Projection Petzvals rear cell design - original or Dallmeyers "switch"?

**Steven Tribe** · 24-Mar-2010, 14:29

First of all, I have not looked through every thread that has covered petzvals - there are just too many! I have rechecked with VM and read CCHarrison's excellent website article. I also know that there have been discussions of "swapped" rear elements - especialy in projection petzvals. My question is basically - "did Dallmeyer's redesign become the optical standard (with necessary small variations because of patent protection) for both later camera and projection Petzvals?". I note that CCHarrison shows a Suter from 1866 which had already adopted the Dallmeyer redesign. I have often been in doubt with projection petzvals which I have collected the last year or so (my budget doesn't stretch to the real thing) as to the correct sequence. But yesterday I received one where there could be no doubt - the inner rear lens was fixed in the barrel along with a similarly fixed spacer. It was the Dallmeyer variant. It's mounting is such that I could easily fix up a softness control - gradual turns away from the spacer ring. This is the only projection lens I have where the two lens weren't loose under the locking ring and it is f2.5 rather than the usual F.6.

**goamules** · 24-Mar-2010, 18:15

Hi Stephen. I've seen mostly the original design. Mostly Bausch and Lomb and several European unknown brands, and Darlots. But I'm sure some used the Dallmeyer patent "swap". The patent may be the reason fewer used the Dallmeyer design, and the original Petzval design was poorly patent protected.

**Jason Greenberg Motamedi** · 24-Mar-2010, 19:53

For what it is worth, the Darlot projection Petzvals I have seen were all original design. In fact, the only lenses I have seen in person which were the Dallmeyer variant were made by either by Dallmeyer or Wollensak. I just checked Kingslake, and he writes that performance-wise there was little, if any difference. He also noted that Bausch & Lomb made lenses of both kinds.

**Steven Tribe** · 25-Mar-2010, 02:12

Many thanks for the replies! My own experience of projection petzvals is that they are mostly the original design - but as they were loose there is no way of telling whether they havd been "incorrectly" remounted after cleaning every decade or so. My curvatures on the "dallmeyer" type projection petzval are slightly different from illustrated x-section for the first Dallmeyer types. It will be interesting to see if an adjusting addition to mine produces the same kind of effects as the original Dallmeyer.

**alon96** · 28-Mar-2010, 07:58

Hi Steven,
after I am very chaotic the Petzvals unit.
When I have demolished the lens picture cleanly, after I discovered I am unable to install the surface element normal order correctly.
You can tell me?
Watches the picture----