Dallmeyer 3B is being reproduced with currently-available glass

I spoke to the owner. Apparently someone from the Collodion Bastards facebook page asked him if he could make these lenses, and he said he could. His main business is consulting and making optical instruments, but this is an interesting side business for him.

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Originally Posted by IanG

Now that Cooke are building a second factory maybe there''s a chance they could re-manufacture some of their oler lenses.

Ian

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Where, pray, will Cooke get ancient glasses?

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Originally Posted by Dan Fromm

Where, pray, will Cooke get ancient glasses?

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I'm not sure, but if anyone could, it would be Cooke.

For anyone dreaming of a re-issued Cooke Triplet, there are plenty of cheap imitations available as projection lenses in 14, 18, and 22 inch fast projection lenses, (Beseler, Buhl, Epis...). They're probably better than the imitations you'd get made in small production runs, and far cheaper. But having used those and Cooke's myself, the imitations fall far short of what a real Cooke can deliver.

The Cooke Triplet is perhaps the most elegant lens ever deigned, zeroing out all seven aberrations with three single elements, yet capable of reintroducing spherical aberration with the movement of one element. But it's also one of the most demanding to produce properly.

I don't know where Cooke got their glass, but Dallmeyer used quite standard optical glass from Chance Brothers of Smethwick, West Midlands. Chance got eaten up by Pilkingtons years ago, but the name continues in a buy-out located in Malvern (where Morgan still make traditional sportscars!

Crown glass was Crown no. 2. refractive index 1.52, disp. index 0.004.
Flint glass was Light Flint no. 1 refractive index 1.57 disp. 0.00473.

Glass in no longer made with these characteristics. But the Chance Brothers' archive are open to the public at a library. There is a register and the papers fill 30 sq. meters.

http://blackcountryhistory.org/colle...ord/GB146_BS6/

Perhaps there is a description of the production mixes - or a list of sand pits where they sourced their raw materials?

As to using contemporary glass - I can recall that a number of rectilinears where made in both pre-Jena glass and in later versions with Schott glass.

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Originally Posted by Dan Fromm

Where, pray, will Cooke get ancient glasses?

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Cooke could re-introduce/re-manufacture one or more of their older lenses with modern glass after all lenses like Tessars (& Xenars) evolved to use more modern glass, that's not the same as a reproduction which implies it's a copy of some sort. Cooke still have all the data on their older lenses.

That's not to detract from this project in the thread title.

Ian

I've edited the thread title to, I hope, more faithfully reflect what's going on here. Thanks to Ian for his comment and Jim for the heads-up.

Very cool project, too - I hope it succeeds!

I've been following this lens since it's inception. While I appreciate using an optical expert to make it, and all the design work to fabricate a body around the ancient Petzval design, it's main claim to fame is that A)It's a Dallmeyer 3B and B) it's going to be cheaper. If you take away the first, because it's NOT a Dallmeyer, all you get is a new Petzval that is $800. Like any fast magic lantern lens, Darlot, or Baush & Lomb projector lens. The hype-meister behind this whole project is a wellspring of energy, but not much experience with Petzval history. If Derogy's or Harrisons had the same current cult following at a Dallmeyer 3B, be assured he would have called it the "new Harrison". Which is probably what I would have done too.

But the real questions remain unanswered. Why was a Dallmeyer considered better than the 20 or so other companies making Petzval Portraits in the day? The JHD patent? Most realize that reversing the elements in the rear and allowing one to have adjustable separation is not really an amazing invention. And it doesn't really do much of anything, certainly not "soft focus" that everyone thinks it does. So why was Dallmeyer a very good lens company? Note how I didn't say "the 3B a very good lens?" ALL of their lenses were very good. Because they had 2 generations of some of the top optical scientists producing their lenses, as well as the confluence of precise, fantastic British Victorian quality control. Dallmeyers are great because they are consistent, every one will be as good as the next, there were no "Monday lemons." The workers were lifetime skilled, their QA checks profuse, their brass fittings heavy and precise.

Which leaves us to ask the other real question. If you just name something a "Dallmeyer" and use a common Petzval formula that is duplicated in hundreds of other lens makes, is it somehow also a very good lens? The story is the optical company "exactly reverse engineered a vintage 3B." How? The Petzval Sum was the first mathematically designed lens in history. It was poorly patent protected so within 10 years it was being copied on every continent by many makers. If you copy a Petzval, you have a new Petzval. Not a Dallmeyer because a slick marketer uses that famous name. Dallmeyer hand ground each lens, making subtle compensations to adjust for glass refractive index variation. In other words, they knew enough to customize each lens, and get it right each time. (no, you can't take a lens out of one Petzval and put it in a missing slot of another, and expect the same, original image quality.)

I've been asking for a year for a side by side, scientific comparison with a real 3B. To see if it stacks up in the important quality realm of a Dallmeyer. Does it have heavy brass fittings? No Same types of glass? We don't know. Same resolution? Same quality control? We don't know. Generations of experience fitting and polishing lenses? It is simply a common Petzval design, put into an aluminium barrel. What makes it of Dallmeyer 3B quality?

With all due respect, goamules.. the latter part of your post is a disingenuous argument without real merit, which sounds good to anyone not familiar with modern optical design and production. To those who are, it sounds like the outburst of a fresh college recruit overwhelmed by tackling his or her first optical task....Or an unpopular program manager unfamiliar with how designers think and work.

A successful and experienced optical designer will consider every single detail you mentioned, plus many, many other nuances... all of which require careful consideration to produce a real piece of equipment. That attention to detail will have been born from a mix of lessons learned the hard way and lessons learned the easy way and -- most importantly -- from handling real equipment under real world conditions.

An unsuccessful designer who would fall into the simplistic pitfalls you haphazardly lay out will have abandoned true optical design work in frustration shortly after leaving the sanctity of college. They would not be known outside their own place of employment and certainly would not be running a successful optical consulting firm. That's just common sense.

You don't last long in the design world making crap.

Sorry to pick on you and please understand it isn't personal at all...but your argument and others in this thread like it is frivolous and does a real a disservice to interested people outside the optical design community. What those guys did back then wasn't magical, it's just not readily understood by the layman. What people like Dallmeyer did was good, quality work born of their experience. I have a profound, *educated* respect for what they did. But the same can be said of designers today. Optical design is definitely not a "lost art", and the pace of design today means the new masters will have completed and produced more successful optical designs in five years than the old masters will have completed in a lifetime.

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Originally Posted by Jason Greenberg Motamedi

Anybody know if it is coated? It would be really nice to have a multicoated Petzval. I know many of the collodion-crowd think that coatings are bad for color-blind processes like wetplate, but from hours of experimentation I can tell you that they have no notable effect on exposure.

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Modern AR coatings can accommodate the full spectral band including that of "normal emulsion". To add, the real limitation in the UV is going to be absorption by the glass itself. Modern exotic glass (high index low dispersion) has issues with this, but the types of glass used for the designs we're discussing here (classic and even modern crowns and flints) will have the same spectral absorption characteristics as the original glass types.

Sounds like Uv coatings would be a great addition, though a break from the Original design.