DOF Calculation for FF Still Lenses on RED One

[Alexander Alexandrov]

I have a question on how to calculate DOF Distance for Red One. I'm using canon full frame still lenses on birger mount.

i know there are apps like pcam, isee4k; but i'm certain i see4k is outdated and when i put say 50mm lens into pcam, it probably thinks it's the S35.

i dont think i can enter crop factor into pcam app, and even if i could, it's correct for the FOV but not DOF i believe.

anyone knows a solution, be it via pcam app or any other way/place.

thanks

 

[Paul Leeming]

Cinema lenses use the lens mm natively, so if I put a Canon EF 50mm lens on my Red One (via the Birger mount) it will look exactly the same as the FoV of a Cooke S4 50mm or Arri Master Prime 50mm etc.

So yes, the apps are correct and you have no conversion to do.

HTH

Paul

 

[Alexander Alexandrov]

thank you Paul.

In this case, how does the calculation go for EFS or in Nikon case - DX lenses,
say the tokina 11-16

 

[Daniel Browning]

In this case, how does the calculation go for EFS or in Nikon case - DX lenses,
say the tokina 11-16

Same.

 

[Chris Kenny]

DoF at a given focal length (and, obviously, stop) is always the same. The only thing that changes with sensor size is field of view at a given focal length. And the format a lens was originally designed for has no impact on either, except, obviously, that you'll need to use a lens that actually covers the sensor.

 

[Joel Kaye]

isee4k; but i'm certain i see4k is outdated and when i put say 50mm lens into pcam, it probably thinks it's the S35.

It is s35 because the sensor size is the critical part of the equation. NOT whether the lens is capable of covering a bigger sensor.

Just use iSee4K as it is and it'll be right.

 

[Brook Willard]

DoF at a given focal length (and, obviously, stop) is always the same. The only thing that changes with sensor size is field of view at a given focal length. And the format a lens was originally designed for has no impact on either, except, obviously, that you'll need to use a lens that actually covers the sensor.

Bingo. A 50mm will have the same depth of field at a given stop on any size imager. It's the lens that determines depth of field, not the sensor.

People get this confused. What changes is the field of view.

For example: a 50mm prime on S16mm film will appear much tighter [with a narrower field of view] than a 50mm prime on S35mm film. Accordingly, to match the fields of view, one would put a 50mm lens on the S35mm camera and a 25mm lens on the S16mm camera. So the inherent depth of field would be different on the S16mm camera when compared to the S35mm camera only because one must put on a different focal length lens to match field of view.

[/sameoldlesson]

 

[Alexander Alexandrov]

So the inherent depth of field would be different on the S16mm camera when compared to the S35mm camera only because one must put on a different focal length lens to match field of view.

thank u.
i got confused with all the talk on DSLRs for example 5D & 7D saying:

since 7D is smaller sensor, DOF (not FOV) will be different.

so i was wondering if i used same lens say on 5D and Red (or 7D) would the DOF be different not because one must put on a different focal length lens to match field of view but something tech. with the sensor itself.

 

[LEON]

Bingo. A 50mm will have the same depth of field at a given stop on any size imager. It's the lens that determines depth of field, not the sensor.

People get this confused. What changes is the field of view.

[/sameoldlesson]

Please consider this naive question: What about the circle of confusion, different in 16mm and 35mm
and of course changing DOF ?

http://en.wikipedia.org/wiki/Circle_of_confusion

 

[Stephen Williams]

Please consider this naive question: What about the circle of confusion, different in 16mm and 35mm
and of course changing DOF ?


Hi,

The resoloution of 16mm & 35 mm are different, that accounts for a different COC.

The DOF is actually identically, the 16mm is just 'cropped'.

Stephen

 

[david farland]

...What about the circle of confusion, different in 16mm and 35mm and of course changing DOF ?

http://en.wikipedia.org/wiki/Circle_of_confusion

The wiki explanation on Coc is great (accept it didn't mention CoC limiting factors such as blurry lens, tiny aperatures and large pixels.

As wiki said most people with 20/20 eyes can discern 5lp (line pairs) per mm at 250mm.
This means I can see detail (spot or line....it's a radial thing thou) every .2mm at a quarter of a metre. This gives an acceptable bluriness or CoC of .2mm.

Now using a lens I squeeze these 5lp/mm lines onto a sensor and find I'm getting 35 line pairs per mm ( 7 times more density), then my CoC becomes 7 times smaller......0.2mm divided by 7 = .028mm.

Another way of looking at it is I have a scene that I'm looking at it from 250mm, then my Coc is 0.2mm. I decide to place a point a camera (lens/sensor) at it and the scene fills my sensor. The distance from the scene to the lens compared to the distance from the lens to the sensor (focal length) is my magnification (reduction) factor. I use this reduction factor to determine my new sensor CoC.

What causes this reduction factor in CoC is effective lens curvature (focal length). Aperature determines the angle these rays hit the sensor and hence how short the travel of the lens to the sensor is from 'spot on' to blurry (greater than CoC). So focal length determines Coc and aperature, how fast it changes as you move the lens. These two things determine range of acceptable focus (DOF). I don't really get this shit either but it's why when people talk of moving from s35 to FF35 sensors, the DOF becomes much tighter and to accommodate (increase) this DOF, they'll need to stop down the aperature. But to do this (and achieve correct exposure) the sensor will need to have a higher asa....thank Jim for extra stops on Monstro.

So with the same lens/aperature you go and change the sensor size from 35mm to 16mm, but still maintaining the same scene (same field of view) on the sensor by moving the camera closer. you're now changing the lens distance/focal length ratio. This changes the multiplication (reduction) factor and thus CoC.
D