A refracting telescope advertised by a local retailer has an objective lens diameter of 80mm and a focal ratio of f/10.
(a) What is the focal length of the telescope? [1 Mark]
(b) How long would you expect the telescope to be physically? [1 Mark]
(c) What is the image scale (plate scale) of the telescope in arc-seconds per mm? [2 Marks]
(d) A competitor company is selling at Newtonian reflector with a focal ratio f/4 and a aperture diameter of 76mm. How does this telescope differ from the refractor? [4 Marks]

Question

A refracting telescope advertised by a local retailer has an objective lens diameter of 80mm and a focal ratio of f/10.
(a) What is the focal length of the telescope? [1 Mark]
(b) How long would you expect the telescope to be physically? [1 Mark]
(c) What is the image scale (plate scale) of the telescope in arc-seconds per mm? [2 Marks]
(d) A competitor company is selling at Newtonian reflector with a focal ratio f/4 and a aperture diameter of 76mm. How does this telescope differ from the refractor? [4 Marks]

z4k4r1y4 · Answer

I got (a) 800mm    (c)258arcsec/mm
I'm stuck on (b) & (d)

masumanwar · Answer

well this problem can be solved like this  f. = D.*fr=80*10=800  mm
then need to calculate the magnification as f./fe then field of view  ...

z4k4r1y4 · Answer

so how would calculating the magnification help?

z4k4r1y4 · Answer

I think (b) is 800mm, i.e. the same as the focal length.

z4k4r1y4 · Answer

http://www.telescopes.com/blogs/helpful-information/18966596-understanding-telescopes could this help with (d)?

anonymous · Answer

Sorry, I am no good at light :/

z4k4r1y4 · Answer

ok np

z4k4r1y4 · Answer

@Astrophysics

farcher · Answer

Attached

z4k4r1y4 · Answer

wow thanks so much (d) definitely makes sense. really appreciate the help.