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UltravioletPhotography

UV transmission of 5x Zeiss Luminar lenses


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I while ago I picked up a 25mm Zeiss Luminar lens, which turned out to the quite a nice UV macro lens (written about it here - https://www.ultravio...dpost__p__35273). A little later I also got a 100mm Luminar, which was not that good in UV, which is also shown in the above thread.

 

A few days ago I was offered 16mm, 40mm and 63mm Luminars, so I thought why not complete the set. Here they all are;

post-148-0-40279900-1597762770.jpg

 

And here are my measured transmission plots between 280nm and 420nm.

post-148-0-70815900-1597762811.jpg

 

I think the 16mm, 25mm, 40mm, and 63mm ones are Version 1 lenses, based on the descriptions in Enrico's site. The 100mm is I believe one of the later ones. The 16mm and 25mm ones are marked with an * in the graph as the apertures for those are very small, and I suspect might be clipping the light beam slightly during the measurement. Therefore the absolute transmission for those are likely slightly higher than in the graph, bringing them in line with the other three.

 

Some interesting characteristics;

 

The 25mm one is the best in terms of how far in to the UV it transmits, and the 100mm is the worst (and I think my version of the 100mm is the 3 element one).

 

The 16mm one is the 2nd worst. This has a relatively complex lens design so its behaviour makes sense (5 elements, 4 groups).

 

The 40mm and 63mm did not behave as well as the 25mm, although they have fewer elements (both 3/3 vs 4/3 in the 25mm).

 

Overall, the 16mm to 63mm ones all look to offer a good to degree of UV transmission especially for UVA imaging, so I'll definitely be using these in future for macro work. They also fit my microscope and throw a huge image circle, so will use them for some microscopy too.

 

I went into this assuming the 40mm and 63mm would have better transmission than the 25mm given their simpler designs. Just goes to show that it's hard to predict lens behaviour in the UV.

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So the moral of the story is once you have a good UV lens, stop. It doesn't get better. But you do have different focal lengths there.
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enricosavazzi

This is good groundwork. Before your report on the 25 mm Luminar, we only had anecdotal reports about UV transmission of a single Luminar focal length, but no quantitative comparison among the different focal lengths.

 

The next step would be finding out how these lenses behave with respect to UV focus shift (i.e. axial chromatic aberration). Even with a large amount of axial CA, it is still possible to use almost-monochromatic UV from 365 nm LEDs, but a broader usable UV spectrum would be good to have for work where UV false color is desirable. There is some overlap in the magnification range of these lenses, but not very much, so the choice of which of the three best focal lengths to choose is pretty much down to a single one at most magnifications.

 

I happen to have all three most useful focal lengths, but this year most of my time is still taken up by work on our house. Maybe in the coming winter, when work outdoors will no longer be possible and voluntary social distancing is still likely to be recommended. But I make no promises, so feel free to go ahead with this type of testing if you wish.

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Enrico, yes I wanted to provide some solid comparative data on these which was the idea behind sharing this. With the kit that I have to hand, measurement of transmission is something I can do quite quickly. At the moment I am not set up for focus shift assessment, so have no plans (currently anyway) to test this systematically. If you get chance, please go ahead this winter. If things do change and I am able to tackle that, I'll update on the forum with the results of course.
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When the Luminars were in use on the Ultraphot microscopes, they also had a set of spectacle lens condensers that went along with them - one for each Luminar lens. The same day I was offered the 16mm, 40mm, and 63mm lenses, I came across an advert on eBay for a set of the 5 condensers which I had never seen before. Here they are.

post-148-0-28704300-1597914319.jpg

 

Each one has a removable clip on diaphragm.

post-148-0-27891000-1597914409.jpg

 

When it came to UV transmission I expected them to all be about the same, perhaps with slight variations as a function of glass thickness. Turns out they are not though.

post-148-0-96267700-1597914453.jpg

 

The one for the 16mm Luminar reaches much further into the UV than the others, and the one for the 25mm Luminar has the highest cutoff. The others are about the same.

 

I'm currently building a UV microscope, and the Condenser for the 16mm Luminar has about the best reach into the UV that I have seen so far. However these are a different diameter to my Olympus microscope condenser mount, so I'll need a little adapter to be made up to fit them to it to try them out.

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Thats interesting, the condenser on my microscope is the only UV limiting component. Its a hard 405nm cutoff. I can't push any UVA through it. But I can remove it. I might look for something similar.

 

Stefano, the 16 might be lucky and have similar to BK5 glass (less than 5% lead and impurities). The other look typically of BK7 glass.

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Jonathan:

If you have been trolling eBay, you probably have seen these, but just in case you haven't:

 

Lomo UV condenser:

https://www.ebay.com...37/184346446422

It is slightly too large in diameter to fit into the BH condenser holder, so an adaption of some kind will be needed.

 

4 Lomo UV objectives:

https://www.ebay.com...5X/224067709538

For the price ($70) it was a no brainer.

The mount is 27mm, but adapters are available to adapt them to RMS and 25mm. 180mm tube length.

They are EPI, but I don't have an EPI fluorescence illuminator, so I will only be using their brightfield capability.

So far it has been 64 days, and my set has not arrived yet.

 

RAFcamera has a 42mm dovetail to M42 adapter

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That lomo uv condenser might be legitimate, but I don't know about those objectives. Seems like UV was just added to the title. Its not in the description.
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Thanks SteveE,

 

Yes I have seen that condenser. To me it looks incomplete though - as though it is missing a part from the top - which is why I didn't consider buying it. I did get a bunch of Lomo UV photoeyepieces for about 25USD ea, and they look to be made from quartz or fused silica as they are great for UVB.

 

'UV' means different things to different people. I have UV microscope objectives from Olympus, and they are just low fluorescence for UV fluorescence imaging. They let through UVA OK, but nothing below 320nm. With regards to what I'm going to call 'actual' UV objective lenses, I've got 3x Leitz ones (16x, 40x and 100x), Zeiss Ultrafluar (32x) and a couple of Beck mirror ones. These all give good transmission down to 280nm with my measurements, and I suspect will be good down to about 220nm.

 

I've bought a few bits from Russia recently, and 2-3 months is about the going rate to get to the UK, so don't give up hope yet.

 

Yes, I know Raf, as I have a few of his bits. I didn't go with his dovetail to M42, but instead went with one I found in Spain. That one was threaded inside the the dovetail, and I got a Raf adapter to go from that internal thread to RMS. This gives me a single piece which goes from M42 to RMS, and has a built in dovetail. That way I can mount the adapter on an Olympus microscope, remove the nosepiece, and use the Olympus focusing mechanism to position the subject. It sounds more complicated than it is.

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Jonathan,

Thanks for the post to your blog. I haven't been following along and just now got caught up.

Wow your almost all set. You have UV objectives, the 16x at least to 280nm. A UV capable condenser. And have a mercury xenon lamp. You should be all set for some excellent UV microscopy. You even have the slides and cover slips sorted out.

I also see you have got phase contrast to work and figured out how to modify the light source for LED dark field. Dark field is my favorite next to DIC. In dark field you gain at least 10x resolution.

Dark field electon microscopy (EM) was a lot of fun.

 

Yes cleaning coverslips is fun. I used to do that all the time. First with methanol soak.

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No problem David. Nearly there now. I should be fine down to about 350nm with what I currently have. But the eventual aim is to get it working down to below 300nm.

 

The old quartz condenser is currently in California, waiting until we next see family out there. The biggest issue then is the internal optics in the microscope. I need to replace 4 lenses and mirror with UV suitable ones. Oh, and I need to modify one of the heads - the Olympus heads have a beamsplitter which cannot be completely removed (it is either 100% to the eyepieces or 50%, when what I want is 0% to the eyepieces and 100% straight through to the camera).

 

I have another BHB on its way to me, the aim being to keep one working one, while the other one gets taken to bits and the internal optics replaced.

 

With all that done I'll be able to image down to about 300nm with the camera I have, or if I go for one of the enhanced UV sensitivity cameras, down to about 250nm.

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If you get that GSENSE2020BSI camera off ebay, please let me know how it works out on the scope.

I have been dreaming about it, but way way outside my budget.

 

But it would justify all your quartz allowing you to see to UVc

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If you get that GSENSE2020BSI camera off ebay, please let me know how it works out on the scope.

I have been dreaming about it, but way way outside my budget.

 

But it would justify all your quartz allowing you to see to UVc

Yeah, especially with what has gone on this year, it is way outside of my budget as well. But if I can ever get hold of one it'll be good to try it out.

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