Jump to content


Photo

Depth of Field


  • Please log in to reply
6 replies to this topic

#1 Gary Lemson

Gary Lemson
  • Basic Members
  • PipPipPip
  • 155 posts
  • Other
  • Santa Cruz Mountains

Posted 18 April 2006 - 09:44 AM

Rookie comment here.

It is my understanding that reducing aperture will increase DOF by reducing light that creates observed circles of confusion. However, I've read that reducing light will decrease DOF. George Lucas commented on the latter in "The Making of American Graffiti". I'm a little "confused" myself. Please help.

Thanks.

Edited by otari99, 18 April 2006 - 09:45 AM.

  • 0

#2 Dominik Muench

Dominik Muench
  • Basic Members
  • PipPipPipPip
  • 443 posts
  • Cinematographer
  • Brisbane

Posted 18 April 2006 - 09:54 AM

assuming that with more Depth of Field you mean: More Background gets in focus it is as followed:

small aperture: f1.3, f 2...... less depth of field (less background is in focus)

big aperture: f8,f11,f16.....more depth of field (more background is in focus)

depth of field depends on a few other things as well, such as the lens focal length and the shooting format (video has lots of dof, the bigger the negative the less dof you can get or the more you can play with it ) for example.

with a lens as wide as 12mm you get even on a small aperture a lot of depth of field.

also simply spoken, the more light you got and the higher your aperture (depending on exposure requirements) you also get more depth of field, maybe george lucas meant that. so:

less light - smaller aperture - less depth of field
more light - higher aperture - more depth of field

Edited by Dmuench, 18 April 2006 - 09:56 AM.

  • 0

#3 Gary Lemson

Gary Lemson
  • Basic Members
  • PipPipPip
  • 155 posts
  • Other
  • Santa Cruz Mountains

Posted 18 April 2006 - 10:39 AM

assuming that with more Depth of Field you mean: More Background gets in focus it is as followed:

small aperture: f1.3, f 2...... less depth of field (less background is in focus)

big aperture: f8,f11,f16.....more depth of field (more background is in focus)

depth of field depends on a few other things as well, such as the lens focal length and the shooting format (video has lots of dof, the bigger the negative the less dof you can get or the more you can play with it ) for example.

with a lens as wide as 12mm you get even on a small aperture a lot of depth of field.

also simply spoken, the more light you got and the higher your aperture (depending on exposure requirements) you also get more depth of field, maybe george lucas meant that. so:

less light - smaller aperture - less depth of field
more light - higher aperture - more depth of field


Isn't the aperture smaller for a bigger "f" number?

Thanks again.

Edited by otari99, 18 April 2006 - 10:40 AM.

  • 0

#4 Dominik Muench

Dominik Muench
  • Basic Members
  • PipPipPipPip
  • 443 posts
  • Cinematographer
  • Brisbane

Posted 18 April 2006 - 11:11 AM

Isn't the aperture smaller for a bigger "f" number?

Thanks again.



yes, the bigger the f or t number, the smaller the physical "hole" in the lens, and therefore the less light gets through, resulting in more depth of field.
  • 0

#5 Dominic Case

Dominic Case
  • Basic Members
  • PipPipPipPip
  • 1357 posts
  • Other
  • Sydney Australia

Posted 18 April 2006 - 05:45 PM

However, I've read that reducing light will decrease DOF.

It's a bad way of describing the effect.

Depth of field is increased by having a narrow cone of light coming through the lens rather than a wide one. (The wider the cone of light, the more rapidly the spot of focus enlarges to an out-of-focus disc as the object distance and the distance of focus change).

So it could be said that reducing light by reducing the aperture (to a higher F number), would increase the DOF. It's not so much reducing light per se, but reducing light (in the camera) from the edges of the cone. That's what you've understood.

I guess what George Lucas is saying is that if you reduce light on the subject, then you need to open your aperture, thereby decreasing depth of field. Not sure if his explanation makes any great contribution to anyone's understanding of the issue.
  • 0

#6 Gary Lemson

Gary Lemson
  • Basic Members
  • PipPipPip
  • 155 posts
  • Other
  • Santa Cruz Mountains

Posted 18 April 2006 - 08:42 PM

It's a bad way of describing the effect.

Depth of field is increased by having a narrow cone of light coming through the lens rather than a wide one. (The wider the cone of light, the more rapidly the spot of focus enlarges to an out-of-focus disc as the object distance and the distance of focus change).

So it could be said that reducing light by reducing the aperture (to a higher F number), would increase the DOF. It's not so much reducing light per se, but reducing light (in the camera) from the edges of the cone. That's what you've understood.

I guess what George Lucas is saying is that if you reduce light on the subject, then you need to open your aperture, thereby decreasing depth of field. Not sure if his explanation makes any great contribution to anyone's understanding of the issue.

Okay. Great explanation. I sort of figured there is a distinction between ambient subject light, and the light within the lens.
I've heard the suggestion that one might use an ND filter to reduce ambient light, and open the aperture to reduce DOF. This seems in concurrence with your statements (and Georges, too). Now I understand this aspect of DOF. Thank you.
  • 0

#7 Laurent Andrieux

Laurent Andrieux
  • Sustaining Members
  • 1527 posts
  • Cinematographer
  • France

Posted 20 April 2006 - 06:13 AM

Opening the iris will lower the DoF. So If you have less light, you will need to open up.

If you close down the iris, you will increase DoF, but thet means you need more light, otherwise you would be underexposed !

If you put a neutral filter, thet will cause you to have to open up, reducing DoF, that means also you have enough light to do so, otherwise you'd be underexposed...

(don't forget the iris does not only acts on DoF, as a second point, the first point is it acts on the quantity of light. The purpose, whatever you do with DoF, is as a first point, to be correctly exposed as well...)
  • 0


Glidecam

Visual Products

Aerial Filmworks

Abel Cine

The Slider

Opal

Media Blackout - Custom Cables and AKS

rebotnix Technologies

Ritter Battery

Broadcast Solutions Inc

Gamma Ray Digital Inc

Technodolly

Metropolis Post

Tai Audio

CineTape

Willys Widgets

Wooden Camera

Paralinx LLC

CineLab

FJS International, LLC

Rig Wheels Passport

The Slider

Broadcast Solutions Inc

Wooden Camera

Metropolis Post

Tai Audio

Media Blackout - Custom Cables and AKS

Ritter Battery

Gamma Ray Digital Inc

Willys Widgets

rebotnix Technologies

Glidecam

Rig Wheels Passport

Visual Products

Paralinx LLC

Opal

CineTape

FJS International, LLC

Aerial Filmworks

CineLab

Abel Cine

Technodolly