I recently had the opportunity to shoot with the Sony Alpha A100 DSLR for a few days. I'd previously previewed the Sony A100 (see Sony A100 Preview), so I won't go into great detail about specifications, control layout etc. which were covered in that article and on the Sony A100 Specifications page. Instead I'll comment more on the actual operation and performance of the camera for a user's perspective.
Just briefly though, here are some of the more significant features of the Sony A100:
Of these features I think the image stabilization system which is built into the body is probably the most interesting and significant, so I'll deal with that first.
There has been debate about the relative effectiveness of sensor-based stabilization vs. Nikon and Canon's lens-based stabilization. To get some idea of their relative performance, I tested the Sony A100 with a 16-80mm zoom set to 80mm and a Canon EOS 20D with an EF-S 17-85IS lens also set to 80mm. Shooting handheld, I obtained a number of images with each camera at shutter speeds from 1/80s to 1/8s. The standard rule of thumb is that an average photographer would need to shoot at a shutter speed of 1/125s or faster in order to have a high probability of getting sharp images. At lower speeds your chance of sharp images should drop significantly. Photographing at 1/60s is 1 stop slower, 1/30s is 2 stops slower, 1/15s is 3 stops slower and 1/8s is 4 stops slower.
The results showed that the effectiveness of the Sony Super SteadyShot system was quite similar to that of the Canon lens-based stabilization system, at least at mid-range focal lengths. Giving numerical results for stabilization effectiveness difficult because it's difficult to quantify sharpness in this context. However at 1/8s (4 stops of stabilization) about 50 percent of the images were acceptably sharp with the Canon system and about 40 percent with the Sony system. Your results could be better or worse than mine, depending on just how steady you can hold the camera.
However, whatever the relative merits of the two stabilization systems, and even if the Canon system is slightly better, it's clear that the Sony Super SteadyShot has the huge advantage of stabilizing all lenses mounted on the A100 body. This includes all wideangle and normal prime lenses, none of which Canon makes available with lens based stabilization. In addition to having all lenses stabilized, you only have to pay for stabilization system once since it is built into the body, rather than paying for it each time you buy a stabilized lens.
Remember of course that any image stabilization system stabilizes camera motion, not subject motion and allows sharp images of static subjects at slow shutter speeds. If your subjects are moving, e.g., at a sporting event, you still need a fast shutter speed to freeze action
The Sony A100 uses a 10 megapixel CCD sensor with an ISO range from 100 to 1600. Noise levels are pretty well controlled up to ISO 400, with noise becoming noticeable at ISO 800 and even more so at ISO 1600. The images below are 100 percent crops from images captured at ISO settings from 100 to 1600 with the Sony A100 and with the Canon EOS 20D. The noise levels of the EOS 20D are very similar to those of the Canon Rebel XT and XTi and all three Canon DSLRs use a similar CMOS sensor.
As you can see, the noise level of the Sony A100 is somewhat higher than that of the Canon EOS 20D. The 20D appears to have an advantage of around one ISO level, i.e., the 20D noise at ISO 800 is equivalent to the Sony at ISO 400. This test (a grey card at 100 percent cropping) is designed to reveal noise. In a typical image printed at 8x12, both cameras would be fine up to ISO 800. Below are crops from images taken at ISO 800 and ISO 200. These are 50 percent crops, so if you are using a 17" monitor at 1280 x 1024 resolution (a typical system), they'd represent sections of a 12" x 18" print.
As I think you can see, even at ISO 800, noise in an actual image is quite acceptable. Noise at ISO 1600 is higher, but again if you aren't making large prints it may not present a practical problem.
In continuous drive mode I was able to shoot at a rate of 2.9 frames/sec storing the images as JPEGs with the A100 set to ISO 100 and a shutter speed of 1/250s. With JPEG mode and a fast memory card, you can keep on photographing until the memory card is full, so there is no buffer size to worry about. When shooting in RAW format, Sony specifies that the buffer will hold 6 frames but this may depend on the image size (which is variable and depends on ISO setting and subject detail). When using a Lexar Pro 133x CF memory card, I captured 9 RAW images at ISO 100 before the buffer filled and the frame rate dropped to around 1.7 frames/sec. High resolution JPEGs varied between 2MB and 5MB in size, depending on ISO setting and subject. Subjects with more detail and photographed at higher ISO settings yielded larger files. RAW files, which come out with a .ARW extension, are typically around 10MB each, though some were as large as 13MB. This would indicate that the .ARW files are compressed, presumably using a lossless algorithm.
The Sony A100 accepts Compact Flash memory cards, types I and II. An adapter is included with the camera to allow the use of Sony Memory Sticks.
Though I didn't make any extensive tests of AF speed and accuracy, in normal use I noticed no problems and I don't think I got any images which were blurred due to failures of the AF system to find correct focus.
The in-viewfinder LCD display is presented just below the image. It shows the usual data: flash exposure compensation, flash mode and readiness, focus confirmation, shutter speed and aperture, exposure compensation and/or metering, and the number of images that can be stored in the camera's buffer memory. The display also shows an indication of how hard the Supersteadyshot system is working to stabilize the image via a multibar display similar to a cell phone signal strength indicator.
There are seven flash modes: Automatic, Fill, Red-eye reduction, Rear sync, Wireless, High-speed sync, and Slow sync. In wireless mode the built-in flash sends a series of optical pulses to an external flash. The external flash first fires a metering pre-flash, which the camera uses to determine exposure. The built-in flash then sends a second series of pulses, which tell the external flash how much power to use. Contrast this with the Canon system, which requires a hot shoe flash such as the 580EX II in order to fire and control a wireless slave such as the 430EX.
Currently (Dec 2007) the Sony A100 sells for just under $600 (body only) or with an 18-70/3.5-5.6 kit lens for just under $700. The kit lens isn't a bad performer and for around $100 is good value and a useful general purpose "starter" lens.