensor knowledge for mobile phones (end)
END
Committed to the exploration and collation of mobile phone knowledge