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Old December 4th, 2009, 11:47 AM   #1
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CB acquisition DOF data: do I have back focus prob?

Only with the new ClipBrowser's Acquisition tab I noticed that - with ND filters on and aperture wide at some F2.8 - after I zoom fully in and focus at (close to) infinity, then back out fully wide - the DOF starts at infinity, but may end as far as 15m away!

Have no idea why I never noticed this before, with my EX1's own DOF indicator bar (perhaps it's not accurate enough)? What I HAVE been noticing recently is that after zooming out fully like this, objects close to me are a bit soft.

Assuming that - in zoom at full wide - my DOF should more or less cover pretty much everything, I started worrying about my camera having the back focus problem. Was just about to try and run the adjustment procedure, when the CB's indications caught my eye. Obviously, with DOF starting as far as 15m, everything closer than that must be soft!

But the question remains: is it completely normal (with iris at F1.9 to F2.8), or do I HAVE back focus problem, after all? Or, to reword this in a more general way:

- when a particular EX camera has bad back focus, will it be reflected in the DOF indications when zoomed back to full wide? Or will they cover all distance range, and just the picture will be soft itself?
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Old December 12th, 2009, 08:54 AM   #2
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Quote:
Originally Posted by Piotr Wozniacki View Post
When a particular EX camera has bad back focus, will it be reflected in the DOF indications when zoomed back to full wide? Or will they cover all distance range, and just the picture will be soft itself?
Bump, bump :)
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Old December 12th, 2009, 11:12 AM   #3
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Piotr,

Don't use your DOF indicator to judge something this subtle. At wide angle it will show nearly everything to be in focus.

If you have a decent monitor that's the best way to test. Even clip browser has less resolution than the imported MOV files (or whatever PC uses, is that AVI) which would be better.

To test first use whatever combo of shutter and/or filter you need to get your iris wide open 1.9. Any more closed iris is worthless to test back focus.

Zoom in on something at infinity and focus. Pull wide and notice if the infinity point still stays sharp as you get wide. Most commonly people found that something in the foreground looked sharper than the infinity point when wide. If its off you can usually find that turning the focus ring when wide can get your focus back to the infinity point. It should track perfectly if the back focus is right.

If you focused on infinity then its OK when you pull back and find objects near you to be soft, after all you focused on infinity. However if the foreground is sharp and infinity is soft you are in trouble.

You could also do the opposite zoom in on something close and then pull back to see if it maintains focus.
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Old December 12th, 2009, 02:40 PM   #4
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Dear Lenny,

Thanks a lot for trying to address my issue. However, I guess it's just my poor English that prevented me from wording my doubts precisely enough for you to address them spot on (and others from even trying to address it).

:)
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