looking for information about a lens signed BD

[arohirohi]

Anyone with information to share about this lens?
On the side of the Waterhouse slot, it's written:
"Extra-rapide
Portraits
Paysages
Reproductions
B D"
Two groups. Back seems a glued doublet. Front is a casket fitted with a bayonet marked "Lentille pour faire plus grand". The corresponding FL is around 430mm measured from the Waterhouse, aperture f8.
The lens has a pleasant spherical aberration :-) and enough coverage for 8x10. Any guess who's B D?

Kind regards,
https://flic.kr/ps/3WKjcu

[Steven Tribe]

Need photos of the engraving and perhaps there is ink/pencil data on the side of the achromat?

The “Lentille pour……….” Needs to be photographed too!

This is the standard text on the Derogy Foyers Multiples Petzval from 1858 - so this could be a truncated lens with the achromat in the rear cell.

The black finish would suggest a 20th century production/modification.
Please more info,

[arohirohi]

Hi Steven,
Please find new uploads to the Flickr stream as I'm taking the lens apart to secure the bayonet.
The rear group is marked "Ex Rapide" and B Darlot with a pencil. Hmmm ... A(lphonse) Darlot would have been easy :-)
I recognize the handwriting style but if I compare with a genuine A. Darlot signature, I notice that the major D is written differently - this one buckles clockwise, A. Darlot anticlockwise.
Definitely not a Petzval.
You can also find the "Lentille pour faire plus grand" on the front casket. Taking the front apart is delicate as the ring has been damaged and I don't want to take the risk. I notice some balsam separation here so I assume it's a front doublet.
No sign of a date, no serial number.

Alain

[Steven Tribe]

OK, this makes it a Little clearer!

This definitely NOT a commercially made lens - even though it has been professionally put together. The engraving is very well done - it is almost too perfect - like a “one off” exercise of love! I reckon you will never know who B D is!

This type of bayonet fitting looks very much like Derogy and I can confirm that the “lens for making..” (translated from French) is taken from a standard Derogy lens from the late 1850’s. There was a set of extra middle lenses which could shorten or lengthen the focal length. Originally, there were sets of 4, 2 with different +ve focal lengths and 2 with different -ve focal lengths.

We can determine that your Derogy lens is early as the text is hand engraved rather than stamped and the text is written on the side of the lens cell- not the face.

I enclose some photos from the Derogy booklet and my own “extra lenses”.



I just happen to have a full set of these extra 4 lenses and enclose the corresponding image of a +ve and -ve for comparison. Note that the brass work is also a complete match.

My guess is that someone had the original Derogy lens from the 1850’s with a destroyed rear cell ( Bayonnet cells do get quite loose!). I think I can read Derogy half hidden in your achromat’s edge.

The diameter of my lens cells is 88mm across brass surround. These extra lenses are achromats too - not simple lenses.