The atmospheric dispersion prevents diffraction limited observation
at higher zenith distances in J- and H-band. To correct this
wavelength dependent aberration, an atmospheric dispersion
corrector can be placed in front of the camera.
Up to now, this instrument is only for experimental use.
Figure 2.6 illustrates the correction for a zenith distance of
.
Figure 2.6: Atmospheric dispersion at an zenith distance
of without correction and using an ADC
This ADC is build of two pairs of prisms made of ZnSe and
ZnS-Multispectral. Each pair of prisms is cemented. All the surfaces
are coated for highest transmission. The average transmission
of the complete ADC in the wavelength range from 1.1 to 2.45 
is 95 %.