(1) The default aperture value of the aperture is the largest. The aperture is the best before the close-up skin cavity is installed. If it is installed, it cannot be adjusted. (Except for the old lens with aperture ring)
(2) Cannot auto focus, need to be completely manual operation;
The close-up skin cavity/close-up ring is an accessory that is connected between the body and the photographic lens. Its function is to open the distance between the main point of the lens and the focus plane to achieve the purpose of magnifying photography.
The close-up skin cavity is used in the same way as the close-up ring. The difference is that the magnification of the former can be continuously adjusted, and the latter can only be adjusted stepwise.
There are a variety of close-up rings on the market. The original factory is not much and expensive, but there are more deputy factories and relatively cheaper prices. Now the Kenko brand is common. The machining precision of these close-up rings is It is very good.
Common close-up rings are sold in sets, usually a set of 3 sections, each with a different length, which can be selected according to the magnification required.
Close-up rings can be divided into two categories: with/without agile levers, the former can be linked by the aperture, the latter will not work. Generally, the close-up ring with the aperture lever is equipped with corresponding electrical contacts according to the bayonet to ensure that the metering in the TTL can work.
For different lenses, how long does the skin cavity/ring be used to achieve the magnification you need? According to the foregoing, the magnification can be calculated as follows:
Magnification = [skin cavity / ring length] / lens focal length
In theory, with a close-up skin/close-up ring, any lens can be used for macro photography. However, to see that with a 400mm focal length lens, if you need to achieve a 1:1 magnification, then the length of the skin cavity / ring needs 400mm long! Obviously this combination is unrealistic.
In addition, if the length of the ring in the hand is 50mm, if the standard lens of 50mm is connected, the magnification will reach 1:1; if the lens of 24mm is connected, the magnification will exceed 2:1.
Connection method: Remove the lens, connect the close-up skin cavity/close-up ring to the body, and then screw the lens to the bayonet on the skin cavity/ring.
The characteristics of this approach are:
1. The aperture has a linkage and a non-linkage, which works for some types of metering; if the original skin cavity can be used for aperture, the price is too high;
2. For AF body and AF lens, when the magnification is relatively high, AF is often slow and ineffective even with AF transmission mechanism due to insufficient light input;
3. When focusing, if the magnification is determined, rely on the moving body to adjust the focus, and adjust the focus ring; when focusing, the aperture should be fully open, and then manually close the aperture when shooting;
4, the magnification can be adjusted, up to 1:1; can be adjusted within a certain range;
5, there is obvious field curvature phenomenon when the large aperture, the effect of shrinking the aperture is not very obvious
6. If there is no metering, it should be compensated by exposure, and the compensation coefficient is calculated by (1+M)2;
7, the image quality is only related to the lens