Why??

[Kyle Mallory]

Hey, not to hi-jack the thread, but...

It was my understanding that DOF if a function of aperture and focal length, and has nothing to do with cropping the sensor. Am I mistaken in this?

If not, then a benefit of RED 2k vs EX1 is that even at 2k, you are still able to achieve a 35mm DOF (even though you are not getting a similar 35mm FOV).

 

[David Mullen ASC]

Because you lose half the horizontal view by cropping the 4K sensor to 2K, you have to compensate by halving the focal length to get back to the same field of view -- hence why you end up with more depth of field.

It's the same issue with the EX1 -- what really matters is the focal lengths needed to get the field of view you want, which thus effect depth of field.

Anyway, the 2K area of the 4K RED sensor gives you the depth of field characteristics of 16mm, not 35mm -- but that's still a little bigger as an area than the 1/2" sensor in the EX1. It's even slightly bigger than a 2/3" sensor.

But no, you don't get 35mm depth of field characteristics when shooting the RED in 2K windowed mode, you get 16mm depth of field characteristics. If all you were going to do is shoot in 2K windowed mode, it would make no difference if the camera switched to a smaller sensor because you are losing the depth of field characteristics from using a larger sensor anyway.

So while it's true that what matters is focal length and f-stop (and distance), the size of the target area affects what focal length you choose -- otherwise you could say that a 1/3" DVX100, the 1/2" EX-1, and the RED ONE all have "35mm depth of field" if you could put the same lens on all three cameras. You can't take the sensor size into account in one case and not the other. What matters is the crop factor, which affects what focal length you chose. It doesn't matter if that crop of the lens' image happens because the sensor is smaller physically or you just crop a larger sensor down -- either way, it's the same image view, which affects what focal length you choose, which affects depth of field.