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Answer.) Keplerian Telescopes ðŸ”. :
The Kepler telescope 🔠as shown in the figure consists of two converging Lens, one is called Objective lens and another is called eyepiece Lens ....
Now it is given that ;
the object is lying in the front focal plane of the first lens
therefore,
magnification m = -fo/fe = -2
Implies , fo ( objective focal length)
= 2 • fe ( eyepiece focal length) ...
image size = m • object size
image size = -2 •5 mm = -1 cm
for normal adjustment Lenght
L = fo + fe = 3 • fe
for calculation and N.A of the objective lens ;
hence , the numerical aperture NA = 0.159
answer.....