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UltravioletPhotography

Astro Berlin 120mm f2.1 Quarz Objektiv


JMC

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Astro Berlin 120mm f2.1 Quarz Objectiv

 

Aperture: f2.1

Elements: 3 elements, 2 groups

Mount: 50mm x 1mm (to be verified)

 

post-148-0-45654100-1608993411.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.

 

post-148-0-28071500-1608993569.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.

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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?

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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,

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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?

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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.

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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.

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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.

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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.
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  • 3 weeks later...

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

 

post-148-0-89880200-1610718317.jpg

 

post-148-0-23385100-1610718323.jpg

 

post-148-0-32737400-1610718327.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.....

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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?

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Andrea, yes these are straight after drilling them, so they are a little rough around the edges. I can sand them slightly to remove those edges. I suppose they could be 3D printed, but for me it was easier just to get an A4 sheet of black plastic and cut them out.
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Andrea, yes these are straight after drilling them, so they are a little rough around the edges. I can sand them slightly to remove those edges. I suppose they could be 3D printed, but for me it was easier just to get an A4 sheet of black plastic and cut them out.

You can also use a counter sink tool or a step-drill if the hole diameters fit the steps.

The stepping edges are often angled and can trim the edges of the holes and make them more thin.

https://www.ebay.com...ecall_filtering

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  • 2 months later...

Yay, the sun's out for once, and I managed to get a quick shot in UV with the lens. This is an informal one, so am adding it here.

 

This is the flower in the visible (camera phone). No idea what it is, but it's one of the ones my wife's put out in the garden.

post-148-0-34874200-1617026951.jpg

 

Firstly, with the d810 UV modified (ACS UV filter) with the Astro Berlin lens using both parts of the lens, a waterhouse stop to make it approx f4, ISO3200. Whitebalanced in Darktable. The flower in UV with the Astro Berlin lens;

post-148-0-80155600-1617027041.jpg

 

The colour surprised me - I've not seen that before, I'm used to strong blue/violet or proper yellow after white balancing. It got me wondering whether it was something peculiar to the lens, so also got a shot with the Rayfact 105mm (f4.5) along with a new white balance for that lens.

post-148-0-96290500-1617027158.jpg

 

ISO was kept quite high to keep exposure times short as there is a bit of breeze here today. It doesn't look like the lens caused the strange colour cast as it was the same with the Rayfact. The Astro Berlin is definitely more of a 'pictorial' lens though. So nice to have a few minutes (and nice weather) to get some shots again.

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That is a garden Ranunulus, Ranunculus asiaticus originally. But the garden varieties are often hybrids.

 

Usually we do see the yellow as either very reflective or very dark, but it can be somewhere in between.

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Andy Perrin
So Andrea, are you saying that this is an example of a flower that is both unusual, yet also garden-variety? :grin:
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There ya go !!! That's it for sure. :lol: :lol: :lol:

 

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

I couldn't find an orange Ranunculus, but I have a pink one which shows both that kind of yellow like the one above and also some blue in UV. FWIW, I also don't think the unusual signature has anything to do with that interesting old Astro-Berlin lens. These flowers seem to have a very metallic or shiny UV look from some of the petals and a "waxy" sheen from others.

ranunculus_uvBaader_sun_20130309wf_4457pnTest.jpg

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Thanks all, and yes Andrea, I'm with you in that the unusual colour is not down to the Astro Berlin lens itself as I got the same colour with the UV Rayfact 105mm lens.
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  • 2 months later...

While the sun is out I got some more UV shots with this lens.

 

Camera - Nikon d810 UV converted by ACS. Aperture approx f5.6 (waterhouse stop), ISO1000, whitebalanced in Darktable. Cropped, curves tweaked and resized for sharing.

 

Buttercup

post-148-0-26941100-1622464444.jpg

 

Dandelion seed head

post-148-0-06208800-1622464503.jpg

 

Ragged Robin (also added to my post on this in the Floral section)

post-148-0-15523900-1622464533.jpg

 

Lens mounted on the camera.

post-148-0-62024700-1622464581.jpg

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The yellow in the buttercup is very nice. It sure is a nice lens for UV.

 

As for the green in the flower, there are possibly two explanations:

- the flower is UV-green (~340 nm), which is unlikely;

- your internal filter leaks a bit, even though your lens has no problem transmitting UVA and B.

 

Your further tests will help clarify this.

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Stefano, yeah it's an odd one, as it seems more to be specific to this flower than an issue with the camera/filter itself. Not sure what to make of it at the moment, although as Andrea pointed out this type of goldy/greeny colour has been seen before and not with the ACS filter. Also I don't have a converted Nikon without an internal filter to compare it to, so I cannot do any like for like comparisons at the moment.
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Is it possible for you to measure the reflectance spectrum of that flower? Now, we cannot establish a color/wavelength relation, since there are too many factors involved (and I do agree, BTW), but you will notice that UV-yellow flowers, for example, have a bump at ~360-370 nm.

 

If your flower has a bump at or below 350 nm, you may have actual UV-green, and that would be a nice discovery. Alternatively, if this isn't too much work, you may shoot it with your 310-390 nm bandpass filters, with a PTFE standard. That would act as a very rough spectrometer.

 

But the first test you should do in my opinion is to use another lens (as you said), and also try other filters, to see if the internal filter in your camera is actually leaking.

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