View Full Version : What became of this?

Neil Purling
13-Apr-2007, 01:10
What appears to be John Henry Dallmeyer's modification of the Petzval design in that his improvement in figure 1 states the glass types of the back combination are reversed.
The outer component is a flint, the interior being the crown.
"suitable means are provided to alter the distance between the two lenses at will".
This means the two components of the back combination, thus altering correction of spherical aberration and diffusion of focus.
The coverage of the lens was estimated as "about sixty degrees", with a flatter field.
This lens had no diaphragm or provision for any stops.

Gene McCluney
13-Apr-2007, 07:33
You are referring to a text or document that is unknown to me. What text are you referring to? Probably, I could speculate that the lens design in question was produced at some point, but in lower volumes, and would be quite difficult to find now days.

Neil Purling
14-Apr-2007, 06:37
US Patent 65729 June 11th 1867
I wondered what Dallemeyer called it if the design was ever produced. It sounds interesting in the way the diffusion could be adjusted.

Jason Greenberg Motamedi
14-Apr-2007, 07:06
From Dallmeyer's American Patent of 1867 (no.65729): "... by a slight variation of distance or separation between its elements, any desired amount of spherical aberration can be obtained... With a lens or objective so constructed the operator can, by sacrificing intense sharpness of definition on one plane, distribute the definition over several planes, and so obtain a more artistic and pleasing result."

The lens you describe is Dallmeyer's patent portrait. Thousands of them were manufactured between 1866 and the 1930s. The lenses, as described, have adjustable rear elements. With the older focusing models you need to reach into the back of the camera and rotate the rear element, while the later models one rotates the barrel to adjust the spacing.

As mentioned this was originally for increasing the apparent depth-of-field with the unfortuate byproduct of diffused focus. Later, during the pictorialist movement, the purpose was touted as a soft-focus adjustment; the unfortunate byproduct became a desirable commodity.

In any case, the adjustment does not produce anything like the bleeding highlights (halation) produced in typical SF lenses. Rather it just looks like a rather dull lens. These are not, IMO, great as SF lenses, although are wondeful when the adjustment is set to zero.

This adjustment is also found in Wollensak's Vitax, a Dallmeyer rip-off.

Jason Greenberg Motamedi
14-Apr-2007, 07:09

Paul Fitzgerald
14-Apr-2007, 09:16
Hi there,

"This adjustment is also found in Wollensak's Vitax, a Dallmeyer rip-off."

Yes, and Dallmeyer ripped-off Voigtlander, Voigtlander ripped-off Dr. Petzval himself. I guess it's the most 'stolen' design in history.

Wollensak added the oh-so convenient thumb wheel adjuster for the soft focus but I prefer how B&L used the same sized threads and pitch on all threads, it makes it a triple-convertable 16", 18" and 28" in one lens. Just be VERY careful with the change-over, very large and extremely fine threads.

Erich Hoeber
19-Apr-2007, 17:09
The widely produced Dallmeyer "patent" variation of the petzval design produces - in my experience - results nearly identical to the original petzval. I believe it was more a way for Dallmeyer to skirt the patent and market a "better" product than anything else. You can introduce sperical aberations by adjusting the spacing of the rear two elements in the original design as well. Dallmeyer just made it a "feature."