Jump to content


Photo

Split focus


  • Please log in to reply
10 replies to this topic

#1 Steven Winant

Steven Winant

    New

  • Basic Members
  • Pip
  • 2 posts
  • Camera Operator

Posted 28 November 2007 - 03:05 AM

Hi,

Could someone tell me what kind of split focus is a good one to use when filming on HD? I can't seem to find a brand or number of lens. Please let me know if you worked with one.

Greetzzz
Stefeuh
  • 0

#2 Jonathan Bowerbank

Jonathan Bowerbank
  • Basic Members
  • PipPipPipPip
  • 2815 posts
  • 1st Assistant Camera
  • San Francisco, CA

Posted 28 November 2007 - 03:28 AM

You mean a split diopter?
  • 0

#3 Steven Winant

Steven Winant

    New

  • Basic Members
  • Pip
  • 2 posts
  • Camera Operator

Posted 28 November 2007 - 02:49 PM

You mean a split diopter?

Well, i guess i mean that, in photography they call it a split focus i think. But if you can you can give me a brand for a split diopter. Thanx man!
  • 0

#4 Leo Anthony Vale

Leo Anthony Vale
  • Basic Members
  • PipPipPipPip
  • 2010 posts
  • Other
  • Pittsburgh PA

Posted 28 November 2007 - 04:26 PM

Well, i guess i mean that, in photography they call it a split focus i think. But if you can you can give me a brand for a split diopter. Thanx man!


What they call in photography a split focus is focusing on a point between two subjects so that the depth of field will carry both subjects in focus.
  • 0

#5 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19761 posts
  • Cinematographer
  • Los Angeles

Posted 28 November 2007 - 04:38 PM

Almost all the filter makers make diopters and split diopters. Those made by Schneider and Tiffen would be the two most commonly ones in motion picture work. You need a set (+1/2, +1, +2, +3).
  • 0

#6 Jonathan Bowerbank

Jonathan Bowerbank
  • Basic Members
  • PipPipPipPip
  • 2815 posts
  • 1st Assistant Camera
  • San Francisco, CA

Posted 28 November 2007 - 05:03 PM

What they call in photography a split focus is focusing on a point between two subjects so that the depth of field will carry both subjects in focus.


This is called "deep focus", which Toland did in many scenes of Citizen Kane (among many other examples). Lighting to an f/16 in order to get that extremely deep depth of field.
  • 0

#7 Chris Keth

Chris Keth
  • Sustaining Members
  • 4427 posts
  • 1st Assistant Camera
  • Los Angeles

Posted 28 November 2007 - 05:17 PM

This is called "deep focus", which Toland did in many scenes of Citizen Kane (among many other examples). Lighting to an f/16 in order to get that extremely deep depth of field.


A focus split doesn't necessarily have to include a lot of depth of field. The idea is just that you're not focusing exactly on anything (the plane of focus is often in dead air) but you're focusing 'good enough' on multiple things.
  • 0

#8 Michael Nash

Michael Nash
  • Sustaining Members
  • 3330 posts
  • Cinematographer
  • Pasadena, CA

Posted 28 November 2007 - 06:11 PM

Exactly. Deep focus means there's a large depth of field, which may be used to hold both close and distant subjects in focus. A focus split just means that the focus is set to a point between two subjects that are within the depth of field (however deep/shallow it may be), in order to hold both of them in focus.

In any case, a "split diopter" or "split field diopter" does neither of these things, instead it creates two separate depths of field.
  • 0

#9 Jonathan Bowerbank

Jonathan Bowerbank
  • Basic Members
  • PipPipPipPip
  • 2815 posts
  • 1st Assistant Camera
  • San Francisco, CA

Posted 29 November 2007 - 02:50 AM

ahhh, I'd never heard anyone refer to it as split focus. Good to know :)
  • 0

#10 Chris Keth

Chris Keth
  • Sustaining Members
  • 4427 posts
  • 1st Assistant Camera
  • Los Angeles

Posted 01 December 2007 - 12:31 AM

I'll toss a bit of useful info into this thread about plus diopters. A lot of people don't know how to use them and do it by trial and error alone. You usually do need some T&E but there is a starting point.

First focus your lens to infinity. Put a +1 diopter in front of it. It will now be focused one meter from the film plane rather than infinity. If you remove the +1 and put a +2 diopter in front of the lens, it will be focused one half meter in front of the film. A +3 diopter would be focused 1/3 of a meter out. See the pattern? The close focus distance will get progressively closer, but I'm not sure of an easy to remember way to know what that will be.

Edited by Chris Keth, 01 December 2007 - 12:33 AM.

  • 0

#11 Leo Anthony Vale

Leo Anthony Vale
  • Basic Members
  • PipPipPipPip
  • 2010 posts
  • Other
  • Pittsburgh PA

Posted 04 December 2007 - 02:59 PM

A +3 diopter would be focused 1/3 of a meter out. See the pattern? The close focus distance will get progressively closer, but I'm not sure of an easy to remember way to know what that will be.


A dioptre is a reciprical of a meter.
Thus a +1 diopter lens has a focal length of 1 meter, a +2 is 1/2 meter, a +3 is 1/3 meter, a +0.5 is 2 meters.
So when the taking lens is set at infinity, the focus is at the focal plane of the diopter.

The distance the taking lens is focused at can also be expressed in diopters.
Infinity focus is zero is diopters. Other distances are the same as the dioter lenses.

We know that stacking diopter lenses produces a combined focal length that is the same as the dioters added together. A +1 and a +2 equal a +3.

The diopter lens and the distance in diopters focused on by the backing lens can be added together in the same way. Thus a +1 diopter on a lens focused at 1/2 meter(2 diopters) will be 3 diopters or 1/3 of a meter or about 13 inches.

A bit of a complication is that the diopter lens' focus will be from the front of it, while camera lenses are calibrated from the focal length. Shouldn't be a real problem with a short prime, but a long zoom wil through the calculation off, particularly at very close distances.
  • 0


Willys Widgets

Metropolis Post

Wooden Camera

FJS International, LLC

The Slider

Aerial Filmworks

Ritter Battery

Glidecam

Broadcast Solutions Inc

Abel Cine

CineLab

Media Blackout - Custom Cables and AKS

Gamma Ray Digital Inc

CineTape

Rig Wheels Passport

Visual Products

Paralinx LLC

Tai Audio

Technodolly

rebotnix Technologies

Opal

Glidecam

Technodolly

Gamma Ray Digital Inc

Metropolis Post

Media Blackout - Custom Cables and AKS

Opal

Tai Audio

Willys Widgets

Aerial Filmworks

Wooden Camera

Ritter Battery

Visual Products

Paralinx LLC

rebotnix Technologies

CineTape

FJS International, LLC

Rig Wheels Passport

CineLab

Abel Cine

Broadcast Solutions Inc

The Slider