SLT a55

[David Kilpatrick]

Leaving the rear screen on saves power. The 55/33 automatically switch between rear screen and EVF, using the eye sensors. The rear screen uses less power than the EVF. People leave the rear screen turned to face the camera because a) it looks and feels more like a traditional camera that way b) it doesn't get scratched c) it doesn't get nose grease! d) it doesn't put unwanted light around when shooting in dark conditions.

But in the process they are saving energy, as the camera then simply turns off the EVF, instead of switching screens.

David

[Greg Beetham]

Hey David, I just had a thought, that makes two for today. If the A55 loses 30% of it's light that should mean also that it gains a 1/3 stop of resolution...hmmm hardly worth mentioning I guess..but I was sort of wondering if a little test were done on some decent target with it and the A580 with the same lens and set the +1/3rd stop? extra on the A580 whether or not that might improve the result for the A580 a bit? Actually I'm now wondering if that's even right, if you took a shot with the A55 at f8, that's 30% of f8 right? which would be a lot more than a third of a stop...am I right?
Greg

[David Kilpatrick]

1/125th at f/8 on the A55 is still f/8. The light loss is made up for by changing the true gain of the sensor.

Sony say 'ISO 100' but actually, that's after taking into account the mirror. The sensor is really working at ISO 160-ish, but the camera as a whole is 'ISO 100'.

David

[Greg Beetham]

Yep I sortof got that from before but the actual physical light loss optically is real whichever way one looks at it, and however the exposure is compensated for, the T value on the sensor side of the mirror would represent a resolution gain over the T value exiting the rear of the lens minus the dispersion of the optical quality of the mirror I guess; so that was my thinking, along those lines. Then again the light coming from the lens is focussed/collimated, whatever, and maybe not further enhanced after it passes through the mirror, so the gain might equal the loss after all...optically.
Greg

[agorabasta]

In principle, the light hitting the mirror at a more oblique angle should be attenuated more than that in the normal direction, so there may be some effect on DOF and additional vignetting...

We really need somebody to put an effort into testing an SLT with/sans the mirror.