A diffraction-limited lens can focus light to a 10-m-diameter spot on a screen. Do the following actions

Question:

A diffraction-limited lens can focus light to a 10-μm-diameter spot on a screen. Do the following actions make the spot diameter larger, make it smaller, or leave it unchanged?
a. Decreasing the wavelength of the light.
b. Decreasing the lens diameter.
c. Decreasing the lens focal length.
d. Decreasing the lens-to-screen distance.