Yup,
although I got a couple of the technical aspects wrong, it does seem like my suspicions have been confirmed and that there is an ever so subtle but nevertheless noticable drift towards the Fat-Chance camp.
Many thanks, for the clarity folks, I'll pass the good news on.
Adam.
> -----Original Message-----
> From: owner-xsi(at)Softimage.COM
> [mailto:owner-xsi(at)Softimage.COM]On Behalf
> Of Kim Aldis
> Sent: 09 January 2007 15:19
> To: XSI(at)Softimage.COM
> Subject: RE: Lens distortion conundrum
>
>
> I think your main problem is going to be that the 16mm is
> going to have a
> smaller fov than the 35mm and you're not going to get as much
> information
> for your grid as you need. Plus, of course, distortion
> generally tends to be
> greater toward the edge so you've got the bit that matters least.
>
> But generally, though, yes, I think it's going to be pretty
> much useless to
> you.
>
> > I also assume that you would need some sort of lens
> conversion ring to
> > mount a 35mm lens on a 16mm camera which would again slightly change
> > the focal length.
>
> The focal length of a lens never changes, regardless of what
> you do with it.
I kind of knew that.
> > My basic, possible naive, understanding of film sizes and
> focal lengths
> > would lead me to believe that you would need double the
> focal length to
> > compensate for the 35mm->16mm film size difference,
>
> Not really double. The relationship - without actually
> thinking about it as
> hard as I should - is trigonometric.
>
> > or that to use the
> > same lens you would have to shimmy the filmback backwards to observe
> > the same amount of distortion across the 16mm film.
>
> Again, no. If you move the film plane back and forth it just
> goes in and out
> of focus. You'd need an entirely different lens to get the
> same fov and this
> is why your grids are wrong. Bearing in mind that you can't
> shift either the
> lens or the film plane (same thing, effectively) then you
> start to see that
> all you're doing is changing the fov when you change film
> formats. The 16mm
> is just smaller.
>
>
> I really don't see a way around this.
>
>
> > -----Original Message-----
> > From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On
> > Behalf Of Adam Seeley
> > Sent: 09 January 2007 14:36
> > To: XSI(at)Softimage.COM
> > Subject: OT: Lens distortion conundrum
> >
> > Hello all,
> >
> > Here's a head scratcher for the day, (well mine anyway).
> >
> > We have a whole bunch of plates that have been shot 35mm
> Full Aperture
> > on various Prime lenses. e.g . 10mm, 24mm, 50mm, 180mm
> >
> > Lens Distortion Grids have been shot for these plates using
> exactly the
> > same lenses (matching serial numbers), but have been shot onto 16mm.
> >
> > My instant reaction is that this is wrong and will give us incorrect
> > results when we get down to the undistortion, tracking and
> ultimately
> > the line up of CG & live action.
> >
> > So, I'm just curious to know whether this what's known in
> the industry
> > as a technical faux pas (to put it mildly), or am I missing
> some basic
> > technical savvy.
> >
> > My basic, possible naive, understanding of film sizes and
> focal lengths
> > would lead me to believe that you would need double the
> focal length to
> > compensate for the 35mm->16mm film size difference, or that
> to use the
> > same lens you would have to shimmy the filmback backwards to observe
> > the same amount of distortion across the 16mm film.
> >
> > I also assume that you would need some sort of lens
> conversion ring to
> > mount a 35mm lens on a 16mm camera which would again slightly change
> > the focal length.
> >
> > Any answers/speculation/inherent knowledge & experience gladly
> > received.
> >
> > Cheers,
> >
> > Adam.
> >
> >
>
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