I came across this lens last week while I was looking for an 8x10 back Deardorff back.
Since I've never heard of a "Deardorff lens", my interest was peaked and I decided to "acquire" ... $249, shipping included, was a risk buy I could take. Not that I needed another Petzval lens in this size and focal length ...
I've seen by now my fair share of brass lenses. The "Extra Rapid Portrait #4" in my mind undoubtedly referred to a Petzval design, most likely an 8x10 lens, possibly covering 11x14 at portrait distance.
On first sight, the lens looked like it was built by Bausch & Lomb. B&L built Petzval lenses for quite a few other "brands" who simply relabeled. Quite common in the industry, even in the beginning of the 20th century.
What peaked my interest though in this particular sample, was the mention of a 1891 patent and the suggestion there was an extra split in the lens tubes before and after the iris.
Googling the patent date brought up a patent from Gundlach covering intellectual property regarding increasing and decreasing the distance between front and rear lens group in function of angle coverage and/or iris opening. The focus curvature, as well as spherical (and other) aberration, is/are "improved" by doing so.
Further online research also resulted in a page out of a 1903 photography catalog sporting Deardorf portrait lenses. Clearly B&L manufactured but no immediate sign, or description, of the ability to change the distance between front and rear lens group.
So the research continued. Odd to see that I paid less than the 1903 quoted catalog price. Finally a steal !!!
Then the following popped up from "The history of L. F. DEARDORFF & SONS, INC, as told by Mr. Merle S. Deardorff" ... I'm only reproducing the relevant text about the Deardorff Petzval and the associated Gundlach Patent
Mystery solved before the lens even arrived on my doorstep.
Now that I've held the above lens, I can confirm there are two shrouds holding the lens groups, driven by a synchronized helicoid, effectively enabling the lens to shrink/extend a total of 2.5".
I'll need some elbow grease to unlock the helicoids and clean possibly over 100 year old dirt from the lenses. Goal is to have this lens mounted on a lensboard for my 8x10 Deardorff Commercial Studio camera. One more project until I can take images with this beautiful find !
I came across some more tidbits and images after my July 20th post on the subject. Not enough for a follow up post, so I'm adding it here since a few sites linked to this post already.
I found few more images on-line regarding this 1891 Gundlach patent Deardorff Petzval lenses.
The image above illustrates as the caption indicates, a No 3 lens. Note the nice handle to turn the helicoid ... then handle is missing on mine. Equally note the aperture scale at the bottom of the ring. [(c) R. Turner]
Next image of two lenses was duplicated from Ken Hough's Deardorff website [(c) L.F Deardorff & Sons] to ensure a permalink here. Equally shows a #3 ... note the differences around the handle to turn the helicoid. I also want to draw attention on the construction of the rear cell. Each lens is mounted in its own ring and the set is screwed together. This allows to change the distance between both rear elements. I've not found markings on my copy but these marks may have well been there in light of another discovery ... keep reading ...
I believe next image to be equally important in this whole discussion. It shows an 18" Deardorff Petzval without the helicoid feature to change the distance between front and rear group.
This confirms there are two types of Bausch & Lomb "Deardorff" labeled Petzvals out there ... with and without the 1891 Gundlach Patent feature. So the patent feature may be quite rare as stated by eBay seller "attrevida" in the 2014 sale on Ebay of a No2 Extra Rapid Portrait Deardorff.
The Ebay posting regarding the above "Deardorff Extra Rapid Portrait #4" doesn't state the 1891 patent date and the knowledgeable seller would have included that tidbit. What the text does mention though is equally important in any discussion on rebranding, Bausch & Lomb and diffusion devices in Petzval lenses.
Bold emphasis is mine ... Cheers,