1. Field of the Invention
The present invention relates to an optical element, an optical apparatus and an imaging apparatus.
2. Description of the Related Art
A liquid crystal optical apparatus containing a guest-host liquid crystal, in which a dichroic coloring matter is guest, has been proposed in the past. However, it is difficult to sufficiently increase the dynamic range of the amount of transmitted light without voltage application and with voltage application.
This depends on the fact that the optical density ratio (absorbance in absorption mode/absorbance in transmittance mode) of a current dichroic coloring matter is not sufficiently high. For camera applications in particular, an absorbance of 90% or higher may be required in the transmittance mode, that is, the maximum transmittance. However, since the optical density ratio of the dichroic coloring matter is not sufficiently high as described above, the minimum transmittance may not be decreased to satisfy the maximum transmittance. In other words, the full performance as a diaphragm (dimmer) may not be delivered. Conversely, satisfying the minimum transmittance may not satisfy the maximum transmittance as high as or higher than 90%, which is a trade-off relationship.
Since the guest-host liquid crystal only may not increase the dynamic range in this way, a dimmer including a mechanical structure with the direction of the polarized light passing through a polarizer, for example, in parallel with the absorption axis of the dichroic coloring matter has been proposed which puts in and out the polarizer to and from the optical path such that both necessary minimum transmittance and maximum transmittance can be obtained (refer to JP-A-11-326894 (Patent Document 1)).