focus at infinity

[hkrautter]

I have 2 Canon lenses a 17-40L and 70-300 DO neither of them ever focuses at the infinity mark, this is in manual and auto. Even looking at the moon I focus before the infinity mark. Is this normal? Camera is 20D.

Thanks

[NHL]

It's normal, every lens does that!

This is to allow for temperature expansion(hot)/contraction(cold) or for converters (front or back) that you might add to the lenses.

... sometime there's an IR mark as well for infrared film which is slighly off because of its wavelenght which you need to compensate for by over-turning the focusing ring

Do a search for Hartmann mask :idea:

[TDM_Canon_User]

Depends on what you mean as infinity. The leg of the L is the proper infinity point. Most of the lenses today focus past infinity to allow the AF functions to hunt.

It is also normal for long lenses to have the focus point shift with temperature. Sometime it will be dead on, other times a little past or a little before the leg.

Trick is: did the image turn out in-focus or not. If yes, then there isn't a problem.

[hkrautter]

Thanks for your replies. I was curious and my questions were answered completely.

Thanks