matching tiltshift

[simon123]

Hi guys

have two photos 1 taken with horizon flat and one 5 degree shift.
both line up in photoshop and i can match the horizontal one in max and vray cam
24mm etc etc

but when i move the cam target and add vertical shift i find i need to add some zoom factor to get the same points to line up on the shifted image..

help

thanks!

[tzaar]

I've had this problem too, and thought that changing the distance to the target to be the same would help (as the field of view is affected by the focus/subject distance on a real camera, as you can notice when changing the focus). And then I hoped that using vertical offsett would help instead. But it doesn't (if someone who knows why that function behaves the odd way it does it would be nice to have it explained.
The only thing I can think of, if you got a perfect match and don't want to eyeball the zoom factor until it's close enough, would be to expand your field of view. Change the focal length to maybe 14-16 mm instead. And calculate the factor (not too certain of the mathematical terms here) between the new old focal length and the new, and use that to figure out your new image size for your render or how much to expand your canvas i photoshop. I some times have the need to do this and mostly do the numbers by hand, but I know there is a script out there that does this for you (never tried it though)

[stef.thomas]

Never raise the camera target when doing a photo match with shift-lens backplate! The view becomes squeezed and you will never get a proper match. You might be fine using a skew modifier on a standard max camera, but the best way is to find the horizon line of your photo then calculate the pixel height between horizon and top. Extend the canvas so that you have an equal distance at the bottom i.e. you will now have blank space. This won't affect your FOV or focal length figures as they only care about the horizontal. Now set your image ratio to match the new backplate dimensions, place your camera and target at the correct height and do your photo match.