Derogy No. 5 Lens -- what is it?

[WallaWalla]

Recently I have won Ebay auction on Derogy Rectilinear No. 5 lens.
This is this lens with some specs: http://www.worthpoint.com/worthopedia/derogy-19-inch-estimated-rectilinear-1774676060

Item was described as 19" (480mm) rectilinear lens, f/4, image circle is enough for 12x10 inches (my camera has 18x24cm ground glass). I asked the seller to weigh it, and it is 674 grams weight, what seems to be nonsense for me. Lens with such specs must weigh at least 1Kg.

I haven't found any information on this lens on the web. Absolute vacuum, like Derogy No.5 never existed. Seller seems to be competent and has a lot of good feedback.

Does anyone know anything about this lens? Will it be suitable for wetplate portraiture?
143766

[Mark Sawyer]

Probably a bit dark for wet plate portraits at f/8, but fine for landscapes, still lifes, or whatever doesn't move during longer exposures. (The f/4 is a Uniform System stop, equating to a standard f/8.) The weight is probably right because this isn't a big lens and has only thin glass doublets front and rear.

[WallaWalla]

Wow. I hear about this scale for a first time in my life. I will clarify this moment with seller. If it is standard f/8 than weight is reasonable.

[Steven Tribe]

This is, indeed, a standard type of Rectilinieaire Aplanetique for general use at (modern) F8.

Derogy began engraving the huge size number on his lenses after serial number 12,000. First with his RR's, then with his Petzvals - there is a Petzval no. 5 shown in the FS archive here (Eddie?).

I have a few sizes/focal lengths from D'Agostini's book. 2 is 15.5cm, 4 is 26cm and 5 is 48.5cm.
There are two no. 5s shown on page 164 of the aforementioned book (18791 and 18792).

It was a highly succesfull lens in France and the later models had an iris and the size number engraving was reduced in size. There is nearly always one or two on offer on ebay.fr or de. Descriptions are always less than perfect!

[Steven Tribe]

These are the no. 5s in D'Agostini's book.

We have permission from the author to post extracts!

[Andrew]

f/Stops............................ f/8... f/11... f/16... f/22... f/32... f/45
U.S. "Uniform System"....... 4...... 8...... 16...... 32..... 64.....128

I think

[WallaWalla]

Yes, thank you for the response, I will ask seller for re-list lens.