Misbehaving lens

[GeorgeM]

Hello all,

I rented a higher quality lens than any of the ones I own, for use in photographing a high school class reunion this weekend. The lens is a Sigma 70-200mm f2.8. Things went very well for the most part.
I was using a nondescript camera strap on my D90 rather than the "steal me" strap. It broke under the weight of an off-camera flash bracket, flash, and a Sigma 70-200mm f2.8. Luckily I had one hand still holding onto the rig.
The Sigma 70-200mm first misbehaved on Saturday night inside a pizza place during a "break-the-ice" get-together. The lens stopped auto-focusing after only 3 or 4 shots. When I pressed the shutter release half-way, the lens would just kind of "stutter" and never achieve focus. I wouldn't say that the lens went through its range of focus, it just kind made noises and did nothing else. I went outside and tried focusing on a pleasure boat sitting at a dock. Same thing, "stutter". I then manually focused, tried auto focus again, and it worked.
I took the lens off and mounted my kit lens, the 18-105mm, and used that the rest of the evening. I figured that perhaps the poor lighting inside the restaurant had "confused" the lens.
The next day, Sunday, I tried the Sigma lens again. After perhaps two dozen shots, it stopped auto-focusing. Again, I went back to my kit lens to finish up.
Later in the day, I remounted the Sigma to see what would happen. I used it for some macro work and a few landscapes. It performed without a hitch.
I'm returning the lens off of rental tomorrow. I am tempted to blame the lens, but it's an expensive, top quality lens. It's worth more than my D90, that's for sure.
Maybe it's my camera battery that's not able to handle that lens motor. Maybe it's some sort of interaction with the flash unit. I can hear the flash unit "focus" as I vary the focal length of the lens.
A weird problem, whatever the cause.

[FrankMi]

Hi George, from your description of the difficulty and the fact that it appeared to work again after swapping lenses, I wonder if the issue was the electrical contacts between the lens and the camera? If it is, then it could be a slight bit of oxide on the contacts or possible a loose contact point. I would definitely bring the concern up with the renter to see if he has any suggestions, but if it were my own lens, I would probably gently rub the contacts with a Pink Pearl eraser as that should not cause any problems and will remove any oxide that might be present. Be sure to hold the camera and/or lens contacts down to avoid having any eraser residue fall into the camera or on the lens.

[tbob]

I had a similar problem with my Nikon 75-300. Of course this happened while I was in China on vacation, at the most inconvenient time possible (of course). On my return I sent the lens in for repair, turned out to be defective electronics (a computer chip if memory serves). May be something of the same ilk. I rather doubt it was any fault of yours despite the near catastrophe.

[GeorgeM]

Hey Frank,

When I read "electrical contacts", I thought about the weight of that lens. When taking a shot I had a grip on both the lens and the camera. At rest the outfit was hanging by the strap with my right hand on the camera grip. Maybe there was a slight separation of those contacts. I thought I tried reseating the lens, though.