Tech

Autofocus Blues

| Sat Oct. 17, 2009 3:02 PM EDT

The world's digital camera manufacturers are driving me crazy.  As longtime readers may recall, I'm an obsessive fan of the articulated LCD viewfinder.  I use mine constantly.  I use it when I want to shoot from waist level or ground level.  I use it when I want to shoot over a crowd.  I use it when I have to hold the camera at a weird angle to get the shot I want.  I use it when I have to steady the camera on some handy rock (or whatnot) and can't crane my neck to look through the viewfinder.  I use it when I'm photographing documents and have to point the camera downward while steadying myself on my elbows.  I use it when the sun is washing out the screen and tilting it a bit helps me see better.

Given all that, I find it odd that articulating LCDs aren't really all that popular.  To me, they're really, really useful, not just some dumb gadget that only a hopeless newbie would seriously think of using.  But apparently the world's serious photographers aren't buying this, and as a result there aren't very many cameras that have them.  I bought a Canon S5 (shown above) a couple of years ago because it was the best I could find with an articulating LCD, but overall it's only so-so.  I'd love to get something better.

So then: why aren't there any DSLRs with articulating LCDs?  Well, there are.  Over the past year three or four have been introduced.  They tend to have weird ideas about how exactly the LCD should move around, but obviously they're getting the idea.  The Nikon D5000 is one of the latest entrants.

But it turns out there's a weird problem with these cameras that I can't find an explanation for.  Maybe someone can help me out.  There are two ways of implementing autofocus on a digital camera: phase detection, which is very fast and is used on high-end cameras, and contrast detection, which is used on everything else.  As I understand it, phase detection requires a mirror, which is why it's available only on SLRs.

Unfortunately, it's apparently hard (impossible?) to implement phase detection in a camera that also has a live-view LCD — that is, one in which the LCD displays the scene continuously.  Needless to say, that's something I want.  But I don't understand why live-view is incompatible with high-performance phase detection autofocus.  Is it a cost issue?  A technical problem?  Or what?

Every time I read about this, things get very fuzzy (no pun intended) when the subject comes up, and I've never really found a good explanation of what's going on.  But the D5000, for example, which has excellent shutter lag and AF acquisition specs when live-view is off, apparently turns into a horrible focusing slug when live-view is activated.  It not only uses contrast detection, but evidently uses a really slow, crappy version of contrast detection that makes the camera almost useless.

This is obviously annoying personally, since I'd love to hand over vast sums of money to Nikon to buy one of their cameras if it actually worked decently.  But at this point, it's mostly technical curiosity on my part.  Anyone know what the deal is here?

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