Focal length and barrel distortion

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DanHD

Well-known member
We're all familiar with the barrel distortion caused by shooting on 1/3" cams at their shortest focal length.
My question is,

Is the same distortion caused when shooting with short focal length 35mm lenses?

A 18mm lens is extremely wide on a 35mm camera, comparable in field of view to a very short focal length on a 1/3" cam, but on that same 1/3" cam, an 18mm lens would produce no barrel distortion.

can a long lens on a 1/3" camera produce barrel distortion when on a 35mm camera?
 
Of course short focal length lenses cause barrel distortion; the extreme of that is the fisheye. Here's a 16mm Zenitar on a 35mm still camera:
http://www.kenrockwell.com/zenit/zenitar-16mm.htm

Some lenses are corrected for this (so-called rectilinear lenses). That's pricey. Looking at Ken Rockwell's page, he shows a Nikon 13mm with zero distortion, and a Nikon 14mm with "strong" distortion. It's not solely about the focal length, it's about the way the lens is designed and the price you're willing to pay.
 
But why does a 16mm lens NOT cause barrel distortion when it's on a 1/3" cam??

Nothing changes only the size of the format
 
DanHD said:
But why does a 16mm lens NOT cause barrel distortion when it's on a 1/3" cam??

Nothing changes only the size of the format
Click to expand...


First of all, very wide lenses distort on any format. Some lenses are specifically designed to be much more acceptable then others. These are usually 35mm motion picture lenses. This is one of the reasons why they are so expensive. Distortion is much more noticeable on moving images versus static photographs.


I've seen some crap lenses for 35mm motion picture cameras... but then again I've looked through many panavision lenses which have considerably less noticeable distortion and a great picture considering the obscene focal length! ;) (I am referring to absurdly wide angle lenses such as the ones Wes Anderson uses)

To answer your question, you have already supplied the answer within it. "Format Size"

You can't take a 28mm 35 lens and stick it on a 16mm camera and still get the same 28mm field of view. Because the 16mm format is about half the size as the 35mm format, the lens's projected image is intended to be much larger then the 16mm film. Therefore only the middle of the image makes it to the film.

This is why a 50mm lens on 35mm is equivalent to a 25mm on 16mm (approx... not exact).

So the reason you are not getting distortion when you put a 16mm lens on a 1/3 camera is most likely because the distortion, which is most apparent at the edges, is not making it to the image plane. You are most likely looking at a 'zoomed' in middle portion of the lens's field of view. That 25mm lens for a 16mm camera that you popped onto a 1/3" camera is not a 25mm lens anymore. I don't know the exact math, but I'd say its more like a 40mm or something now.

I hope I made sense. I usually edit these long posts, but I've got family and eggo waffles waiting for me... (yes it's 2pm eastern time and I'm just getting up after last night. :P )
 
Check out Ken Rockwell's pix from a 16mm Zenitar.
http://www.kenrockwell.com/zenit/zenitar-16mm.htm

The cropped one still shows some distortion, but nothing like the full-frame one. But look at the center of the full-frame shot, and you'll see it's practically rectilinear at the center, vs. wildly distorted on the edges.

As for frame size, that full frame image is coming from a 36mm x 24mm frame size. The 1/3" chip is usually about 5mm x 3mm. So you're talking about the 1/3" chip using 15mm2 out of 864mm2. Or, in other words, the 1/3" chip is only using about the central 1/60th of the image. Things aren't too distorted down there!
 
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