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Backfocus on Canon 814XL


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#1 Andrew Sobey

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Posted 08 July 2008 - 10:57 PM

Looking at my test footage from a Canon 814 XL, and it's only in focus at the wide end of the zoom. When I zoomed in the focal depth went way down, so only the stuff in the foreground was in focus.

I didn't see this in the viewfinder, and my upcoming project involves a lot of med-long lens stuff, so does anyone have any idea how to adjust the backfocus on this camera? Or other solutions? Or am I just SOL?
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#2 Richard Tuohy

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Posted 09 July 2008 - 02:54 AM

Looking at my test footage from a Canon 814 XL, and it's only in focus at the wide end of the zoom. When I zoomed in the focal depth went way down, so only the stuff in the foreground was in focus.

I didn't see this in the viewfinder, and my upcoming project involves a lot of med-long lens stuff, so does anyone have any idea how to adjust the backfocus on this camera? Or other solutions? Or am I just SOL?


Hi andrew,
because super 8 cameras (with very few exceptions) use an aereal image viewfinder system rather than a ground glass, you have to take a lot of care with focus. It is IMHO very unlikely that the lens has been adjusted such that it needs fixing. Much more likely is that the eye piece diopter is not correctly set, and/or you didn't rely on the focus aid strongly enough. Yes, focus is much more critical the longer the lens is (ie less 'wide'). The longer the telephoto lens, the more care you have to take. And you can't simply rely on apparent image sharpness in the viewfinder - you have to use the split image focus aid. Remember, your eye can readily 'pull in' or adjust for a soft image in the viewfinder since it isn't looking at a ground glass at a fixed location, but rather just the aerial image which is merely 'floating'. So, make sure you have focused the eyepiece dopter. Do this:
zoom all the way in
focus on infinity
choose a vertical subject as far away as possible (well over 15 meters away) such as the side of a building.
with your fingers on the diopter focus control, adjust the diopter until the two halves of the split image focus aid are in exact allignment.
now you are ready.
And use the focusing aid in the same way on subjects when filming - especially if they are in the middle distance and you are using a longish lens.
And you can always use a tape and the distance markings on the lens. These will be correct, unless the front element of the lens has been removed at some point.
good luck.
Richard
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#3 Andrew Sobey

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Posted 11 July 2008 - 02:36 PM

First off, to correct my original post, focal distance went way down when I zoomed in. I guess it goes without saying that focal depth would go down.

As for the diopter, I set that before shooting anything, and I can't imagine that it went out of focus over the course of one 50' roll. I'll shoot another test and see how it goes.

Thanks.
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