50mm Lens - 16mm vs. 35mm

[ledbird]

I've got a question to which I am having trouble finding a definitive answer:

Technically (not aesthetically), is a 50mm lens shot on 16mm film the same as a 50mm shot on 35mm film?

I've heard two seemingly opposing answers:

1) "No, in order to get the look of a 50mm lens in 16mm, you have to use a 25mm lens."

2) "Yes, a 50mm lens will always be a 50mm lens, no matter what you're shooting on (16mm, 35mm, etc). The only difference will be the coverage angle of the lens, with it being half as wide 16mm compared to 35mm."

My brain tells me that only one of these answers can be true.

Thank you for your time,
Ledbird

 

[David Mullen ASC]

A 50mm is a 50mm is a 50mm...

It's just that on a 16mm camera, a 50mm has a narrower field of view (acts more telephoto) than when on a 35mm camera. So if you want to match the field of view of a 50mm lens on a 35mm camera, you have to use a 25mm lens on a 16mm camera.

So both answers are correct.

 

[ledbird]

Thanks for the quick response!

I'm not so concerned about duplicating the width of view, but more so the rendering of depth. So, using a 25mm, although achieving the same field of view as a 50mm in 35, would elongate objects along the axis perpendicular to the film plane, the same way a 25mm would in 35mm.

Thanks again!

 

[David Mullen ASC]

No, you don't seem to understand...

A 50mm on a 35mm camera will have the same perspective, elongation, and field of view as a 25mm on a 16mm camera. "Elongation" is an aspect of perspective, which is controlled by the field of view.

A 25mm lens on a 35mm camera will have the same "elongation" as a 12.5mm lens in 16mm.

The difference is not elongation, it's depth of field: how much objects that are not at the point of focus look in focus. A 25mm lens has more depth of field than a 50mm lens if both are focused at the same distance and shot at the same f-stop. So if you are five feet away from something and are using a 50mm lens on a 35mm camera, and you switch to a 25mm lens on a 16mm camera, then you would have a deeper focus with the 16mm footage because a 25mm lens has more depth of field than a 50mm lens. But in terms of elongation, a 50mm lens on a 35mm camera would look the same as 25mm lens on a 16mm camera.

 

[ledbird]

Thanks again. I think I got it now. To summarize:

When shooting in 16mm:

- In order to duplicate the PERSPECTIVE and FIELD OF VIEW of something shot in 35, you halve the focal length. Thus, a 25mm in 16 would duplicate the perspective and field of view of a 50mm in 35.

- In order to duplicate the DEPTH OF FIELD of something shot in 35, use the same focal length (at the same aperture and camera-to-subject distance.)

 

[David Mullen ASC]

Yes, that's more or less correct if you ignore circles of confusion issues, but I won't go into that...

Although you have to realize that since the same lens will LOOK more telephoto on a 16mm camera, even though the depth of field doesn't change... the APPEARANCE of depth of field changes since the more telephoto look makes the far background larger in frame, and therefore you can see more clearly that it is not in focus compared to the foreground subject.