Using a soft focus brass lens

[badler]

I recently acquired a large brass lens from a trusted source. It is marked 2A Cervees. It doesn’t have a knob and tread, but the rear element has four markings suggesting turning the element will adjust the degree of softness. Am I correct? Is there some thread to help me figure out how to properly use this lens. I hope to do some experiments but removing and re setting the lens will take almost as much time as waiting for the plate to sensitize. Thanks for any information.
Brent

[Steven Tribe]

…….. Am I correct?
Brent

Probably!

The Dallmeyer redesign of the two lenses in the rear cell of the standard Petzval Portrait lens was extensively copied from the late 19th Century - the Golden Age of Studio Portraiture! Mostly in France, but even Ross in the UK did it! Remember that Patent protection period used to be much shorter at this time and the second patent associated with the patent portrait Dallmeyer was only the front turning adjustment system - which left the rear half of the rear cell unscrewing mechanism unprotected!

The Dallmeyer “soft effect” is not much of a pictorialist’s wet dream! Best to even out freckles and less than perfect complexions, whilst still giving sharpness to the eyes.

[badler]

Thanks Steve
Searching the threads for “ Dallmeyer and soft effect” I was able to learn a good deal. Seems there maybe hundreds of similar lens designed sold in this era. Cervees doesn’t seem to have warranted much notice as a company. But the glass looks clean and it moves smoothly through stops and the rear element turns. Is there a good reference about this era? I don’t fully understand the physics of increasing the depth of field.

[badler]

Another question? Do you know when the system of naming F stops changed from the universal to the current system?

[BrianShaw]

1920 at the latest.

[Steven Tribe]

There is no universal aperture system!

US stands for Uniform system. But there were LOTS of different scales at the same time - see here.

https://www.largeformatphotography.info/forum/showthread.php?65419-Historic-Aperture-Systems

Every nation stuck to their own scale until quite late(WW1?). This means that the early successful lens makers (Goerz especially) made the same lens with an aperture scale that was acceptable to the country where it was going to be on sale.

Dan has a very clear, concise and correct article on the Petzval here:

https://www.antiquecameras.net/petzvallens.html

[Steven Tribe]

taking a break from painting windows, I have done a quick search for cervees.
It is a short period product from the New York lens company. Who were also a short lived company, I seem to remember. They made at least 2 series. The A and the B (like Dallmeyer!). There are eBay sales data for a 3B and a 3A. Almost certainly a rebadged French made lens.

yes it is the standard rear adjustment soft lens - see here.

[BrianShaw]

http://throughavintagelens.com/2010/01/the-u-s-f-stop-system/

[badler]

Thanks to you both for the information. I’m still interested in the technical explanation of the increase in “depth of field”. I’ll download Dan’s article.
Thanks again for this generous community

[badler]

Here are two examples from this lens. 218791218792

[Steven Tribe]

good examples.
You just missed the curved focal plane of Petzval in the double portrait - but it still makes for a very interesting shot. Quite timeless- could be 1952!
The single portrait is exactly on the iris and very shallow depth of focus gives a special atmosphere to the image.

[CCHarrison]

Read all about soft focus lenses here: https://antiquecameras.net/softfocuslenses.html