Thursday, December 11, 2008

Lens beating

Everyone worries about their lenses not being up to the task. Unless you're shooting architecture or test charts and are a pro, even Nikon's least lenses are up to the task. I'm more interested in how fast a lens is (lower f numbers are better), how good autofocus is, and whether or not it has VR (Vibration Reduction, called Image Stablization in Canon parlance and anti-shake in many mags) than I am in distortion and that sort of thing.

Even the best lenses can be pushed a little too hard. In between ryes tonight, I thought I might see how much abuse my best glass could handle. I was surprised. Our test subject is a Nikon Zoom-Nikkor 17-35mm f:2.8 IF-ED, which is capable of taking better photos than the D90 can capture (and frequently better than I can compose) and doubles as a self defense tool, it's so bloody heavy.

Ouch! Here we've got a terrible shot: that bright light in the photo makes a ghost, the green blob to the left of the bulb. It's caused by being an idiot: shooting with a large aperture into bright light. Here, we're at f:2.8, wide open. Let's see what happens when we blotto overexpose?

Yuck! Short of hitting someone over the head with it, you couldn't abuse this lens much worse. You'll also note I've performed some pretty heavy post-processing here, dumping the exposure EV -3, boosting the shadows and adding heavy sharpening. The ghost is huge!

Ghosts are caused by intense light bouncing around between the various pieces of glass (elements) inside the lens. Modern lenses are multicoated to help minimize this. This lens also has ED glass, or extremely low dispersion. The ED elements reduce ghosts and glare even more. But this is just too challenging a shot for even the 17-35.

But I was still shocked when I pulled this image up in Photoshop. Have a look:

This is an enlargement of the ghost-blob-from-hell, rotated 180°. You can read parts of the ghost of the super-blotto-overexposed lightbulb itself and the lamp shroud. Whoa!

Even pushed way past its design tolerances, the 17-35 continues to surprise.

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