Sony A100 Exposure
The Sony A100 offers excellent exposure control, with fairly fine-grained adjustment of image attributes like sharpness, contrast, and color saturation, as well as extensive White Balance offerings. The Exposure Mode dial on the top panel selects the main shooting mode, offering Manual, Shutter Priority, Aperture Priority, Program AE (Program Shift), Full Auto, and six Scene settings.
In straight Auto mode, the camera controls everything about the exposure, except for flash, zoom, and focus. Program AE mode keeps the camera in charge of the exposure,while you have control over all other exposure options. While in Program AE mode, you can rotate the control dial with or without holding the Exposure Compensation button to scroll through a range of equivalent exposure settings. Thus, you can bias your exposure toward a faster shutter speed or greater depth of field as circumstances dictate. Aperture Priority mode lets you select the lens aperture setting, while the camera selects the most appropriate corresponding shutter speed. In Shutter Priority mode, the user selects the shutter speed, from 1/4,000 to 30 seconds, while the camera chooses the best corresponding aperture setting. Switching to Manual mode gives you control over both shutter speed and aperture, with a Bulb setting available for longer exposures. Exposure time in Bulb mode is determined by how long you hold down the Shutter button. There doesn't appear to be any limit to the duration of Bulb exposures, but it appears that the dark-frame subtraction will only compensate for exposures up to 30 seconds long. (I strongly recommend use of the optional wired remote in Bulb mode, as the pressure of your finger on the Shutter button is bound to jiggle the camera somewhat, blurring the image.)
Scene Modes & DOF Preview
The six Scene modes include Portrait, Landscape, Macro, Sports Action, Sunset, and Night Portrait. Each optimizes the camera's exposure, white balance, and image processing systems for the particular program.
Portrait biases toward wider apertures to defocus the background while capturing warm, soft skin tones. Sports Action maximizes shutter speeds with Continuous Autofocus and Continuous Advance Drive modes. Landscape produces sharp, colorful shots of outdoor scenery. Sunset handles the rich warm palettes of sunsets. The Macro setting boosts color in smaller subjects, and Night Portrait balances ambient light with the flash.
A Depth of Field Preview button on the front of the camera lets you view a scene through the viewfinder with the aperture stopped down, previewing the depth of field before actually capturing the image.
The Sony A100 offers three metering modes: Multi-segment, Center-Weighted, and Spot. The default metering mode takes readings throughout the image to determine exposure. Center-Weighted gives precedence to the center of the image while reading the whole frame. Spot metering options are also available via the Metering Mode dial on the rear panel. Spot metering, useful for high-contrast subjects, bases the exposure reading on the very center of the image, letting you set the exposure based on a small portion of your subject. You can also lock an exposure reading by pressing the AE Lock button on the back panel. Halfway pressing the Shutter button also locks exposure and focus, but only in autofocus mode.
ISO Range, Noise Reduction, and Exposure Compensation
The A100's light sensitivity can be set to ISO equivalents of 100, 200, 400, 800, or 1,600, or it can be left in Auto mode for the camera to adjust as it sees fit. Two special options called Lo 80 and Hi 200 offer special tone curves for low-key and high-key subjects at ISOs of 80 and 200 respectively. A Noise Reduction option is available for longer exposures and higher ISO settings, and greatly reduces the amount of image noise that would otherwise result. Exposure compensation is adjustable from -2 to +2 exposure equivalents (EV) in one-third-step increments by turning the Control dial while pressing the Exposure Compensation button, which displays the scale and setting on the LCD monitor. An Auto Exposure Bracketing option can snap three shots in rapid succession if you hold down the shutter, varying the exposure between each in steps of 0.3 or 0.7 EV units. You can also bracket the exposures using the flash. The A100's Drive mode dial offers Auto Exposure Bracketing for either Single Advance or Continuous Advance drive settings.
White Balance Options
The A100 offers convenient control over white balance, color rendition, and tonal range. You adjust white balance by first turning the Function dial to the WB setting, and selecting either Auto, Preset, Color Temperature, or Custom. Auto lets the camera choose the white balance itself. Preset lets you set the white balance to a specific light source. Options include Daylight, Shade, Cloudy, Tungsten, Fluorescent, and Flash. Within the preset modes, you can also fine tune the white balance by pressing the up and down arrow keys. Custom allows you to calibrate the camera to a specific lighting situation by pointing to a white or neutral object. Color Temperature lets you select a specific color temperature in degrees Kelvin.
The Digital Effects Control (DEC on the Function dial), offers control over image contrast, saturation, and sharpness in five steps from -2 to +2 arbitrary units. The Color Mode option of the Digital Effects Control, available in P, A, S, and M exposure modes, sRGB color space options of Standard (faithful color reproduction), Vivid (increased contrast and sharpness), Portrait (optimized skin tones), Landscape (optimized daytime outdoor scenery), Sunset (optimized landscapes at dusk or dawn), Night view (optimized for nighttime scenery without flash), Black & White (monochrome), and Adobe RGB.
The A100's Drive Mode button on the top panel accesses a range of shooting modes, including Single Frame Advance, Continuous Advance, 10-second and Two-second Self-timer modes, Continuous Advance Bracketing, Single Frame Bracketing, and White Balance Bracketing. The first two bracketing modes access the camera's Auto Exposure Bracketing system. In Continuous Advance mode, the A100 captures a rapid series of images, with a maximum frame rate of three frames per second. Actual frame rates will vary, depending on the image size and quality settings, as will the total number of images in the series, due to the amount of memory card space. White Balance Bracketing lets you capture a series of images as well, though with bracketed white balance values.
The two Self-Timer modes lock the mirror up, then fire the shutter a short delay after the Shutter button is pressed. The shorter, two-second delay is very handy when you need to prop the camera on something to take a photo in dim lighting, and don't want the pressure of your finger on the shutter button to jiggle the camera. The 10-second delay is long enough that you can run around to get into the photo yourself. An LED lamp on the front of the A100 blinks and the camera beeps as the 10-second Self-Timer is counting down, the blink and beeps becoming faster in the last few seconds.