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Using ND filter to create narrower D.O.F?

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Christopher Travis
Using ND filter to create narrower D.O.F?
on Feb 20, 2010 at 10:12:33 am

Hello all,

Sorry if this is a repost, if it is please feel free to roll your eyes and make sarcastic comments, as long as you direct me to a good thread that discusses this issue it's all the same to me.

So I was wondering if, by using the ND filter in low/mid light situations and opening the aperture right up to compensate, then I could decrease the D.O.F. giving my footage a bit more of that lovely effect everyone seems to crave these days?

Or have I just got everything backwards?

Thanks
Chris


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Rafael Amador
Re: Using ND filter to create narrower D.O.F?
on Feb 20, 2010 at 11:41:45 am

Hi Christopher,
That's the proper way to get a shorter DOF when there is a lot of light.
Rafael

http://www.nagavideo.com


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Kevin Jones
Re: Using ND filter to create narrower D.O.F?
on Feb 20, 2010 at 5:36:19 pm

Try placing your camera as far as you can from the subject and zooming in.
This will also help to create a shallower depth of field.

Kevin Jones



2.5GHz Quad-core PowerPC G5
Final Cut Studio 2


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john sharaf
Re: Using ND filter to create narrower D.O.F?
on Feb 20, 2010 at 6:18:16 pm

While intuitively this may seem like the best approach, a better means of exploiting the DOF characteristics of small imager cameras is to place your subject at about 6' from the camera, use a portrait focal length (equivalent to 85mm on a 35mm still camera and put the background as far away as possible. This often entails shooting through a door (if sound from the next room is not an issue) in small rooms like offices. By backing way away from the subject (assuming the same subject to back wall dimension as above) the in-focus zone is actually much bigger.

JS





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Kevin Jones
Re: Using ND filter to create narrower D.O.F?
on Feb 20, 2010 at 8:55:56 pm

I agree.
As a general rule of thumb, you should try to put as mush distance as possible between your talent and the background. Not so easy in small room interview locations.
Case the location and look for the area best suited.
In post you can also fake it pretty well with multiple layers of your video, garbage mattes and subtle use of blurs.

Kevin Jones



2.5GHz Quad-core PowerPC G5
Final Cut Studio 2


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Jim Mulleder
Re: Using ND filter to create narrower D.O.F?
on Feb 21, 2010 at 1:49:48 am

I always look forward to your insight on various problems John so I would ask you, why is it that further away formula not working? I shoot with a old D-30 or 600 and I have no problem with this move further away formula. What is it that the stock lenses on an EX-3 or EX-1 are doing that make them not react like, what I would call a "real" lenses?

This could be for anybody not just the all knowing one.
Cheers,
Jim


Jim Mulleder
Level Horizon Productions
Cameraman/Editor
778.888.4336


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Rafael Amador
Re: Using ND filter to create narrower D.O.F?
on Feb 21, 2010 at 2:17:44 am

[Jim Mulleder] " I shoot with a old D-30 or 600 and I have no problem with this move further away formula. What is it that the stock lenses on an EX-3 or EX-1 are doing that make them not react like,"
A 1/2"CMOS vs a 2/3" CCD?
Rafael


http://www.nagavideo.com


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john sharaf
Re: Using ND filter to create narrower D.O.F?
on Feb 21, 2010 at 2:54:13 am

Jim,

EX1/3 lenses are "real" lenses, just like those you use on the 2/3" cameras you mention, and they conform to the same laws of physics and mathematics, except of course you're using a "wider" lens with a longer depth of field to cover the same field of view, this the origin of the dilemma to begin with!

My point is that to back way up and use extreme telephoto sized lenses for portraiture tends to flatten the faces and create an unusual effect. That is why for example in 35mm still photography "portrait" lenses are the 85 and 105mm focal length. These sizes put the camera at an ideal distance to the subject to fill the frame with head and shoulders, while not foreshortening the look and to be at a comfortable "working" distance. I find that with 2/3" cameras this converts to about 40mm and I'd guess that in 1/2" it would be about 28mm.

Intuitively, and by observation I believe the best way to accomplish the goal of "fuzzing up" the background where there is a limited amount of physical depth therefore is to bring the subject closer to the camera and increase the distance from the subject to the back wall. A closeup of a person is usually meant to convey an intimacy, similar to talking to someone in real life when they are standing next to you; when you make that shot with an extreme telephoto lens it's an entirely different effect.

Furthermore, when you compare the depth of field (using charts in the ASC Manual) for example of a 50mm lens at 6' and a 100mm lens at 12' (both wide open at F1.4), which both have the same "field of view" (about 2x3') they also both have the same depth of field, which is about 4", so there is not really much to be gained by backing up and using a longer lens. in fact I just tested my "theory" and of course I'm right:

Assuming the available distance is 15', putting the subject at 5' from the camera throws the back wall (15' away) way more out of focus than if the subject is 10' from the camera and the lens is twice as long.

Try it yourself!

JS

JS








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Jim Mulleder
Re: Using ND filter to create narrower D.O.F?
on Mar 7, 2010 at 6:31:18 am

Thanks John. I fully understand your portrait comment, this really spells it out for me. Just when you think you know it all, or at least most of it!As stately earlier, I really appreciate your insight.

Much appreciated,
Jim

Jim Mulleder
Level Horizon Productions
Cameraman/Editor
778.888.4336


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