John Ferguson
New member
How about the new 17-55 F 2.8 IS?
Have searched haven't been able to find an official answer. Thanks in advance!
Have searched haven't been able to find an official answer. Thanks in advance!
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Is the 24-105L parfocal?
- Thread starter John Ferguson
- Start date
Sid Jervis
pro member
This list does not include the 24-105, but may be helpful to others.
http://www.photozone.de/8Reviews/canonFAQ.htm#3Q5f
http://www.photozone.de/8Reviews/canonFAQ.htm#3Q5f
John Ferguson
New member
Sid,
Thanks for pointing that out but I believe that list, like many others, was developed before the 24-105L was manufactured. The closest answer I can find is "constant aperture L lens are parfocal" in a statement attributed to Chuck Westfall but I would like to know for certain on these lens.
Thanks for pointing that out but I believe that list, like many others, was developed before the 24-105L was manufactured. The closest answer I can find is "constant aperture L lens are parfocal" in a statement attributed to Chuck Westfall but I would like to know for certain on these lens.
Sid Jervis
pro member
You may well be right, although the 24-105 is mentioned in other sections of that document.
I tend to take CW's official statements as fact
$0.02
I tend to take CW's official statements as fact
$0.02
Stan Jirman
New member
Yes it is. All Canon L zooms are parfocal as far as I can tell, even the 28-300LIS
Chuck Westfall(Canon USA)
pro member
Hi, John:
There is no official answer, because Canon Inc. won't comment on it. Based on actual product testing, though, both of these lenses are parfocal as long as you start out by focusing sharply at the maximum focal length and then zoom back to a shorter focal length without refocusing. Look at the files on a computer monitor at 100% magnification to verify.
If you autofocus after zooming out, the camera may drive the lens to a slightly different distance. This is possible because depth of field is greater at the shorter focal lengths of the zoom lens, assuming a fixed subject distance. But if the image remains sharp after focusing accurately at maximum focal length and then zooming to minimum focal length without refocusing, the lens is parfocal.
Best Regards,
Chuck Westfall
Director/Media & Customer Relationship
Camera Marketing Group/Canon U.S.A., Inc.
There is no official answer, because Canon Inc. won't comment on it. Based on actual product testing, though, both of these lenses are parfocal as long as you start out by focusing sharply at the maximum focal length and then zoom back to a shorter focal length without refocusing. Look at the files on a computer monitor at 100% magnification to verify.
If you autofocus after zooming out, the camera may drive the lens to a slightly different distance. This is possible because depth of field is greater at the shorter focal lengths of the zoom lens, assuming a fixed subject distance. But if the image remains sharp after focusing accurately at maximum focal length and then zooming to minimum focal length without refocusing, the lens is parfocal.
Best Regards,
Chuck Westfall
Director/Media & Customer Relationship
Camera Marketing Group/Canon U.S.A., Inc.
John Ferguson
New member
Chuck,
Thank you very much for replying and for supporting this forum. Have focused my 24-70L in the method you mention with excellent results and sincerely appreciate you confirming the other lens work that way as well.
Regards,
John
Thank you very much for replying and for supporting this forum. Have focused my 24-70L in the method you mention with excellent results and sincerely appreciate you confirming the other lens work that way as well.
Regards,
John
Stan Jirman
New member
Aha, so there isn't an official answer. I dropped a 24-70L and had it repaired by Canon; in my description of the problem I have specifically said that the lens is not parfocal anymore (the main problem was that the zoom ring was excessively tight, but the pictures it took were still sharp). When the lens came back from repair, the zoom ring was nice smooth but the lens was no longer parfocal.
I guess since officially it isn't, there was nothing "wrong" with it and thus they didn't fix it. For that reason I sold it (with full disclosure and money back offer) and bought a new one; now I am happy again. I didn't even think about it much, but as far back as I can think - my FD 35-70 zoom in the 80s - I always focused at the long end and then zoomed out, so when this stopped working it was a disaster for me.
This is also the main problem I have with the 28-300LIS: because it's a push-pull zoom, it's very hard to zoom out after focusing. It can be done, but it's tricky and you have to hold the lens at the right place on the barrell...
I guess since officially it isn't, there was nothing "wrong" with it and thus they didn't fix it. For that reason I sold it (with full disclosure and money back offer) and bought a new one; now I am happy again. I didn't even think about it much, but as far back as I can think - my FD 35-70 zoom in the 80s - I always focused at the long end and then zoomed out, so when this stopped working it was a disaster for me.
This is also the main problem I have with the 28-300LIS: because it's a push-pull zoom, it's very hard to zoom out after focusing. It can be done, but it's tricky and you have to hold the lens at the right place on the barrell...