Lens Focal Length matching

[ajaxrobinson]

Hello

I am trying to composite a 3d object within a photograph and attempting to get the perspective correct etc.

I know the photograph Lens Focal Length was 20mm, but when I set the lightwave camera Lens Focal Length to this, the object becomes way to big and the perspective is wrong.

If I move the object away from the camera it gets too small, and then I can't zoom in because this changes the focal length!

Basically my question is this: should I be trying to match the lens focal length to make the 3d look authentic ?

Has anyone else done/tried this?

Is it possible that the size of my object is wrong?

Any help would be greatly appreciated. Thanks for reading

[Captain Obvious]

Set the aperture height to 24 mm, and then set the focal length to the "35 mm equivalent" of the focal length you used.

Regular film in an SLR is 36 by 24 mm per frame. Digital SLRs usually have smaller sensors, so look for a "35 mm equivalent" focal length.

[Giacomo99]

I'm not expert and I haven't seen exactly what you're trying to do, but there's also the fact that a real-world camera lens has spherical distortion and a 3D "camera" has none. If you use the "advanced" Camera in Lightwave you can compensate for this to some degree.

Compositing a 3D object into a real-world photo is often a tedious process, and generally involves a lot of tweaking even if you know the technical specs of your real-world camera.

[wavk]

or use dpont's cushioncamera ...


mlon

[ajaxrobinson]

thanks for all the suggestions guys. i am still having a lot of trouble with the particular shot I was talking about. I haven't had a chance to make the camera lens wide / rounder yet, but I'll try that.

I checked out CushionCamera, unfortunately it's for PC and not Mac, and I am using LW on a Mac. but thanks all the same for pointing it out to me.