But ouch — that name. Even if you know what S.L.R. stands for (“single-lens reflex”), you have no idea what it means. “Single lens” is misleading, because the whole point of these cameras is that you can attach dozens of different lenses. And to most people, “reflex” refers only to wincing when they see the price.
Kidding aside, historically, there was a point to the term “single-lens reflex” (yes, I use Wikipedia, too). It describes the mirrors and prisms inside that bend the light from the lens to your eye.
Recently, a new generation of mirrorless cameras have hit the market. They look and work like S.L.R.’s — interchangeable lenses, no shutter lag and so on — but they’re smaller and they capture high-definition video. (Since they’re not technically S.L.R.’s anymore, Popular Photography magazine proposes the term I.L.C. for them, for “interchangeable-lens compacts.” Let’s run with it.)
Sony’s new Alpha A55 camera, available in October ($850 with 3X zoom lens), is an S.L.R. — sorry, an I.L.C. — that changes a bunch of games at once. It accepts any of Sony’s existing 33 Alpha lenses, but its radically different guts give it talents no other camera has had before.
This will require a paragraph or two of technical slogging, but you’ll feel rosy and smart when it’s over.
In a typical S.L.R., light from the lens hits a mirror, which bounces light up to your eye and onto a focusing sensor. The blessing: you see what the lens sees. The curse: when you take the actual photo, the mirror has to flip out of the way so that the light falls on the main image sensor (the “film”). For that fraction of a second, the camera can’t focus. If someone or something is hurtling toward you, a typical S.L.R. may have trouble keeping rapid-fire shots in focus.
That’s also why most S.L.R.’s can’t change focus when you’re shooting video. If you start filming on something close up, and then pan to something across the room, the video goes out of focus.
Still with me?
All right. Sony’s A55 camera adopts a new spin on a decades-old photographic idea: the mirror is translucent. It splits light between the focusing sensor and the image sensor — all the time. The mirror never has to flip up to take a picture, so the autofocus never goes blind when you take a shot.
As a result, the camera can shoot an incredible 10 shots a second, refocusing all the way. Sony says no other camera in the world can do that.
The camera also shoots beautiful, high-definition video — and it can change focus as you pan the camera, gorgeously and cinematically.
Very few S.L.R.’s, or even I.L.C.’s, can do that trick, refocusing while filming.
But the Sony doesn’t just change focus in video. It changes focus fast. According to Sony, the A55 is the first camera — or camcorder, for that matter — to use what’s called phase-detection focusing for video. (Other cameras, and all camcorders, use a slower system called contrast detection.) That’s only possible because, in this camera, the autofocus sensor can see the scene all the time.
Now, to pull off this unusual design, something had to go, and it was the optical viewfinder. When you hold this camera to your eye, you’re basically looking at a tiny TV screen in the eyepiece, rather then peering out through the glass of the lens. In other words, it’s an electronic viewfinder.
Photographers usually pooh-pooh electronic viewfinders, because no screen is as sharp as real life. But Sony’s viewfinder is extremely big, bright and sharp (how does 1.4 million pixels strike you?). And having a screen in the eyepiece gives you all kinds of advantages you don’t get when you’re just looking through glass.