Will the depth of field become shallow after adding a zoom lens to a small digital camera?

Zoom lens is also called range increasing lens or expanding lens. The quality of the early shots was poor and the reputation was not very good. However, with the improvement of lens design and manufacturing technology, all lenses with lenses can now take satisfactory photos.

The focus intensifier consists of a lens group and an extension tube, which looks like a short lens. Usually installed between the fuselage and the lens, the focal length of the original lens can be increased and extended at a fixed magnification. Common zoom lenses are 1.4x, 2x and 3x, which can respectively extend the focal length of the original lens by 1.4 times, 2 times and 3 times. For example, a 2x zoom lens can increase the focal length of the original 50mm lens to 50 mm..

Focusing lens increases the focal length of the lens, and the amount of light reaching the film is also reduced. Therefore, when using the focusing lens, it is necessary to appropriately increase the exposure. By increasing the zoom lens by 2 times, the correct conversion exposure can be obtained by multiplying the original aperture coefficient by 2. For example, the original aperture is P 1 1, and it should be converted to F22 after adding a bifocal lens. Of course, if the camera you use has the M-metering function and the zoom lens also has the automatic metering information transfer function, you can determine the exposure value through the lens according to the automatic metering system.

At present, all camera factories are producing zoom lenses that match our lenses (except domestic camera factories). Of course, this is based on the listing of large aperture lenses. The focus intensifier not only doubles the focal length, but also magnifies the aberration produced by the original photographic lens. In order to obtain high-quality imaging effect, the use of focus intensifier must be combined with high-performance lens with small aberration. In addition, it is best not to use the maximum aperture of the lens, but to reduce it by 2-3 levels. At the same time, due to the reduction of viewing angle, a smaller hood can be used than the one used in the original lens.

When using the focusing lens, you can still focus according to the original depth of field ratio. For example, the original aperture is F 1 1. After using the double focus lens, the aperture is actually equivalent to F22, but the depth of field is still checked according to the original ratio of F 1 1 aperture.

Early focus-increasing lenses were generally only produced by professional lens factories and consisted of 2-3 lenses. Things are different now. Major camera factories have their own focusing lenses, such as SMC Pentax-FA fadapter 1. 7 produced by Pentax, which is 7 times that of 6 lenses and 4 groups. Some zoom lenses also use 7 lenses and 6 groups, and the lenses are coated with multiple layers to obtain maximum light transmittance and minimum ghost and glare. Now many professional lens manufacturers have also improved their products. For example, the optical structure of zoom lens in Tuli Factory is 7 pieces and 6 groups, and the image quality has also been improved. Zoom lens is a small, cheap and widely used additional lens, which can increase the focal length and keep the recent focal length unchanged, so it can increase the magnification (the magnification is the same as the focal length), and is often used in macro photography. In macro photography, recently, in addition to the development of special zoom lenses matched with macro lenses, there are also general macro focus zoom lenses. For example, VIDA 2x Marcocusing Teleconverter not only acts as a bifocal lens, but also with the help of the internal spiral expansion device, the original lens has the full magnification of 1: 1, which exceeds the maximum magnification of the general macro lens 1:2, and the imaging quality is particularly commendable. 1995, the author bought a double macro zoom lens from David. At that time, the price was more than 700 yuan, and now it has reached about 1000 yuan. The optical structure of the lens is 7 pieces, 5 groups, multilayer coating, weighing 280g, PK bayonet, and it works well with the author's standard lens of 50 mm/ 1: 1.7. It is particularly commendable that the standard lens used by the author is the domestic Phoenix lens, and the body is Ricoh XR- 10M. In addition to the standard lens of 50mm, this zoom lens can also be used with fixed-focus lenses, high-quality zoom lenses and macro lenses with other focal lengths to increase the focal length and magnification.

The zoom lens produced by Tuli Company is also very distinctive (take Tuli AT-x macro zoom lens as an example). When this lens is used with AT-XM90 lens of Tuli Company, the magnification can reach 1: 1, and the shortest distance is only 0.35m m. This macro lens specially designed for AT-XM90 has excellent light transmission and optical performance. Of course, any combination of lens and zoom lens will inevitably affect the image quality, and its influence degree depends on the quality of lens and zoom lens and the matching state between them. In recent years, in the development of zoom lens, its additional functions have been continuously expanded, and some special multi-purpose zoom lenses have appeared. Among them, the 1.6x zoom lens is the most praised by photographers, which can change the manual focus lens into the autofocus lens. Later, Pentax also produced SMC 1.7x autofocus lens, which can connect many manual focusing lenses with PK bayonet to Pentax Z series and MZ series to realize autofocus function.

Finally, I want to talk about the domestic situation of zoom lens. It may be because the domestic "big" camera factory is dismissive of zoom lenses, so far no one has produced them, and only some auxiliary lens manufacturers are producing them. For example, the Bega brand zoom lens produced by Zhejiang Yuyao Optical Instrument Factory in the 1980s has the obvious advantage of removing the inner tube, that is, the close-range ring, but the disadvantage is that the camera cannot automatically measure light after being installed on the fuselage. In fact, compared with telephoto lens, zoom lens has the characteristics of small size, light weight and low price, and can be used for multiple purposes, especially macro photography, so it is attractive to both professional photographers and amateur photographers. It is expected that Seagull, Phoenix and Mingjia Factory will produce focal lenses that are deeply loved by the majority of filmmakers.