Bahtinov mask for Vixen Ark 80mm binocular

The Bahtinov focusing mask is remixed for Vixen (Giant) Ark *x80 binocular. Internal diameter of the ring is 94 mm. It perfectly fits on the rubber hood of each binocular side. Can be used with
Vixen (Giant) Ark 12x80
Vixen (Giant) Ark 16x80
Vixen (Giant) Ark 20x80
Vixen (Giant) Ark 30x80
Vixen (Giant) Ark 16-40x80

PS: I'm not sure if it works properly since Focal length divided by mask step should be inside [150,200] or [50,66]. While this mask has 4mm step and unclear F of binocular. I can only suggest that F=300mm for these binoculars, since it looks natural for the binocular size.
PPS: Test has shown that it works nice with point sources of light (with stars shall work as well) even with this mask params.
Relationship of 75 if considered good (inside [75,100]) according to the source as second order spot use for optimal focusing.
http://www.astronomy.ru/forum/index.php/topic,10421.msg426807.html#msg426807 (in Russian, use translate.google.com if required)