Characteristics of macro photography from object distance, image distance and focal length

Macro photography is a special photography mode different from conventional photography. Macro photography is to shoot related objects at close range and get greater magnification. If an image as large as the original can be formed on the film, the magnification will reach 1: 1. Of course, the magnification of macro photography can not only reach1:1,but also be larger with special equipment. Macro photography not only has its unique charm, but also plays a role in scientific research and medicine. Macro photography is different from conventional photography in equipment. First of all, there are certain restrictions on cameras. Only SLR cameras, including 35 mm and 120 SLR cameras, are suitable for macro photography. Mainly because of this camera, the viewfinder has no parallax, and all subjects can be seen in the viewfinder. Paraxial camera has a large parallax when shooting at close range, because it cannot observe all the scenes in the viewfinder, so it is not suitable for macro photography. Secondly, the shortest shooting distance of conventional photographic lens often cannot meet the requirements of macro photography. Because the shooting distance of general macro photography is within tens of centimeters, even as close as several centimeters. Therefore, in order to achieve the purpose of macro photography, we must use special equipment and methods. There are many ways to realize macro photography, the most common one is to add a close-up lens to the front of the conventional lens. Close-ups are convex lenses made of optical glass, usually with different diopters. Close-ups are numbered 1, 2, 3, 4, etc. In case a different magnification is required. Generally speaking, the greater the number of close-ups, the closer the shooting distance. Different manufacturers have different numbering methods, which should be selected according to actual needs. In addition, the magnification is related to the focal length of the lens used. The longer the focal length of the lens, the greater the magnification. Close-ups should use screws with the same caliber as the filter of their own lens, so that they can be screwed to their own lens. The close-up lens is screwed in front of the lens, which is equivalent to adding a lens in front of the optical lens group of the lens. Its quality directly affects the imaging quality, so we must pay attention to it when purchasing. Some close-ups are composed of two achromatic lenses, which can achieve better results. Close-up lenses are cheap and can only be used in occasions with low magnification and less strict requirements for aberration. In addition, the use of close-up lens has little effect on the camera's automatic exposure and autofocus performance. At present, many zoom lenses of 35mm cameras have close-up function, but the magnification does not exceed 1∶2, that is, the image on the film will not exceed the original size of 1/2. Some zoom lenses can achieve full focal length close-ups, called full macro; Some zoom lenses can only achieve close-up function at a certain focal length, mostly at the long focal length end of the zoom lens. Because the zoom lens is designed as a conventional lens, the design of the conventional lens is based on the focal length of dozens or even more object distances; The aberration correction of the lens is also based on the conventional lens, which is not as strict as the macro lens. So the close-up function of zoom lens is just an additional function. In actual shooting, distortion and spherical aberration have great influence on imaging quality. Therefore, this close-up function of the zoom lens will not have much influence when shooting real objects, such as flowers; On the shooting plane, such as remake photos, materials, etc. This close-up function is not enough. At present, only Nikon has a macro zoom lens AF70-180mm4.5-5.6, which is a real macro lens with the maximum magnification of 1: 1.33. There is also a close-up attachment, which is a close-up ring. A close-up ring is installed between the lens and the fuselage, which is equivalent to extending the image distance of the lens, thus obtaining a larger magnification. Close-up collar accessories usually consist of several collars with different lengths, such as 12 mm, 25 mm, etc. , can be used alone or in combination. For example, a 50mm lens with a 25mm frame can achieve a magnification of 1∶2; Add a 50 mm collar (or two 25 mm collars) and you can get the magnification of 1: 1. With close-ups, the magnification will not change continuously. There is also a close-up leather cavity, which, like a close-up collar, is installed between the lens and the fuselage. Because the expansion and contraction of the close-up skin cavity is controlled by the frame, the skin cavity can be continuously expanded and contracted, so the magnification is also continuously adjustable. Using these two close-up accessories, the magnification of1:1can be obtained. However, the camera's automatic exposure, autofocus and other functions will be affected to varying degrees. Automatic exposure can only be realized by using special automatic connecting ring and double-ended cable releaser. The price of close-up collar is higher than that of close-up lens, and the price of close-up leather cavity is higher. But with these two accessories, better imaging quality can be obtained. The close-range leather cavity can also be equipped with a reverse film remake frame, which is specially used to remake the reverse film. In addition, there is a close-up attachment-inverted ring, which can flip the lens on the camera and get a magnification of about1:1. This method of connecting lenses backwards can only be applied to standard lenses, wide-angle lenses and partial zoom lenses. If you want to get excellent image quality in macro photography, macro lens is the only choice. Macro lens is specially designed for macro photography. When designing the optical lens group of macro lens, it is different from the conventional lens. As mentioned above, the shooting distance of conventional lenses is considered according to the focal length of dozens or even more times. The shooting distance of macro lens is much closer, and the nearest shooting distance is only several times the focal length. More importantly, it is necessary to correct all kinds of aberrations when shooting at close range. In particular, spherical aberration and distortion must be strictly corrected to ensure that plane objects, such as photos and drawings, can be truly restored. Macro lenses of 35 mm cameras produced by various manufacturers generally have three specifications: 50mm (including 55 mm and 60 mm); 100mm (including 90 and105 mm); ); 180mm (including 200mm), and the magnification can reach1:1. The longer the focal length of the macro lens, the farther the recent shooting distance. Therefore, the long focal length macro lens is more suitable for shooting difficult-to-access objects such as insects. In addition to macro photography, the above macro lens can be used as a conventional lens with excellent imaging. In addition, Canon and Minolta each have a special macro lens, which can only be used for macro photography. If the magnification exceeds1:1,the image on the film will be larger than the original one. Canon MP-E65MM F2.8 1-5x macro photo, the magnification of this lens can reach 5 ∶1; The Minolta af macro zoom is 3x- 1xf 1.7-2.8, and the maximum magnification of this lens reaches 3∶ 1. 120 SLR cameras also have corresponding macro lenses. For example, in Hasselblad's supporting lens, Zeiss Makro-Planna CF 120 and Zeiss Makro-Planna CF 135 are two macro lenses, and the latter, together with a close-up leather cavity, can reach the magnification of1:1. In addition, major camera manufacturers also have special macro flash for macro photography. The flash index of macro flash is relatively small, which is only suitable for close shooting. The automatic function of special flash can also be realized in macro flash. In addition, the macro flash is set in front of the lens, which can create a shadowless shooting effect. Canon has a macro ring flash MR- 14EX and a macro double-lamp flash mt-14ex; Minolta has a macro double-lamp flash T-2400 and a macro ring flash R-1200; Nikon has a macro ring flash SB-29; Hasselblad also has a set of macro double-lamp flash. Because of the particularity of macro photography, it has formed a unique category. Most of the photos taken by macro photography are scenes that people rarely see with the naked eye, so they have a certain freshness and strong visual impact.