DIY mask for mattebox

[shiny4]

i have received my new mattebox and cannot waiting for the release of the new wideangle mask.
i would like to know if you can give me more info about how to create different mask for different lens size(i have 24-35-50-100-180mm lens)
something like this:
http://geardear.com/mask4x5.htm
my question is how i can do to calculate the different dimension of the mask for each lens for not vignetting.
i wait your news
ivan

 

[Moz]

DIY way is cardboard with trial and error.

 

[Greg_E]

Dragging this back up from the depths...


Is it as simple as taking the angle of view for each lens (with your given sensor) and measuring from the iris to the plane where the mask goes to figure the second (opposite the angle) side of the triangle with some trigonometry?

I have flags for my matte box, but they double the size and look pretentious in a lot of circumstances. I'd really rather use the masks to block most of the stray light, then grab a flag or two if I have a specific problem. Trial and error without some kind of general direction just doesn't work well for me. Refining the process so that when I get a new lens I can just whip off a mask is where I want to get.