PX284 - T7 - telescopes

d \approx θ f_{1} \approx α f_{2}

\frac{α}{θ} \approx \frac{f_{1}}{f_{2}}

to match $D_{o b j}$ and $D_{e y e}$ , require:
$D_{o b j} = \frac{f_{1}}{f_{2}} D_{e y e} = M D_{e y e}$
$D_{e y e}$ should match the geometry of the human eye
diameter of the pupil $\sim 5$ mm
using binoculars/telescopes, more light enters the eye
this allows to see faint objects
increased by ${(\frac{D_{o b j}}{D_{e y e}})}^{2} = M^{2}$
but spread out over a large area increased by ${(\frac{α}{θ})}^{2} = M^{2}$
therefore, intensity of light at retina (power power unit area per unit solid angle) is unchanged