Tuesday, February 2, 2010

The A500's Metering has Nothing to do with Face Detection


 In December's blog entry I raved about how unexpectedly good the A500 / A550's metering system was, and at the time I had attributed it to the integration of Face Detection into the metering algorithms.  It made perfect sense, and if I were on the design team, I too would have said, "Hey, look, it's reasonable to assume that the face is what you want to focus on, and it's equally reasonable to place a great emphasis on the light on the face when determining what the exposure should be!".  Placing such emphasis on the face meant getting great shots in very difficult light - even shots of people who are backlit!  (See the December blog for examples.)

It turns out that I was completely wrong.  I did some follow-up tests with a backlit subject and shot with Face Detection ON and OFF, with Live View ON and OFF, with Multi-segment metering and Center-weighted metering, and even with Autofocus set to ON and OFF.  They ALL came out exposed identically to the left figure above.  So Face Detection really had nothing to do with it.  Then I grabbed my A700 and took the same shot of the same subject.  It took a darker shot, as I have been trained to expect from all built-in light meters made since the 1960's.
This is both a welcome surprise and a little unsettling.  It's welcome because don't we all want the camera to just "make the picture look like what I'm seeing right now?" when we're shooting snapshots, and not have to think like an engineer?  It's unsettling because I spent a considerable amount of time in my career understanding how exposure meters worked, knowing under what circumstances they would fail, and how to compensate for it (and by how much) when they do.  This new behavior tosses that knowledge out the window.  (Of course it would be worse if I were still shooting slides.  At least with Live View you can know right away if your camera's making the right decisions or not, and with Exposure Compensation you can make whatever changes are necessary on the spot.)

So what's going on?  Here's my best guess: A few key guys from Sony's camcorder division were loaned to the DSLR division to help with the metering algorithms.  For at least a decade I have always been impressed at how camcorders from all major brands handle difficult light much better than your typical DSLR.  And now it seems that that knowledge is starting to creep into our modern cameras.  Is this a good thing?  Well, the truth is that I rarely ever have to invoke Exposure Compensation with the A550.  The other truth is that the new algorithms do a miserable job of fill-flash on a bright day in AUTO mode (as documented in the December blog).

And speaking of the A550, the new book on this camera is out!  Click here to learn more.  And it, like my other titles, a Spanish version is available as well.

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