Has anyone else ever considered whether we're headed toward electronic viewfinders (EVFs) someday? It seems to me that they'll make sense once the technology advances far enough, specifically if they could get the pixels of the viewfinder small enough so that your eye couldn't tell the difference between looking through it or a pentaprism viewfinder.
Here are some pros that I can see:
1. No mirror to design lenses around. The lens can come up as close to the sensor as you'd like. I'm not an optical engineer, so I don't know how much of a constraint it actually is.
2. No prism. This should cut down on weight and perhaps size (I guess it depends on what the optics for the EVF look like before you can actually say either size or weight will improve).
3. More versatile camera status display. I'm currently annoyed that on my D90, I have to choose whether to have either the number of pictures remaining on the card or the ISO in the viewfinder. I choose ISO, but it would be nice to have complete customization of what's displayed in the viewfinder, including a real-time histogram to help with exposure (I almost exclusively shoot manual and watch the meter, but a live histogram would be so much more useful to me than the segmented meter display). You could also have it display in B&W but simulate different color filters for B&W photography.
4. More extensible (if that's the word I'm looking for). Imagine having something like that Nikon UP300x that has an eyepiece that could display your EVF image while you point the camera however and wherever you want. I'm guessing that would be sweet for photojournalism. I'd love it for weddings, even though it would make me look like a cyborg wedding photographer. For someone who mods their camera to shoot IR, it could also double as a night vision scope.
5. 100% accurate viewfinder frame coverage. No more guessing at how much of the edge is missing from your VF image (I know some cameras have 100%, but every camera with an EVF would).
6. Takes advantage of sensor's amplification circuitry. I'd rather not have around half of the light lost from bouncing around in the prism. I'd love to be able to see in the dark, which is about what you can do with the ridiculously high ISO sensitivities available these days. Besides, you could amplify it for the EVF but shoot at a lower ISO if, for example, you were going to shoot a long exposure.
and the cons:
1. No phase-detected autofocus. Yikes! Is this enough to kill the idea? I can't see a way to overcome this since as I understand it you actually need a prism between the lens and the sensor to do phase AF. Someone brilliant may prove me wrong, though, and there might be a way to improve the contrast AF algorithms or speed up the processors running them to get AF times to an acceptable level. Alternatives could be some other type of ranging--maybe infrared laser or ultrasonic pulses (hey, laser ranging works for golf caddies, right?). I'm imagining a touch screen under my left thumb that lets me tell the camera where to focus, while the camera tracks that location and superposes a small box on the image in the EVF that changes color when it's focused.
2. Sensor overheating and battery life issues. These could be overcome by improving the efficiency of the sensor's circuits, but for now heating is a problem--you can actually feel the D90 or the D300 heating up in live view mode.
3. Not completely real-time. Imagine the rolling shutter (jello) effect in your viewfinder. On second thought, don't, it's making me dizzy. Could this also be fixed, maybe alongside improvements to the video of newer cameras?
Does anyone have any other pros or cons? You can also call me a looney, but I'm convinced that someday (maybe soon) it will be an option.