In search of a missing element for Dallmeyer 3B

[Steven Tribe]

I don't have my 3B at home at the moment, but perhaps someone else can measure the sort of focal length you should be looking for in a front achromat?

[alex from holland]

Ok, now you have a almost working 3b
Now the search starts or sell this one in parts.

Steven, maybe your change to get an original 3b tube......

With a bit of patience and loads of alcohol I managed to free the rear element and put the whole group together as it should be. Thank you for your advise Steven, since finding real lenses may proof impossible I might look into doing just that!

Maurits and Alex - thanks again for all your help!

[Steven Tribe]

The thought did occur to me Alex.

But this is the older style - with focussing sleeve - but then again, the front achromat mounting might be the same in both versions.
2 new complete "3B"s would be better than just one with mixed parentage!

My new 3B is, by the way, making excellent wetplate images in Sweden at the moment.

[Bruce Schultz]

I have a 5A with a cracked front lens. Isn't there somewhere we could get new elements made?

[E. von Hoegh]

I have a 5A with a cracked front lens. Isn't there somewhere we could get new elements made?

New elements? Of course. But you'll find it less expensive to just get another lens. Grinding and polishing a one-off element will likely cost thousands, specialised tooling will have to be made for each surface which is ground and polished. But, it certainly is possible. I'm thinking of the man who spent roughly 30,000 GBP to have a new cylinder head made for a Rolls-Royce P3. At the time, the pound was exchanging for a bit over 2 USD.

[Steven Tribe]

It is quite possible to make a replacement achromat for a 3B or a 5A!

You need:

2 pieces of glass with the approximately correct size and refractive index. This quite ordinary crown and flint glass.

Knowledge of R1, R2, R3 and R4. This is the radius of the four surfaces where R2 is identical to R3 as it is a balsam join. These can be measured on an existing lens using a spherometer.

A home rigged vertical lathe with working area. 4 metal tools made to the surface diameters - convex for concave surfaces and vice versa. Various quantities of pitch and grinding/polishing compounds. Plenty of spit (used to keep the right dampness of the grinding mixture) and a copy of the book "Lens-work for Amateurs" by Henry Orford.

And lots of "hobby" time!

[E. von Hoegh]

It is quite possible to make a replacement achromat for a 3B or a 5A!

You need:

2 pieces of glass with the approximately correct size and refractive index. This quite ordinary crown and flint glass.

Knowledge of R1, R2, R3 and R4. This is the radius of the four surfaces where R2 is identical to R3 as it is a balsam join. These can be measured on an existing lens using a spherometer.

A home rigged vertical lathe with working area. 4 metal tools made to the surface diameters - convex for concave surfaces and vice versa. Various quantities of pitch and grinding/polishing compounds. Plenty of spit (used to keep the right dampness of the grinding mixture) and a copy of the book "Lens-work for Amateurs" by Henry Orford.

And lots of "hobby" time!

Quite correct. Many amateurs have succesfully made telescope mirrors.
However it is nowhere near as simple as you make it sound. It takes time, knowledge, and experience to acquire the neccesary skills. A telescope mirror is relatively simple, you don't have two vertices of polished surfaces to keep in line, nor do you have two spherical surfaces to keep in perfect alignment. You also need to edge the finished lenses accurately enough to mount in the existing objective while keeping them perfectly centered.. You need at least three polishing tools for each radius: roughing, finishing, polishing, then you switch to pitch in another metal holder for the final polishing, and you need the tools to make the polishing tools - a metal lathe with a very accurate sphere turning attachment, plus the skills to use it. I've looked into this with the idea of making my own long focal length Dagor. It's certainly doable. But it's just as certainly not for the faint hearted.

[Kasia Kesicka]

Quite correct. Many amateurs have succesfully made telescope mirrors.
However it is nowhere near as simple as you make it sound. It takes time, knowledge, and experience to acquire the neccesary skills. A telescope mirror is relatively simple, you don't have two vertices of polished surfaces to keep in line, nor do you have two spherical surfaces to keep in perfect alignment. You also need to edge the finished lenses accurately enough to mount in the existing objective while keeping them perfectly centered.. You need at least three polishing tools for each radius: roughing, finishing, polishing, then you switch to pitch in another metal holder for the final polishing, and you need the tools to make the polishing tools - a metal lathe with a very accurate sphere turning attachment, plus the skills to use it. I've looked into this with the idea of making my own long focal length Dagor. It's certainly doable. But it's just as certainly not for the faint hearted.

Sooner or later due to demand someone will be offering such services, for sure though at the high price. Exciting as it sounds, making my own cells requires specifically what I don't have (knowledge, tools and time). For now I'll keep my eyes open for another incomplete 3B or a suitable focal length front achromat that will fit in the front thread as advised by Steven earlier in this thread.

[Steven Tribe]

I don't like to be pessimistic, but I think the chances of increasing availability of specialised lens replacement services is zero.
Recent decades have seen the demise of all sorts of similar speciality services. Even in the field of vintage car restoration services, which attracts more people than we do, there are fewer people/companies and these run on very commercial principles!

The days of the Gentleman (woman) amateur who used hours each day on their hobby (alchemy, astronomy, photography, golf etc.) has gone for ever. The emancipation of women, absence of domestic staff, contractual employment and the falling comparitive incomes of the middle case compared with artisans, have all contributed.

[E. von Hoegh]

I don't like to be pessimistic, but I think the chances of increasing availability of specialised lens replacement services is zero.
Recent decades have seen the demise of all sorts of similar speciality services. Even in the field of vintage car restoration services, which attracts more people than we do, there are fewer people/companies and these run on very commercial principles!

The days of the Gentleman (woman) amateur who used hours each day on their hobby (alchemy, astronomy, photography, golf etc.) has gone for ever. The emancipation of women, absence of domestic staff, contractual employment and the falling comparitive incomes of the middle case compared with artisans, have all contributed.

The demise of the Gentleman enthusiast/amateur was a while ago, it coincided with the demise of the independently wealthy class. It's a real shame, too, because there was quite a bit of very good science done by these folks.

There are still some left, look up Duncan Pittaway who is restoring one of the two Fiat S76 LSR cars from a frame and an engine. There are others in various fields.