Sony alpha cameras

I am still debating my first dSLR and had my sights set on the new Nikon D5100. There are many features I like about the D5100, and some that I don't (for example, the more plastic body versus magnesium in the D7000).

I thought I had made up my mind but now I am wondering if I can get a better bang for my buck by buying one of the sony alpha cameras (33 or 55).

My concern is the following statement from their website:

By transforming the fundamental way DSLR cameras work, you'll experience best-in-class speed3, up to 10 fps continuous shooting at full 16.2MP resolution with exposure fixed at the first frame. This is made possible by a Translucent Mirror that always stays in place. You also get standard continuous shooting at up to 6 fps.

Does this mean that there is no tracking auto-focus? This is important to me since I am going to shoot some moving objects (dogs, kids, sports). I may be confusing it with different Sony camera models that I thought also said that the focus was set at the first frame.

Any advice is appreciated.
Thanks.

spectoau said:

I am still debating my first dSLR and had my sights set on the new Nikon D5100. There are many features I like about the D5100, and some that I don't (for example, the more plastic body versus magnesium in the D7000).

I thought I had made up my mind but now I am wondering if I can get a better bang for my buck by buying one of the sony alpha cameras (33 or 55).

My concern is the following statement from their website:

By transforming the fundamental way DSLR cameras work, you'll experience best-in-class speed3, up to 10 fps continuous shooting at full 16.2MP resolution with exposure fixed at the first frame. This is made possible by a Translucent Mirror that always stays in place. You also get standard continuous shooting at up to 6 fps.

Does this mean that there is no tracking auto-focus? This is important to me since I am going to shoot some moving objects (dogs, kids, sports). I may be confusing it with different Sony camera models that I thought also said that the focus was set at the first frame.

Click to expand...

There is full tracking AF available in the 10fps mode as explained in the countless reviews. Also, the fixed exposure isn't completely true either. If you decide to use full AF during the 10fps burst mode, aperture is fixed at the widest aperture of your lens (but no larger than F3.5) at the chosen focal length. Shutterspeed and/or ISO will (if needed) vary to keep the subject well exposed. Here's an example:
http://www.youtube.com/watch?v=q_EdU4tB8Gk&feature=related

The only current Sony cameras that do set focus at the first frame at the highest burst speed (7fps) are the A580 and A560. On the other hand, they offer a 5fps alternative with full autofocus too (which is still faster than their direct competitors).

I don't know if the Sony models that you mention have tracking auto-focus, but it would be possible for a camera to freeze the (shutter speed, aperture, ISO) for all shots, while continuing to adjust the focus from frame to frame. So I wouldn't take the comment about freezing the exposure as a reason to give up researching the camera.

Note that "SLT" cameras have electronic viewfinders in place of optical ones. The purpose of the (fixed) mirror is to enable the use of SLR-style phase-detect auto-focus (which is usually faster than P&S-style contrast-detect auto-focus).

These are marketing lines. These people are not too technical.

These SLT have an advantage in burst shooting and some disadvantages. If you are only doing burst shooting maybe they are the most suitable for you. Try to see them in a store and verify you get along well with the EVF.
Note that you permanently have a slight ND filter over your sensor.
--
Victor
Bucuresti, Romania
http://picasaweb.google.com/victorpetcu69/
http://picasaweb.google.com/teodor.nitica/
http://picasaweb.google.com/vpreallize/
http://picasaweb.google.com/v.petcu.gci/
http://picasaweb.google.com/vpetcu.gci.arhiva/