H.ROUSSEL PARIS 150mm/f4.5 lens type?

JPD said:

Where did the OP go?

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JPD said:

Look at the reflections of the rear group under a lamp. If you see two clear reflections and one faint, it's an achromat, which makes the lens a Tessar-type, but if you only see two clear reflections it's a triplet. That the whole lens is "taller" on the table could just mean that the formula is different from the Zeiss Tessar, even if the type is the same. The Ross Xpres lens on the Ensign cameras are slightly slower at f:3,8 than the Zeiss Tessar, but the front element is larger due to the forumula being different, but it's still a Tessar-type.

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1. Optical Design: The Stylor is frequently described in expert circles as a six-lens construction in three groups, similar to the Heliar, which was patented by Hans Harting at Voigtländer in 1900 (Patent DRP 123144). The Heliar consists of five lenses in three groups, but later variants and interpretations by other manufacturers, like H. Roussel, often added a lens or adjusted the arrangement to further correct imaging errors. This similarity is noted in discussions among collectors and in forums like the Large Format Photography Forum or Photrio, where users compare the optical characteristics (e.g., soft bokeh, high center sharpness).
2. Historical Catalogs and Literature: In old H. Roussel catalogs (which unfortunately aren’t widely available digitally but exist in archives like the Bibliothèque Nationale de France or with collectors), the Stylor is described as a high-quality anastigmat. Anastigmats with six lenses were often variations of triplet or Heliar designs at the time. Books like Rudolf Kingslake’s A History of the Photographic Lens (1989) or Sidney Ray’s The Photographic Lens indirectly mention that French manufacturers like Roussel adapted designs from German pioneers, including the Heliar.
3. Collector and Auction Descriptions: At auction houses like Westlicht (now Leitz Photographica Auction) or on platforms like eBay, Stylor lenses are occasionally labeled as “Heliar-type” or “Heliar-like.” This classification is based on observed optical performance and lens structure, confirmed through X-ray images or disassembly by restorers.
4. Practical Experience: Wet-plate photographers and large-format enthusiasts who use the Stylor report in blogs and forums (e.g., The Wet Plate Collodion Forum) that it behaves similarly to a Heliar—sharp in the center with a gentle fall-off toward the edges, which is typical of this design.

Dan Fromm said:

Garbage in, garbage out. The 'net may be the home of all truths -- I disagree strongly -- but there's no room for doubt that it is the home of many errors.

When I do a Google search, Google often gives me what it says is an AI Overview. So far most have been wrong.

For a Stylor cross-section, see https://cnum.cnam.fr/pgi/sresrech.php?M13674/14/stTxt/M13674/1/stTxt/&catsel1=stAllFr&mot_cat1=roussel stylor&ope2=OR&catsel2=stTdmstTdp&mot_cat2=roussel stylor&ope3=OR&catsel3=stTxt&mot_cat3=roussel stylor&var_solr_qs=2&type_date=cle_date&date_prefix=de&date_debut=AAAA&date_fin=AAAA&ope5=AND&catsel5=id&mot_cat5=M13674&type_affichage_paragraphes_stTxt=1#l-14

It is a tessar type.

OP, I did a Google search on Roussel and Stylor and Tessar. Try it.

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