Problems with my Sigma 120-400

Submitted by Syv Ritch on 8. December 2011 - 6:26

I bought the Sigma 120-400 OS HSM f/4-5.6 a little bit more than a year ago. Why did I buy it?

  1. It was cheap, very cheap. I paid half, exactly half, of the price of the Canon 100-400L zoom.
  2. I was and am still waiting for the “new” Canon 100-400L zoom that is supposed to be coming soon, real soon according to the 3 years old rumors.

I was happy with it. It took me about 6 month to learn to use it. What 6 month? Am I a retard or is it that difficult. Actually it is, it's not just pointing the lens. It has to hold, be steady, learn to focus quickly while tracking the birds… It's not that easy.

Over the last couple of month, I've been having problems achieving focus. The worst was last weekend when the lens kept on hunting, back and forth and no auto-focus. I had to switch to manual focus. The last time that I used manual focus, to track moving subjects, was in the mid-1990s. I regularly use manual focus with static scenes and I use the hyperfocal distance for the focus1.

Here's one of the photo that I manage in taking:

reifel-20111203-7334

Sandhill Cranes Cleaning Themselves   click on image for gallery

Upon searching, I found that Sigma recalled a few of the 120-400, but not my serial number. I checked and rechecked that the lens was properly mounted on the camera. I searched the rest of the internet, aka scroogle, and found people suggesting to clean the contacts. I checked the contacts and there was a small oil film on them! I took my trusted LCD cleaner solution, a lint free rag and sprayed on the rag, cleaned the contacts on the both the camera and the lens.

Instant gratification, nice quick, positive focus even on close range and low light. Perfect.

Now the question, where does the oil film comes from? I don't know, must be something from the Sigma lens. It's not from the camera, the other lenses are not affected by it. So now it will be regular monthly cleanups and next summer when I won't need the lens, I'll send it back for warranty repair.

People on the Internet were mentioning to use pure alcohol. But because of the various plastic parts around, I was afraid to use the pure alcohol. There is something called “contact solvent” or “electronic degreaser” and the LCD cleaning solutions are close enough.

  1. Hyperfocal distance: the distance beyond which all objects appear to be in an “acceptable” focus. i.e. With a 17mm lens on an APS-C like the Canon 7D, at f/11, the hyperfocal distance is at around 3 feet or 93 cm. Everything will be in an an “acceptable” focus from 3 feet to ∞/infinity. ↩