[W&B] What is it ? Cone lenses

Sat Jun 9 13:09:11 EDT 2007

Chris,

What little most folks know about the cone comes from that citation by
Kingslake which is at best limited and perhaps a bit understated.  Kingslake
was addressing the Portrait aspects of the design - and just the tapered
'cone' -  and doesn't get into the combination possibilities (as he does
with the Chevalier Photographe lens a few pages earlier).  His description
is more applicable to the second lens from the left in my pic than to the
illustration that he actually used.

Yes, other companies also used a cone-like rear element, mostly French.
Hermagis, for one - I think.  And many companies used the idea of
combination lenses.  But you'll see far more Jamin and Darlot variations
than everyone else combined.

My full-plate or 8x10 lens has a back-focus of 10" in portrait mode, 22" in
landscape mode.

mz

-----Original Message-----
From: woodandbrass-bounces at kjsl.com [mailto:woodandbrass-bounces at kjsl.com]
On Behalf Of Christopher Wright
Sent: Saturday, June 09, 2007 9:55 AM
To: Collectors of 19th Century Cameras &amp;Photographica
Subject: RE: [W&B] What is it ? Cone lenses

Milan:

Thank you for your reply, and the link. 
There is a point that might need clarification, and it is that Jamin
submitted a very large "Cone Centralisateur" to the Academy of Sciences in
the early 1840's.  This lens ended up in the Spiro Collection, from which it
was auctioned off this past year.  It was described as being the prototype
for succeeding Cone Centralisateur lenses that his firm made.  (???)  Rudolf
Kingslake (A History of the Photographic Lens; Elsevier, 1989) has a bit on
the Cone Centralisateur.  He uses the date of 1855 when Jamin submitted the
lens to French Photographic Society, which body found the lens
"satisfactory."  He also described the purpose of the cone "to prevent
internal reflection of sunlight from falling on the sensitized plate." (p.
38)

Do you know of any other manufacturer of lenses producing a "Cone"-type of
Petzval design?

According to the dictionary, Centralisateur appears as a term in mathematics
(algebra).  Perhaps there is also an application in optics? theoretical
optics?

 Christopher

PS: What is the focal length of your "full-plate" Centralisateur?

At 9:50 AM -0700 6/8/07, Milan Zahorcak wrote:

Chris,

The lens on my deck is a Jamin-Darlot, full-plate combination with "cone
centralisateur" with the full-complement of portrait and landscape bits and
pieces.

There was some discussion (and much confusion) a while back about the proper
names for these things.  Turns out that in the 1850s, they started out as
just portrait lenses.  Then the 'cone' was added for unlikely optical
benefits, then it was offered with a landscape conversion option.

The term "cone centralisateur'' describes just the conical rear end and any
lens that has it, simply has a cone centralisateur rear end.  On the other
hand, there were also combination lenses with or without cones.  Another of
those noun, proper noun, adjectives issues.

Soooo . . . depending on configuration, certain Jamin/Jamin-Darlot/Darlot
portrait lenses could be had as:

1. a portrait lens

2. a portrait lens with cone centralisateur

3. a combination portrait/landscape lens without con centralisateur

4. a combination portrait/landscape lens with cone centralisateur

 <http://www.pacificrimcamera.com/milanpub/Misc-pics/variations2.jpg>
http://www.pacificrimcamera.com/milanpub/Misc-pics/variations2.jpg

More fun,

mz

-----Original Message-----
From: woodandbrass-bounces at kjsl.com [mailto:woodandbrass-bounces at kjsl.com]
On Behalf Of Christopher Wright
Sent: Friday, June 08, 2007 9:09 AM
To: Collectors of 19th Century Cameras &amp;Photographica
Subject: Re: [W&B] What is it ? redux

Hello Steve:

Seems like there is a confusion as to which lens we are talking about.  I
was responding to Milan's picture of the large lens on a table outdoors, not
to your camera and lens question.

Serves me for jumping into a discussion without first reading the miles of
emails beforehand.

Sorry for the confusion.

(BTW: Your camera looks to me like a kind of "mouse trap" a la Talbot, for
making Calotype negatives.)

Christopher Wright

 .  At 5:31 PM -0400 6/7/07, SBShohet at aol.com wrote: 

Hello Bernard and Christopher,

Bernard, I think your idea is the most reasonable so far.  There are indeed
interior threads inside the slightly extended lips at both ends of the lens
tube. (these look like filter threads on conventional lenses, though they
might be there to receive the 'collets' which hold the glasses in place).
There are certainly no Jamin or Darlot marks anywhere.

Christopher, I'm still a bit unclear of how a Centralizateur worked or was
arranged, but I can tell you that the optics here were not particularly fast
like a Petzvel. The glass diameter is about 30 mm. which with the stated
focal length of 175 mm. translates to a speed of just a bit better than F 6.

The mystery continues.  Steve

**************************************

See what's free at http://www.aol.com.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kjsl.com/pipermail/woodandbrass/attachments/20070609/a0e42c37/attachment-0001.htm