Questions about calibration

[S Taylor]

Hey folks,

I see it often written around here that some send their lenses off to get them 'calibrated'. Why does this have to be done with some lenses? Is it more common with other brands, or are all susceptible to whatever condition(s) make calibration necessary? And what exactly is adjusted about the lens during calibration... the focusing mechanisms?

Thanks for putting up w/another noobish question.

William

[robertwgross]

Mostly the focus mechanism.

Autofocus is electronically detected down in the bottom of the camera body, and then it sends "focus drive" information to the lens, like how far to go to hit that perfect focus point.

If overall focus operation seems bad, then it might be caused by a uncalibrated lens, or by an uncalibrated body. These things probably all met spec perfectly at the factory, but after they were dropped once or twice, something wiggled loose.

---Bob Gross---

[willg]

i sent my 70-200 in to canon after i did a few tests with a ruler and a tripod...it came back and i did the same tests again and it was more accurate. i still have about the same keeper rate though...i learned the hard way that using long lenses is hard and its not always the cameras fault. I am glad I sent it in though because now it is surely calibrated and I know the problem should lie with me now....also if you are using a long lens remember that even at f/4 the dof is pretty thin at 200mm and focusing mistakes could be caused by slight movement of the camera after focus before shutter release

[Juan Zas]

hi to all,

I have sent back also my new 70-200 f/4 L lens due to back focusing (I checked it using the different focus charts available). Yesterday I have received a new one from Canon through my dealer; and I can tell you this is another thing !!! it´s sharp as I have dreamed !!

I don´t know if it has been already posted, but AUTOFOCUS CALIBRATION FOR CANON EOS it´s a very nice link that explain how to do it by yourself. The procedure looks generic for Canon EOS cameras but the decription is made on the 350D/XT. I did posted it in another forum and got good results.

The first link it´s for the procedure itself (original french version), the 2nd link it´s for an authomatic translation in english and the 3th link it´s to the results of one coleague after done by himself the adjustment. I think always an image it´s better than thousand words ...

http://www.astrosurf.org/buil/autofocus/adjust.htm

http://216.239.39.104/translate_c?hl=en&langpair=fr%7Cen&u=http://www.astrosurf.org/buil/autofocus/adjust.htm

http://forums.dpreview.com/forums/read.asp?forum=1031&message=15039875

Cheers

[Juan Zas]

Sorry, I did not mention above THAT PROCEDURE IT´S USED WHEN YOUR CAMERA BODY IT´S THE GUILTY OF BAD FOCUSING !!! People said this is that Canon service do about this point, if you send to them, you must wait 4-5 weeks to receive back your camera. But remember that all you do it´s at your own risk !!

In my case; I have 3 lenses with my 350D: Kit lens 18-55; a 50 mm f/1.4 USM & the 70-200 f/4 L USM -->> The problem WAS ONLY with th 70-200; the other two performed pretty well from the focus point of view

Cheers.

[S Taylor]

Thanks for the explanation Bob!

Hopefully I'll be lucky enough to avoid ever having to do this, seems to be a hassle.

William