Fiber MOSs have also been implemented for use with Schmidt telescopes, making the fiber technique attractive for objects with surface-number densities of less than a few per square degree. An effective use of the corrected field can als be obtained by placing several slitlets at the positions of desired sources in the focal plane, coupled with an imaging camera with a dispersing element such as a transmission prism in its collimated beam. The dispersed sky photons overlapping the object spectrum, as in the case of objective-prism plates, can be avoided by having the slits placed in an aperture plate. As in the case with fiber MOSs, technical developments toward having automatic positioning of slitlets in the field of view have been pursued. Because sky subtraction is generally more effective with slits than with fibers, slit MOSs can target fainter sources, and they can thus simultaneously obtain a fair number of targets in spite of their relatively small fields of view.
Several variables determine the relative quality of the performance of fiber and slit MOSs.
The size of the field of view can be much larger in fiber MOSs, which can sample the whole field of view of the telescope rather than just that physically spanned by the detector. Additional concerns involve sensitivity, ease and the agility of operation, and the need for elaborate preparation and versatility. The lack of agility in the observations and the need for elaborate and sometimes uneconomical preparation required by systems with specially manufactured aperture plates impose the strongest inhibition to their extensive use. This page is maintained by Cren Frayer.