Help with Gasc and Charconnet lens

[Rob Tooley]

I have come across a lens by Gasc & Charconnet it is an ordinary Petzval design with the addition of a third lens placed between the other two. The extra lens is a cemented achromat. The third lens and the front element are both mounted in a tube which slides relative to the rear lens group.
With the third lens removed and the tube retracted the back focus of the lens is 6". With the third lens in place and the tube extended the focal length is reduced and gives a smaller image with a back focus of 4 1/2".
Eder gives the start date for Gasc & Charconnet as 1860. I believe Derogy made a similar lens in 1858.
Does anyone have further information, especially advertisements, for such a lens?

[Stephen Bottomore]

Hello,

At the Photographica 22 event, which took place yesterday, on one of the dealers’ tables I saw three thick books listing, respectively, French, British and German lenses. These volumes seemed to be privately published and well researched. Perhaps your lens is listed? Also, I would be interested in knowing the actual titles and publisher(?) of the three volumes. Can anyone help?

Stephen

[Michael Pritchard]

Stephen I bought a copy of the British volume. I have some comments about it.  I can provide details of the imprint. Frederic Hoch was holding copies of all three on his table, but said that eBay was the place to buy. I'll add details tonight when I am at home. 

[Scott Bilotta]

Photographic Lenses of the 1800's in France by Corrado D'Augustini mentions a Derogy convertible lens of 1858.  Perhaps you have this book? 

On p347 the author wrote that "Gasc & Charconnet built an  Objectif Universal similar to Derogy's but without a convergent lens".  There are two lens diagrams that illustrate the use of three lenses.  One diagram shows the middle lens to be divergent and the other to be convergent. 

Without a middle lens in  place you have a portrait Petzval.

A convergent 3rd lens gives a shorter focal length portrait combination; the divergent lens results in a longer focal length portrait lens.

The optical diagrams do not show the middle lens to be an achromat.

Scott

[Michael Pritchard]

Corrado D'Agnostini & Ivan Rose, Dallmeyer, Grubb, Ross, Taylor, taylor & Hobson, Horne, Thorthwaite & Wood. Photographic Lenses 19th Century Great Britain and Ireland. NAJS Editzioni, 2021. ISBN: 978-88-940997-8-2.

[Stephen Bottomore]

Thanks Michael. Based on your info, the others on French and German lenses can be found by searching on “Corrado D'Agnostini” in http://www.worldcat.org/search . 

Stephen

[Rob Tooley]

Thanks all, I don't have the D'Agostini book but have seen diagrams of the Derogy lens which looks as if it can be assembled in many different combinations. There is a letter in an early British Journal of Photography which mentions the Derogy as being suitable for either cabinet or CdV work depending on whether the third lens was present.

Rob