I recently picked up a Canon 7D and three lenses: 17-40L, 50/1.4, and 70-300IS. It took me a while to learn how to use the 17-40L (my first lens), but once I learned its quirks it's indispensable for close-quarters group shots (the 17-55 would have given me an extra stop and IS to boot, but I was after the weather-sealing qualities of the L series). The 17-40L was great right out of the box. I pretty much attached it to my camera and started shooting, no problems.
The first copy of the 50/1.4 I got didn't focus right, so I returned it and got another. The new one focuses well, and it's easily my favorite lens of the three. The background blur is amazing and taking pictures full of blurred backgrounds is probably single most fun thing I've done in photography in recent years.
Next, I got the 70-300IS. I've shot extensively with it on other bodies, so I know it's a good lens. I was surprised when it didn't seem to be focusing right on my 7D. The pictures were just a little bit soft. This is where I learned about auto-focus microadjustments on new camera bodies. Apparently, instead of having to send the camera and the lens into Canon to get calibrated, you can make lens-specific adjustments that will correct for focusing abnormalities on your lenses. I believe what it does is it varies the distance of the sensor from the rear lens element to achieve slightly altered focus.
I tried microadjusting the 70-300IS and managed to get it sharp as a tack at 300mm, but it was way off at 70mm. Nothing I could do fixed it, so I'm sending it back to B&H for a replacement. Hopefully the next lens will be better. In light of this, I'm going to test out my other lenses to see if they need adjusting. They look okay by cursory inspection, but it can't hurt to hone them and make 'em sharper.
The upshot of this is that I'm curious how many gerbils use microadjustment on their cameras. I suppose you could get lucky and get a perfect match between the lens and the body, but I'm guessing that happens less of the time.
So, what's been the gerbil experience with AF microadjust?
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