Archive | April, 2013

Why an electronic viewfinder (EVF)?

30 Apr

Much debate has surrounded the decision by some camera makers to replace traditional optical viewfinders with an electronic substitute, in which the user looks at an LED display rather than some direct optical projection designed to resemble the image captured.

Chief among these companies is Sony, who have gone as far as to implement such a system in a line of cameras that are direct successors to Minolta’s venerable film SLR business and early digital efforts (Sony continued the SLR legacy for a while after buying Minolta, then switched to its current “SLT” design). But why would you want a camera with an EVF?

As it turns out, there are a number of reasons, all controversially discussed at length among camera enthusiasts.

  1. An EVF protects your eyes. An EVF allows a manufacturer to completely control the spectrum emitted by the device. Therefore, UV radiation may be absent from such images, and there is no risk of blinding yourself by turning the camera at the sun – the image will never be brighter than the LEDs are capable of. Better to stress the sensor than your eyes, right?
  2. An EVF allows exact control of manual focus. While in SLR cameras, your eyes can compensate and thus give you a false sense of sharpness, an EVF gives you an image ”as the sensor sees it”. In this case, if the image is blurry, your eyes or brain can do very little to make it seem sharp. However, equally keep in mind that your assessment of the sharpness is limited by the resolution of the EVF, and small detail that would have been visible at the “retinal” resolution of your eye plus sharpness of your lens, may not be resolved by the EVF’s display.
  3. If sensor stabilisation is used, currently only an EVF can show you the image post-stabilisation, as it would appear on the sensor. So you’re getting a clear, jitter-free image. However, a brief excursion into stabilisation technologies is necessary here. Lens-based, “optical” stabilisation will give you a stable image no matter how you capture the image after it has passed through the lens – directly with your eye or through a display intermediary. Only with sensor-shift stabilisation technology does it make a difference where you capture the image. To give a full explanation of the pros and cons of lens- vs. sensor-based stabilisation, there will be another article in this series. What is important to remember is that image stabilisation never works perfectly. and so having to rely on it is always a flawed compromise. The combination of optical viewfinder and sensor-based stabilisation is perfect in at least this one sense, that it disciplines you to stabilise your camera properly, by giving you the means to learn how to do this. If the image is shaky, you will see it. And you will be able to counteract the shake – in fact, you will inevitably do so in an attempt to see the image better yourself. Additionally, keep in mind that sensor stabilisation drains your battery – this could lead to overall compromises such as a heavier camera with a bigger battery and bulkier grip, or the need for carrying spare batteries and swapping them out more often. In an OVF camera, the stabilisation will only be active during image capture, saving you battery life.
  4. An EVF allows displaying a brightened image in very dark conditions, where a “slow” lens on an OVF may not allow you to see much at all. However, this is counteracted by bullet point no. 4, as the above-mentioned alternate uses do not return the light for use by the sensor, but rather whisk it off to the side somewhere, in a little light prison. While an EVF may still not allow you to see in pitch darkness, it may be useful for older people whose night vision has declined. Also note that whatever noise the sensor generates will affect the EVF image, so younger people will likely prefer an OVF at night, especially with fast lenses.
  5. Compared to a through-the-lens optical viewfinder, which requires a mirror to be placed in front of the sensor to deflect the image towards the photographer’s eye, exclusive use of an EVF allows the mirror to be dropped from the design. This allows for a slimmer camera, but has several other benefits: (a) it eliminates camera shake that’s caused by the mirror, which is a major source of image blur at certain exposures (typically 1/100s), (b) it may allow lower shutter lag and higher frame rates because the mirror does not need to be used, and (c) it reduces the auditory noise emitted by the camera, useful particularly in street and wildlife photography. Additionally, in theory there does not need to be any blackout with an EVF; however, in practice, the image processing abilities of current-day cameras lag behind this theoretical tenet, for no particularly good reason.

Okay, that all sounds fairly good, so why wouldn’t you want an EVF? Disadvantages:

  1. We’ve touched on the lack of resolution.
  2. We’ve touched on the shorter battery life due to image stabilisation being permanently active except when the camera is already stable (e.g. tripod-mounted).
  3. Viewfinder lag. In the same way that we’re still waiting for blackout to be eliminated, we’re also being disappointed so far in that the transmission of video from sensor to viewfinder is not instantaneous with an EVF. Since there’s also no sufficiently large image buffer to allow shots to be recorded after they’ve happened, and panning decisions may have to be made instantaneously (or as close as you can get giving human reaction times) by the photographer, current-day EVFs can be frustrating to sports and wildlife photographers.
  4. No image when battery is drained. You can’t use your camera as a binoculars replacement. You may therefore have to additionally carry a pair of “binos”.
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