35mm-sized chip vs 1/3 chip - why greater DOF?

[Matthew Bennett]

I often hear that a 35mm sized chip has different DOF characteristics than a 1/3 inch chip.

I guess I wrongly assumed that the Depth of Field was created solely by the lens, and that the chips (whatever their size) were merely recording the light captured by the lens. What exactly does the chip do to alter, increase or decrease the DOF??

If anyone could give me an explanation I appreciate it...

 

[Graeme_Nattress]

The chip doesn't alter DOF at all. But.... The bigger the chip, the wider a lens attached to it will appear. Given that a longer lens is needed to make DOF appear shallower, you can put a longer lens on a bigger chip to get shallower DOF without that longer lens looking too long.

Graeme

 

[Damon Botsford]

Hey man, who let you out of your cage?!
Get back to work!

Seriously Graeme, I sure hope Jim's treating you right. What you're
doing over there is pure magic! We're all extremely appreciative and
quite envious!

 

[Graeme_Nattress]

Thanks!

 

[evinsky]

Grame is right,
to be more specific FOV (Field of View) is a direct result of your image area (Sensor) and the focal length of the lens used. To maintain the same FOV as your sensor size increases you need to use progressively longer lenses. DOF (Depth of field) is the one variable linked only to the focal length of the lens. For example, 50mm is normal for 35mm still slightly tele for Red and downright long for the HVX but all the cameras will display exactly the same amount in focus (DOF) despite their very different FOVs.

Here is a quick rundown of normal focal lengths for comparison.
1/3" Video-6mm
16mm-17mm
35mm Film-28mm
35mm Still-43mm
6x6cm Still-80mm
4"x5" Still-150mm

 

[Y.Goh]

Grame is right,
to be more specific FOV (Field of View) is a direct result of your image area (Sensor) and the focal length of the lens used. To maintain the same FOV as your sensor size increases you need to use progressively longer lenses. DOF (Depth of field) is the one variable linked only to the focal length of the lens. For example, 50mm is normal for 35mm still slightly tele for Red and downright long for the HVX but all the cameras will display exactly the same amount in focus (DOF) despite their very different FOVs.

Here is a quick rundown of normal focal lengths for comparison.
1/3" Video-6mm
16mm-17mm
35mm Film-28mm
35mm Still-43mm
6x6cm Still-80mm
4"x5" Still-150mm

Graeme and Evinsky, So for the same focal length lenses in both the 2/3" and FF (35mm) sensors the DOF is exactly the same, but the FF sensor will have larger FOV and also it will shows more of the out of focus than the 2/3" sensor. Is this the reason that larger sensor size is associated with smaller DOF even though it's the same, assuming same focal length lenses are used?

 

[GabrielR]

It's kind of a hard one to wrap your head around at first. But, once you get it you got it!

This article is fairly easy to read with some animated GIFS demonstrating how different length lenses affect the circle of confusion.

http://www.aesthetic-endeavors.com/photo/dof/

 

[Beat Takeshi]

And your lenses have PL mounts?

 

[Gibby]

Stock RED One mount is PL. Optional mounts offered by RED will be Nikon, Canon, and eventually a B4 mount (later in 2007). Undoubedly there will also be 3rd party mounts fabricated.

 

[TimurCivan]

PL mounts are the way to go. Glad they didint make Proprietary lens mounts....

CAnon mounts will be VERY VERY interesting however. Only because of how the older lenses have a Dated look ot them. CAnon FD's especially, give a light soft pastel colometry, and a slight greenish shift.

 

[Matthew Bennett]

Thanks for the responses... I'm getting it... it has to do more with the effects of FOV and the specific lenses. Mystery almost completely solved in my brain!