1.6 extender won't hold focus?? at DVinfo.net

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Old August 27th, 2003, 08:31 AM   #1
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1.6 extender won't hold focus??

I find this strange; when I put on my extender (using the servo lens), focus my shot and zoom out just slightly, I'm out of focus. I take it off and everything is fine. Any suggestions appreciated.
TIA,
Randy
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Old August 27th, 2003, 09:26 AM   #2
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Which lens are you using?
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Old August 27th, 2003, 09:40 AM   #3
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The servo that came with the cam.
Thanks,
Randy
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Old August 27th, 2003, 10:03 AM   #4
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Is the image stabilization turned on? Try the lens, extender both ways and see if there is any difference.
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Old August 27th, 2003, 10:33 AM   #5
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I just went outside to perform your test and the problem seems to have magically disappeared! Are my 50 year old eyes deceiving me or could the difference between daylight and the indoor gymnasium I shot in last night? (I'm not sure what kind of lights they were though, the typical gym lighting ;perhaps halogen?).
Your novice pal,
Randy
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Old August 28th, 2003, 02:47 PM   #6
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Losing focus

If you experience the problem indoors but not outdoors you may simply be seeing the result of increased depth of field resulting from a smaller iris in the brighter light. To check back focus, set up your camera indoors with lighting that creates a good picture but also causes the iris opens fully. Set the zoom to full telephoto and aim the camera at an object that is 15-20 feet away. press the Exposure Lock button so the iris stays put, turn off the autofocus and zoom out. If you lose focus there is a problem with the backfocus setting on your lens. If you have the manual 16x lens you can fix that quite easily. Apparently the fix for the stock IS/Auto lens involves buying a $200 adapter and some complicated programming. (There's a thread elsewhere.)
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Old August 28th, 2003, 04:53 PM   #7
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Thanks Mike,
I tried your test and it does get out of focus so I guess it's time for the shop. Fortunately it's still under warranty and I have a back-up. BTW, if I'm running fully manual do I still need to hit the exp lock?
Thanks again Mike,
Randy
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Old August 28th, 2003, 07:51 PM   #8
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The manual 14X and 16X lenses (like all pro lenses) have a back focus adjustment mechanism built in. The XL mount 16X IS and 3X IS have to be sent, with the camera, to Canon to have the back focus adjusted.
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Old August 29th, 2003, 09:15 AM   #9
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Checking back focus setting

Randy,
If you do not set Exposure Lock when zoomed in all the way your iris setting may change as you zoom out and the camera 'sees' the area surrounding your focus test-subject. If the surrounding area is darker, no problem. But if it is brighter the iris will close, your depth of field will increase and your test is far less effective. By the way, when doing the back focus check it really helps to have the camera's video output connected to the largest monitor you have because (especially for old farts like me) it is much easier to judge sharpness.
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Old August 29th, 2003, 02:04 PM   #10
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Thanks Mike, I'll take your word for it even though I don't see how the iris could change with everything running in manual. I'll try to remember that though.
Thanks again Mike,
Randy
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Old August 29th, 2003, 02:39 PM   #11
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oops

My oversight, Randy. You are exactly correct. If you are running full Manual operation pressing the Exposure Lock is not necessary. The intent is the same, though...to keep the iris open so change in depth of field doesn't give you a spurious result.
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Old August 29th, 2003, 03:26 PM   #12
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Thanks Mike.
Randy
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Old August 29th, 2003, 06:38 PM   #13
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DOF will change, no matter what. The lens is a variable aperture lens (smaller the aperture=more DOF) and DOF will change as you zoom from WA to Tele (WA has more DOF than Tele).
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Old August 30th, 2003, 08:43 AM   #14
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Good to know Jeff, thanks for the info.
Randy
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