Adjustable Spacing in Jamin Darlot Petzval Lenses

[Mark Sawyer]

Jamin and Darlot produced for a few years around 1860, a couple of versions of Petzval Portrait Lenses with adjustable spacing between the front and rear group. (Not to be confused with Dallmeyer's 1867 introduction of variable spacing in the rear group for increasing depth of field via spherical aberration.) The adjustable spacing was on at least some models of the Cone Centralize, but also on a more conventional model of their Petzval. An Eastman House publication on the Cone Centralisateur states:

"Although basically nothing but a Petzval objective, this lens embodied several interesting features, the most distinguishing characteristic being the conical shape of the rear half of the lens barrel (cone centralisateur) which was intended to prevent internally reflected light from reaching the photographic plate. Also the separation between the front and rear components could be varied, either by simply drawing out the front portion of the barrel or by use of a rack and pinion mechanism, the purpose of this being to enable the user to obtain the best possible aberration correction for any particular object distance."

Does anyone know any more detail about which aberration corrections were possible by varying the spacing? Or know of any information on using the feature?

BTW, here's a photo of the more conventional Jamin Darlot Petzval, showing how the feature can vary the length by about two inches. The smaller knob is a friction lock allowing the front section to slide in and out independently from moving the rear section:

[Steven Tribe]

Just a quick response, as it is well past my bedtime!

Surely, the illustrated version (which I have not seen in real life!) is another ingenious brass design to facilitate extra use of the Petzval as a landscape lens. I can see an extra flange thread on the short lens hood.
So the Petzval is only used when the extended piece is pushed right in. OK, the extension can be placed at different positions and locked down. But it was never meant to be used like this! The locking screw is removed - the extension piece removed completely from the rest of the barrel (complete with meniscus lens) and mounted in the flange after it has been reversed.

Here is another Darlot/Jamin design which I think must be a convertible too.

https://www.largeformatphotography.i...darlot+petzval

The French were very doubtful about Dallmeyer's claims with his Patent Petzval "softness" and preferred their "flou" created by small extensions of the barrel as in Darlot's Universal from 1865. But the movements possible were under a centimetre!

[Amedeus]

Just a quick response, as it is well past my bedtime!

So the Petzval is only used when the extended piece is pushed right in. OK, the extension can be placed at different positions and locked down. But it was never meant to be used like this! The locking screw is removed - the extension piece removed completely from the rest of the barrel (complete with meniscus lens) and mounted in the flange after it has been reversed.

I'll have to check mine, never shot with it and it came with a hood, so that one must then be removed before using as a landscape lens ... I'll back on this when I get to it ... one more project ...

Cheers,

[alex from holland]

As Rudi says, it made it possible to use the front part only as a landscape lens.
As far as i know it wasn’t meant to correct anything.

[Mark Sawyer]

I just played with mine, and if you unscrew and remove the rear cell, the front tube will push into the rear for use as a landscape lens. But only friction holds it in, and not very well.

I found another brief reference to adjustable spacing in the Cone Centralizer in Kingslike's History of the Photographic Lens, p. 38:

"In some models the separation between the lenses could be altered by the user."

I also ran across an old Eddie Gunks youtube video, which shows quite a bit about the inner-workings of this lens. Eddie shows a different way of converting it to a landscape lens: removing the hood and screwing it into the flange directly, which is how most Petzvals work. Near the end he notes adjusting the spacing will change the focal length. I haven't got mine on a board yet, so I can't say.

https://www.youtube.com/watch?v=tfFHw4mEkbs

[Amedeus]

I also ran across an old Eddie Gunks youtube video, which shows quite a bit about the inner-workings of this lens. Eddie shows a different way of converting it to a landscape lens: removing the hood and screwing it into the flange directly, which is how most Petzvals work. Near the end he notes adjusting the spacing will change the focal length. I haven't got mine on a board yet, so I can't say.

https://www.youtube.com/watch?v=tfFHw4mEkbs

Interesting approach on the Jamin lens in the video link ... the front has actually two positive lenses and there are a few combinations possible. Now I need to check if i have that inner element or the space (thread) to put it in.

Was not aware of this configuration.

Cheers