View Full Version : Front Projection "canvas" or screen: exact fit-how?

05-15-2012, 12:00 PM
I'm following a camera matchmoving procedure (http://forums.newtek.com/showthread.php?t=94121)detailed by Mr. Rid (hattip :thumbsup: ) and wondered the following: :question:

1) To make a Front Projection canvas of the proper aspect ratio, is it sufficient to create a rectangle that is "Frame Aspect Ratio"x(units) by (1xunits) in dimension?

2) What is the mathematically correct distance to place a properly dimensioned canvas away from the camera to exactly fill the camera's FOV? (This used to be an integer(?) multiple of the "Zoom Factor" setting, but I'm not sure that's still valid.)

(These may not be pertinent to Mr. Rid's procedure, but I've been wondering about them anyway, so.....)

EDIT: FWIW, a distance of 1/2 the Zoom Factor seems to fit the horizontal aspect perfectly, but a bit of the canvas object extends above and below the frame. Not sure where I went wrong there.
EDIT2: ahh, I had the "Alternative Aspect Overlay (1.85)" on. (What's that thing for??) So, it looks like Zoom Factor/2 is the correct distance! Huzzah.

05-16-2012, 05:41 AM
Another option is to check out the Object Properties custom object 'Camera mask'.

You make a polygon with the correct aspect ratio, parent it to the camera, and add Camera Mask. Enter the dimensions of the polygon, and it returns the correct distance the polygon should be from the camera.


05-16-2012, 08:21 AM
Another option is to check out the Object Properties custom object 'Camera mask'.
Well, that would have good to know! :thumbsup: :D

So many little nooks and crannies.

05-16-2012, 10:02 AM
So many little nooks and crannies.

Welcome to the ongoing LW discovery process. :)

05-16-2012, 10:03 AM
Welcome to the ongoing LW discovery process. :)
Dongle #99, bro. :grumpy: :cursin:

I'm not sure why they chose to call it "Camera Mask", though. Pour moi, this is like a the opposite of a camera mask.

While you could cut holes in the relevant object and use it as a mask, I'd think a feature called "mask" would have more mask functionality, tools to help you use objects as a mask. Naming is important, and NewTek isn't especially good at it ("adequate" or "average" is more like it). Again, sometimes it seems like a lot of features were named by non-English speakers.

I would have maybe called this feature "Camera Object", or "Front Projection Object".

05-16-2012, 03:18 PM
I'm not sure precisely what you are trying to do, but I usually just parent a plane tot eh camera, make it bigger than the field of view, and then front project whatever I want onto that plane.

BTW, the Alt Aspect overlay is designed for setting up your scene as a 16:9 scene, but then displaying 4:3 center cut markings. Some stations that broadcast in SD still centercut HD footage that you give them, and some clients still request both 4:3 and 16:9 versions of footage. So this lets you compose for both 16:9 and 4:3 as best you can (which is terribly, as any DP will tell you... Clients need to commit to one or the other).

A real motion picture camera has a ground glass (which is what you see when you look through the viewfinder) which frequently has marking lines for two or three different formats so the DP can see these through the camera... The Alt Aspect overlay is the same thing...