Saturday, July 9 2005

Minolta Maxxum 7D glitch

[Update 7/23/05: okay, the rule of thumb seems to be, “if you can’t handhold a 50mm f/1.4 at ISO 100-400 and get the shot, spot-meter off a gray card and check the histogram before trusting the exposure meter”. This suggests some peculiarities in the low-light metering algorithm, which is supported by the fact that flash exposures are always dead-on, even in extremely dim light.]

[Update 7/22/05: after fiddling around with assorted settings, resetting the camera, and testing various lenses with a gray card, the camera’s behavior has changed. Now all the lenses are consistently underexposing by 2/3 of a stop. This is progress of a sort, since I can freely swap lenses and get excellent exposures… as long as I set +2/3 exposure compensation. I think my next step is going to be reapplying the firmware update. Sigh.]

The only flaw I’ve noticed in my 7D was what looked at first like a random failure in the white-balancing system. Sometimes, as I shot pictures around the house, the colors just came out wrong, and no adjustment seemed to fix it in-camera.

Tonight, I started seeing it consistently. I took a series of test shots (starting with the sake bottle, moving on to the stack of Pocky boxes…) at various white balance settings, loaded them into Photoshop, and tried to figure out what was going on. Somewhere in there, I hit the Auto Levels function, and suddenly realized that the damn thing was simply underexposing by 2/3 to 1 full stop.

Minolta has always been ahead of the curve at ambient-light exposure metering, which is probably why I didn’t think of that first. It just seemed more reasonable to blame a digital-specific feature than one that they’ve been refining for so many years.

With that figured out, I started writing up a bug report, going back over every step to provide a precise repeat-by. Firmware revision, lens, camera settings, test conditions, etc. I dug out my Maxxum 9 and Maxxum 7 and mounted the same lens, added a gray card to the scene, and even pulled out my Flash Meter V to record the guaranteed-correct exposure. All Minolta gear, all known to produce correct exposures.

Turns out it’s the lens. More precisely, my two variable-aperture zoom lenses exhibited the problem (24-105/3.5-4.5 D, 100-400/4.5-6.7 APO). The fixed focal-length lenses (50/1.4, 85/1.4, 200/2.8) and fixed-aperture “pro” zoom lenses (28-70/2.8, 80-200/2.8) worked just fine with the 7D, on the exact same scene. Manually selecting the correct exposure with the variable-aperture zooms worked as well.

These are the sort of details that make a customer service request useful to tech support. I know I’m always happier when I get them.