我也在想，网上找到的优缺点，不知道有用否
50D----
Pro:
• Excellent 15.1 megapixel sensor with very low noise and superb detail
• ISO 100 to 1,600 usable at 13x19 inches
• Dust removal technology reduces sensor cleaning chores
• High-resolution 3.0-inch LCD makes checking focus and composing in Live View an excellent experience
• Status display includes more detail
• Quick menu integrated into rear Status display for fast changes without delving into menu
• Two Camera User Settings on mode dial
• Print/Share button enables quick and easy printing and image transfer
• Live View button frees up Set button for other purposes
• Fast image transfer eliminates the need for a card reader
• Excellent grip for most hand sizes
• New Creative Auto mode
• Live View mode is great when shooting from odd angles
• Live View works from computer via cable or WiFi (with WiFi grip)
• Interchangeable focusing screens
• Picture Styles makes choosing and customizing color modes fast and easy
• Compatible with over 50 lenses and accessories
• Uses CF cards like most other Canon digital SLRs
• Selectable auto-rotation feature rotates on the camera or only in the computer
• Large buffer depth allows for many followup shots
• Excellent detail from the sensor
• Highlight detail is well preserved at default settings
• Highlight Tone Priority makes it even better
• Adjustable Auto Lighting Optimization
• Images are sharp, but not oversharpened, and noise suppression is kept well under control
• Noise suppression is also adjustable
• Color is very accurate, with only red being a little off, which consumers generally like
• Auto white balance handles most situations very well
• High ISO images are impressive, all the way up to ISO 3,200
• Print quality is excellent, making sharp 13x19-inch prints
• RAW images can easily produce 20x30-inch images
• Great shot-to-shot, shutter lag, and cycle time numbers
• RAW files are very clean
• Under-3-second flash recycle time
• Sealed flash hot shoe
• AF microadjustment
• Vignetting correction
• HDMI Output
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Con:
• AF assist only works when flash is up, though flash can be forced off
• Auto-rotation doesn't play well with all computer programs
• Soft images with the 28-135mm kit lens; demands very good optics
• Kit lens doesn't really reach wide angle
• Indoor white balance is a little yellow
• Battery capacity is reduced from the larger screen and dust off system
• Autofocus sometimes just seeks and seeks
• AI Servo autofocus mode is not reliable
• Some horizontal banding at ISO 6,400 and worse at 12,800, making those
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D90
Pro:
• Exceptional feature set for its price point in the market
• World's first SLR capable of recording HD-resolution video
• New kit lens has good optical quality, much better than average for kit lenses
• New kit lens offers VR (image stabilization)
• Camera automatically corrects chromatic aberration in camera JPEGs, further increasing the apparent quality of the lens
• Great dynamic range, among the best we've seen
• Excellent high-ISO performance
• Active D-Lighting (brought over from the D300) is a worthwhile feature
• Excellent user-interface design
• Fast AF system, good shutter response
• Higher-endurance, 100,000-shot rated shutter mechanism
• Faster 4.5 frames/second JPEG improves on D80 (but again, with specific settings only; enabling AF, using shutter speeds below 1/250 will slow frame rate, ISOs of 800 and higher will drastically reduce buffer depth.)
• AF system works down to very low light levels, even without the AF-assist light
• Bright AF-assist lamp does not require flash to be deployed
• LCD display is well organized and informative, auto rotates; 3.0" screen quality is superb
• Magnified Live View display helps with manual focusing
• Supports older non-AF-S lenses (screwdriver-type AF drive available, with in-body focus motor)
• Kit lens focuses down to 17.7 inches (from focal plane) at any focal length
• New automated dust-removal system
• Accurate and consistent metering, works to very low light levels (but only in manual mode at the darkest levels)
• Nikon 3D matrix metering produces very accurate flash exposures
• Onboard flash is quite powerful, has good range
• Built-in flash supports Nikon's Creative Lighting System (wireless flash control) with any CLS-capable external flash units. (Camera can be controller, no need for separate flash to be attached to the camera as a controller.)
• Grip is comfortable for a wide range of hand sizes
• Programmable function button is very handy, position under right middle finger is convenient, makes it easy to manipulate main command dial at the same time
• Playback zoom operation is very convenient
• Playback display is very fast, refreshes quickly as you scroll through captured images
• In-camera "retouch" menu is great, permits significant image adjustment without resorting to the computer
• Able to "develop" RAW-format images into JPEG files in-camera
• RAW+JPEG mode offers fine/normal/basic JPEG quality settings
• Four-way controller disc works well
• Strap eyelets are recessed, won't gouge your hand when holding the camera
• Very extensive custom function menu
• Digital "image overlay" permits creative multiple-exposure shots
• "Pictmotion" Stop-Action movie mode is a lot of fun (great with kids!)
• Very fast downloads to a computer
• Optional wireless remote control transmitter available
• Supports new Nikon-branded GPS receiver for automatic geotagging of images
• Uses same MB-D80 battery grip as D80 - Nice for D80 users moving up, and a good grip on its own merits
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Con:
• "Rolling-shutter" motion artifacts in HD movie recording are distracting
• No provision for external audio input for movie recording
• Autofocus in Live View mode is slow, limited to contrast-detect only; no phase-detect AF option with Live View
• Magnification/resolution in Live View mode isn't as great as it could be: More resolution at maximum magnification would make it easier to focus manually
• 1/200 second x-sync speed for flash isn't quite as high as some competing models
• Maximum frame rate of 4.5 fps is lower than competing models
• Adding battery grip doesn't increase shooting speed
• Auto white balance setting doesn't handle household incandescent lighting well
• Some kit lenses focus closer than the 18-105mm does
• Limited support for older, non-CPU lenses
• AF assist lamp may be blocked by your fingers when holding the camera
• AF point is easily changed accidentally by hitting the four-way control pad while shooting
• Battery charger requires large external cord, just one thing more to lug along on a trip
• Bundled software gives only limited processing options for RAW conversion
