Re: Conversion calculator real 35mm camera to softimage fov

["Marc Bourbonnais" <marc(at)hybride.com>]

Ahh, that's the kind of stuff TDs eat for breakfast.

Thanks for the input Chris.
--
Marc Bourbonnais
3D TD
Hybride
(450)227-4245
----- Original Message ----- 
From: "Chris Shaw" <cjdshaw.bulk(at)blueyonder.co.uk>
To: <XSI(at)Softimage.COM>
Sent: Tuesday, March 14, 2006 7:13 AM
Subject: Re: Conversion calculator real 35mm camera to softimage fov


It's because the scanning chip has pixels exactly 6microns by 6microns.
That means that a full ap scan should really be 4149x3111. To make the
numbers nicer, they scan a little less on the left, and a hair more
vertically to give 4096x3112. What we usually deal with is
half-resolution scans, hence 2048x1556.

Chris

Marc Bourbonnais wrote:
> That's why you have to take scanning into account. The real real real size 
> of a modern 35mm Full Aperture frame is 0.980"x0.735", so 1.333 ratio.
> -but-
> depending on the scanner, slight cropping can/might/will occur. For most 
> Cineon scans (what I see coming in here anyway), you'll get a 1.3162 ratio 
> image; 2048x1556 for 2K scans. To be honest I don't exactly know why, some 
> engineering issues had to be dealt with the scanners I believe. Kinda like 
> color NTSC is now 29.97 fps, not 30 fps. If anyone can give me a straight 
> history lesson on film scan cropping, be my guest. I've asked around and 
> all I can do is take these numbers and go with it.
>
> Since these values have very small variations, and we're talking about an 
> optical lens effect, projected on a mechanical moving reel, the cropped 
> with a machine that reprojects it frame by frame for a digitally scanned 
> image result, a 100th+ of an inch precision is a bit overkill. But hey, 
> it's always better to base everything on true values.
>
> --
> Marc Bourbonnais
> 3D TD
> Hybride
> (450)227-4245
> ----- Original Message ----- From: "Francois Lord" 
> <francoislord(at)gmail.com>
> To: <XSI(at)Softimage.COM>
> Sent: Monday, March 13, 2006 3:14 PM
> Subject: Re: Conversion calculator real 35mm camera to softimage fov
>
>
> This chart says that 35mm Full Aperture in 2K is 2048 x 1556 with a
> ratio of 1.33.
> But 2048 / 1556 gives 1.3162.
>
> Marc Bourbonnais wrote:
>
> > Ah. I was wondering about your original figures. You're correct about the 
> > scanning area, it's all that matters really.
> >
> > And yes, there are slight crops on a regular FA scans, but since it 
> > varies just a slight 1.3% I forgot about it long ago, my mistake. We 
> > usually nudge camera lens a few mm when we adjust trackings anyway. I 
> > bother with crops & shifts when we get to Academy framing, to keep our 
> > cameras as simple as possible; it's already a pain to keep everyone using 
> > decent camera values in prod. But your numbers are true to what's really 
> > happening.
> >
> > Cinesite has a hard-to-find scanning chart here:
> > http://www.cinesite.com/CineonTech/resoultions/ResChart.html
> >
> > --
> > Marc Bourbonnais
> > 3D TD
> > Hybride
> > (450)227-4245
> > ----- Original Message ----- From: "Chris Shaw" 
> > <cjdshaw.bulk(at)blueyonder.co.uk>
> > To: <XSI(at)Softimage.COM>
> > Sent: Monday, March 13, 2006 1:02 PM
> > Subject: Re: Conversion calculator real 35mm camera to softimage fov
> >
> >
> > The key thing is really the area which is scanned though. The size of
> > the mask will only affect whether you get black edges on your scans.
> > I've been over this in detail with Cinesite's scanning department. It
> > may vary between scan houses, of course.
> >
> > Incidentally, my last mail had a type. It should be 0.967"x0.735". My 
> > bad.
> >
> > Chris
> >
> > Andi Farhall wrote:
> >
> > > I was at a shoot last week and was bugging the cameraman about stuff and 
> > > he pulled out the mask from the arri camera they were using and showed 
> > > me the mask which was arri's version of open gate and was 24.25mm*18.6mm 
> > > and isn't 4:3 and there is also a tiny horizontal shift . Apparently 
> > > these mask sizes vary depending on which camera manufacturer the mask is 
> > > for. I downloaded "The ARRI-Guide for Ground Glasses.pdf from arri's 
> > > website which has the dimensions for all of the masks that they make 
> > > which is handy.
> > > Andi
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf 
> > > Of Chris Shaw
> > > Sent: Monday, March 13, 2006 3:29 PM
> > > To: XSI(at)Softimage.COM
> > > Subject: Re: Conversion calculator real 35mm camera to softimage fov
> > >
> > > Actually, a 2k scan looses a little bit on the left compared with the 
> > > full 35mm frame. Hence 0.976" x 0.735". Technically, you should also 
> > > offset your optical center slightly to the left, but there's enough 
> > > error in the lens to make this shift irrelevant.
> > > Chris
> > >
> > > Marc Bourbonnais wrote:
> > >
> > > > true 35 mm Full Aperture is 0.980"x0.735". That's for 1.333 ratio.
> > > > Sometimes scans can come in with a little more pixels in height, so you 
> > > > should use 0.980"x0.745" for a 1.3162 image ratio if it's the case.
> > > > --
> > > > Marc Bourbonnais
> > > > 3D TD
> > > > Hybride
> > > > (450)227-4245
> > > >
> > > >    ----- Original Message -----
> > > >    *From:* Marc Bommersheim <mailto:marc(at)freie-digitale.de>
> > > >    *To:* XSI(at)Softimage.COM <mailto:XSI(at)Softimage.COM>
> > > >    *Sent:* Monday, March 13, 2006 8:46 AM
> > > >    *Subject:* Re: Conversion calculator real 35mm camera to softimage 
> > > > fov
> > > >
> > > >    Thank you. Do you know the arperture size of open gate 35mm?
> > > >
> > > >    On Mar 13, 2006, at 10:05 0AM, Aleš Dlabač wrote:
> > > >
> > > >
> > > > >    if you know aperture size in inches you could use XSI. in camera
> > > > >    properties/projection plane tab. enter proper values including
> > > > >    focal length(mm) and your angle is computed.
> > > > >
> > > > >    Hope this helps you a little
> > > > >
> > > > >    Ales Dlabac
> > > > >
> > > > > >    Hi,
> > > > > >    is there an easy way to calculate softimage xsi fov angles from
> > > > > >    real  world 35mm lenses?
> > > > > >
> > > > > >    Kind regards
> > > > > >
> > > > > >    Marc
> > > > > >
> > > > > >
> > > > > >    ---
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> > > >
> > > >    Mit freundlichen Grüßen
> > > >
> > > >    Marc Bommersheim
> > > >
> > > >
> > > >    +49 69 97206740
> > > >    marc(at)freie-digitale.de <mailto:marc(at)freie-digitale.de>
> > >
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