Originally posted by pathdoc Remember that the thing the LX is famous (though IIRC not quite unique) for is its ability to take night exposures lasting forever (in automatic mode). Part of that was the fact that it did meter off the film - the mirror being up and acting as a natural eyepiece curtain certainly helps with that. The rest of it was the way the circuitry was arranged; why can we not duplicate this today? Now that we have direct light input to the actual recording medium (the sensor), it should easily be solvable in firmware.
Getting back to the LX's longer exposure capability, I reckon a slower-responding diode is probably better for that (in some abstruse way I do not understand).
The LX is not the only camera with off the film metering. Canon and Minolta did research and filed patents for this but never released a product using it as far as I know. The Olympus was first to release a product using this metering system with the OM2 then with the OM4 which added spot metering. The Pentax LX was second to the OM2 and improved on the OM2's metering by having the ability to expose for as long as it takes - or batteries die, all the while monitoring the scene for changes in lighting and adjusting exposure time accordingly. To date, it is the only camera by any brand - past or present, that can do this. Both the OM2&4 react to changes in lighting of the scene but have considerably limited aperture priority autoexposure times compared to the LX. All other cameras meter at the time of shutter closure and have varying autoexposure times.
As far as digisensors are concerned, it is not only firmware that will address it. Having power for that long and keeping the sensor cool are just some problems. Even for short exposure times in the seconds, there are already some additional overhead in processing times - practically doubling the time to record. Likely there are other reasons but also is there a demand for it?
Regarding photodiode reaction time to light changes, the silicon and gallium types are essentially the same and considerably faster then the previous selenium and CDS types.