The electronic viewfinder (EVF) in the latest Sony DSLT cameras, including the A77 and A65, tries to show you the scene you are shooting as it will appear in the capture file. If you're photographing a scene with a dynamic range that the camera can handle easily, then it can be said that the EVF is WYSIWYG ("what you see is what you get"), at least with respect to exposure. What you see through the EVF is going to be too dark if it's underexposed, too bright if it's overexposed, and just right if it's, um, exposed just right. By way of contrast, if you are shooting the same scene with an old-fashioned optical viewfinder (OVF), what you see through the viewfinder is not what you're going to get at all.
Here for example is a shot taken with my A580, which has an OVF:
The scene I saw through the OVF looked fine, because it's midday and my dining room (where I took the shot) is well lit. The problem is, the camera was in M mode and the exposure settings were way off. Now I knew this because the exposure meter shown beneath the image in the OVF indicated that the shot was overexposed by more than 2 stops. Experienced and careful photographers would notice that little meter and respond to it. But they wouldn't know just how overexposed the shot was going to be. The overexposure was outside the exposure meter's range. It's like having a thermometer that only goes to 100° F. If it's at 100°, you know your kid has a fever, but you can't tell if it's 100.1, or 106.
If I'd taken that shot with the A77, and if the settings had been off by the same amount, then the image above represents pretty well what I would see through the EVF. That's WYSIWYG.
EVF and high-contrast scenes
Of course, the EVF isn't perfect. One of the criticisms of the EVF in the latest Sony DSLT cameras is that it doesn't "do a good job" in high contrast scenes. There is some truth to this claim but not as much many people think.
I hope I can be permitted a little paradox. The A77's EVF is indeed WYSIWYG. What it is NOT is WYSIWYS: What You See [through the EVF] Is What You See [looking directly at the scene].
What I mean is, your eyes can respond well to a high dynamic range scene; the camera, not so much. That's true of all digital cameras. Now the EVF shows you what the camera "sees". Now this precisely what makes the EVF so valuable. But yes, it is occasionally a problem. If the dynamic range of the scene is high, you're going to blow something out somewhere. And if you're looking through an EVF, you'll see the problem directly.
Here's an example I just shot from my front porch. It's an overcast day here in Dallas so this example isn't as dramatic as it might be if it were a bright day. But I think I can make the point anyway. The next two photos are two versions exported from the same raw file. The raw file was exposed for the sky (pointed camera at sky and locked exposure, then recomposed and focused). This first shot shows pretty well what I saw looking through the EVF:
That's an export from the raw file with no adjustments.
Now, here's what I was able to tease out of the same raw file, using Lightroom 4. This represents more closely what my eyes actually saw when I looked at the scene directly:
With this in mind, perhaps I should say that the EVF is WYSIWYGI: "what you see is what you get initially", where "initially" means "before post-processing." Taking photographs requires that you know what you're doing and trust your equipment. This has always been the case.
Advantages of EVF
So does this make the EVF good or bad? Neither. It makes the EVF different. Okay, perhaps that's a bit too diplomatic.
An OVF doesn't tell you if the scene is properly exposed and, if it's not, the OVF doesn't tell you what the faulty exposure will look like. Yes, the exposure meter below the image in an OVF gives you some technical info which an experienced photographer can interpret pretty reliably, especially if the exposure isn't so far off that it's outside the bounds of the meter. If I'm shooting in M mode with an OVF camera and the meter says the shot is one stop "overrexposed," I know how to decide for myself if that's really a problem or not. If I am shooting in a hurry and forget to look at the meter, well, drop by some time and I'll show you the photos I took when I shot my first wedding, at the moment that the wedding party stepped out of the church and into the bright sunlight. I was working fast, not looking at the meter, and admittedly, not thinking. I took a dozen badly overexposed shots and when I noticed my mistake, the bride was in the car and I couldn't redo those shots.
The EVF, on the other hand, will tell me this clearly — most of the time — and "directly," without requiring me to do any calculating based on my experience with the meter. Had I been shooting with an EVF at that first wedding five years ago, I'd have noticed the instant that I stepped outside that the exposure needed to be adjusted.
I suspect that I used to chimp more when using OVF than I do with EVF. In particular, I would look at the pictures I'd just taken to see the histogram or looking for "blinkies" (flashing areas indicating blown highlights or lost shadows). With the EVF, I can see what the camera sees and will record, before I trip the shutter.
Two final notes
First, this particular problem ONLY occurs when there is a pretty high contrast scene. That type of scene is a relatively small percentage of the stuff I shoot. The rest of the time, the EVF gives me a view that is entirely satisfactory for purposes of composition, focusing, noticing detail, etc.
Second, I have noticed that my ability to see detail in high-contrast scenes is worst when I'm wearing glasses and better when I'm wearing contacts, is greatly enhanced if I cup my free hand and place it up against the camera and my face, to block extraneous light, and I get the very best view if I put a light-blocking towel or cloth over my head and the camera. Okay, I look like a fool. But if you aren't willing to look like a fool, you shouldn't go into photography.