This is new-old stock literally from the turn of the century. These were achromatic objective lenses used to make our SV80/9D telescopes - the longer and better color corrected version of the Nighthawk. They are 80 mm f-9.4 mounted objectives using slightly lower dispersion FK5 optical glass. The achromatic color correction is very good owning to the longer focal length. Mounted in a heavy duty aluminum cell that threads onto an M90X1 male tube thread and was used with a sliding dew shield that had a 4.2" I.D. We do not have the tube or dew shield. These were discontinued when we moved to ED telescopes and ran out of tubes and focusers. Limited to stock on hand. Fully-multi-coated.
These lenses were made long before we did any interferometric testing. We consider these to be grade a or grade b. They will make a wonderful telescope making project.
