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|| SportsShooter.com: Member Message Board
Canon 70-200 2.8 IS II focus and recompose problems
Avi Gerver, Photographer
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New York | NY | USA | Posted: 11:21 AM on 10.30.10 |
->> Hi,
For those with Canon's 70-200 2.8 IS II lens: If you zoom in to focus on a static subject, and then zoom out to recompose the shot, does the plane of focus move slightly, forcing you to refocus to get a tack sharp image? On the one I just bought, it does, which seems strange to me. On the original 70-200 2.8 IS and 70-200 f4 IS I can zoom in to focus, zoom back out, and the plane of focus doesn't move.
I just want to make sure I don't have a bad copy. It's otherwise a very sharp lens.
Thanks,
Avi |
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Stew Milne, Photographer
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Providence | RI | USA | Posted: 12:00 PM on 10.30.10 |
| ->> I believe this topic has been covered, but I don't remember which thread it was. We discussed this and I think the conclusion was that yes, you do have to refocus. A certain type of lens (I can't remember the technical name right now) will keep the focus when you zoom, but others will not. |
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Colin Hackley, Photographer
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Tallahassee | FL | USA | Posted: 1:03 PM on 10.30.10 |
->> The safest policy with any zoom is to focus at the focal length you plan to shoot at, it saves time and avoids the focus problem you described.
In general Canon lenses do adhere to your theory, but I choose to re-focus after every zoom because the DOF for the 70-200 2.8 is so unforgiving. |
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Jim Colburn, Photo Editor, Photographer
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McAllen | TX | USA | Posted: 1:05 PM on 10.30.10 |
| ->> A zoom lens should, in theory, hold its focus at all focal lengths but I've never been really happy with any zoom lens' ability to do that. Go with Colin's advice and focus at the focal length you want to shoot at. |
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Peter Buehner, Photographer
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Orono | ME | USA | Posted: 9:13 PM on 10.30.10 |
->> http://en.wikipedia.org/wiki/Parfocal_lens
The 70-200 is supposed to be parfocal (as opposed to varifocal) but I think the manual says that zooming may affect focus (in the old version, not sure of the version II) |
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Yamil Sued, Photographer, Photo Editor
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Peoria | AZ | USA | Posted: 9:37 PM on 10.30.10 |
->> The lens that holds focus when you zoom in and out is called "PARFOCAL"
Not all lenses are "PARFOCAL".
Most Video camera lenses on high enc Video cameras ARE "PARFOCAL"
Most SLR and DSLR lenses ARE NOT "PARFOCAL"
so...... To answer everyone's questions, YES, if you zoom in and out YOU MUST FOCUS AGAIN!!!
Y |
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Yamil Sued, Photographer, Photo Editor
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Peoria | AZ | USA | Posted: 11:15 PM on 10.30.10 |
->> Zoom lenses (sometimes referred to as "true" zoom) are ideally parfocal in that focus is maintained as the lens is zoomed (focal length and magnification changed), which not only is convenient, but also has the advantage of allowing more accurate focusing at maximum focal length and then zooming back to a shorter focal length to compose the image. However, not all so-called "zoom" lenses are actually parfocal.[1]
Many "zoom" lenses, particularly in the case of fixed lens cameras, are actually varifocal lenses, which gives lens designers more flexibility in optical design trade-offs (focal length range, maximum aperture, size, weight, cost) than parfocal zoom, and which is practical because of auto-focus, and because the camera processor can automatically adjust the lens to keep it in focus while changing focal length ("zooming") making operation essentially the same as a parfocal zoom. |
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Avi Gerver, Photographer
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New York | NY | USA | Posted: 9:00 AM on 10.31.10 |
| ->> Thanks for all the responses! I sorta figured that's the case, it's just a shame because the plane of focus moves only ever so slightly with this lens, unlike some other zooms like the 28-300 and 100-400 which are obviously not designed to be parfocal. |
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