Nikon patents flip-up semi-transparent mirror construction

By admin On Feb 17, 2011

Spread the love

Nikon has obtained a patent in Japan for a camera system with a semi-transparent mirror that can be flipped up and down. This makes it possible to continue using the optical viewfinder during recordings.

According to the recently published Japanese patent, picked up by NikonRumors, when the mirror is folded down, some light is reflected to the optical viewfinder, while most of the light passes through the mirror onto the image sensor. This allows the user to keep an eye on the composition, for example in movie mode or continuous mode for photos.

The disadvantage of this system compared to a normal dslr is that the viewfinder image is darker and less light falls on the image sensor, which increases the noise level. The folded mirror can also cause a ghosting effect on images.

For those who are only interested in maximum image quality for photos and video, the mirror can also be folded up. According to the patent, the viewfinder is then physically closed, so that no stray light can enter the mirror housing. When taking pictures in single mode, the composition can be made via the optical viewfinder or the rear LCD, but the mirror will be raised during the exposure phase.

Unlike a normal SLR, the patented construction with the semi-transparent mirror on the back has no sub-mirror that directs part of the light to the AF module at the bottom of the camera, so that the user has to rely on the slower contrast-detection autofocus. Because the mirror housing still requires the larger dimensions of a DSLR, it is unlikely that Nikon will actually use this patent in future products. The patent application was filed in July 2009.

The patented camera system is similar to that of the Sony Alpha A33 and A55V cameras. Those systems also have a mirror that, when folded down, allows most of the incoming light to pass through so that it falls on the image sensor. A smaller portion is reflected upwards to a phase detect off module. With the Sony system, the mirror does not fold up during use.