The short wavelength cut-off of the PR130L prism at 1250 Å excludes the geocoronal Lyman-alpha line, making it the disperser of choice for faint object detection in the 1250 Å to 1800 Å window. The dispersion varies from 1.65 Å/pixel at 1250 Å to 20.2 Å/pixel at 1800 Å. Figure 6.23 shows the sensitivity versus wavelength, with the resolving power (R) and the offset from the direct image in pixels (x) as functions of wavelength. Bright Object Protection considerations similar to the case of PR110L also apply to the use of this prism, except that the background count rate is lower (see Section 4.6). As for the other prisms, the direct and dispersed images use different apertures with a small angle maneuver between them.
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