How Do You Calculate Luminous Flux in a Projected Solar Image?

[Pep04]

Homework Statement

What diameter will have an image of the Sun (α=32’) projected in the focal plane of a f/7 lens with a focal length of 40 cm? What will be the luminous flux in the image?

Homework Equations

image diameter = α×f
focal ratio = f/D
1 radian = 206265’’

The Attempt at a Solution

In the first question I calculated the diameter of the image of the sun by multiplying its angular size by the focal length of the lens, resulting in approximately 0.37 cm. Moreover, the diameter of the lens will be equal to the focal length divided by the focal ratio, which is approximately 5.71 cm. I know the flow will be directly proportional to the diameter of the lens squared, but how do I calculate its value?

 

[BvU]

Hello Pep,

A rather late response, I'm afraid. Not an expert reply either, more an attempt to help:

Your relevant equations don't mention anything related to flux. But you do mention the area of the lens, so you need something to multiply that with. Have you heard about the solar constant ?
You want to check if you need to reduce this to visible light only, I don't know, but I guess not.