I don't know whether anybody's interested, but here goes with a very simplifed and generalised explanation of the differences between Sonnars and Planars. I ain't no Erwin Puts.

Sometimes it's a good game to compare the groups rather than the elements - and more of a pattern may emerge. However, compounding and splitting can affect both the number of elements and the number of groups without altering the basic lens type.

The Sonnar is generally an 'improved triplet' design - ie three groups with the addition of a positive meniscus in front. The triplet itself may be compounded and it may be split. Lots of variations on the theme. They are generally compact for their focal length - the rear node may be very close to the front of the lens - ie the lens isn't much longer than its focal length.

The Tessar is a simpler improvement of the triplet, usually by compounding only but splitting is also used.

The Planar is a 'double Gauss derivative': Ed's diagram is a good illustration of meniscus groups with the concave surface facing the iris - a characteristic feature of the double Gauss arrangement. Meniscus lenses have both their surfaces curving the same way, but with different curvatures. Double Gauss derivatives represent some of the finest fast standard lenses around.

Zeiss seem to use the lens names to describe the type, pretty much. Leica, on the other hand, tend to link the name to the maximum aperture.

So there you go.

PS It's ages since I used a Hasselblad - but I use Planars and Sonnars etc with my Rolleiflexes.