Trying To Make Sense Of Auto-Focus and Manual Focus! (20D)

Mike-DT6 · 25th of December 2007 (Tue)

EDIT: Unfortunately all my original image links are now broken. My photographs are now hosted at Flickr and on my website. Links to both of these sites are in my signature section.

Apologies for any broken image links that are now showing in any of my threads or posts.

Thanks,

Mike

Mike-DT6 · 25th of December 2007 (Tue)

EDIT: Unfortunately all my original image links are now broken. My photographs are now hosted at Flickr and on my website. Links to both of these sites are in my signature section.

Apologies for any broken image links that are now showing in any of my threads or posts.

Thanks,

Mike

Doug Pardee · 25th of December 2007 (Tue)

The first thing to be aware of is that there isn't "an infinity" point in the focus. There is a range, marked with an L-shaped line, depending on the temperature. At normal temperatures the infinity focus point will be near the "corner" of the L, not near the lemniscate (infinity symbol). This picture from Canon shows the lens set (approximately) to infinity at normal temperatures:

Second, autofocus doesn't use the distance scale. The camera measures the amount that the image is out of focus and tells the lens to correct for that. Even if the distance scale is incorrect, the lens might very well end up focused reasonably close to the correct distance. Of course, if the distance scale is incorrect there could be other problems with the lens, too.

Mike-DT6 · 25th of December 2007 (Tue)

EDIT: Unfortunately all my original image links are now broken. My photographs are now hosted at Flickr and on my website. Links to both of these sites are in my signature section.

Apologies for any broken image links that are now showing in any of my threads or posts.

Thanks,

Mike

25th of December 2007 (Tue)	#1
Mike-DT6 Goldmember Join Date: Oct 2007 Location: The Jurassic Coast, Dorset, England. Posts: 3,885	Trying To Make Sense Of Auto-Focus and Manual Focus! (20D) EDIT: Unfortunately all my original image links are now broken. My photographs are now hosted at Flickr and on my website. Links to both of these sites are in my signature section. Apologies for any broken image links that are now showing in any of my threads or posts. Thanks, Mike __________________ . Gear \| Flickr \| Website \| Twitter If at first you don't succeed, lose your temper and smash it to pieces. . Last edited by Mike-DT6 : 17th of January 2009 (Sat) at 22:06.

25th of December 2007 (Tue)	#2
Mike-DT6 Goldmember Join Date: Oct 2007 Location: The Jurassic Coast, Dorset, England. Posts: 3,885	Re: Trying To Make Sense Of Auto-Focus and Manual Focus! (20D) EDIT: Unfortunately all my original image links are now broken. My photographs are now hosted at Flickr and on my website. Links to both of these sites are in my signature section. Apologies for any broken image links that are now showing in any of my threads or posts. Thanks, Mike __________________ . Gear \| Flickr \| Website \| Twitter If at first you don't succeed, lose your temper and smash it to pieces. . Last edited by Mike-DT6 : 17th of January 2009 (Sat) at 22:06.

25th of December 2007 (Tue)	#3
Doug Pardee Member Join Date: Feb 2007 Location: Southern California, USA Posts: 838	Re: Trying To Make Sense Of Auto-Focus and Manual Focus! (20D) The first thing to be aware of is that there isn't "an infinity" point in the focus. There is a range, marked with an L-shaped line, depending on the temperature. At normal temperatures the infinity focus point will be near the "corner" of the L, not near the lemniscate (infinity symbol). This picture from Canon shows the lens set (approximately) to infinity at normal temperatures: Second, autofocus doesn't use the distance scale. The camera measures the amount that the image is out of focus and tells the lens to correct for that. Even if the distance scale is incorrect, the lens might very well end up focused reasonably close to the correct distance. Of course, if the distance scale is incorrect there could be other problems with the lens, too.

25th of December 2007 (Tue)	#4
Mike-DT6 Goldmember Join Date: Oct 2007 Location: The Jurassic Coast, Dorset, England. Posts: 3,885	Re: Trying To Make Sense Of Auto-Focus and Manual Focus! (20D) EDIT: Unfortunately all my original image links are now broken. My photographs are now hosted at Flickr and on my website. Links to both of these sites are in my signature section. Apologies for any broken image links that are now showing in any of my threads or posts. Thanks, Mike __________________ . Gear \| Flickr \| Website \| Twitter If at first you don't succeed, lose your temper and smash it to pieces. . Last edited by Mike-DT6 : 17th of January 2009 (Sat) at 22:06.

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