Fig. 15.3. Geometry for finding orientation and curvature of focal surface for Czemy-Tumer
spectrograph.
can be used to find the image surface curvature. Substituting Bi in
K:^
in Table 5.7,
and noting that
Q'
= i/^, we find
K. =•
R.
^0
RJ
(15.1.7)
where W is the distance OG in Fig. 15.3. The center of curvature of the image
surface is on the line (7C, and a flat image surface is perpendicular to this line.
Setting
Kf
= 0 gives the condition for a flat image surface as
W/R2 =
1
=b
\/y/3,
with the minus sign a more convenient choice. With this
value for W/R2, the coma measures for the preceding example ar
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