needs ome help with this lens design

[Steven Tribe]

Everything new about periscopes helps. I believe some of the more economy-priced early casket sets were periscope based, rather than double achromats (RRs or Aplanats). I can push the date of the first periscope back to before 1858 with an Edinburgh lens.
They are, of course, deeply "flawed" with chromatic aberration, which is why the Objectif d'Artiste versions have a very long explanation (and sometimes aide de memoire" engraving on the barrel and sleeve) about corrections necessary for the various focussing distance.

[Marko Trebusak]

Hi Steven,

I found the design on dioptrique.info site. It might be similar to Objectif d'Artiste or might not. I didn't check - yet.

Cheers,
Marko

[Steven Tribe]

The best thing about this reference (which I haven't looked at for some time) is that it gives a refractive index for old (German) Crown glass. Which is a bit lower than the D (yellow) of 1.53 given for the O d'A (French Crown around 1895).

[Marko Trebusak]

Steven, l checked the curves of Periskop and Objectif d'Artiste, and as much as l can determmine, they are not the same design. Curvatures and lens thickness are different.
Marko

[Marko Trebusak]

It looks that Puyo and Puligny were very productive! There is another objective on dioptrique.info that is different still. It uses two plano convex lenses instead of two positive meniscii.

Marko

[Emil Schildt]

I just bought a casket set - a no name version with lenses from "15" to "75"..

It actually looks like a Darlot (type) lens set and unscrewing the lenses ther's only one thin glass in each.. concavo - convex...

interesting... (?)

[Steven Tribe]

Marko - the extra lenses in the Objectif d'Artiste casket set are plano/concave and plano/convex, respectively.
Emil, I don't know what your experience with the Duploich is, but these periscopes have enormous chromatic aberration which makes focussing difficult - or rather matching seen sharpness with registration sharpness. One really has to think about using filters to focus on the GG and the colour sensitivity of the emulsion you are using.

[Jim Galli]

Eddie had one just like this. No markings. We compared it to my smaller Puyo Anachromatique and it was a dead ringer. Everything the same, just one with markings, and one without. Somewhere I've got pics of the 2 lenses next to each other. Eddie's was larger, like 21" focus to my 15" focus, but all else identical.

[Marko Trebusak]

Marko - the extra lenses in the Objectif d'Artiste casket set are plano/concave and plano/convex, respectively.

I now, because you told me . Did you check the distance between the lenses in this last configuration? The design on dioptrique.info site have lenses very close together. You are of course right, Steven: focusing this lens is very dificult, but doable.

Marko

[Steven Tribe]

Jim/Eddie, I have the advert for the post Darlot range of Anachromatique (1900-1905) and this show 3 sizes for the lens. The approximate 30cm for 5x7", the 40cm for 8x10 and a larger/longer one for ?.
I'll try and find the advert again.
There are a lot for unmarked and unique engraved O d'A lenses from this period. The only explanation is that this is Darlot's new old stock that found a way into the marketplace, the new owners of Darlot being uninterested (they had the Eidoscope).