In order to get effective
focal length, I need the magnification factor to multiply by my focal
length (2000). Don't know how to get the magnification factor on a
203 Diameter - focal length 2000 with 26 mm lens. I believe it should
be 1.6x but I don't know how to verify this data.

Here is the formula I am trying to confirm:

effective focal length= 57.3 X (image/field of view)(31.75/0.6)

For this formula to work effective focal length should be 3,200 which
would be 2000 (focal length) X 1.6 magnification factor.