Which design tends to be shorter and lighter?

Which design tends to be shorter and lighter?

• A. Galilean
• B. Keplerian
• C. Both
• D. Neither

Answer: (A)

A Galilean design tends to be shorter and lighter because it uses a concave eyepiece with a convex objective, which allows the two lenses to be placed closer together. For the same magnification, the tube length in this arrangement ends up shorter, since the separation is fo minus the magnitude of the eyepiece focal length, whereas in a Keplerian design the two convex lenses add their focal lengths, giving a longer tube. With a shorter tube comes less glass and weight, so the Galilean setup is typically the more compact and lighter option. (Also, it produces an upright image, unlike the Keplerian, which is inverted.)

A Galilean design tends to be shorter and lighter because it uses a concave eyepiece with a convex objective, which allows the two lenses to be placed closer together. For the same magnification, the tube length in this arrangement ends up shorter, since the separation is fo minus the magnitude of the eyepiece focal length, whereas in a Keplerian design the two convex lenses add their focal lengths, giving a longer tube. With a shorter tube comes less glass and weight, so the Galilean setup is typically the more compact and lighter option. (Also, it produces an upright image, unlike the Keplerian, which is inverted.)