Optical devices for planetary spectral surveying and mapping, e.g. for Mars missions, require small-size lens systems of low mass. An optical system called `Apo- Orthometar 5.6/175' for such applications has been already manufactured and successfully tested. This system consists of conventional optical glasses. It uses a quartz glass plate in front and has an enlarged thickness of the mounting for shielding against cosmic radiation. A new camera lay-out for the Mars Surveyor 98 Orbiter requires the application of completely radiation resistant glasses and a further mass reduction. Investigations have shown that the Orthometer lens type is less suitable for the new requirement and for an application in the 440 nm to 1000 nm spectral region. More suitable lenses are of the extended triplet type at f- numbers of 8.