In rec.photo.equipment.medium-format Robin Faichney <robin@reborntechnology.invalid> wrote:

 image circle equals = tan(angle/2) X focal lengthX2
 
 A 6x9 frame needs at least 108mm of image circle. You can figure out the
angle by working back. But that only gives you the smallest angle that will
cover. Nothing stops Fuji from using a design with a greater angle.

      Some how I think you might have meant something else.
     
      Nick

There's a difference between the angle of coverage and the angle of view, the
former generally being wider than the latter.

I believe from your question that you're after the angle of view. The angle of
coverage is given by the manufacturer, supposedly after some rigorous tests and
compliance with ANSI standards.

There are three angles of view: diagonal, vertical, and horizontal. It's the
latter that's typically given for a lens and film format combination.

Use the following formula:

Angle of view =  2  x  Arctangent (negative width divided by twice the focal
length),

Arctangent is shorthand for "what is the angle whose trigonometric tangent is
x?"

Angle of view  =  2Arctan (w/2F)

It's not difficult to derive the formula, it follows straight from the
Pythagorean Theorem.

In your case, for a 6x9 negative, the width is around 82mm, if I recall
(measure one of your negatives for more precision).

Hence, Angle of View = 2 Arctan (82/180) = about 49 degrees.

A wide angle Fuji with a 65mm lens would yield an angle of view of about 65
degrees.

Bob G