Viewfinders vary widely and, even within the same type of viewfinder, the experience still varies. Among optical reflex viewfinders, the difference between the best and the worst OVF is easily visible but does not impair working that much. The same cannot be said about electronic viewfinders. It may sound obvious but:
Good EVFs are very good and bad EVFs are really bad
For this reason, it is crucial to know how well an EVF works. Unfortunately, specifications alone only tell a very minor part of the story and one had to read camera reviews which pay attention to viewfinder-ergonomics if you cannot try the camera in various conditions yourself. Here are differences to pay attention to:
- Resolution: EVFs exist with resolutions of 115,000 pixels all the way to 2.4 megapixels. This makes a significant difference in showing fine-details. Anything below 1 MP generally spells trouble. At 1.4 MP and up, one can at least see when a camera has focused properly or not. This number is almost always quoted in camera specifications.
- Size: Various sizes of EVFs from 0.2″ to 0.5″ are used in digital cameras. This is the physical size of the viewfinder. However, an optical element in front of it may provide some magnification. For this reason, comparing viewfinder size is not exact yet it remains a good indicator. A large viewfinder, at least 0.4″ diagonally, makes it much easier to identify small details. When taking photos of people, animals or other changing objects, this can greatly help to see when no one is blinking and expressions are good. EVF size is frequently specified.
- Magnification: This number relates the perceived size of the viewfinder relative to the camera’s sensor-size. Dividing the magnification by the crop-factor gives an absolute measure of apparent-size. Anything above 0.6X, so 1.2X on a Four-Thirds camera, or 0.9X on an APS-C one, shows a large and bright view. As a comparison point, top-of-the-line full-frame DSLRs have a viewfinder with 0.7X or more of magnification. See DSLR viewfinder sizes for more examples. This number is seldom quoted.
- Dynamic-Range: The dynamic-range of an EVF affects its usability when faced with high-contrast scenes. Ideally, the DR of the EVF should match or exceed that of the sensor. When the DR is too low, some part of the scene will appear over-exposed or under-exposed without being so. Crucially, one is not capable watching what happens in areas where the EVF does not show any details. This is illustrated in Luminous Landscape’s Why I Hate EVFs.
- Brightness: As a viewfinder, an EVF’s sole purpose is to let one frame subjects. In normal daylight conditions and typical household lighting, EVFs are easily capable of showing the scene clearly. When light levels are low, an EVF must be able to amplify the signal to maintain the preview sufficiently bright. The best EVFs can do so remarkably well and even amplify the image so that it is more visible than with the naked eye. This makes them usable even with a strong ND filter which OVFs cannot handle. On the other hand, poor EVFs become dim in low-light which makes the camera useless for such conditions. Those who intend to shoot in low-light must therefore know if an EVF can hold up.
- Lag: By its nature, an OVF is updated at the speed-of-light. EVFs are updated by reading the sensor and processing the RAW signal into a digital preview. The time it takes for this to happen causes a lag and is of great concern to action photographers. The latest generation of high-end EVF can update at up to 120Hz which makes for a very short lag. However, this lag is not fixed. In low-light conditions, most EVFs slow down to refresh rate in order to provide a bright display with less grain. This compromise is fixed on a digital camera, so some will produce less grain and more lag, while others will show more grain and less lag.
- Refresh Rate: An EVF is updated periodically, usually at between 15 and 120 Hz. A faster refresh-rate means a shorter lag and vice-versa. Action photographers should look for ones with high refresh-rates. Just as the lag is variable, so is the refresh-rate, so things nearly always slow down in low-light.
- Exposure-Priority: EVFs are very advantageous in that they can show a relatively accurate preview of how an image will be exposed. When they work this way, they are said to be Exposure-Priority. This is really nice to have and greatly reduces the need to check shots after they are taken. It also makes it clear when a change of exposure is needed. Keep in mind that Exposure-Priority is impossible when using flash, so most EVFs revert to Display-Priority when the camera thinks the flash will fire. Display-Priority shows a bright image regardless of exposure, so be sure to check shots regularly to avoid surprises. Unfortunately, not all cameras are Exposure-Priority even when they could be and some are neither that nor Display-Priority, rendering the view mysterious at best.
- HUD: This is a bonus feature of EVFs. A good EVF, combined with well thought-out camera ergonomics, lets the camera be completely operated at eye-level. At least one should be able to see a good amount of information on the EVF, including exposure-parameters, battery-status, digital-levels, image-parameters and other modes. The flip-side of this is that some EVFs show too much information and watching the edge of the frame for proper framing becomes quite difficult.
If we were not worried about EVFs before, this should give you plenty of reasons! It pays and will remove plenty of frustrations to read about how a camera’s EVF performs. At the same time, one can also see how far the very best EVFs have come since their invention.