Ever since I sold my A77 and all my APS-C lenses to go full-frame with the A99, I've sorely missed the compactness of the A77. The A99 beat the old A77 in low-light performance by a solid two stops, and the colors in the A99 are terrific. But the A99 is a boat anchor. While I can't give it up, I've been looking for something smaller-lighter as a second camera. At the top of my list have been the A7r and the Leica T. Both of those cameras have walk-around zooms that are somewhat compromised, apparently due to an attempt to attain the last measure of compactness.
One of the things I truly loved about the A77 was the superb 16-50 lens. It doesn't have the Zeiss name or even the G-designation, but it is relatively compact and a fantastic value. Its only significant flaw was some mid-image, barrel-like distortion that I noticed most when comparing RAW images to camera-corrected jpegs of the same shot. The A77 II with the 16-50 lens is a tempting package to me.
By my calculation, a loss of 30 percent of the collected light to the mirror equates to a reduction of 0.514 EV, not "approximately 0.4." The review says that is negligible, but it is half a stop. What about all this work that Sony has done to improve the light collection by detectors? I'll bet the improvement is less than 30 percent. If you want to get 30% more light collection out of a lens, you have to increase the frontal optic area by 30 %. Is that negligible? I guess it depends on who you are.
I'm buying an A99 to get improved noise performance over the A77. It will be interesting to compare it head-to-head against my A850. The question to be answered: are Sony's sensor improvements since the A850 enough to compensate for the mirror losses? Some say that modern digital technology has made noise a non factor. Those people apparently don't use sharpening, which makes noise jump off the screen.
Blorf: I'm planning to upgrade soon and I've been considering the A77 which has a similar pixel count on a smaller sensor. If it has the same number of pixels on a smaller sensor shouldn't the image come out sharper? I've never seen pixel density addressed in a review and I'd like to know how it affects image quality.
No, it will not result in a sharper picture. There are two things that determine sharpness in a raw image: lens resolution and pixel count. Having a smaller sensor means a greater demand on resolution from your lens. That said, the A77 with the f/2.8 16-50mm kit lens produces extremely sharp images. They are as good as high-end glass on a full-frame camera. I have that matchup as well as an A850 with a Zeiss 24-70. Believe it or not, the A77 with the kit lens is essentially just as good in terms of sharpness. There is more geometric distortion with the 16-50 lens, but, if you don't mind jpeg output, the A77 corrects the distortion.
Others have pointed out that smaller pixels mean more noise. That's true if all other factors are equal. I've found that my aging A850 has lower RAW noise than the A580 or the A77. The noisiest of the three is the A77. The multi-frame noise reduction feature can reduce noise by two to three stops.