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Manual Focus Set - Then goes out of Focus?

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Lindsey Baker
Manual Focus Set - Then goes out of Focus?
on Sep 13, 2012 at 1:51:30 pm

Hello,
I had a problem the other day. Normally I use manual focus when shooting an interview, even if the camera is on auto. I zoom in and focus on the eyes. It should be a fool proof way to get a good focus. But when I look at my footage, it looks a little soft. Even in between shots when we took a break I noticed I had to re-focus the eyes. Is it because was filming too close to her? How can focus change once I have already set it if its in manual mode?
Thank you - Lindsey


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Todd Terry
Re: Manual Focus Set - Then goes out of Focus?
on Sep 13, 2012 at 2:30:52 pm

Well this is all just a guess, especially since you didn't say what camera or type of lens(es) you are using...

But my first guess would note that you say you use manual focus "even if the camera is on auto." With most cameras, if they are in full auto mode, you can still turn the focus ring and manually focus. BUT... that doesn't mean it will stick. After you set the focus with your hand, after that the camera will still take over and try to focus for you. Maybe it is doing that, and shifting your focal plane.

If you are going to shoot in auto, make sure the lens is set to full manual. Some cameras allow you to do that, some do not. If yours does not, shoot everything in full manual... the way the good lord intended anyway. :)

Secondly, maybe you have a poor lens. Most zoom lenses should allow you to zoom all the way in, focus, and then retain that focus when you zoom back out. But I've seen some that do not. The old "varifocal" lenses definitely do not, whereas a modern "zoom" lens will (that focus retention is the only real thing that differentiates a varifocal from a zoom). Maybe you are having a lens issue.

Thirdly, is depth of field. Again, not knowing your camera, format, or lens this is just a guess, but maybe your depth of field is too shallow and even a small movement by your talent is moving them out of the focal plane. I personally sometimes like to shoot extremely shallow DoFs (sometimes a DoF that's an inch deep, or less), and often a person's eyes are pin-sharp yet their nose or even their cheekbones are starting to go soft (and you're right, the eyes are the key... if eyes are sharp then we perceive the shot to be in focus even if other parts of the frame are soft.... and if eyes are soft we perceive the frame to be out of focus even if other parts are sharp). You might try shooting with a deeper depth of field (smaller iris and/or shorter focal lengths with your lens).

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Mark Suszko
Re: Manual Focus Set - Then goes out of Focus?
on Sep 13, 2012 at 3:15:17 pm

One other thing to check is back-focus: if this got knocked out of adjustment, any focusing you do when zoomed in will be undone by zooming back out. To adjust back-focus usually takes no tools, but does require a chart or some type of focuing aid.


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Todd Terry
Re: Manual Focus Set - Then goes out of Focus?
on Sep 13, 2012 at 4:42:55 pm

Duh.... Mark is absolutely right about the backfocus... I should have thought of that as well. That would very definitely account for focal planes that change while zooming. I didn't think of it because (I guess I'm lucky) I haven't had to adjust a backfocus in just years.

To adjust that you'll need a good FULL resolution (I'm assuming 1080) monitor, and you'll need the chart that's known as a "Siemens chart" or a "Siemens star."

You can buy them at various film supply places... OR, you can do a Google image search and probably find one large enough that you can print out yourself (as long as you print it at a very high DPI). I just made the one we use myself in Photoshop.

I'd say one of the problems with the backfocus issue is... again we don't know what your camera is. On higher-end cameras the backfocus is fairly easily adjustable. On lower-end cameras (and especially cameras that do not have removable lenses), it is impossible for the user to adjust the backfocus.

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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janusz sikora
Re: Manual Focus Set - Then goes out of Focus?
on Oct 28, 2012 at 2:50:38 pm

First thing first - Eyepiece Focus.

can be a nightmare if your glasses (if you wear them) are not prescription glasses.

*It's about Light*


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janusz sikora
Re: Manual Focus Set - Then goes out of Focus?
on Oct 28, 2012 at 2:58:53 pm

First thing first - Eyepiece Focus.

... can be a nightmare if your glasses (if you wear them) are not prescription glasses.


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