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|| SportsShooter.com: Member Message Board Autofocus and IS Les Schofer, Assistant Lynchburg | VA | USA | Posted: 10:46 AM on 10.21.09 ->> Thank all for responses concerning tele Xtenders and autofocus. I would like to pose the same question regarding use of IS and how it may affect autofocusing speed and accuracy. A followup may be if the new Mk IV's dual processor setup would have an impact on this speed.  This post is:  Informative (0) | Funny (0) | Huh? (0) | Off Topic (0) | Inappropriate (0) |   Definitions Preston Mack, Photographer Orlando | FL | USA | Posted: 11:10 AM on 10.21.09 ->> I believe IS is only engaged when your shutter speed is slow. It is to prevent camera shake with long glass. It doesn't affect AF when shooting sports.  This post is:  Informative (0) | Funny (0) | Huh? (0) | Off Topic (0) | Inappropriate (0) |   Definitions Jed Strahm, Photographer Phoenix | AZ | USA | Posted: 1:29 PM on 10.21.09 ->> Les, I have heard folklore about this too. "They" have said that using IS robs your AF from being as fast as possible. I don't know if there is any truth to this or is this is, like I said folklore. Let's see if there are any camera Gurus that can weigh in on this with factual data.  This post is:  Informative (0) | Funny (0) | Huh? (0) | Off Topic (0) | Inappropriate (0) |   Definitions N. Scott Trimble, Photographer Lake Oswego | OR | USA | Posted: 2:56 PM on 10.21.09 ->> IS I somewhat based on gyroscope mechanics, so, when you think of the XYZ axis, you have your body movement, autofocus engine moving around, and the IS compensator in action, its two movements against one, which somewhat interrupts. Body motion against IS, stability. Autofocus against body motion, stability. All three, then either the autofocus engine is slowed down (plus, you have two powered driving devices that bleed each other of 100% effectiveness) ore the IS overcompensates. That is at least my viewpoint. My granddad helped develop the gyroscope "IS" for airplane spy cameras in WWII and Korea and used to explain their function to me when I was growing up until my eyes glazed over, which was usually within a minute to a minute and a half! Sorry, too much coffee on a rainy morning!  This post is:  Informative (0) | Funny (0) | Huh? (0) | Off Topic (0) | Inappropriate (0) |   Definitions David Harpe, Photographer Louisville | KY | USA | Posted: 12:51 AM on 10.22.09 ->> The general rule of thumb I've always heard is it's pointless to use IS when you're shooting above around 1/300th or so (recip of the focal length rule). IS does impact autofocus...I've read it theoretically and empirically. Easy to test - just try shooting a few series with and without it at the same shutter speed and check the keeper count.  This post is:  Informative (0) | Funny (0) | Huh? (0) | Off Topic (0) | Inappropriate (0) |   Definitions Add your comments... If you'd like to add your comments to this thread, use this form. You need to be an active (paying) member of SportsShooter.com in order to post messages to the system. NOTE: If you would like to report a problem you've found within the SportsShooter.com website, please let us know via the 'Contact Us' form, which alerts us immediately. It is not guaranteed that a member of the staff will see your message board post. Thread Title: Autofocus and IS Thread Started By: Les Schofer Message: Member Login: Password: Return to --> Message Board Main Index

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