... Gregorian.1
The prime examples among 8-meter-class telescopes are the Magellan telescopes, which have an f/11 Gregorian secondary. 
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... detector2
Anamorphic demagnification comes from the relation of incident to diffracted angles. At fixed wavelength, ${\rm cos} \alpha d\alpha + {\rm cos} \beta d\beta =0$. If the grating tilt is set up such that $\alpha \neq \beta$, then $d\beta \neq d\alpha$. Astronomical spectrographs are typically configured so that $\beta \geq \alpha$ and $d\alpha/d\beta \sim 1-1.5$. The diffracted beams from the slit are spread over a smaller angle than the incident beams were, and the slit is demagnified at the detector. This affects the translation of slit size into spectral resolution, giving higher resolution by $\times 1-1.5$ than we will calculate for the simple case. See Schweizer (1979, PASP, 91, 149) for a detailed explanation. 
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