Minolta Dimage S304Minolta packs Dimage technology & optics into a compact 3.3 megapixel prosumer camera!<<Viewfinder :(Previous) | (Next): Exposure & Flash>> Page 5:OpticsReview First Posted: 9/13/2001 |
OpticsThe Dimage S304 is equipped with a 7.15-28.6mm aspherical glass lens, the equivalent of a 35-140mm lens on a 35mm camera. This lens is made up of 11 elements in 9 groups, including one AD glass element and two double-sided aspheric elements. Aperture is manually or automatically controlled, with a maximum setting of f/3 at wide angle and f/3.6 at telephoto. Focus ranges from 1.6 feet (50cm) to infinity in normal mode, and 6 inches to 2 feet (16 to 60 centimeters) in Macro mode. The Macro mode is one of the five preset program modes, and when set, automatically adjusts the lens to its maximum telephoto range. A plastic lens cap with a spring-loaded catch hooks into the inside lip of the lens, protecting it from dirt and scratches, and a small eyelet on the side allows you to tether the lens cap to the camera's neck strap to prevent accidental loss.
The S304 provides Manual, Autofocus, and Full-Time AF controls. The camera's specification sheet describes the autofocus system as a "Video AF system." While we're not familiar with that terminology, conversations with Minolta engineers revealed that the three new Dimage cameras (7, 5, and S304) all use phase-detection focusing rather than the more common contrast-detection system. The advantage of the more complex phase-detect approach is that the camera not only determines whether or not the lens is in focus, but also how far out of focus it is, and in which direction (near or far). With this information, the camera should be able to focus much more quickly, since it "knows" roughly how much, and in which direction, to adjust the focus, rather than having to "hunt" for the best focus at the outset. The AF system will still have to do some hunting for the best setting, but it should spend less time doing so than a contrast-based system. In practice, we've found that Minolta's autofocus technology is neither more nor less effective than the schemes used on other cameras, but is definitely different in what it'll focus on and what will give it problems. We've seen the Minolta cameras sometimes have trouble focusing even when the subject contained sharply contrasting detail, which would be an ideal target for conventional contrast-detect autofocus systems. On the other hand, we've seen the Dimage cameras focus very well with low-contrast, lightly textured subjects that would give normal autofocus fits. The final chapter on digicam autofocus technology clearly isn't written yet, and in the real world, Minolta's phase-detect AF appears to be just a different approach, without overwhelming strengths or weaknesses.
In normal Autofocus, the camera sets the focus when the Shutter button is halfway depressed. In Full-Time AF mode, it adjusts focus at all times, continuously keeping the frame in focus. You can also determine the area of the image the camera uses to judge the focus, by selecting one of two autofocus options: Wide Focus Area and Focus Area Selection. The default option is Wide Focus area, indicated by a wide set of brackets in the viewfinder frame. By pressing (and holding) down on the center of the Five-Way Arrow controller pad, the camera switches between Wide Area and Spot Point autofocusing modes (the latter indicated by a series of five "boxed" spot focus targets in the viewfinder). If you release the controller pad when the Spot AF targets are displayed, you can then use the four arrow buttons to move around the focus areas, highlighting the selected target in blue when it's activated (On the Dimage 5 & 7, this is known as Flex Focus Point AF).
Wide Area AF bases its focus on the most prominent subject detail in the center of the frame, delineated by the viewfinder area that falls within the brackets. If you watch closely, you will see one of the five targets appear on the LCD monitor when Autofocus is set, indicating the exact area used to determine focus.
You can switch to Manual Focus through the Multi-Function's Basic menu. In Manual Focus, you use the Up and Down Arrows to adjust focus, and the distance is displayed in meters at the bottom of the LCD monitor. The camera appears to have a fairly continuous range of focus adjustment, judging by the sound of the stepper motor driving the focus assembly, but it only displays the focus distance on the screen in fairly broadly-spaced steps. To access the Manual Focus function when that mode is enabled, you press down on the center of the Five-Way Controller pad to highlight the word "Focus" at the top of the monitor. To go back to "Zoom," press down on the center until Zoom is highlighted.
In addition to the optical zoom, the Dimage 7 offers a 2x Digital zoom which is turned on or off through the on-screen menu system. When turned on, Digital Zoom automatically engages when you zoom past the maximum optical telephoto. (Keep in mind that digital zoom simply enlarges the central portion of the CCD image digitally, rather than magnifying it optically and, as a result, image quality is usually degraded in the form of lower resolution and increased noise.)
A set of 35.5mm filter threads around the inside lip of the lens accommodates accessory filters and conversion lens kits. (We really liked having the fixed filter threads on the front element of the zoom lens, making it easy to attach auxiliary lenses and filters without any additional adapters or other gadgets, but do worry somewhat about the delicacy of the telescoping lens mechanism. Certainly, caution is called for in attaching or removing filters, and you'd want to avoid heavy auxiliary lenses altogether.)
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