Biomedical Engineering Reference
In-Depth Information
A
Galilean
B
Keplerian
Figure 12-8.
A telescope's exit pupil is the image of the objective lens as seen from
the eyepiece side of the telescope.
A.
For a Galilean telescope, the exit pupil can be
seen floating within the tube; it is a virtual image.
B.
For a Keplerian telescope, the exit
pupil can be seen floating in space, outside of the tube; it is a real image.
For a Galilean telescope, the exit pupil is virtual and located within the tele-
scope, while for a Keplerian system, it is real and located outside of the telescope
(Figs. 12-8 and A-1 and A-2 in Appendix A). When the eyepiece end of the tele-
scope is viewed from about 40 cm, the Galilean exit pupil is seen as a small circle
within the telescope, while the Keplerian exit pupil is seen as a small circle floating
in space outside the telescope.
The diameters of the entrance and exit pupils can be used to determine the mag-
nification produced by a telescope. The formula is as follows:
entrance pupil diameter
M
ang
=
exit pupil diameter
This formula is useful to the clinician because it provides a quick and straightfor-
ward method to determine (or confirm) angular magnification. Table 12-3 sum-
marizes the characteristics of Galilean and Keplerian systems.
