Sony alpha A55

[bakubo]

I'm tempted to say that in the long term phase detection off of the sensor (note Fuji's F300exr) will likely be a more suitable solution for cameras of this type.

Yeah, something like that is probably where we will end up in a few years. Here is an interesting post about using the main sensor for fast AF:

http://forums.dpreview.com/forums/read. ... e=35860053

[dynax800si]

SEE THE CROPS HERE

That are shots taken with Zeiss 135mm from the owner of this Bulgarian site - photo-forum.net
Here are the full size shots uploaded from him - http://belfo.photo-forum.net/a55/car.rar

This are 100% crops, what do You think about the 'blinks' ?

[KevinBarrett]

Update, Sorry for the misinformation.

The guy with the a33 told me that you can't attach a lens. That is Pity.

It's a missed opportunity (or intentionally engineered to avoid a complication). It seems to me that the mirror could be placed in such a way that this was an option.

I wonder whether the option was explored to make the mirror more reflective and less transparent so that the main sensor saw a reflection and the AF sensor saw what passed through it? Would this not minimize some of the odd aberations or is there a complication in that idea that I am missing?

[David Kilpatrick]

No, there is no complication, except that phase detect AF would be peculiarly sensitive to repeated (ghosted) amplitude patterns. You are correct in thinking that the reflected image may indeed by purer than the transmitted one, and that reversal is irrelevant with digital sensors, unlike film.

David

[KevinBarrett]

So the trade off is slightly quirky AF for better image quality? No doubt it would introduce complications in packaging, but I'd make that trade any day.

It would seem that an NEX or traditional DSLR already deliver on that goal. So, were the SLTs an answer to a question that nobody was asking, or just a slightly miscalculated answer to a very good question?

[dynax800si]

I really like this SLT things, but I hope that SONY will realize higher class camera with the possibility to lift the mirror and take pictures with contrast AF or something for landscape and static scenes.

[bakubo]

I really like this SLT things, but I hope that SONY will realize higher class camera with the possibility to lift the mirror and take pictures with contrast AF or something for landscape and static scenes.

Or, something like the new Fuji phase detect AF system using the main sensor and no mirror:

http://www.dpreview.com/news/1008/10080 ... filmpd.asp

[bakubo]

I was just wondering something. I know that until David and others actually have one in hand no one is likely to know the answer to this yet, but do you think that the A55 will be more, less, or just as likely to have AF problems with wide angle lenses? I guess the reason I am wondering is because of the different configuration in this camera. Will it make a difference? It would be nice if Sony could finally get a PDAF system that works reliably at wide angles with all their lenses.

[David Kilpatrick]

The use of three cross-sensors is likely to improve w/a performance (they are not f/2.8 sensors as stated on some website/reviews, and do not improve performance with faster lenses).

There is a caveat here. If you take a typical wide-angle lens, you will find it has a waveform distortion not simple. Distortion at any point in the image can be mapped to effective focal length at that point (that is how distortion happens). This in turn affects the point of focus; lenses with wavefrom distortion usually have a focus plane which resembles the surface of water after you have dropped a pebble in, or the surface of those old bullseye glass windows in 17th century houses.

Because of this the off-centre cross sensors are likely to set a different focus position to the centre sensor, when using wide angle lenses.

David

[bakubo]

The use of three cross-sensors is likely to improve w/a performance (they are not f/2.8 sensors as stated on some website/reviews, and do not improve performance with faster lenses).

I read somewhere, maybe it was just speculation, that they are f3.5 sensors rather than f2.8 sensors. Darn, my memory is pretty good about things I have read, but not good about where I read it. Any truth to this as far as you know? It sounded like what was being said was that like the A700/A900/A850 can focus more precisely with f2.8 lenses these new cameras can do the same with f3.5 lenses. I probably just misunderstood.

There is a caveat here. If you take a typical wide-angle lens, you will find it has a waveform distortion not simple. Distortion at any point in the image can be mapped to effective focal length at that point (that is how distortion happens). This in turn affects the point of focus; lenses with wavefrom distortion usually have a focus plane which resembles the surface of water after you have dropped a pebble in, or the surface of those old bullseye glass windows in 17th century houses.

Because of this the off-centre cross sensors are likely to set a different focus position to the centre sensor, when using wide angle lenses.

I would be pretty happy if they could focus reliably even if it is only with the center sensor.

[David Kilpatrick]

Sony's default aperture setting for all lenses when using the sensors for video is f/3.5 - the comment is mine, and it indicates that the cross sensors may be f/3.5 capable, or that they are definitely not f/2.8 capable or faster lenses would default to f/2.8 to get better video AF tracking. We know that f/5.6 has been mentioned as a setting for all sensors line or cross, which corresponds exactly to Nikon's modules.

All I can be fairly sure of is that none of the sensors are improved by using f/2.8 or faster lenses, because if that we true, these lenses would default to f/2.8 for video-AF.

David

[dynax800si]

A33/A55 User Manual is here.

[bakubo]

Sony's default aperture setting for all lenses when using the sensors for video is f/3.5 - the comment is mine, and it indicates that the cross sensors may be f/3.5 capable, or that they are definitely not f/2.8 capable or faster lenses would default to f/2.8 to get better video AF tracking. We know that f/5.6 has been mentioned as a setting for all sensors line or cross, which corresponds exactly to Nikon's modules.

Now that you mention it I am sure it was you that said it. Sorry for not remembering that before. I read stuff in several places and sometimes follow links to other places and before I know it I have read so many things that I don't know what I read where.

It would be cool if Sony has new AF sensors that can do with f3.5 what they previously needed f2.8 to do.

All I can be fairly sure of is that none of the sensors are improved by using f/2.8 or faster lenses, because if that we true, these lenses would default to f/2.8 for video-AF.

[KevinBarrett]

This "f/3.5 capable" business makes little sense to me. Wouldn't such sensors be useless then for most of Sony's telphoto zooms that start at f/4 or f/4.5? That is, if the f/3.5 figure is to be interpreted like the extra f/2.8 sensor of the a700.

[Greg Beetham]

I think the f3.5 AF sensor is ok for f3.5 and slower, if it's an f2.8 lens it'll be stopped down to f3.5 (at least)..in Auto...that's the impression I get anyway.
Greg