Strange focus on 300D

[digitalfailure]

Hi all

I've just got a new 17-40L lens to use on my 300D :)

Today i was trying to do some indoor shots and i've noticed something strange goings on with the focus.

when the lens is set to manual and the 300D is set to either Tv,Av or manual it's twitching and trying to autofocus :confused:

does the lens gain a rough focus automatically before allowing you to fine tune the focus?

or have I got a problem with the lens?

[robertwgross]

Before you sort out whether it is a problem or not, think about a few things first.

1. Is this going on in that one lens alone, or is it with the other lenses? Note that this L lens is a lot sharper than anything else you have, so you might be able to see things that were previously unseen.

2. Double check that your viewfinder diopter setting is correct. If that is set wrong, then you might be mis-adjusting focus manually. If the viewfinder diopter is set correctly, it should be correct for all of your lenses.

3. If an EF lens is set to manual focus, then it should not autofocus. The camera should not be able to kick the focus. On the other hand, if you set the lens to autofocus, and then you manually focus the ring, and then if you half-press again, it is possible for the camera to kick it back to where it thinks it ought to be, which may or may not be where you think it ought to be.

---Bob Gross---

[digitalfailure]

Thanks for the reply :)

The 18-55 kit lens doesn't do it at all when set to the MF position.

Re fitting the 17-40 to my body and selecting MF, and the camera does kick the focus, It's not all the time, and not at constant distance.

The view finders setting is spot on for my eye.

One little test to check i did was to

set the focus ring to the infinity setting and half press the shutter button when pointing the camera at an item under 10ft away.
Every so often the camera will attempt to focus on the item. you not only see the previously out of focus image becoming clearer, but you feel the usm kick too.

On auto it works perfectly.

Anyone with a 300D and the 17-40L come across this?

[cmM]

your lens is posessed!
I though the autofocus should be off when the lens is switched to manual focusing. The focus points in the viewfinder do light up when there's objects at the prefocused distance, but the focus never changes. At least it didn't happen on my 300D (or 20D) with the 17-40 on.

[digitalfailure]

I'm guessing the lens is fubar too

My 18-55 doesn't do it, and the 75-300 IS doesn't do it either.
Both will illuminate the red focus point dot (in this case the centre point) when you manually adjust the focus to the correct distance.

But the 17-40 actually spins the focus when set on MF, I was boring the wife with my ranting just now, and while she recreated the concern, I watched the focus distance window on the lens, it spun from 28 to infinity almost straight away.!!!!!!!!!!

I thought L series stuff was supposed to be the dogs danglies.......

not feckin happy I can tell you, I tried doing some arty shots today involving a CD and some water drops and they all sucked! this was how I noticed this focus issue.