Are all Goerz Double Anastigmats Dagors?

[Greg]

Me thinks it might be very helpful if some knowledgable member pipes in on how to difinitively recognize a Dagor optic, most probably by the number of internal reflections. In the way/far past, had once acquired a lens that had the Dagor formula but was not branded "Goerz", "Double Anastigmat", or "Dagor".

[Mark Sawyer]

The Dagor is a cemented triplet front and rear, only two internal air-glass surfaces to reflect. But there are other lenses with multiple cemented elements and only two internal surfaces, so don't jump to conclusions too quickly.

[Tin Can]

I may have asked this before...

Is this a Dagor?

I definitely see 2 bright reflections and I think 2 weak ones in both elements which look identical.

Symmar 300mm f6.8 # 204310 by TIN CAN COLLEGE, on Flickr

[karl french]

Yes, it's a Dagor copy.

[Tin Can]

Thank you.

Yes, it's a Dagor copy.

[Drew Wiley]

Like the tessar design, the dagor concept was both early and enduring, so it stands to reason that competing manufacturers designed workarounds to the Goerz patent.