Sony A55 Viewfinder
Sony A55V Viewfinder
The Sony A55V features a translucent mirror design that necessitates use of full-time live view, and so adopts an electronic viewfinder, rather than the true optical viewfinder of a traditional SLR. (While it would perhaps have been possible for Sony to adopt a true optical viewfinder using light reflected by the translucent mirror, as was done with certain film SLRs in decades gone by, it would by necessity have been very dim. Hence, the decision to use an EVF is undoubtedly the correct one.)
An important advantage of the Sony A55's electronic viewfinder, as compared to a tradition SLR's optical viewfinder, is that the effect of white balance, exposure settings, and the like can be previewed. This allows the photographer to better understand what to expect from their final image. Also, since an EVF can display essentially anything the main LCD can, it allows you to view the same overlays that you'd see on the LCD, including things like a live histogram that would be simply impossible with an optical viewfinder. (A full list of the possible overlays that can be shown on the electronic viewfinder can be found on the Operation page. The only display mode offered by the A55's LCD that isn't available on the EVF is a full-screen status display that simply wouldn't make sense to use with the viewfinder, since it would prevent any view of the subject itself.) If you're suitably familiar with the A55's external controls, the EVF even allows you to browse menus and quickly change settings without taking the viewfinder away from your eye. Optical viewfinders have advantages of their own, though. They use no battery power, providing a significant advantage over framing images on an LCD display -- and this is particularly significant given that the A55's EVF actually uses more power than the main LCD panel does. (Battery life with flash usage, to CIPA standards, is rated as 390 shots when using the LCD, but falls significantly to 350 shots with the EVF.) There's also something to be said for the image viewed through a really nice optical viewfinder, something even the best electronic finders struggle to match with current technology.
We don't currently have details on the precise viewfinder type employed by the Sony SLT-series cameras, but Sony describes it as a 0.46-inch diagonal (0.43-inch effective) Xtra Fine LCD Tru-Finder. Whatever the type, it clearly employs a time-multiplexed method to display red, green, and blue color information at every pixel location, suggesting that it is likely to be a ferroelectric LCD. These differ from traditional LCD displays, which mostly create color information with a cluster of three adjacent red, green, and blue subpixels (commonly called 'dots'), for each pixel location. When compared to standard LCD electronic viewfinders, ferroelectric types bring both advantages and disadvantages. They've proven somewhat divisive in the past, due to their tendency to demonstrate RGB "rainbow" artifacts when you blink or move your eyes, or with fast-moving subjects. On the positive side, though, since each pixel provides full color, ferroelectric LCDs tend to look much smoother and more detailed than their traditional LCD siblings, with less obvious pixel structure. They also tend to have higher refresh rates, and indeed Sony specs the EVF used in the A55V, A55, and A33 as offering a 60Hz refresh rate. It's perhaps not surprising to see such a display adopted by Sony, since Konica Minolta -- the company Sony absorbed to create its DSLR division -- was a particular proponent of their use.
We're pleased to report that the EVF in the Sony A55V, A55, and A33 provides better dynamic range than most. Resolution is good, with no noticeable gaps between pixels, and the EVF also does a decent job of preserving highlight detail in high-contrast scenes. The slight distraction caused by the "rainbow" effect is relatively easy to ignore in most usage. In spec sheets for the A55, Sony lists its EVF as having 1,440,000 dots, of which 1,152,000 are effective in the viewfinder display. We believe that the company is following precedent here, by simply reporting a dot count as if each pixel consituted three separate color dots, rather than being time-multiplexed. If that's the case, the actual pixel resolution would be 480,000 total pixels, of which 384,000 are effective in the final image.
It's a little unusual to see an effective pixel resolution for an electronic viewfinder, but we believe the reason effective resolution is some 20% lower than the EVF's actual pixel count is that Sony have selected an LCD with approximately a 4:3 aspect ratio, but are only using the central 16:9 aspect ratio swathe of the display. This is likely done both to match the rear-panel LCD display aspect, and also because even with this crop, the EVF already has a generous 1.1x magnification -- much higher than that of most APS-C DSLRs -- and a somewhat tight eyepoint of 19mm from the viewfinder eyepiece (18mm from the eyepiece frame). Were the whole display used, the eyepoint would fall uncomfortably low -- it's already just a little tight for eyeglass wearers. Thankfully, it includes an unusually wide -4 to +4 diopter adjustment range, better mitigating the tight eyepoint for those with eyeglass prescriptions inside this range. The EVF also has a 100% field of view, and provides three step automatic / manual brightness control.
A pair of horizontal infrared sensors, visibly just beneath the viewfinder in the image above, detect your eye as it approaches, and deactivates the tilt / swivel LCD display if you have the Finder / LCD Setting option in the Custom menu set to "Auto". Alternatively, you can disable this function and switch between displays manually, using the Finder / LCD button. This might be advisable if you tend to leave the camera switched on and hanging on its neckstrap, given that it can't diffentiate between your eye and chest, and will potentially waste battery life by switching to the more power-hungy EVF panel. You can also set the infrared sensors to initiate autofocus whenever your eye is in range of the eyepiece (Eye-Start AF), which makes the A55's autofocus seem even more responsive.
Viewfinder Test Results
Excellent accuracy from the electronic viewfinder and LCD monitor.
The Sony Alpha SLT-A55V's electronic viewfinder and LCD monitor showed slightly above 100% coverage with our Sigma 70mm f/2.8 prime lens. This is excellent performance, though not a surprise given the viewfinder is electronic and is deriving its image from the main imaging sensor.