[deadalvs]

hey all.

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this is a very fundamental thread if someone wants to place rendered objects in a photo.
or matchmoving for real-world footage.

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i personally have the problem that i have understood that the film back is basically the dcc of the camera, but how can i determine the exact measurements (which units?) for example for my digicam ?

i have an ixus II (canon) and i have found the specifications of the dcc, but i don't know if this is the length of the diagonal or what ever...
1/2.7"

if this were the diagonal at a ratio of 3:4, then the diagonal is 0.37037 inches long, thus the side lengths of the dcc would be 0.222222 and 0.296296 inches. is that correct ?

when i use maya with the units of meters, what units do i have to put into the film back ?
since the focal length is always in mm, there are a lot of missteps one can take concerning the units...

can someone help me on this ?
thanks a lot !

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deadalvs

[mverta]

Generally speaking, you have to find the measurements of the "filmback" - in this case, a ccd - either online or in the documentation or manual, or by calling the company.

However you get it, it will probably be in millimeters. Like my Canon D30, for example is 22.7mm x 15.1mm.

So, what you do then, is convert those to inches, for entry into the filmback in the Maya camera (multiply by .03937). So for the D30, it's .894 x .594.

Having done that, you can then enter the focal length you shot the scene with into the focal length attribute, and the plates should match. Be aware though, that your real camera has lens distortion, which increases with the shortness of focal length, so it could look significantly different at the edges.

What I do is "undistort" my images first using a utility in my matchmoving software, and then load the undistorted plates into Maya's background image to work with. Then I apply the reverse process to my renders to distort them to match the original camera.

Make sure your image output settings (Common Tab, Render Globals) match the same Device Aspect Ratio as your Camera Aperture Aspect Ratio.

Also, it doesn't matter what units you work in for your scene, as long as you use real-world scale IN those units. The plug-in will handle the conversion to meters (Maxwell's units) automatically.

_Mike

[deadalvs]

thanks, Mike !

i'll try to find or get the exact measurements !

that distortion thing could be a little tricky because this is advanced and surely does matter, but for arch viz it should be enough.
of course, when working with distorted lenses in film, this should be perfectly matched to the cg shot.

it would be great to have a few more possible selections for film backs in maya... or maxwell.

i'll go on with that...

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maybe other users can post their camera settings with a small scene, so other users can learn from...

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deadalvs