Focusing under relatively low light with Extreme / EX1

Rob Collins · July 6th, 2008, 09:50 AM

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

George Kroonder · July 6th, 2008, 11:34 AM

Quote:

Originally Posted by Rob Collins

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/

Bob Hart · July 6th, 2008, 05:30 PM

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.

Rob Collins · July 7th, 2008, 03:37 PM

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!"

Rob Collins · July 10th, 2008, 09:32 AM

Followed Phil's advice and it worked well. Here's a frame grab straight from the camera. 50mm lens at 5.6.

July 6th, 2008, 09:50 AM	#1
Rob Collins Regular Crew Join Date: Jul 2007 Location: Richmond, VA Posts: 128	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 __________________ robcollins.net

July 7th, 2008, 03:37 PM	#4
Rob Collins Regular Crew Join Date: Jul 2007 Location: Richmond, VA Posts: 128	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!" __________________ robcollins.net

July 10th, 2008, 09:32 AM	#5
Rob Collins Regular Crew Join Date: Jul 2007 Location: Richmond, VA Posts: 128	Followed Phil's advice and it worked well. Here's a frame grab straight from the camera. 50mm lens at 5.6. Attached Thumbnails __________________ robcollins.net

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July 6th, 2008, 05:30 PM	#3
Bob Hart Inner Circle Join Date: Dec 2003 Location: PERTH. W.A. AUSTRALIA. Posts: 2,385	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.