This webpage contains figures of the WHT's optical systems and their characteristics.

Optical layout of the WHT

Primary focus

 

The layout of the WHT (with only the primary mirror), showing an Y ray fan. The effect of the central obscuration could be seen.   The PSF (point Spread Function) about an on-axis object point (wavelength 550 nm), the size of the Airy disc is approx 3.5um. 
The PSF linear scale (box size is 177um). The PSF plotted in a logarithmic scale shows the diffraction pattern of the spider obscuration (box size is 177um).

Cassegrain focus

The layout of the WHT (with the primary and secondary mirrors), showing an Y ray fan, the effect of the central obscuration could be seen here as well.   The PSF (point Spread Function) about an on-axis object point (wavelength 550 nm), the size of the Airy disc is approx 13um (the scaling is not the same as in the upper PSF). 
Another layout of the WHT with the primary and secondary mirrors. The encircled energy for three different fields: 0; 0.05; and 0.1 degree (0; 3; 6 arcmin respectively)
 

 

Nasmyth foci

 

The layout of the WHT (with the primary, secondary and tertiary mirrors), showing an Y ray fan, the effect of the central obscuration could be seen here as well.   Another layout of the WHT with the primary and secondary mirrors.