Telephotography of restricted areas
A bit more on F-stops
In the text above, I counted out the F-stops from 5.6 to 16. This is
pretty simple stuff; just keep multiplying the focal ratio by the
square root of two. You can set up all sorts of spread sheets to do
optical computations, but there is a handy program that has most of what
you need. It is called F-Calc, and
costs as much as all this advice I've given you. As you can see below,
f5.6 plus 3 stops is f15.84, which I rounded to f16.
The program has a few other tricks.For instance, say the
equivalent focal length of our set up is 2500mm. The distance from
Tikaboo to the non-existent base is about 42km. For a 35mm camera,
how wide is the field of view in meters?
Survey says: 756 meters, or 2480ft. With this information, you can estimate the size of objects at the base.