IS-II Zoom focusing issue

[Barry Goyette]

I've posted in the past about some sharpness problems I had with my Xl1s, which were rectified upon returning the camera and lens to canon. I don't know what they did to fix the problem, although I'm guessing it was a back focus adjustment.

However, yesterday I noticed something, and I thought I'd bring it up to see if anyone else was seeing the same thing.

With the lens on manual focus, and at maximum zoom, it will not focus at infinity..it will only focus out to about 200-300 feet, and then it stops. If I back the zoom off about 5% it focuses fine (and in fact I was able to -once- rezoom back out to maximum, and the focus held...I couldn't repeat it as there seems to be something screwy with the servo at that length).

I'm curious...it's not a huge problem to me as I don't go on safari much, but if anyone with an xl1s has time to run outside and focus on the mountains...I'd sure like to know what you see.

Barry Goyette

[Chris Hurd]

Hmm... anybody else notice this?

[Barry Goyette]

My original test was at shot at f2.8. I went back and looked again, and noticed that the problem "almost" disappeared at f5.6, and was gone at f8...it didn't appear that the focus was shifting, only that depth of field was increasing enough to cover the distance.

cheers,

Barry Goyette

[Chris Hurd]

Ah yes, the "sweet spot."

[Barry Goyette]

well..no..I don't think this is a "sweet spot" issue..the lens still isn't focusing anywhere close to infinity when at maximum zoom...I included that info so anyone else trying to check wouldn't have their "vision clouded" by all that extra depth of field..

cheers

Barry Goyette

[Jeff Donald]

Hi,

I am not sure I understand your problem. What are you saying is infinity? Infinity (as marked on the lens barrel) is like focusing on the moon. Most lenses will actually focus *beyond* infinity. The extra range beyond the infinity mark is to compensate for expansion of the lens elements when they are used in hot enviorments. The heat causes the elements to expand and this shifts the focus slightly. Thus, the need to focus *beyond* infinity. Geez, I feel like Buzz Lightyear. So, my question is, what does the barrel indicate when you focus on an object several hundred feet away and then when you focus on the moon? Thanks for helping me to better understand the dificulties.

Jeff

[Chris Hurd]

Hi Jeff, Barry is talking about the IS II lens, this is the white auto lens that comes stock with the camera, which ain't marked at all, no infinity, no nothing.

I'm wondering if his issue is a result of pixel averaging, but usually you see that at full wide shots, not full telephoto.

[Barry Goyette]

When I say infinity..I'm just referring to stuff that's far away..beyond say... 300 feet. What I'm seeing is just like what happens at the macro end of the focus range when zoomed out...you focus at the minimum focusing distance and that's it..anything closer and you can't bring it into focus...the same thing is happening to me at the far range...zoomed all the way out, I can focus to a point about 300 feet away, but can't focus on something behind it...yet if I back the zoom off just a titch I have no problem bringing the farther objects into focus (and see the closer objects go out of focus just like you'd expect)..as jeff says there should be a little bit of extra focus range built into the design, but In my case there isn't.

To me, this appears to be an servo/optical issue, not one related to the ccd. Love to know if anyone else see's it...or did canon fix one problem only to bring on another.

cheers

Barry Goyette

[Jeff Donald]

Try my test of focusing on the moon. Set lens to max zoom then try to focus on the moon. If that doesn't work, you probably have a back focus problem. I would then call Canon and discuss your issues with them.

Jeff