The steel lens cell has been lowered away from one of the original Kenwood objectives shortly after it had been removed from long-term storage circa 1995. The glass is rust-stained from the cell, although the steel had been nickel-plated. (The nickel coating is visible under a coat of grey paint.) It is necessary to occasionally disassemble and clean old objective cells, because corrosion is surprisingly common even when cells are not directly exposed to moist night air. This is true even for brass cells. The particular danger is that internal corrosion can become so thick that the glass jams inside the cell. (This was not the case with either of the Kenwood objectives, but we mention the problem here, in passing.) The thinner element shown here is the crown glass. As found upon disassembly, the crown had previously been installed towards the sky, which was incorrect given C.A. Hasting's flint-forward design. It's very common for Hastings-Brashear lenses to be assembled backwards in their cells. When misassembled, an objective displays severe spherical aberration that, at least in larger apertures, is easy to recognize during a simple star test.
first
previous
