Why does the image quality of the lens deteriorate at the maximum aperture?

We all know that the light passes through the lens of the lens and is imaged by the image sensor, the smaller the aperture, the less light passes through, the more concentrated it is in the center of the lens, and the larger the aperture, the more light passes through the lens, and the more dispersed it is on the edge of the lens. There are many kinds of geometric aberrations that affect the imaging quality of the lens, such as spherical aberration, coma, astigmatism, field curvature, distortion, etc. ‍‍

It is obvious that when the aperture is closed, the light only passes through the center area of the lens, which can be very good for imaging, that is, the spherical aberration is small, so the imaging is ***. When the aperture is magnified, the light will enter from the edge of the lens, and due to the influence of the process and curved surface, the light cannot be perfectly imaged at one point, so it will produce aberration, so it will affect the image quality. It's not just this one reason that affects the image quality, there are many factors.

Just use this spherical aberration to illustrate the problem. ‍‍

The main reasons for the degradation of lens image quality come from two aspects, aberration and diffraction. The main cause of image quality degradation at maximum aperture is usually aberration, as lens aberrations are maximized in imaging when the aperture is opened to the maximum. Aberrations cause color halos, smearing, and reduce image resolution and contrast, resulting in lower resolution.

However, most aberrations can be improved by shielding light from the edges of the lens, i.e., using a lens hood and stopping down, especially when stopping down slightly can be very effective in scenes where aberrations are noticeable. ‍‍

Monochromatic aberrations caused by the shape of the lens are manifested as spherical aberrations, comet aberrations, radial halos, astigmatism, and image plane curvature, and, in theory and practice, the lens has an additional aberration. Aberrations are corrected to improve image quality. ‍‍

The main reason for this is the lenses used in current lens systems. When light passes through the lens of the lens, the light of different colors shifts due to different wavelengths and different shooting angles, resulting in dispersion mainly caused by the difference in refractive index, and the focus position is deviated on the image sensor, resulting in "blurring". ‍

The wider the aperture, the more light enters, and the brighter the shot will be at the same shutter time; Conversely, the smaller the aperture, the darker it becomes. Accuracy of focus, sharpness of the picture, sharpness, sometimes referred to as "sharpness", is an indicator of how sharp the image is and how sharp the edges of the image are. If you turn the sharpness up, the image will also have a higher contrast of detail and will look clearer.

For example, in the case of high sharpness, not only the wrinkles and spots on the face are more clear, but also the bulging or concave muscles of the face are also vividly expressed. ‍‍

The reason is simple, because when the aperture is reduced to a certain extent, another major factor that affects the image quality will be maximized on **, that is, the mentioned "diffraction". ‍

Hehe, it's more difficult to manufacture at the maximum aperture.

Aperture 1 is the maximum, and the other values are the denominator, so the larger the denominator, the smaller the aperture, in detail, the aperture value (f) is the relative value obtained from the focal length (f) of the lens and the clear diameter of the lens (d).

The formula is: f=f d

The larger the lens clear diameter (d), the smaller the aperture value (f), so the amount of light entering the aperture is greater than the aperture.

This is one way to express this, and sometimes the aperture size is expressed in terms of the focal length aperture value.

The formula is: f=f d

The smaller the aperture (f), the larger the lens clear diameter (d), so the amount of light entering the f-aperture is greater than the f-aperture.

1. The reason why the depth of field is smaller when the aperture is larger, that is, the small hole in the imaging is wider, then the small things in the distance will be blurred, and the larger ones will be clear.

2. Depth of field is the optical characteristics of the lens, the depth of field comes from the depth of focus, because the object is far from the lens, the gathering point of the phase plane is also divided into front and back, some are solid points, some become virtual points, this virtual point is called the diffusion circle, if the diameter of the diffusion circle is less than the ability of human identification, the distance between the virtual point and the real point is called the depth of focus. Experiments have proved that the longer the focal length, the larger the aperture, and the smaller the depth of field, as the name suggests, is the depth of the scene, which is the depth of the scene before and after the image is clear.

Aperture is an important parameter in photography, which affects the quality, depth of field, and image quality. In common lenses, the optical chain is represented by the diagonal focal length and the aperture type of the aperture, such as 50mm. where represents the maximum aperture of the lens, i.e., the aperture of the aperture is a multiple of the focal length.

On this basis, we can understand the effect of aperture size on depth of field.

The larger the aperture, that is, the larger the aperture of the aperture, the more light the lens can pass through, and the brighter the light entering the camera, which is equivalent to receiving more light from the camera. This allows light to enter the imaging plane more easily, resulting in a shallower depth of field. Depth of field refers to the extent in which the lens captures ** that is sharp.

When the aperture is wider, the depth of field is smaller, which means that only objects near the focal point will appear sharp. Other objects lose their clarity due to blurring.

Broadenedly, in addition to aperture size, depth of field is also affected by factors such as focal length, shooting distance, and sensor size. In this case, both the focal length and aperture remain the same, so the aperture size is a key factor in changing the depth of field. In addition, for those who need a large depth of field**, we can use a smaller aperture or increase the shooting distance to extend the depth of field.

In practical applications, we need to choose the appropriate aperture size according to the needs of shooting and lighting conditions. If you want to highlight an object and blur the background, you need to choose a wide aperture to achieve this, and if you need more items to be clear, you need to choose a smaller aperture aperture. <>

From the above, you can understand the principle. The depth of field marked above should actually be the depth of focus, the same principle, the depth of focus is larger, and the depth of field is also larger. Depth of field is the optical characteristics of the lens, depth of field comes from the depth of focus, because the object is far from the lens, in the phase of the gathering point there is also a front and back division, some into a solid point, some become the dotted point, this dotted point is called the diffusion circle, if the diameter of the diffuse circle is less than the person's ability to identify, the distance between the dotted point and the real point is called the depth of focus.

Experiments have shown that the longer the focal length and the larger the aperture, the smaller the depth of field. Depth of field, as the name suggests, is the depth of the scene, which is the depth of the scene before and after the image is clear.

What is depth of field, the larger the aperture, the smaller the depth of field.

The aperture value is a divisor, so a higher value means a smaller aperture, and a smaller value means a larger aperture. The aperture value is calculated by dividing the focal length by the actual aperture, that is, the focal length divided by the aperture value also gives the actual aperture size.

Focusing distance refers to the closest distance that a lens can be in focus, usually independent of aperture, but related to focal length. The longer the focal length of the lens, the smaller the angle of incidence of the light, and the farther the focal distance, so the telephoto lens usually has to run farther to close the focus properly, and the wide-angle lens can be in focus if it is closer. Of course, manufacturers can also use specific lens groups to adjust the angle of light incidence, so that the lens can get a very close focusing distance even at non-wide angles, this kind of lens is called a macro lens, but due to the difficulty of adjustment, the lens is also more expensive.

The aperture size actually affects the depth of field, which refers to the sharp range before and after the focal point. The larger the aperture (the smaller the value), the shallower the depth of field, the smaller the sharpness range, and the easier it is for the background to blur; Conversely, the smaller the aperture (the higher the value), the deeper the depth of field, the greater the sharpness range, and the sharper the background.

People often use a wide aperture to shoot portraits, blurring the background to highlight the subject, and also use a small aperture to shoot landscapes to ensure that they can be seen from near and far.

Ordinary telephoto lenses are all floating aperture lenses, with the maximum aperture at the wide-angle end and the aperture at the telephoto end becoming smaller. The three elements of bokeh background: large aperture, long focal length, and close focus.

If you want to get a good bokeh background, you can use the telephoto end to reduce the focusing distance while moving away from the subject's background (macro shots can definitely do bokeh the background).

Aperture f-number = focal length of the lens The diameter of the lens aperture, so the longer the focal length of the zoom head, the smaller the aperture.

Is it better to have a wider lens aperture? Whether it is the SLR world or the mobile phone world, people are pursuing a large aperture. Let's take a look at whether the lens aperture is as wide as possible.

In fact, for portrait shooting, a simple and effective way to scale the aperture is to widen the aperture, on the one hand, it can highlight the character by blurring the background, and on the other hand, it can also reduce the ** time, so as to prevent shaking.

Portrait mode is designed to automatically open the aperture to the maximum for portrait shooting, so why do we recommend using aperture priority?

The reason is simple: while a wide aperture is good for portrait shooting, a wider aperture is not always better. At the same time, we need to ask you a question, from the parameters of the lens, we can know the maximum aperture value and the optimal aperture value of this lens, but that is the data in the laboratory.

Do you know what the optimal aperture value for this lens is for you?

So, for the aperture of the lens, keep three points in mind:

1. It is incorrect to open the maximum aperture at all times.

2. It is unwise to blindly pursue the theoretical best aperture at all times.

3. Only the point that is closest to the optimal aperture value and can ensure that there is no jitter is your best aperture value. This can only be found if you experience it yourself.

Creating depth of field through the aperture is a common technique in photography, but it is not always possible to have a wider aperture

Aperture is an important measure of lens performance. We tend to use the maximum aperture of a lens to indicate how powerful the lens is, and the higher the maximum aperture value, the stronger the lens. As a result, many friends habitually open the aperture to the maximum when shooting, thinking that this can give full play to the performance of the lens.

This is not the case.

Each lens has an optimal aperture value. Although the optimal aperture value is different for each lens, it is almost certain that the maximum aperture value is not necessarily the best value. It should also be noted here that the best aperture value we often refer to in terms of optical quality alone.

From this point of view, the optimal aperture value in the parameters is the result of the laboratory. The only way for you to know which aperture value is best is to take a few more shots of the same object to find the point that guarantees no jitter and produces the sharpest image quality.

If you find yourself fumbling around, there is an easy way to lower the maximum aperture by two stops, and at this aperture value, you can often get good imaging results.

However, this method is only applicable to some lenses, and it is not universal for all Song Sleepy lenses, such as Canon's 50mm prime head, which has an optimal aperture value of f8, which is a full 5 stops down.

Finally, a small reminder, that is, jitter, if you say that after adjusting to the best aperture value, the shake of your hand will have a greater impact on the picture, then continue to increase the dimming aperture.