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Soft Focus Back grounds (Shallow DOF)


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#1 Carl Berkley

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Posted 06 September 2007 - 03:09 AM

I ve been asked on a few ocasions to achieve a very shallow D.O.F in backgrounds and cant seem to get the look that has been asked of me. It seems to be very common look on TVC's and music videos at the moment. I ve shot wide open on primos, cookes S4, and Ultra primes and the cant seem to get the desired one plane of focus look that I m after. I know I can achieve it a lot easier on 85mm lens or longer. But what about using wider lenses such as 20mm close in on the subject or 32 mm or 40 mm. I ve asked the focus puller to roll the focus forward on the lens as well. A. Any suggestions on what I should try? B. Should you be able to see this effect in the viewfinder? I really would like to achieve a face in focus on a head shot but have the back of the head soft and the background beyond soft using something like a 40mm lens.

Any Suggestions would be welcomed!

Thanks
Carl Berkley
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#2 Robert Hughes

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Posted 06 September 2007 - 10:44 AM

Depth of Field is directly related to focal length. Wide angle lenses such as 20mm lenses inherently have a very wide depth of field. Shoot wide open, move your subject very close to the camera, but other than that? Can't do much about the laws of physics.

Edited by Robert Hughes, 06 September 2007 - 10:45 AM.

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#3 Jonathan Bowerbank

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Posted 06 September 2007 - 12:55 PM

...I ve asked the focus puller to roll the focus forward on the lens as well.
A. Any suggestions on what I should try?
B. Should you be able to see this effect in the viewfinder?


If you set the focus just a little in front of your subject (but still have the depth-of-field so he/she is in focus), then that could help you in softening the background a bit more.

A: Shoot at wider apertures with longer lenses, and make sure there's enough room for you to move the camera back far enough. I was on a shoot once (shooting SD on a Panasonic DVX) where I was in an 8' x 10' room. The director wanted a wide shot of the actress but still wanted the shallow depth of field, even though I was only 4' from her...it was impossible under those conditions. So keep that in mind when scouting locations.

B: When looking through the viewfinder, you can't really trust your eye when working in shallow DoF's. Check your measurements, check the DoF chart and make sure you know what is and isn't in focus.
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#4 Tim Terner

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Posted 06 September 2007 - 01:03 PM

If you've shot wide open on primos, cooke S4's and Ultra primes, and can't achieve shallow DOF, then I really think this thread has to be a wind up
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#5 Kieran Scannell

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Posted 06 September 2007 - 01:35 PM

I'm glad Tim posted! I've been racking my brain trying to figure out how you can't achieve a shallow DOF using Cooke S4's! maybe heavily NDing
would help!

Kieran.
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#6 David Auner aac

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Posted 06 September 2007 - 03:52 PM

Depth of Field is directly related to focal length. Wide angle lenses such as 20mm lenses inherently have a very wide depth of field.


No, DOF is not directly related to focal length.
It is directly related to f stop and image reproduction ration.

The image reproduction ratio is a function of film area, distance to subject and field of view. Wide angle lenses have a larger DOF because they reproduce a smaller image on film than a longer focal length would. The same happens when you move closer to your subject. DOF decreases because the subject is reproduced on film at a larger scale. That is why e.g. in macro photography DOF is so extremely small, many times only a fraction of a millimeter is in acceptable focus.
The whole concept of DOF is prone to causing confusion, I hope that clears things up a bit.

Read the article on wikipedia: DOF.

Regards, Dave
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