what does all these lens lerms mean?

[Ole]

My Dogmar is on a One Shot Camera so what is the reason - is it cheap or does it serve a purpose.

Precisely. It's cheap, and serves it's purpose.

My Grandagon is a 90 f4.5 - big piece of glass - how does it rate?

Gord

Big glass, big price, big rating.

The Dogmar isn't necessarily so bad, as long as you don't expect too much. Dagors aren't necessarily good, if you expect too much of them...

Since I've started, I'll continue...

The Dagor, like the Protar of similar age (and construction) were horrendously expensive lenses in their time. The reason for the price was not exotic materials or extra tight tolerances, but rather that the process of aligning and cementing so many elements in each group was very complicated and time-consuming! Cementing two lenses is fairly simple - but then add a third element without getting the first two out of alignment - and then in some cases a fourth one! At the very least you would have to start with lens blanks significantly larger than the finished lens, as each new cementing would lead to re-grinding the diameter...

"Simpler" constructions like four air-spaced elements can actually be far better corrected than the "massive glass sandwiches". One such was the Rodenstock Eurynar, which was famous for its resolution and infamous for its flare. The main reason for cementing all this glass together was primarily to reduce flare! Compared to the Protar Series VII (IIRC), the Eurynar had half the number of glass elements and twice the number of glass/air surfaces - and about one fourth the price.

This is also the reason for the enduring popularity of the Tessar construction: Only two cemented elements, and the increased correction possible with two air-spaced elements, is a good compromise between corrections and surfaces.

With modern multi-coating the number of surfaces is less important, which is why modern lenses are generally better corrected, with lower flare than older types. Making a Dagor or Protar lens today would be horrendously expensive, and optically inferior to what a simple four-element airspaced design could be. I mentioned earlier that the first Symmars were Dagor-design which was changed to Plasmat with the introduction of good coatings...