Variable reflectance pellicle mirror?

[bakubo]

This evening as my wife and I were walking along the beach I started wondering about something. My Minolta 707si had an LCD overlay on the viewing screen that could display things like the AF areas, spot-metering area, etc. and the camera controlled what was displayed depending on camera settings. I was just wondering if a pellicle mirror could be made using some sort of current technology that would allow the reflectance of the mirror to be varied? Being able to do this might mitigate the problem of dimmer vf, less light reaching the sensor, etc. with a normal pellicle mirror. Especially if the reflectance could be varied very quickly.

Sure, although I have never seen anyone suggest this sort of thing, it probably has been discussed somewhere. Probably someone who knows about this stuff will say it isn't even possible. I admit, I don't know. That is why I am asking about it. Don't worry, I am prepared to be told this is ridiculous and impossible.

By the way, I have such romantic thoughts while walking with my wife on the beach...

[David Kilpatrick]

The possibility exists, and it is used in data projectors all the time - the Optoma projectors for example use an imager which has electronically activated mirror pixels. The problem is the response time, it's difficult to get the elements to work faster than around 60Hz, or 1/60th of a second 'exposure time'. Even the fastest responding pixel-based arrays can barely achieve 1/500th in terms of what would be a clean photographic exposure, and in their transmissive state would impose a big reduction in light and also some loss of MTF as they do not have the same properties as optical glass.

Attempts have been made to combine the mirror with the shutter several times. The most successful was the Exa I-II series, a compact SLR designed in Dresden by Exakta as part of the Pentacon optical group. The mirror was mounted diametrically in a rotating drum with a variable shutter slot immediately below it. To make an exposure, the drum simply rotated at various speeds, doing a complete circuit. There was no focal plane shutter. It was limited if I remember to a range of speeds from aroud 1/15th to 1/500th.

David

[agorabasta]

Liquid crystal overlays are really too slow for shutter speeds - that's the nature of the beast. There may be though some development with using micromirrors suspended in viscous liquid film - this should be much faster, but still too raw as a technology.

A more interesting application of such overlays could be to replace aperture blades in lenses. An STF effect could be easily possible too...

[bakubo]

Okay, thanks for the replies! Well, maybe someday using nanotechnology or something else it can be done. Of course, by then the EVF tech and contrast detect AF tech (or some other AF tech) may be so good that it doesn't really matter anymore.