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Note to fig.6 SCHEME OF THE CONE OF LIGHT BETWEEN SECONDARY AND FOCUS in the coma free device
y2s > y2m
It is | and |
It must be | a) |
therefore | b) |
Being the convergence Um of the meridional rays in F′m and the convergence Us of the saggital rays in F′s, we get c) since and we can write formula c) d) Formula d) soluted for a1m will then give our formula 18) q.e.d.
In fig.6 is shown that, if the corrector is placed in the plane X, ( y3m = y3s ), the final convergence of the meridional rays U1m equals the final convergance Us of the saggital rays, i.e., Fm and Fs are equalized and the astigmatical difference of focal- lengths is eliminated.