While people are divided on whether an electronic viewfinder (EVF) or an optical viewfinder (OVF) is better, most have a strong preference based on what they are used to. DSLR users, by definition, use an optical viewfinder which is based on the well established design that has existed since the launch of the first SLR camera.
Mirrorless cameras, on the other hand, use an electronic viewfinder as they cannot have a reflex optical viewfinder that sees through the lens since they lack the mirror to bend the light path that way. The good news is that companies have been working hard at improving EVF technology.
There are both advantages and disadvantages to EVFs compared to OVFs. The very best ones with high-resolution and high-refresh rates are actually quite suitable for most uses when well-implemented.
EVFs can have the following advantages:
- WYSYWYG: With an Exposure-Priority display, like those of Sony SLT and NEX cameras, you see something much closer to the results before shooting. With an OVF, you see with your eye and therefore have no way of knowing how an image will be exposed. The same is true of White-Balance.
- Sensitivity: EVF are electronic and can have the signals amplified to produce a bright image even in dark conditions. This makes them usable for framing with ND filters. When using a very dark filter, say an ND400 for example, an EVF still shows an image while an OVF becomes too dark.
- HUD: An EVF can show detailed information overlaid on the image, including a Live-Histogram and detailed camera status. One can also navigate menus and change almost any setting with the camera at eye-level.
EVFs also have disadvantages:
- Lag: There is a short lag between action happening in front of the camera and what you see.
- Dynamic-Range: EVFs are small LCD screens and have limited dynamic-range.
Lag is a problem for action and photography where following action is critical. The limited dynamic-range means that it is possible for areas to be either fully white or full black without any details even though details will be captured.
A few aspects are not so clear-cut:
- Focus: With 1.5 – 2.4 MP EVF it is now quite easy to judge focus. The same cannot be said about most EVFs which have around 200K-350K pixels. Additionally, a lot of cameras can magnify the EVF to assist MF and some can highlight high-contrast edges which is called focus-peaking. The remaining problem for manual focus is lag. Just like the EVF lags action, it lags behind the focus-ring too and on some cameras it is rather hard to get focus exactly right without back-and-forth movements.
- Coverage: The vast majority of EVFs show 100% coverage. For OVFs, it is sadly the minority.
Keep in mind that implementations vary widely and plenty of EVFs are inexplicably not Exposure-Priority and some do not show the ideal image brightness in low-light. Some EVFs also show an incorrect Live-Histogram.
There are also some minor annoyances such as the need for a camera to be on to see something. With an OVF, it is possible to frame and focus (except for lenses with fly-by-wire focus rings) while the camera is off.
Finally EVFs require a lot of power, often as much as having the rear LCD on, despite being smaller. This makes battery-life similar to using Live-View and roughly half of what it is with an OVF. The actual drain depends on the specific camera of course, usage and power-saving settings.
All in all, modern EVFs are quite usable and Exposure-Priority ones are more helpful to photographers under most circumstances other than fast action.