Hi, I'm wanting to make a viewing frame for pre-visualizing 4x5 shots.I ran into this at Toyo's website

"Buy a 4x5 cut-out black presentation mat to use as a "viewing frame," and a small ruler. Hold the frame about 6 inches from your eye and you will see the approximate area that a 150mm lens "sees." Bring it about 3-1/2 inches from your eye and you now have simulated the area viewed by a 90mm lens"

But in an article by Howard Bond he mentioned making the cutout size 3" x 3 3/4" for 4x5.My only lens right now is a Nikkor W 150mm.So what size cutout do most of you use for a viewing frame?I was planning on doing mine with a piece of white 8x10 matt board then spraying it with matt clear krylon for protection.

Thanks....Chris