0.667X teleconverter
 

Science fiction, but would it be great to have 0.667X TC (1/1.5X DSLR crop factor) This would allow 35mm SLR lenses to be used on digital SLR cameras but instead of loosing light, the TC would gain one stop by concentrating light and turning f5.6 into f4 but with f5.6 depth. Another gain would be full-frame usage from existing 35mm lenses.

I suppose it could be called a full frame converter.

I can see that it would reverse the crop factor, but I can't see that it would give you a 1 stop light "boost".

Nice idea.

Light boost would come by concentrating light on a smaller area, like using a magnifying glass to start a fire from the suns rays. I expect one stop loss from 1.4X TC so the reciprocal should give one stop gain.

OK, I can see that. I think it would con the camera into thinking that it was a "brighter day", giving you effectively 1 stop extra light, but the camera would still read the aperture correctly.

I wonder if this is possible, because I'd buy one.

In a way its already done by Canon at least (and probably other manufacturers) who put a filter with millions of tiny lenses in front of their CMOS sensors to concentrate the light onto each pixel in order to decrease the amount of amplification needed hence reduce the amount of digital noise. The extra stop is in a sense shown by having higher iso's available without excessive noise.

The micro-lenses serve (as I recall) two functions:

1: trap light that would otherwise fall in-between two pixels and be wasted

2: massage the angle at which light falls onto the sensor elements - because unlike film, a CCD or CMOS sensor isn't very sensitive to light which strikes it at an angle, only straight-on.

I'm sure you are right although one of the aspects of "digital" lenses apart from anti reflective coatings is to improve the angle of the light striking the sensor. I also recall reading what I said as well (in Amateur Photographer I think) complete with diagrams showing the front area of the micro lenses larger than the rear area so increasing the light gathering power. My mind just boggles at the thought of being able to manufacture the filter with millions of little lenses!

I'd buy this, if it would still provide a 1 stop increse on 1.4 or 2x teleconverter.