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Old July 6th, 2008, 10:50 AM   #1
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Focusing under relatively low light with Extreme / EX1

So everything's been going great, love the Letus, until I set up my first interview using a large 1080p TV as monitor. My basic lighting set up--Rifa 55 with grid as key, bounce fill, small backlight. Using a Zeiss 50mm 1.4 lens, the EX1 meticulously focused on the ground glass.

To get a decent exposure, I turned the shutter off, gain at 0 (prefer -3). Both the Zeiss and the EX1 were at f2. It looked great--except that the depth of field was so shallow that I couldn't really keep the subject in sharp focus. There was literally only a few inches of play, so any moving back and forth in the chair brought the face out of focus.

So is this just the way it is, or might I have a backfocus issue with the Letus Extreme? Any rules of thumb about ideal f-stop for both EX1 and 35mm lens? Does the EX1's iris affect DOF at all?

Any advice is greatly appreciated!

Rob
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Old July 6th, 2008, 12:34 PM   #2
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Originally Posted by Rob Collins View Post
Does the EX1's iris affect DOF at all?
No The EX's lens is just 'rephotographing' the groundglas. To increase the DoF you can choose a smaller aperture, but that depends on lighting (may need to increase that). Or use a wider lens (and bring the camera in).

Sounds af if you may actually have been better off without the Letus ;-)

George/

Last edited by George Kroonder; July 6th, 2008 at 04:22 PM.
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Old July 6th, 2008, 06:30 PM   #3
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Relay (via camcorder's own lens) seems to be sweetest at about f4 on the camcorder lens.

Resolution-wise this should not affect anything but the sharpness of focus on the groundglass.

I would be inclined to come off f1.4 on the Zeiss lens to maybe f2.8 and bring the lighting up if needed.

Another inclination, my personal preference perhaps, would be to use a wider lens, maybe 35mm or 28mm, move closer to subject and compose if possible to position background furthur away.

Take more notice of the accomplished videographer-cinematographers here than my comments.
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Old July 7th, 2008, 04:37 PM   #4
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Thanks for the advice. A wide lens is definitely on the wish list. Phil Bloom's response on his forum was helpful too:

"you need more light

"the rifa 55 with egg crate only kicks out just enough light.

"take the egg crate off and keep ex1 wide open. set 35mm lens to around f3.5 to f5.6 if the interviewee is a twitcher!"
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Old July 10th, 2008, 10:32 AM   #5
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Followed Phil's advice and it worked well. Here's a frame grab straight from the camera. 50mm lens at 5.6.
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Focusing under relatively low light with Extreme / EX1-int.png  
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