Tessar

The 80mm f/2.8 Tessar lens consists of 4 elements in 3 groups and, on the Certo Six, is of the unit-focusing type. Here is a small Wiki article on the Tessar. Here is a PDF article from the Zeiss website. The 2.8 debuted in 1932. To this date, about 5 million Tessar design lenses have been produced. Crown glass is in blue, flint glass is in green.

Telescope Adapter

ScopeTronix has numerous adapters that work with digital cameras with 40.5mm filters (the same as the Certo Six). I see no reason why these wouln't work with the Certo an allow you to do astrophotography with medium format!

Exposure Meters

While I have no experience with hand-held meters, I decided that they would be inpractical to carry about. I went with the Voightlander VC II meter. This meter is VERY compact at 42.5mm X 37mm X 19.5mm and weighs a mere 42 grams. I got mine here. I am VERY happy with my purchase even though it cost as much as my Certo Six did. It is nice and simple and seems to be accurate. It fits atop the Certo and easily clears the film wind lever. The other nice thing is that it transferrable to your other cameras. My father-in-law tried it with his Realist stereo camera over Christmas.