How do I change the field of view of camera while keeping amount of shadow ?

Development Rendering
, , , , ,
1

Hi.
Please excuse my poor English.

Please look at these pictures.
These have different field of view.

image

image
image739×389 20.4 KB

The former(A) is an angle of 90 degrees.
The latter(B) is an angle of 26 degrees.

Why are there different shadow?

I want to adjust amount of shadow A as B.
And keep field of view of 26 degrees.

Is there any good method?