1. Field of the Invention
The present invention relates to a photographic lens which can focus from infinity to a very close distance. In particular, the present invention is directed to such photographic lens which can be used at 1:1 magnification at maximum.
2. Description of the Prior Art
Lenses hitherto known useful for photography at a very short object distance are classified into two groups.
(1) Lenses of the type comprising a common photographic lens and a supplementary lens for close-up photography (so-called close-up lens) mounted on the common photographic lens; PA1 (2) Lenses of the type which are particularly designed for short distance photography. This type of lens is, when used, shifted forward as a unit from the film plane.
These known systems for photographing a very close object have the following disadvantages in any case:
In the case of the first mentioned system it is impossible to continuously change the magnification at which photography is carried out. For photography within a desired range of magnification, a number of supplementary lenses are required. In addition, exchange of such supplementary lenses is very troublesome to the user.
In the case of the latter mentioned system, it is possible to continuously change the magnification. However, a large and complicated mechanism is needed for shifting the lens. If portability is a consideration, the range of focusing movement available for the lens is limited. For the known system, the available photographic magnification is generally in the order of .times.0.5 at most.
Furthermore, it is desired that a close-up photographic lens satisfy various requirements at the same time. The lens should not only be able to take a photography approaching the object but also to take a photograph at a sufficiently large magnification while keeping a sufficiently large distance from the object to the lens (working distance). The lens should also be as small as possible in size. All of the lenses according to the prior art can not fully satisfy these requirements at the same time.