Video mapping using Cinema 4d

[Contraband]

I have a video mapping project I'm working on. I have created the geometry I wish to project on in Cinema 4d, I now want to place cameras to emulate real life projectors, but I'm not sure how I should setup the cameras in Cinema to achieve this? Things like focal length, aperture width and field of view. Is there a formula to matching these with the projector so that the geometry will line up with the real life projection? Any help would be greatly appreciated!

[alfaleader]

You can try to match the camera with the projector but it won't be 100% perfect.

The best thing is to take a zoom lens (take 100) and make your content (with a more wide angle lens you might have more fisheye lines). Then map your video to the physical object with mapping software. (irmapio, madmapper...)

[Contraband]

Thanks By 100, do you mean a 100mm lens?

[deepvisual]

this comes up often.

perspective and parallax should not vary whatever lens you use.

Lens angle is the only thing that will change and this is best deal with by ratios.
A 35mm lens on a 35mm (stills) camera is very close to 1:1 (all lenses have a 5% margin of error)
in the real world you'll never get your projector exactly in the same position as your virtual camera, only close, so its normal to warp the output using mapping software.

[Contraband]

Thanks, I will be using resolume arena for fine tuning on the mapping side, but I do want to get the camera frame as close as possible for content creation. So in cinema 4d I have 3 attributes on the camera, focal length, aperture width and field of view. I assume aperture width is your lens so I should go with 35 for that? What of the other 2?

[deepvisual]

no
in a word.
35mm is the focal length.
find out the lens angle of your projector and use the same one in C4D.
its easiest to do this with ratios

http://en.wikipedia.org/wiki/Angle_of_view

[jamesamcpherson]

ive just been through all this in my thread if you read it you might find something helpful. i also found this thread which helped me
http://vjforums.com/showthread.php?t=37625
you need to know the lens throw ratio of the projector lens your using, and it helps if you know the size of screen at the distance your projector will be at and the width/height of the thing your mapping and work out the distance from the thing your mapping . a 10m wide object on a projector with a 1.5:1 ratio will be the projector ( or in your case render camera ) 15 meters back. a 35mm lens =27degrees angle of view at 1:1 so a 1.5:1 is 27 + (27/2) = about 40 degrees.

make sure your gate is set to 1.33 and not 1.5 or 2.35 if your using xga or any other 4:3 format
some people say render orthographic but i didnt find this mattered for mine

[Contraband]

Still not sure if I'm getting this...

Projector I'm using is Sanyo XU78 which has the following lens:
F = 1.65 ~ 1.81
f = 22.5 ~ 27mm

So if I use a focal length of 35mm and an aperture width anywhere from 22.5 to 27mm (the field of view auto adjusts accordingly), I should be fairly close to what the projector will be doing in reality?

[Hfour]

If you know exactly where the projectors are going to be, and what their range of throw is, you can set the camera in c4d to an approximate middle ground as long as it is in the same location in the virtual scene as the projectors will be in reality.

[deepvisual]

now then, this got me thinking.
there is a difference between projectors and camera lenses after all.
projector lenses project off centre. projectors are traditionally at the top or bottom of the screen and only half of the lens is used..
I'm wondering if this accounts for the problems people seem to be having with lenses in 3D programs.