$D_{mars}/D_{earth}=1/2$
Also, $D_{earth}/D_{sun}=1/100$
So, $D_{mars}/D_{sun}=1/2\times 1/100$
At 1AU, the sun’s diameter is = (1/2) degree
Therefore, diameter of mars will be = (1/400) degree
At 1/2 AU, mars diameter = (1/400)(2) = (1/200) degree
With 100 magnification, mars diameter = (1/2) degree = 30’
As a result, because of atmospheric variations, the value is larger than the resolution limit, and hence seems magnified.