Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Canon Lenses

Reply
 
Thread Tools Search this Thread
Old Feb 6, 2005, 10:45 PM   #1
Member
 
Join Date: Jan 2005
Posts: 56
Default

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
hkrautter is offline   Reply With Quote
Sponsored Links
Old Feb 7, 2005, 1:37 AM   #2
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

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:
NHL is offline   Reply With Quote
Old Feb 7, 2005, 2:58 AM   #3
Member
 
TDM_Canon_User's Avatar
 
Join Date: Jan 2005
Posts: 90
Default

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.




TDM_Canon_User is offline   Reply With Quote
Old Feb 7, 2005, 3:01 AM   #4
Member
 
Join Date: Jan 2005
Posts: 56
Default

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

Thanks
hkrautter is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 8:59 PM.