Sometimes, rumours are really weird but they still have to be listened to and discussed. Recently, SonyAlphaRumors.com reported an “information” they received from an anonymous source that they indicated was new and possibly unreliable. To me, it was so weird that I thought it would not be worth mentioning (it is my role to filter out and choose the news I report here), but people keep asking questions about that.
So, let’s debunk it once and for all. The proposal is that Sony is designing the A77 with two semi-transparent mirrors instead of one. Starting from a A33/A55-type of semi-transparent SLT mirror, the anonymous source proposes that they wil add a second one essentially to mix Electronic ViewFinder and real images.
Unfortunately, it does not add up. Industrial problems crop everywhere in this design. For any reasonably seasoned engineer, it would be a nightmare to align correctly the two images, but any optician will quickly notice that super-imposing a pixelated image (70%) and a real image (30%) will probably make it only bizarre looking, not improved.
But it gets worse. The drawing provided here shows that the AF sensor would get its image from the EVF not the real word light source. Let’s say this would remove all usability of phase detection and it would be better to use the direct data from the sensor to do contrast detection as this position would only allow it. So, let’s suppose that this is slight error in the drawing and the AF sensor will receive 70% (or even 30%) of the light going up. This time, there is even less light going directly to the eye (90% from EVF and 10% from outside? What an effort for so little!)
The, the advantage of getting the real image in the viewfinder is to be able to do a fine focus on the focusing screen, but where is it? Certainly not in the usual position in the way up for light reflected from the primary mirror. This would actually reduce light going a little more and add another handicap for the AF sensor.
Let’s say that this is certainly not what Sony has in mind for the Sony A77. And let’s wait for leaked information rather than pure amateur phantasm.