引用:
原帖由 irvingtin 於 2010-8-26 00:29 發表
講真, 除左 10FPS 之外, 仲有D咩比 D90 / 550D 好???
對焦系統連 08年出既 D90 都比唔上
Dpreview 個 cons 講左, 追焦差
多而唔中焦有用咩???
GPS 幾何會開??? 550 ...
7k內o既價錢，best of class，夠殺囉....
Conclusion - Pros
* Reliably good image quality at lower sensitivities
* High ISO JPEG output usable up to ISO 12800 for smaller prints
* Excellent LCD and good EVF, with efficient automatic switch.
* Versatile and capable (for its class) 15-point AF system
* Accurate metering and focus
* Very Good JPEG resolution
* Very good (almost 9EV) dynamic range
* Good quality HD video output
* Swivel-screen useful for overhead- and video shooting
* Good ergonomics all around, good build quality, nice handling
* Very compact design
* Excellent digital level gauge in EVF/LCD
* Useful Fn menu allows direct access to many important settings
* Very usable manual focus mode (including up to 15x image magnification)
* Lots of cool features - 10fps, Auto HDR, Multi-shot NR etc., (automatically selected in Auto+ mode)
* Auto+ mode makes the various continuous shooting modes (see above) available to novices
* Efficient image stabilization system
* Built-in GPS handy for organising images (though it can struggle in built-up areas)
Conclusion - Cons
* Limited control in 10fps and movie modes
* AF system not quite up to capturing fast action
* No live view in 10fps/6fps shooting makes panning almost impossible
* Slow (50 seconds) buffer clear time (RAW-mode)
* Little control over high ISO noise reduction ('auto' or 'weak')
* Visible loss of detail at anything over ISO 400 (noise reduction too strong)
* Menu system a little confusing (hard to orientate yourself sometimes)
* EVF slightly more prone to RGB 'tearing' than competitors
* Image review not separately configurable for EVF and LCD
* Awkward to navigate between stills and movie playback modes
* LCD unusually prone to finger prints and smearing (reducing visibility in very bright light)
Overall conclusion
Arguably, the age of the consumer-level DSLR dawned in 2000 with the Canon EOS D30, and although a lot has happened in the intervening decade - higher and higher pixel counts, huge improvements in low-light image quality, speed and usability - much has remained the same. A surprising amount, actually. Mechanically, today's DSLRs operate in exactly the same way as their film predecessors. A Sony Alpha A900 might look very different to a Pentax Spotmatic, but the basic principles of their operation are the same.
The Sony Alpha SLT A55 and A33 are completely new designs which offer several key advantages over 'traditional' DSLR technology. Their large, bright EVFs are at least a match for conventional optical finders in many situations (and better than the finders in the majority of entry-level DSLRs) and full-time phase-detection AF in movie mode is a revelation compared to the slow, clunky contrast-detection focusing that we've become used to in live view from some other cameras.
The 'headline' 10fps shooting mode is useful in some situations, but ultimately we can't help feeling that it is something of a red herring. The A55 is an excellent camera but it is not the ideal tool for shooting fast action. The limitations of using the 10fps mode - (no live view updates, no aperture control if you want AF during the burst) limit its effectiveness, and although it is good for its class, the A55's 15-point AF system is not in the same league as higher-end cameras when it comes to predictive focusing. This shouldn't be taken as a serious criticism (the A55 is after all a mid-range camera), but anyone looking for EOS-1D Mark IV AF performance on a budget will be disappointed.
Image Quality
The A55's 16.2MP CMOS sensor is new, and in collaboration with the camera's image processing, it offers excellent image quality. Detail capture is excellent at low ISO settings, though strong noise reduction does take its toll on detail at anything over ISO 400 (though it must be said that we're talking pixel-level detail here, which isn't something most people are going to worry about when shooting at ISO 1600).
Although we are currently unable to take a detailed look at the A55's RAW output, JPEG image quality is promising, and - for normal viewing magnifications, remains useable up to ISO 12,800 in a pinch. At lower ISO settings the A55 is able to resolve almost the same amount of visible detail as the Canon EOS 550D, which is currently the highest resolution camera in its class. Dynamic range is excellent too, at almost 9EV, which matches the best of the competition.
The A55's extension ISO 25,600 setting, where 6 JPEG images are taken in quick succession and blended together to reduce noise is interesting and, assuming your subject is static, it works very well. Because it's a JPEG combination mode this highest setting is not available in RAW - it's a shame as we'd be curious to see what careful processing could get out of such a file.
Overall, image quality gives little cause for complaint (and is often excellent), with reliable exposure, color, white balance and focus (when not shooting at high burst rates) reliable enough that you can concentrate on the important stuff, like framing and actually taking the picture.
Image quality in movie mode is very good too, and like the NEX-5, the A55 can produce excellent HD movie footage in either Motion JPEG or the more efficient but slightly awkward AVCHD format. Some rolling shutter effect and occasional focus-shots are visible in certain shots, but no worse than other video-enabled cameras in its class.
Handling
The A55's handling is defined by its innovative design. In use, the A55 feels like a cross between a good midrange DSLR and a high-end 'bridge' model, but its focus system and large, high-resolution viewfinder surpass our expectations of both types of camera. Because the A55's EVF is so large, it easily matches most optical viewfinders for clarity, and outclasses most of Sony's own Alpha DSLR range. Compared to the A55 the viewfinder of Sony's own Alpha 550, for example, is simply unpleasant - cramped, dim and low in contrast.
That said, a lot of the display area is wasted when shooting in the 3:2 aspect ratio. Even when shooting in 16:9, there are still two narrow bands of unused pixels at the top and bottom of the main image. This isn't a problem, (the image is certainly crisp and detailed enough) but it is a little odd. And it means that when the A55 is shooting in its highest resolution mode, the scene area is covered by roughly 80% of the total 1.44 million pixels, leaving 20% effectively unused.
In most respects, the A55 is a pleasure to use. Its control layout is to some extent 'classic' Sony Alpha but the changes that have been made compared to a model like the A550 make it easier, and more pleasant to operate. No longer, for example, is the ISO button blocked by the neck strap, no longer do you have to switch into a separate live view mode in order to magnify the image for accurate focusing and no more do you have your shooting experience interrupted by warning of mode/feature conflicts.
The A55 also features the neat 'Fn' menu that is so sorely lacking in the NEX-3 and NEX-5, which makes accessing most key settings very easy, and saves diving into the rather tedious menu system (which is badly in need of a refresh). Poorly signposted menu aside, in terms of handling, the A55 is definitely our favorite Sony Alpha since the much-missed Alpha 700.
The Final Word
With the Alpha SLT A55 (and its near-relation the A33) Sony has thrown down the gauntlet to the other major manufacturers. These new cameras are both genuinely innovative, and very capable. Sony first introduced phase-detection AF in live view mode with the A350, but the A55 takes things to a completely different level, thanks to its fixed mirror design. Rather than being an optional mode with some disadvantages (less than 100% view, no magnification in Fast AF Live View mode) live view is absolutely integral to the A55's operation and works very well.
Coupled with what appears to be an excellent sensor, and good ergonomics the A55 must count as one of the strongest contenders in its category, and one that in some respects completely re-aligns our expectations of what is possible in consumer-level equipment. Naturally though, we have some criticisms - when shooting fast action the A55's 15-point AF system cannot deliver on the promise of its 10fps shooting rate, and the lack of live view refreshes except at its lowest 3fps setting makes panning very hard to judge. The lack of aperture control in AF-C mode at 10fps is an inevitable but unfortunate consequence of full-time AF, too, and manual control over movie shooting is limited as well.
Ultimately though it is the 'bread and butter' stuff - the excellent all-round performance of the A55's key systems, its fluid ergonomics and largely hassle-free handling that really make it stand out, and we have no hesitation in giving it a gold award.
