Pa said:

Chris101 said:

Yes Pa, you have it correct. The DX lenses have the angle of view for a DX sensor given on Nikon's page, while the lenses designed to cover a film frame show the '135' format angle.

O.K. so how do I figure out the "true" FOV for the 28-200 at 28mm on my D70? Divide 74 degrees 20 minutes by 1.5 ? That, of course, would get me down to about 50 degrees.

I am on the road now so I don't have my formulas with me.

It is something like this

2*(inverse tangent(2*(sensor size)/(focal length)))

Width of sensor is one of the sensor lengths, widths, or diagonals. Focal length is the Focal Length of the lens. Inverse Tangent is the arctan function. I think Nikon's spec guys use the diagonal all the time.

Presuming my memory is correct, this is the proper way to calculate the angle of view.

You can find out sensor sizes pretty easily since the 35mm sensor is

36 x 24 mm, D70 is 1.5X multiplier so divide by 1.5 and you get

23.7 x 15.6 mm

You can calculate the diagonal using Pythagoreum's theorem

(23.7^2+15.6^2)^.5 == diag or about 28.37