DK on the a99

You have ask Sony about that, but I guess it could be simple a case of newer models having better features.

SLR cameras from other brands can also expose for many hours on one battery, in spite of having mirrors. Now, some cameras are (for somewhat unclear reasons) limited to say 30 minutes or 1 hour bulb exposures, but can do longer with external shutter triggers (which has to be bought separately, which might explain why this feature is not built-in in the cameras ;))

When it comes to power consumtion in any digital camera, the sensor and imaging processor is almost always the biggest culprit. And the power consumption grows with a) the intensity of readout (like when shooting video with its high bitrate) and b) with sensor area.

A rear screen or a EVF in itself does not use much power at all. Nor does the mirror mechanism in a traditional SLR.

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I don't suffer from insanity, I enjoy every moment of it!
By the way, film is not dead.
It just smell funny