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Astro Berlin 120mm f2.1 Quarz Objektiv

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#1 JMC

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Posted 26 December 2020 - 14:44

Astro Berlin 120mm f2.1 Quarz Objectiv

Aperture: f2.1
Elements: 3 elements, 2 groups
Mount: 50mm x 1mm (to be verified)

Attached Image: 20201222_104330 small.jpg

A rather unusual lens, and not one I've been able to find anything out about. Could be a prototype or a one off, or it could just be that the documentation hasn't survived.

The front element is a quartz plano convex singlet. In the middle is a removable section which takes Waterhouse stops, and then at the rear is a cemented doublet (which is not quartz as far as I can tell). Transmission data of the component papers and the full lens between 280nm and 420nm is shown below.

Attached Image: Astro Berlin 120mm quarz objektiv trans.jpg

No good for UVB obviously (at least when the whole lens is used), but hopefully good for UVA.

Mount looks to be 50mm x 1mm and I have an adapter to M65 on order, so I can use it with my M65 helicoid. It should be able to cover up to 6x9cm.

Will update more when then adapter arrives, and I can do some proper testing.
Jonathan M. Crowther

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#2 Stefano

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Posted 26 December 2020 - 15:41

That lens is surely very good for UVA. It reaches 320 nm and a bit below, looks similar to a Kuribayashi.

#3 Bernard Foot

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Posted 26 December 2020 - 19:31

Weird. As you say, no information around about this lens, although it looks like there was one like yours available on ebay (details now gone). Astro-Berlin seemed to have made some very interesting lenses, and there are some on ebay at multi-$K prices.

They did make some lenses for UV photography (Quarz-Tachar, Quarz-Anastigmat), but what I don't get is that if your lens was intended for UV why would they fit such a UV-mediocre rear element?
Bernard Foot

#4 JMC

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Posted 26 December 2020 - 20:23

Bernard, yes it was the one on eBay. I agreed a price with the vendor as he was accepting offers for it. I've come across a couple of references about the Quarz Tachar and Anastigmat you metioned, but nothing on this, apart from a mention of someone using it on a couple of forums (which may well have been the vendor, although I haven't confirmed that).

As for the rear element, I can think of a few options. The original purchaser wasn't bothered about short wavelength UV. It they wanted UVA performance then the quartz front element would maximise transmission, without needing the complexity of making a quartz rear group. They wanted to correct for chromatic abberation, by using glasses with different refractive indices. Perhaps the rear group is not original and has been replaced at some point. Perhaps one element of thr rear cemented doublet is quartz and the other is glass. Given they are painted aroud the edge I'm not about to damage that to test it. Perhaps the Canada balsam glue in the doublet is absorbing the UV. I shall have a look around for information on that, as "glued lenses aren't good for UV" is something I hear alot. I can't verify any of these hypotheses though, so it will remain a mystery for now, and an interesting piece of history,
Jonathan M. Crowther

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#5 Bernard Foot

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Posted 26 December 2020 - 21:48

View PostJMC, on 26 December 2020 - 20:23, said:

Perhaps the Canada balsam glue in the doublet is absorbing the UV. I shall have a look around for information on that, as "glued lenses aren't good for UV" is something I hear alot.

I thought that was to do with the canada balsam fluorescing rather than it absorbing UV? Or am I smoking dope?
Bernard Foot

#6 Cadmium

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Posted 26 December 2020 - 21:56

Jonathan, Really cool stove too! :smile:

#7 Andy Perrin

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Posted 26 December 2020 - 22:09

View PostBernard Foot, on 26 December 2020 - 21:48, said:

I thought that was to do with the canada balsam fluorescing rather than it absorbing UV? Or am I smoking dope?
Bernard, not dope, but the fluorescence comes from absorbing UV. Double problem.

Edited by Andy Perrin, 27 December 2020 - 00:14.


#8 dabateman

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Posted 27 December 2020 - 00:07

View PostCadmium, on 26 December 2020 - 21:56, said:

Jonathan, Really cool stove too! :smile:

Yes very neat. I had one similar when I lived in Worcester MA. But it had a gas heater part on the left side. Was what we used to heat most of the apartment.

#9 JMC

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Posted 27 December 2020 - 08:47

Thanks for the comments on the kitchen. At least I managed to stay out of the reflection.

Yes I'll take a look at fluorescence too. I've not seen anything on Canada Balsam absorption in the UV, hence I'd like to find out if possible which is why I'm interested in that.
Jonathan M. Crowther

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#10 Cadmium

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Posted 27 December 2020 - 09:01

View PostBernard Foot, on 26 December 2020 - 21:48, said:

I thought that was to do with the canada balsam fluorescing rather than it absorbing UV? Or am I smoking dope?

Lens fluorescence can come from the glass itself.

#11 JMC

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Posted 27 December 2020 - 10:28

Absolutely Steve, it'll be fluorescence if the 2 lens elements and the balsam. I'll try and get hold of some Canada Balsam too, to do some additional tests.
Jonathan M. Crowther

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#12 JMC

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Posted Yesterday, 13:48

Little bit of an update. I bought some 1mm thick black plastic and made a set of waterhouse stops for the lens.

Attached Image: 20210115_131052 small.jpg

Attached Image: 20210115_131126 small.jpg

Attached Image: 20210115_131144.jpg

Should allow me to vary the aperture between wide open f2.1 and about f16. When the weather breaks a bit I'll get some sample shots with them.

Also, got some Canada balsam and xylene and some 1mm fused silica plates, so I can do some assessment of transmission and fluorescence from it. It's added to the overall list of experiments.....
Jonathan M. Crowther

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#13 Andrea B.

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Posted Yesterday, 17:50

Now that is really cool, JMC. I've not seen a lens which uses waterhouse aperture stops before. Indeed, I'm not sure I actually knew myself exactly how to make use of them.

I was wondering if sandpaper or (what we call here in the US) an emery board (for fingernails) might smooth the aperture edges a bit?
I was also wondering whether these might be made with a 3D-printer?
Andrea G. Blum
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