In search of a missing element for Dallmeyer 3B

[Vincent Pidone]

Steven, you're right of course, but...

I seem to recall that Surplus Shed offers to custom make lenses in small batches to the users' specifications, so:

What if we ask what it would cost to duplicate one of the most popular lens designs (a 3B maybe?) ?

Someone would have to come up with the glass for them to measure before they could come up with a quote.

I kind of wonder why Rhinehold doesn't try to do this, he's 1/3 of the way there already.

[VPooler]

No doubt you can get a workable achromat for a simple landscape lens with character, but to think that you can a replacement lens for any Petzval at Surplus Shed is just not correct.

You never know what you might find :P

[Steven Tribe]

What would be more useful would be an up-to-date register of incomplete lenses and parts.

These are so special that it requires guts to list them in the Wanted/ For Sale.

From memory, I have, for example ( and only as an example), the following items which would almost certainly not find a buyer but might make someone's day, sometime.

1. Ross/Goerz series III 5" Barrel - for someone has the cells.
2. Ross/Zeiss F6.3 140mm - for someone who has the cells - plus can repair the iris.
3. Dallmeyer 3B rear turn barrel. Lost identity on shortened sleeve. But it would contribute to a workable lens.
4. Dallmeyer 3B inner (fixed) rear cell. This is a simple lens which is well protected from damage/loss - but you never know.

[VPooler]

Steven, you're right of course, but...

I seem to recall that Surplus Shed offers to custom make lenses in small batches to the users' specifications, so:

What if we ask what it would cost to duplicate one of the most popular lens designs (a 3B maybe?) ?

Someone would have to come up with the glass for them to measure before they could come up with a quote.

I kind of wonder why Rhinehold doesn't try to do this, he's 1/3 of the way there already.

This needs to happen. I believe they might have a lot of the necessary lenses for recreations in stock and if only a few custom parts are needed, the price can be quite affordable. I have thought of making a Petzval myself in the far future. Someone who lives in the states, possibly near them ought to have a talk with them.

[goamules]

You should understand the grind curves and refractive indexes of each piece of glass is matched to the other pieces of glass in individual lenses. Just grabbing a "double convex" or "achromat doublet" that happens to be in a box of glass and trying to get an optimal image from a 1902 Dallmeyer or 1858 CC Harrison (I have one missing the rear glass) is not going to work. Each piece is mated to the others. Will you get an image? Yes, but it will not be a Dallmeyer or CC Harrison image. Petzvals might be easier than some, but the problem with them is they changed over time (the Lerebours color correction was just one modification) and each manufacturer had slightly different modifications. Petzvals were made from 1840 to 1940 , and they're all slightly different. Their glass is not like out of a cookie cutter.

[Steven Tribe]

Which, of course, is why an earlier thread pointed out all the problems in great detail.

English lenses used the glass available from Chance Bros. and French makers used SGO or St. Gobain. Even when Jena glass made new glass products around 1890 (basically higher refractive indices), each major lens maker was able to order glass (refractive index) which suited their existing designs or specific new products.
This prosed new production is only possible with combinations of simple lens where the refractive index is the same.

[Steven Tribe]

I thought I would up-date this as there has been a project in the Colloidion Bastards group relating to the remanufacture of the Dallmeyer. I can't see any recent information on their site, but a certain number were made for evaluation. What is most relevant here, though, is the fact that it was found that the glass used in the Dallmeyer Patent Portrait series is unobtainable and that "alternatives" were employed. I have no knowledge of how satisfactory the results have been, other than there are differences!

Part classical lenses seem to be offered for sale quite regularly at the moment (perhaps due to shortage of the regular items?) and I have seen listers who insist that missing lenses can be replaced by "Ordering" them somewhere. These part lenses always seem to be missing the complex brass mountings and really only have the value of the intact lenses in their cells.

[Steven Tribe]

You should understand the grind curves and refractive indexes of each piece of glass is matched to the other pieces of glass in individual lenses. Just grabbing a "double convex" or "achromat doublet" that happens to be in a box of glass and trying to get an optimal image from a 1902 Dallmeyer or 1858 CC Harrison (I have one missing the rear glass) is not going to work. Each piece is mated to the others. Will you get an image? Yes, but it will not be a Dallmeyer or CC Harrison image. Petzvals might be easier than some, but the problem with them is they changed over time (the Lerebours color correction was just one modification) and each manufacturer had slightly different modifications. Petzvals were made from 1840 to 1940 , and they're all slightly different. Their glass is not like out of a cookie cutter.

I think these are very wise words, also in retrospect!
I have "played around" with quite a few "parts" lenses since this thread was active and have some conclusions.

Mixing the front achromats/rear cells from different periods of Dallmeyer 3b does work. That is, within the rear unscrew and front turn models. The rear cells have at least two different designs (internal thread sizes), so this section (a pair) has to from the same lens.

Using a "foreign" achromat to repair a "beloved" Petzval does work if the focal length is near the original and you have possibilities for fine adjusting the distance between the cells. Replacing the rear pair is probably a very frustrating exercise, with little chance of success.

[Amedeus]

As Garret and Steve have stated, it is not that simple.

There seems to be little appreciation for the fact that the old glass is simply no longer available and even fewer know that even with modern glass, there are differences from batch to batch.

This means that one has to update the design each and every time the glass changes composition. There is more to glass than refractive index ...

And matching the front cell with modern glass to the rear cell of historic glass is just not going to cut it if one wants the same optical characteristics.

When the company I'm a CTO for acquired Rodenstock few year back, I enthusiastically approached the Rodenstock engineering team to whip me up a Ronar APO 1800mm ... lol ... after all, they might have a few parts still around ? Got an internal quote of $500K to redesign the glass, produce all needed tooling and they would deliver 10 lenses. Extra lenses would be $15k each.

So no, in spite of all experimenting with glass out of the toolbox, high hopes, fingers crossed ... as soon as good enough is not good enough, exact duplication is not easy and cost real money.

YMMV,

Cheers,

Rudi A.

Steven, you're right of course, but...

I seem to recall that Surplus Shed offers to custom make lenses in small batches to the users' specifications, so:

What if we ask what it would cost to duplicate one of the most popular lens designs (a 3B maybe?) ?

Someone would have to come up with the glass for them to measure before they could come up with a quote.

I kind of wonder why Rhinehold doesn't try to do this, he's 1/3 of the way there already.

[Bernice Loui]

Optical glass batches are cast with a mould area for a test prism. This test prism is used to test that specific batch of optical glass for expected specifications. Due to recent CE requirements, some ingredients once used in optical glass manufacturing can no longer be used adding another layer of difficulty to produce vintage optical glass.

Creation of a replacement lens element is only the beginning. How does one ascertain proper match and performance of the replacement lens element. Most if not all optics created during this era were hand ground, hand matched, hand assembled-tested and assessed for proper performance by highly skilled experts at their craft.

The lens might function, question is does the lens function as intended by the individual or folks who designed the lens, this is no small difference.



Bernice

As Garret and Steve have stated, it is not that simple.

There seems to be little appreciation for the fact that the old glass is simply no longer available and even fewer know that even with modern glass, there are differences from batch to batch.

This means that one has to update the design each and every time the glass changes composition. There is more to glass than refractive index ...

And matching the front cell with modern glass to the rear cell of historic glass is just not going to cut it if one wants the same optical characteristics.

When the company I'm a CTO for acquired Rodenstock few year back, I enthusiastically approached the Rodenstock engineering team to whip me up a Ronar APO 1800mm ... lol ... after all, they might have a few parts still around ? Got an internal quote of $500K to redesign the glass, produce all needed tooling and they would deliver 10 lenses. Extra lenses would be $15k each.

So no, in spite of all experimenting with glass out of the toolbox, high hopes, fingers crossed ... as soon as good enough is not good enough, exact duplication is not easy and cost real money.

YMMV,

Cheers,

Rudi A.