Which design tends to have a smaller field of view?

Which design tends to have a smaller field of view?

• A. Galilean
• B. Keplerian
• C. Both
• D. None

Answer: (A)

Field of view is largely set by how the eyepiece uses the objective’s light. In a Galilean arrangement, the eyepiece is a concave lens placed after the objective. This diverging eyepiece limits how much of the objective’s aperture can be effectively used, causing significant vignetting for off-axis rays and placing the exit pupil inside the instrument. The result is a narrower angular field seen through the eyepiece. In a Keplerian design, the eyepiece is a convex lens, which allows more of the objective’s light across a wider angular range and reduces the edge-vignetting effect. The field of view is therefore wider, even though the image is inverted. So, the Galilean design tends to have the smaller field of view.

Field of view is largely set by how the eyepiece uses the objective’s light. In a Galilean arrangement, the eyepiece is a concave lens placed after the objective. This diverging eyepiece limits how much of the objective’s aperture can be effectively used, causing significant vignetting for off-axis rays and placing the exit pupil inside the instrument. The result is a narrower angular field seen through the eyepiece.

In a Keplerian design, the eyepiece is a convex lens, which allows more of the objective’s light across a wider angular range and reduces the edge-vignetting effect. The field of view is therefore wider, even though the image is inverted.

So, the Galilean design tends to have the smaller field of view.