UV Microscopy objectives

[JMC]

Over the last year or so I've been working on microscopy as it was an imaging technique I had little experience with and thought it might be fun to learn more about. Within a couple of months of starting on it, I got to wondering about whether I could convert my normal microscope into one which I could UV transmission imaging with, down to and even below 300 nm. As well as a lot of other aspects which would require changing, I'd need to move away from glass optics, into quartz, calcium fluoride and mirror setups, in order to get the transmission needed. It proved to be a big challenge, but I am now using it for some sunscreen research. I've been fortunate enough to be able to find a range of objectives which are usable for this type of imaging over the last year, things which I never knew existed before. The engineering that goes into making these is amazing, especially when you consider the size of them.

 

In this thread, I'd like to share a few of these with you, and I'll add to it as and when I can. Unless specifically noted, these will be objectives which do not contain glass, but are quartz, calcium fluoride and/or mirror based. I wont be covering UV fluorescence objectives, as these are typically of traditional glass design, just made with low fluorescence glass with reasonable UV transmission properties.

 

To start with a couple of my more recent acquisitions, but some of earlier examples of this type of objective - the Zeiss Monochromats.

 

Zeiss Monochromat objectives

 

These are quartz only objectives and the two below were designed and corrected for use at 275 nm - the Cadmium emission line. Both are RMS threaded.

 

The first one is a 1.7 mm / NA 1.25 glycerin immersion one.

 

 

And the second is a 16 mm / NA 0.20 one.

 

 

Zeiss also produced some of these for the 257 nm mercury line, and other manufacturers such as Cooke also made some. There's a bit more background to them here on my site - https://jmcscientifi...-monochromats/. Since writing that I have done the UV lens transmission test, and they behave as expected for quartz objectives.

 

When you think these are about an inch tall, it really is amazing how they were able to make them.

[colinbm]

Impressive Jonathan

What magnification are these objectives Please ?

Are you aware that 275nm is in the range of the most destructive wavelength for DNA & Humans ?

[JMC]

Hi Col, Yes, 275 nm is very damaging. These early pioneers did some things which I've no doubt we would think were crazy - I have no great desire to build myself a cadmium arc lamp any time soon, and these are more of historical interest to me, although I will of course have a play with them at some point. Be interesting to know how many of these early researchers had skin and eye problems as they got older.

 

Overall magnification wise, it depends on the tube length and the eyepiece they are being used with, but think of the 1.7 mm one as being similar to a 100x objective (so with 10x eyepieces this would be about 1000x magnification), and the 16mm as a 10x objective (so, 100x with 10x eyepieces).

[colinbm]

Thanks Jonathan

It is interesting watching your progressing.

[dabateman]

Odd that they called it a 1.7mm, rather than using its correct magnification.

 

I need to catch up on your blog now. You have some interesting new entries.

 

Congratulations on the award!

 

I would be surprised if they could only be used at 275nm. I think they should still work at 313nm. I don't think there is a coating that would restrict you to that wavelength.

 

The only issue might be working distance. The focus point at 255nm is significantly different than 313nm. So that might be the only issue. If the working distance is large enough for the 1.7mm, than you might be ok.

 

Alternatively, just use a tube and a camera, rather than fixed microscope and you should be able to image anything with them.

[JMC]

Thanks Col, David.

 

Not sure as to the reason that these older lenses are in 'mm' rather than magnification, but they use lots of different eyepieces and tube lengths, so perhaps it was simpler to just describe the lens like that.

 

No, there's no coatings on the lenses, so that's not a problem. They were just designed to be best at yhe given wavelength. Given I'm using monochromatic sources anyway, I'll probably still get something useful out of them.

[nfoto]

Designed to be used with glycerine as the immersion medium, apparently. Personally I dislike the immersion objectives as cleaning off the goo always ends up with stuff being deposited in the wrong spots. However it cannot be denied resolution improves.

 

So, every thing else is UV-compatible with your compound microscope then?

[JMC]

Birna, yes the 1.7 mm one is glycerin immersion, although the 16 mm one is a dry lens. With the samples I have at the moment I tend not to need immersion objectives, as I'm typically using 10x and 32x objectives (rather than 100x).

 

Yes, I've changed everything in the microscope to be either UV fused silica or quartz or calcium fluoride. With the camera, filters and light source I have at the moment I can image down to 313 nm, but it should be good to about 250 nm if I ever get the need to go that low. Resolution at 313 nm is about 1 micron, which give it is a home built/modified setup using components from various manufacturers (and me) I'm quite happy with.

[JMC]

Zeiss Ultrafluars

 

This addition to the microscope objective thread is for the Zeiss Ultrafluar objectives. These are quartz/calcium fluoride objectives, and for the 160 mm finite tube length microscope were produced with a range of magnifications from 10x to 100x. They are to be used with 0.35 mm thick quartz coverslips. Some were made for phase contrast work (with the phase ring inside) and others were available with low strain elements for polarised light work. They are RMS threaded.

 

Zeiss also produced an Ultrafluar condenser, and a number of short barrel objectives for their Photometer 01K (still RMS threaded but shorter length than the usual ones for the microscope). I was told these short ones wouldn't work on a microscope, but I've tried them with small RMS threaded extension tubes and they work ok.

 

On the image below, on the back row, left to right, are a 32x, a 10x, a 10x for polarised light (with the red writing) and another 10x. On the front row, left to right, an Ultrafluar condenser, 32x and 100x objectives for the Photometer 01K.

 

Zeiss have also produced Ultrafluars for infinity length microscopes. As I do all my work with finite tube lengths I generally don't keep a look out for these, but I did get one interesting one. This a 10x one designed for use at 193 nm, and has a port in the side for removing the air from it.

 

This one was designed for use with a very thick window - 9 mm of quartz - and I suspect was not for normal microscopy. Zeiss unfortunately haven't been able to tell me anything about it, and I think it was used for photolithography rather than microscopy.

 

All as expected for quartz/calcium fluoride lenses have very good transmission down into the deep UV.

[Andy Perrin]

I’m surprised such a tiny amount of air is worth removing at that wavelength. It must be a lot more opaque at 193nm than in the 250’s.

[JMC]

Apparently so Andy. I think it's due to the oxygen.

[ulf]

Sometimes air is replaced by flushing with Argon.

I have seen some spectrometers for deeper UV having that feature.

[Stefano]

So this means that air played a role in David's 185 nm test? I thought air was a problem like below 150 nm.

[dabateman]

So this means that air played a role in David's 185 nm test? I thought air was a problem like below 150 nm.

 

Humidity also plays a major role too. Its about 84% humid here now. I have a dehumidifier going crazy in the basement to try and knock that down to 40%

But it definitely affects image deep into UV.

[JMC]

An interesting piece of history to add which turned up recently. It contains a Bausch and Lomb 53x UV reflecting condenser and objective (marked up as Polaroid Grey) and a 10x UV eyepiece. The eyepiece has quartz elements, and the objective and condenser are a mix of quartz, calcium fluoride and mirrors and are designed for UV use. The objective and condenser are RMS threaded. I've measured the transmission, and they all show good UV transmission down to 280nm.

 

They are mentioned in the B&L 'Microscope accessories' brochure from 1958 (although the eyepiece looks a little different to the one in the picture). Never thought I'd ever see any of these, nevermind finding a set like this. These look like they were bought and then left in a cupboard.

 

 

 

 

 

 

[Lou Jost]

Jonathan, do you know the proper coverslip thicknesses for the Monochromats? Thanks!

[JMC]

3 hours ago, Lou Jost said:

Jonathan, do you know the proper coverslip thicknesses for the Monochromats? Thanks!

That is a very good question, and took a bit of looking to find the answer. I eventually found it in Needham's "The practical use of the microscope". The Monochromats were intended for use with 0.17mm thick quartz coverslips. This is different to the later Ultrafluars which are designed for 0.35mm thick quartz ones.

 

Also the Monochromats were originally designed for use in a 160mm tube length setup.

[Lou Jost]

Thank you very much for figuring this out! That's a surprising answer; I expected the Ultrafluars had inherited their coverslip thickness from the Monochromats. Did your test diatom photos use that coverslip thickness?

[JMC]

59 minutes ago, Lou Jost said:

Thank you very much for figuring this out! That's a surprising answer; I expected the Ultrafluars had inherited their coverslip thickness from the Monochromats. Did your test diatom photos use that coverslip thickness?

Yes, I'm a bit surprised as well. No, my diatom slides with quartz slide/coverslip have 0.35mm coverslips. I do have some 0.17mm coverslips but no prepared slides with them.

[Lou Jost]

That's interesting. Your Monochromat shots were quite sharp. This means they would be even better if you had used 0.17mm cover slips. Maybe on a par with your Ultrafluar?

[JMC]

13 hours ago, Lou Jost said:

That's interesting. Your Monochromat shots were quite sharp. This means they would be even better if you had used 0.17mm cover slips. Maybe on a par with your Ultrafluar?

Yes maybe, especially if I use the right wavelength as well. Amazing, the lenses they were able to make. Also, if you look back over the literature there was definitely some variability in the coverslips they used, even from the same manufacturer. Zeiss made something called the Ultramicroscope with a glycerine immersion 60x objective - that I think used 0.75mm thick coverslips. Leitz made some reflecting objectives which were designed to be used in the UV, vis and IR. Those used 0.5mm slides and 0.17mm coverslips. The Ultrafluars now use 0.35mm thick coverslips. Getting quartz coverslips is expensive enough, let alone getting them in different thicknesses for different objectives.

[JCDowdy]

A really excellent presentation of such a unique collection.

[JMC]

16 hours ago, JCDowdy said:

A really excellent presentation of such a unique collection.

Cheers John. I really must update this with more information, as my collection has gradually grown since I started.