Au_sujet_de l'objectif de_6_pouces_de_foyer. Compléments sur le portrait de Mr Huet.
Le portrait de Dorothee-COTTE par Daguerre
effectué par Daguerre en 1844.
"A Note by R. Derek Wood on the Daguerréotype Portrait said to be of "M. Huet, 1837" " But it would be extremely surprising, indeed entirely inconsistent with all other sources, that Daguerre, two years before he was ready to divulge the technique to the world, had apparently (on such poorly considered evidence) already obtained an image by an exposure short enough to take a likeness of a living man. " Nota: Les informations suivantes montrent le décalage existant dans l'interprétation des textes, entre un auteur qui s'en remet à ses impressions et un auteur qui en démontre la faisabilité. R Derek Wood seems to forget that the first source of information is Daguerre. Remarks of Gay-Lussac and Lubbock demonstrate that we have not made errors.(J R)
Gay-Lussac has seen tests of portrait of Daguerre, before August 1839.
Daguerre has done a portrait of himself, said to be excellent. (lettre de LUBBOCK John William à Talbot datée du 2 Novr 1839 http://foxtalbot.dmu.ac.uk/letters/name.php?bcode=Lubb-JW&pageNo=1
PS: The objection of some authors on the portrait of Mr Huet puzzling, especially when these same authors do not identify fake paintings Daguerre and their knowledge of the birth of the daguerreotype are virtually nonexistent. (example: Stephen C Pinson)
(par Jacques ROQUENCOURT)
(collection Marc PAGNEUX:ne peut-être reproduite sans son autorisation)
While closing down the issue # 5 of Etudes Photographiques, I put together the daguerreotype featuring fossils, held in Arts et Métiers (CNAM), and the Huet family, officials painters to the Museum d'Histoire Naturelle, and I expressed the hypothesis it could be Nicolas Huet's.
This non authentificated hypothesis asked for conditionnal mood, which wasn't used in the different communications made out of myself. I therefore asked for a correcting Paris Match's journalist for the nov 26, 1988 issue and M. Guérin from Le Monde for the dec 27, 1988 issue. This correcting was to be published in issue #6 of Etudes Photographiques in mars/april 1999; unfortunately, its publication was delayed.
We've already made a clarification with André Gunther,( .etudes.photographiques. ) but it seems that doubt remains about the portrait's authenticity. In the notes to our article about "Daguerre and Optics" we gave what we believed to be sufficient . Daguerre's mail to Isidore, dated 1835, Dec. 15, provides significant information: "In this season I obtain in a quarter of an hour results I couldn't get in less than three hours in summer by the other means, and the same results I obtain in a quarter of an hour, in the summer, don't call for more than three or four minutes."
1836, May 9: "You won't choose to wait for two or three hours, for what you can do in two or three minutes." [T.P. Kravets, PP. 440 & 495]
In this paragraph Daguerre compares the sensitivity of the process he discovered (process using lavender essence residue) and the sensitivity of the new process that will become daguerreotype. This information about exposure time allows us to confirm his use of a 6 inch focus lens. We announced in N° 5 of "Etudes Photographiques" that the lens discovered in 1832 gave fine results at f/6, and that we made portrait tests, obtained in 3 minutes at f/5.6 in the shade. Necessary exposure with the 14 inch focus lens (380 mm) for a spot in summer is within 15 minutes at f/14; from this remark it follows that the duration of 3 minutes could only be obtained with a different lens: the 6 inch lens opened at f/6. This remark implies that turning the lens around as discussed in the aforementioned article, one obtains an expected exposure time of 1.5 minute at f/4. This matches experimental results of portraits reproduced below and also our tests on lavender essence residue made during the summers of 1991 and 1992*. The indication of 3 hours in summer for the lavender essence residue process matches the length of time necessary to obtain the "famous Set Table"**, which isn't, as many authors say, by Niépce.
Performances of the lens at f/6: MTF (Modulation Transfer Function)
- MTF: average of radial MTF and tangential MTF.
- Resolution of the eye is 3 lp/mm and 6 lp/mm (for an adult subject and young subject) at a distance of observation of 300 mm.
- The picture field of 2 x 60 mm fits the diagonal of the picture of a 70 x 100 mm wide rectangle (size of the images below).
*Au sujet de ces essais nous avions assurés nos droits par l'envoi de deux courriers recommandés:à l'auteur ainsi qu'au rédacteur de la revue.
**La table servie a été obtenue avec l'objectif de 6 pouces.Daguerre mentionne un objectif de 5 pouces, mais celui-ci n'a pas été réalisé.
***La lentille de cet objectif a été fabriquée par la Société Angénieux
-Daguerre et l'optique: J Roquencourt,
Etudes Photographiques: n°5 1998 (Société Française de Photographie).
-Note sur le portrait de M Huet: J Roquencourt, A Gunthert.
Etudes Photographiques: n°6 1999 (Société Française de Photographie).
-L'invention de la photographie: une tragédie (à paraitre)
* obligatory mention: title and author