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Old October 2nd, 2009, 07:33 AM   #1
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Join Date: Jan 2009
Location: London, England
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Maintaining focus

How do you guys maintain focus if your subject is moving and/or if you're not moving a tripod while the Letus is working? Is it simply the case that you need to practice so you know how to make the correct adjustments?
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Old October 2nd, 2009, 11:22 AM   #2
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Some comments until better comes along.

If your project is a traditional controlled action drama, then follow the established practices. A sharp monitor is desireable.

The usual practices, during rehearsal, blocking through, taking focus points and marking them on the set and on the white rim of a follow focus, using a camera assistant. Actors often are directed to work to marks and your camera assistant move the focus to the rehearsed matching marks on the rim of the follow focus.

If it is unrehearseable work you are doing, then I would try to use a very decent monitor so that fine focus errors can be observed and caught.

I myself take a Palsonic LCD TV along to music gigs, use the viewfinder or camera LCD for framing and run vision to the TV and check it often to observe the image sharpness.

If I can find landmarks on the performance stage, such as microphones for vocalists, keyboards for finger cutaways or a bit sticking out from a drum kit, I mark my lens barrel or follow-focus with those points, so if in doubt, I pull the lens to one of those marks, then trim as opportunity permits. I do this way because my eyesight is a bit off.

It is also handy to have the lens marks for doing focus pulls from one performer to the other and snapping to sharp focus without hunting back and forth.

Just because your lenses may be able to open up to f1.4, it is not always that you must use them wide-open if lighting permits otherwise and no groundglass artifacts are apparent. It is more sensible to close them up to about f3.5 - f4 and use the deeper depth of field to hold a moving subject sharper as you track it with the focus.

Not all lenses were made equal and at f4 some lenses may provoke a groundglass textural artifact, corner brightness falloff artifact or vignette, depending on the diameter of the exit pupil (the hole in the back of the lens).

A good monitor is essential to see defects in the image no camera LCD screen or viewfinder will show you.

Otherwise, use a follow-focus lever, set your lenses focus rings to a mid-point when the followfocus lever is centred, say 1.5M or 5 feet and practice focusing by eye and camera viewfinder on a Siemens chart and remembering by feel, the position of the follow-focus lever at these points for each lens - far from perfect but with practice and a good eye for distance, more predictable.

Unlike cine lens sets which tend to have an identical range of focus movement, still lenses have a lot of variety in their range of focus movement, so you would have to build sets of reflexes to each lens, a lot harder to keep track of, doable but lots of practice needed.

Hopefully people like Chris Barcellos or Charles Papert, who know what they are about will give you better advice.

Last edited by Bob Hart; October 2nd, 2009 at 11:33 AM. Reason: error
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