Sony DSLR-A100 Optics

Sony A100 Optics

The Sony A100 features a bayonet lens mount, which accommodates a range of Sony and Konica Minolta lenses. The A100 comes with a Sony 18-70mm f/3.5 kit lens. A small button on the front of the camera releases the lens from its mount, so it can be turned and removed. The A100's CCD is smaller than a 35mm frame, so the angle of view at any given focal length will not be the same as on a 35mm camera. To find the approximate 35mm equivalent focal length, multiply the focal length of the lens by 1.5. (Thus, a 100mm lens will provide about the same view as a 150mm lens on a 35mm camera.)

The A100 provides both manual and automatic focus control modes, set by the Focus Mode switch on the left side of the camera. You can select between Auto and Manual focus modes. But the Function dial and button provide access to additional Auto Focus Area and Auto Focus Mode options.

Auto Focus Area has three options: Wide Focus Area, Spot AF Area, and Focus Area Selection. The default option is a nine-point Wide Focus area, indicated by an array of dashes inset within four widely-spaced brackets in the viewfinder image. You can override the chosen AF mode by pressing the Spot AF / OK button in the center of the Multi-controller, which defaults to the more accurate center AF point (the latter indicated by a target box in the center of the viewfinder). Wide Area AF bases its focus on the most prominent subject detail in the portion of the image that falls within the AF brackets. Spot Focus bases its focus on the very center of the frame, where the square target resides. The Focus Area Selection lets you manually set the main AF point by using the Multi-controller to highlight one of the nine AF points. The active AF area is briefly illuminated in the viewfinder. Once you've set the AF area, sliding the switch to the Focus Area Lock position locks the AF point.

Auto Focus Mode offers four options: Single Shot AF, Automatic AF, Continuous AF, and Direct Manual Focus. Single Shot AF is a general purpose autofocusing mode that sets focus when you half press the Shutter button. Automatic AF automatically switches between single and continuous AF depending on the subject's motion. Continuous AF is designed for subjects in motion, continuously focusing on the subject even when the Shutter button is half-pressed. Direct Manual Focus operates like Automatic AF, but after focus is automatically found, it can be adjusted manually. The focus signal in the viewfinder tells you when you can manually adjust focus.

Sony A100 AF Assist

The Sony A100 uses its built-in flash head as a very bright AF-assist light for better focusing in dim lighting. This has the advantage that the light from the flash is very bright, but the downside is that you can only get AF assist when the flash head is raised. This is a real limitation for available-light photography, as the camera can expose at light levels below those it can focus at. (Although its low-light focusing ability is much better than average.) If the camera is fixed on a tripod, you can work around this limitation, but it's somewhat awkward: With the flash head up, half-press the shutter button to make the camera focus. Then switch the focus mode to manual focus, being careful not to touch the focus ring on the lens. Stow the flash head, and then take your picture. (But don't forget to switch back to AF mode for the rest of your shooting!)

Sony A100 Anti-Shake

The A100 also employs Sony's Super SteadyShot anti-shake technology, which uses a highly sensitive angular rotation sensor and Smooth Impact Drive Mechanism (SIDM) to move the CCD assembly itself to counteract camera movement, rather than the more common approach of moving an optical element inside the lens. This body-based anti-shake approach is based on technology Sony acquired from Konica Minolta, but Sony claims that a more powerful processor in the A100 increases the system's effectiveness beyond that of similar systems in previous Konica Minolta SLR models. (Theoretically, a faster CPU could let the system respond to and compensate for higher-frequency vibrations.)

Sony claims that the Super SteadyShot anti-shake system in the A100 provides a 2 to 3.5 stop reduction in the blurring produced by camera shake. Translating that into real-world shutter speeds, a two-stop improvement means that a shutter speed of 1/30 second would give you the same resistance to blur from camera shake that a speed of 1/120 would without anti-shake. A 3.5 stop improvement would mean you could shoot as slow as 1/11 second and get the same results (blur-wise) as when shooting at 1/120 second unaided. Even the lower end of the specified range of effectiveness means a pretty significant improvement in one's ability to hand-hold long exposures.

When Super SteadyShot is activated, the SteadyShot scale on the right side of the viewfinder display indicates the degree of stabilization. A downside to Sony's body-based SteadyShot approach is that while you can see the results of stabilization on competing lens-based designs, you have only this scale to tell you how the A100's SteadyShot mechanism is doing. SteadyShot minimizes the effect of blurring caused by slight camera movement, which is more noticeable at long focal lengths.

We don't have a quantitative way of measuring anti-shake performance, but the system on the Sony A100 seemed to be pretty effective. In the past, we've generally found that body-based anti-shake systems were more effective at compensating for lower-frequency, larger-amplitude camera shake than were lens-based systems, but less effective with higher-frequency vibration. Body-based systems have also generally seemed to be more effective with shorter focal length lenses than long telephotos, perhaps because body-based sensors may be less sensitive to angular movement than lens-based sensors are to the corresponding linear motion out along the lens barrel. Finally, lens-based anti-shake systems do have a practical advantage in that they also stabilize the view in the optical viewfinder, while sensor-based ones do not. We'll report more on our experience with the A100's anti-shake and make some quantitative comparisons with the performance of some other systems soon, hopefully in the near future. There's no question, though, that even with telephoto lenses, the A100's Super SteadyShot anti-shake system produces a dramatic improvement in the sharpness of handheld photos at slow shutter speeds.

Anti-Dust Too?

In an interesting wrinkle, Sony also appears to be using the same actuators used in the anti-shake system to deliberately vibrate the sensor at startup and shut down to dislodge dust particles that may have landed on its surface. This is reminiscent of the hypersonic dust-removal system pioneered by Olympus and also recently adopted by Canon, but at this point we don't know whether the vibrational frequencies used by the two systems are similar or not, nor how the effectiveness of the two compare.

Sony A100 Optical Test Results

Below are the results of our optical tests on the Sony A100. We used the 18-70mm kit lens as the benchmark, since most people will buy and use the camera in this configuration.

The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Sony Alpha DSLR-A100 Photo Gallery .