Quote Originally Posted by karl french View Post
In 1866 Dallmeyer introduced the Patent Portrait Petzval. Flipping the rear air spaced pair and slightly changing the curves of the elements. Also allowing the two rear elements to be separated to introduce diffusion. Many people copied Dallmeyer's changes. Those copies are rightly called "Dallmeyer copies" as an easy way to identify them in comparison to the "standard" or original Petzval design.

In fact this lens is a Dallmeyer copy. Not by the mere fact that it's an f4 lens, but because it has the flipped rear elements and diffusion control at the rear.
Quite so!.
But we are not going to enter into patent discussions that I think we already have clear, or in wars of European or American manufactures. The important thing is to rescue this lens to be able to enjoy its qualities.

As for the curvature of the elements, both the front and the two rear, look like the design of a RR. - less pronounced concave faces- Is there much difference between this design and an "original" petzval???
Talking about sharpness and swirly
Thanks Karl.