Sony SLT-A55 Digital Camera Review$899.99
Speed and Timing
The SLT-A55 also offers a good amount of control over the burst shooting, providing two levels of burst: a 10 fps mode that can shoot a burst of up to 39 images (in JPEG format: using RAW+JPEG limits this to 20 shots), and a 6 fps mode that can shoot continuously up to the capacity of the card. One quirk of the burst mode is that, while the camera automatically adjusts the shutter speed to compensate for changing lighting while shooting, the camera can only control aperture if you put the auto focus mode to the AF-S setting, so it only focuses once at the start of the burst of images. What this means in practice is that you are forced to choose between having the camera continually focusing or having control over the aperture for no adequately explained reason, which limits the usefulness of the mode. Using the 10fps mode also slows the camera down a lot after shooting, as it has to take time to write the images out to the memory card. It is still possible to take images, but only intermittently and in a seemingly random pattern. So, although the 10fps burst mode works as advertised, it does have a few caveats that make it less flexible than we had hoped.
Because the mirror stays in place when shooting, the the SLT-A55 is a speedy shooter: we measured it at an impressive 10 frames a second (fps), which is exactly what Sony claims. This does come with a caveat, though: it can only manage this speed for a burst of 39 or so frames. After this, the speed slows to between 4 and 6 frames per second, which is heavily dependent on the speed of the memory card in use. The camera also offers a continuous shooting mode, which we measured at about 6 fps, but which could be sustained for as long as their is space on the memory card. Our review unit had no problem maintaining this speed with out test card (a Sandisk 4GB SDHC card).
This speed puts it ahead of the pack when compared with other SLRs: it is significantly faster than all of our comparison models. The only conventional SLRs to get close to this speed are some professional models, such as the Canon 7D and the Nikon D300s, both of which can manage about 7 to 8 frames a second, but which cost much more than the SLT-A55.
The usual options are available for taking delayed images: a 2 and 10 second delay, plus a smile detect mode that only takes the photo when it detects a smile.
In addition, the SLT-A55 supports an optional IR remote, which can be used to take photos. No pricing is currently available for this remote control.
The SLT-A55 tries to include the best of both worlds when it comes to focusing, combining the flexibility of the SLR (which has dedicated focus sensors) with the speed of mirrorless cameras (which use the image sensor to focus). The SLT-A55 has a fixed mirror which is translucent: it lets most of the light through to the image sensor, but bounces some up to the 15 dedicated focus sensors in the viewfinder housing. The theory is that this arrangement allows the camera to focus and shoot at the same time, because the camera does not have to focus then wait for the mirror to move out of the way to shoot: the mirror remains in place. This theory is most borne out in practice: the camera focuses quickly, and there is much less delay between pressing the shutter and the camera taking the shot. It also means that the camera can focus and take shots at the same time, which makes the cameras burst mode both faster and more accurate, as the camera can keep focusing while it is shooting.
There are three options for how these 15 AF spots are used: Wide allows the camera to choose, while Spot uses the center group of 7 and Local allows you to choose an individual spot. We found that the SLT-A55 focused quickly in most situations, although it did swim a bit in low light, focusing back and forth to look for the focus point. The center group of focus points are the best ones to use in low light: they are cross-type sensors that work better in low light, and we found that the camera had some issues focusing on off-center objects in low light settings.