Lens
Lens diameter:
The size of the physical aperture of the lens will have a great impact on the image quality. The larger the physical aperture, the greater the brightness, and theoretically, the better the imaging quality of the lens. But at the same time, a lens with a larger caliber is larger in size and weight. In order to facilitate photographers to install filters, the calibers of hundreds of SLR lenses have been unified into several common specifications: 58mm, 62, 72, 77, 82mm. Among them, 77mm is the common caliber of professional zoom lenses. Therefore, it is a common practice for professional photographers to unify one’s own lens caliber and equip multiple lenses with a set of universal filters.
Closest focusing distance and magnification:
The closest focusing distance refers to the minimum distance at which the lens can focus and image clearly. When the shooting distance is less than this value, the camera cannot focus. The calculation of the closest focus distance is the distance from the photosensitive element to the subject, rather than starting from the front end of the lens as generally believed.
The magnification of the lens refers to the ratio of the actual size of the image on the sensor to the actual size. For example, Canon’s 50mm fixed focus has a maximum magnification of 0.15 times, which means that a 10cm-sized object is at its “closest focus distance” (0.45 m), it will be a 1.5cm image on the sensor. Another example is Canon Xinbaiwei, whose maximum magnification is 1x, which means that at the closest focusing distance (0.3m) of Xinbaiwei, the actual object will become an equal-sized image on the sensor. The greater the magnification, the stronger the macro shooting capability of the lens.
Fixed focus lens and zoom lens:
→Prime lens, as the name implies, is a fixed focal length lens that cannot be zoomed. Very commonly used in documentary photography. The main varieties are 20mm, 24, 28, 35, 50mm focal lengths. In the film age, the 35mm lens is most commonly used. This focal length is slightly wider than the normal viewing angle of the human eye.
Compared with a zoom lens, the biggest advantage of a fixed focus lens is its excellent image quality. The imaging quality of a fixed focal length lens is generally better than that of a zoom lens of the same focal length. In addition, the fixed focus lens has a simple structure, a large aperture, a lower failure rate, and a lighter volume and weight. However, fixed-focus lenses are not as convenient as zoom lenses. In the digital age, the usage rate of fixed-focus lenses has dropped a lot.
→Almost all zoom telephoto lenses have better imaging at the short focal end than at the telephoto end, even professional-grade ones. The telephoto section is easily affected by dispersion, which reduces the resolution of the picture.
Due to the insurmountable optical characteristics, the distortion and vignetting of the zoom lens are more serious than the fixed focus lens.
In addition to the highly versatile zoom lens, there are 3 types of lens products in the fixed focus lens that are more suitable for shooting portraits.
①Standard lens: According to optical principles, the design of standard lens is the easiest to achieve excellent image quality. The maximum aperture of the standard lens reaches F1.0.
②85mm lens: This is a lens product specially designed for portrait photography.
③Macro lens: The macro lens combines the shooting functions of macro photography and portrait photography. Compared with the above two lenses, the aperture is slightly smaller. Macro lenses are mostly fixed-focus lenses, which have a very short “closest focusing distance” and 1:1 magnification.
Using a telephoto lens with a focal length of more than 135mm to shoot portraits, you can get an unparalleled background blur effect. The characters and the background will be clearly distinguished. Some people like this effect, but others think that the blur is excessive.
Constant and non-constant aperture:
The fixed focus lens only has a single maximum aperture setting. There are two types of zoom lenses: ① One has a non-constant maximum aperture setting that can vary with the focal length, that is, its maximum aperture will decrease as the focal length increases. ②The other is a product with a constant maximum aperture at all focal lengths.
Anti-shake technology:
Anti-shake technology is divided into two camps, Canon and Nikon use “optical anti-shake”, and Sony uses “photosensitive element anti-shake.” The optical image stabilization device (detected by a gyroscope) is configured on the lens, which increases the cost of the lens, but the actual effect is better. The image stabilization of the photosensitive element is integrated in the body, and the cost is lower, and it can realize the stabilization function with any lens.
Lens focal length and equivalent focal length (correspondence between focal length and angle of view):
Angle of view refers to the angle of the frame range that the lens can capture. When the focal length of the lens is shorter, the angle of view covered by the lens is larger and the picture is wider. When the focal length of the lens is long, the shooting angle of the lens is gradually reduced, and the captured image becomes narrower.
The area of the photosensitive element of the popular APS-C format is smaller than that of 35mm film. Therefore, when shooting with the same lens, the photosensitive element of the APS-C frame can only receive a narrower picture range than the full frame. Conversely speaking, the subject of the photo taken by the APS-C format occupies a larger area of the entire photo frame, and its effect is equivalent to that of a full frame with a longer focal length lens. Therefore, when using an APS-C frame with a traditional lens, you need to multiply the focal length of the lens by about 1.5 times to get the effect of the focal length equivalent to that of the full frame. This is the concept of “equivalent focal length”.
The equivalent focal length is only the equivalent in the angle of view. In the case of the same shooting distance, when shooting with the APS frame and full frame with the same lens, only the angle of view changes. Other factors such as the depth of field and perspective produced by the lens are unchanged.
Because the focal length of the APS frame needs to be multiplied by a conversion factor, it can achieve a telephoto effect with a relatively short focal length.
Focal length
Ultra wide-angle lens:
The equivalent focal length is less than the field of view of 24mm. The picture effect at this time is very open, but at the same time it is accompanied by more serious perspective distortion.
Wide-angle lens:
The equivalent focal length is between 24-40mm. The common focal lengths are 24mm, 28mm, and 35mm. It is a focal length commonly used in daily photography, and on the APS frame, it is close to the field of view of a full-frame standard lens.
Standard lens:
The standard lens is a lens with an angle of view close to that of the human eye on the 135 full frame, and the focal length is between 40-60mm. The standard lens has a simple structure, a large aperture and a low price.
Medium focal lens:
The equivalent focal length is between 60-150mm. The medium focal length lens has soft background blur ability and moderate perspective performance, which is very suitable for shooting half-length and close-up portraits.
Telephoto lens:
The equivalent focal length is more than 150mm. The telephoto lens can make people and scenery in the distance vivid (like a telescope), so it is widely used in ecology, sports, landscape and other photography.
Super telephoto lens:
The equivalent focal length is above 300mm.
In short, the telephoto shoots the local and close-ups; the wide-angle shoots the overall situation and momentum.
The ultra-wide-angle lens can accommodate a wider field of view. However, many beginners will also find that the photos taken with such a lens are very hollow, often large areas of sky and open space, and the beautiful scenery seen at that time is only a little bit in the picture. The telephoto lens can cut the picture and find the wonderful part in the ordinary environment. The ultra-wide-angle lens also frames in some things that should have been removed from the screen, but weakens the subject. When shooting large scenes, the farther scenery will also appear smaller because of the exaggerated perspective of the near and far. The ultra-wide-angle lens strengthens the near and far. If there is no object in the foreground, the picture is naturally hollow.
| Lens | Ultra wide angle | Wide angle | Standard (naked eye) | Middle coke | Telephoto | Super telephoto |
| Equivalent focal length | <24 mm | 24-40mm | 40-60 mm | 60-150 mm | >150 mm | > 300 mm |
We can find that the focal length is close to the range of 50mm, which is the closest to what we can see with the naked eye. Many SLR camera kit lenses cover this focal length range. Such as 18-55, 18-105, 18-135 and so on.
→Wide angle:
The shorter the focal length of the lens, the stronger the sense of space and the “perspective”. Perspective is “near big and far small”. This kind of perspective relationship looks closest to what the human eye sees in a lens with an “equivalent focal length” of about 50mm. In the ultra-wide angle, the perspective relationship becomes exaggerated, that is, the closer is larger and the far smaller.
→Mid-focus (85-135mm focal length, APS-C format 50-80mm) lens, is the most versatile portrait photography lens. The medium-focus lens will not cause sudden perspective distortion. The medium-focus fixed-focus lens has the best imaging quality and practical large aperture of all lens products. Large aperture and shallow depth of field are most common in portrait photography.
→Telephoto:
In the telephoto lens, the perspective relationship is weakened, and the distances and sizes are not so obvious, that is, they become “flattened”. Compressed perspective can be said to be the biggest feature of long focal length lenses. In layman’s terms, an object that is actually far away will appear very close after shooting with a telephoto.
Therefore, if you capture a portrait of a person from a distance, the three-dimensional sense of the face will be weakened. If you want to take a close-up of the face with a strong sense of three-dimensional, it is best to get as close as possible to the subject.