Sigma Focus Problem

Just received a Sigma 18-200 for my dad's XSI and when it's attached it shoots a couple shots then stops. When I looked at the back of the camera, it kept switching really fast back and forth from "Manual" to "One shot" as if i was change it with the scroll wheel. Tried it on the XSI and my 50D, same problem. Anybody else ever have this problem? I'm guessing the lens has to go back, but considering it was the 1st non Canon lens I've ever used, it doesn't leave me with a good first impression.

I have 2 lenses which are not of the brand of my camera, nikon vs tokina and sigma.
With the tokina some times autofocus will not work, the problem is that it can be mounted but not fully engaged with the electrical contacts. With the sigma I had zero problems.

In your case you tried it on 2 different bodies so I'm guessing you are right and the lens has a problem

I have heard Sigma mentioned alongside focusing problems all too often. This sounds typical. Sorry to be dogging on Sigma, but I just hear this problem occurring waaay too often.

Man wish I would have found that out before we ordered, read a lot of reviews and did my research, but didn't hear that. I wasn't expecting an amazing considering I only payed $340, just wish it worked. I called the place I ordered from and their contacting Sigma, so hopefully I'll hear back from them soon.

Sigma, like the other 3rd party lens makers reverse engineer their lenses for the various platforms. Sometimes they get it right, some times they have issued. Sigma seems to have, from the number of post like this that I have seen, seems to have issues more than the others such as Tamron or Tokina.

Do you know which 18-200 version? The OS or non-OS version? If its the OS version and has the High Speed Motor variant, be sure that it is has the AF/Man switch firmly set to the right choice. I have seen several OS lens (different manufacturers) play tricks when the switches for AF/Manual is not firmly set. If you also switch the OS selector back and forth a few times to be sure it is making good contact!

If you have the non-OS/HSM version check with Sigma Service to be sure that you have a new enough chip version to work with those two cameras. They will re-chip for free if the lens was purchased through an authorized dealer.

Sigma is doesn't really reverse engineer like some of the third party lens manufacturers. Sigma has had contracts with Canon and Nikon to produce compatible products and thus had access to the full spec of the interface.

A link you may find helpful

Sigma Photo Service & Support

Let us know how it works out. I've used Sigma lens in several different mounts and with different bodies with little or no trouble other than two I've flooded in pouring rain.

Its the OS version, I noticed when ever I set the AF/MF switch to manual mode, it will instantly start going crazy, If I leave it on the AF mode it will take about 3 minutes before it goes crazy. Flipping the switch at that point doesn't do anything. The company I ordered from said I should contact Sigma, and if I don't like their resolution to send it back to them and they will send me a new lens. Tomorrows Sunday, I'll have to give Sigma a call, not sure if they'll be open though. Thanks for the link DRG. Keep you posted.

After a little research, we actually found out Sigma had a location right by us on Long Island. My dad went there today, told the tech what was happening. He took the lens and within 10 minutes he came back with it all fixed. Said he had to adjust the Af/Mf Switch. Maybe there was a loose wire or something, but it's all fixed now. Thanks for the responses guys. He also said we should shut the OS off everytime we turn off the camera for some strange reason. Not sure why, but might as well forward what he told us onto you.

Glad to know it was the 'easy' fix.

OS may not always be something you want turned on each time you use the lens, so turning it off first means it won't come on by default.

OS also uses battery power. There may be a small risk of the lens temporarily locking up on power up too if it's shut down quickly and not resetting immediately on power up.

Interesting tip none the less!

Thanks and glad to know you lens is back up and functioning.