Abstract

A failure of the second and third orders from a concave grating to focus in the same curve is described. The fourth and fifth orders show no anomaly. No logical explanation seems possible at present but it is pointed out that the effect may be common though undetected.

© 1963 Optical Society of America

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Figures (5)

Fig. 1
Fig. 1

Focus of third order—focus of second order. Abscissa is corresponding first order.

Fig. 2
Fig. 2

Photograph of grating in light of second order only.

Fig. 3
Fig. 3

Photograph of grating in light of third order only.

Fig. 4
Fig. 4

Group of second- and third-order lines (×3) about 9060 Å (first order).

Fig. 5
Fig. 5

Same group of lines as Fig. 4 on sloping plate to show differences in focus (×0.3) of second- and third-order lines.

Equations (6)

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n λ = a ( sin θ 1 + sin θ 2 )
cos θ 1 ( cos θ 1 r 1 - 1 R ) + cos θ 2 ( cos θ 2 r 2 - 1 R ) = 0
- δ θ 2 = δ a n λ / a 2 cos θ 2 .
2 ϕ r 2 = w cos θ 2 , - δ ϕ = ( w / 2 ) cos θ 2 ( δ r 2 / r 2 2 ) .
δ a a = w a 2 cos 2 θ 2 r 2 2 δ r 2 = w a 2 n λ δ r 2 R 2 .
δ a / a = 0.66 × 10 - 5 .