Category Archives: General

Microscopy – resolution benefits with 390nm light

In my early days of UV microscopy, I got to wondering what the resolution was with my setup. I ended up buying a Newport USAF resolution test slide designed for really high end microscopes, and doing some tests with that to see what the resolution was when using 313nm, 365nm and 546nm light from a mercury xenon lamp (you can see that test here). However since then I have done more work on the microscope, and I have also started doing my diatom imaging. For looking at ready made diatom slides, where the coverslip and slides are glass and standard thickness, this effectively eliminates the ability to use 313nm light, and I am limited to 365nm and above. My preferred condenser (Olympus Aplanat Achromat) stops me from using 365nm light as it blocks it, and until recently I have been using filtered 450nm light as my preferred approach. Recently though I got myself a 395nm LED torch, the thought being to combine that with a 390nm Thorlabs bandpass filter. I can then use this with my preferred condenser for imaging diatom slides.

As an example of the types of images I can use this setup to create, the images below was taken on my Olympus BHB microscope using 390nm light with a 63x Leitz Pl Apo NA 1.40 objective with oil immersion, the Olympus Aplanat Achromat condenser, oil immersion, bright field (I’ve reduced the resolution sharing, but it gives an example of what can be done). The slide was by CN Walter.

Actinoptychus heliopelta imaged using 390nm light

This looked nice and sharp to me, but I wanted to get some more numbers to put behind this. I got my Newport test slide out again, and took three images where I changed the lighting – 390nm, 450nm, and unfiltered white LED light (400-700nm) – while keeping the rest of the setup the same. The objective was my 63x Leitz Pl Apo NA 1.40 with oil immersion, the condenser the Olympus Aplanat Achromat, oil immersion, bright field set to about NA 1.1. ISO100 for all images, although exposure time was varied so that overall image exposure was about the same for each one. Image was refocused for each one (although an Apo objective some minor correction of focus will pretty much always be needed with a NA 1.40 objective which has a tiny depth of field). Same small degree of sharpening I use for images from this objective, and finally an auto contrast. Shown below are crops from the centre of each image concentrating on the smallest sized features on the test slide.

The part of the images above to concentrate on is the ’11’ with 6 sets of bars underneath it. These dark bars are chromium deposited on the quartz substrate of the slide. Group 11 has 6 Elements below it, which become smaller and smaller. Elements 1-3 are numbered, and then 4-6 just have dots next to them (you can see 1-6 for Group 10 to help with visualizing what is going on). The bar/space widths are as follows;

Group 11, Element 1 – 244nm

Group 11, Element 2 – 218nm

Group 11, Element 3 – 194nm

Group 11, Element 4 – 173nm

Group 11, Element 5 – 154nm

Group 11, Element 6 – 137nm

There’s more info on the Newport Test slide here – mine is a Highres 2 with dark lines on a clear background.

There is a difference between the different light sources, with a higher resolution being seen with the 390nm light vs 450nm vs white light – the shorter the wavelength the better the resolution. It’s perhaps easiest to see by looking at Group 11, Element 6 (the smallest of the sets of bars below the ’11’ in the images). With unfiltered white LED light the bars of Element 6 all blur together, while they are just about visible with the 450nm light and 390nm light. The difference between 390nm and 450nm light is more subtle, but just about visible on these images.

One thing to note – the 63x Leitz objective is designed to be used with a 0.17mm thick coverslip and immersion fluid. However no coverslip was used here. The reason for this is a practical one – with a coverslip on the slide, a small amount of oil is needed between the coverslip and slide, and with the extremely small working distance of the 63x Leitz objective, there is a risk of grinding the coverslip into an extremely expensive test slide, and this is something I do not want to do. This will hamper the maximum achievable resolution a bit but in theory not too much as the refractive index of the immersion fluid should be close to that of glass, however it should allow for comparative testing between the different wavelengths.

On the plus point, resolution looks to be down below 200nm for this setup especially for the 390nm light.

Looking back at my original resolution testing, these longer wavelengths stack up very well against the deeper UV images in terms of achievable resolution. This seems odd, as shorter wavelengths improve resolutions (thank you Abbe). However the setup is different here to the previous images – here the objective and condenser are higher NA vs for the deeper UV images. The higher NA’s here improve resolution for a given wavelength. As always, the whole system needs to be considered when looking at resolution. Yes shorter wavelengths can improve resolution, but the overall effect depends on everything in the optical path. Know your kit….

Where does this leave us? The use of 390nm light is a long enough wavelength to allow for the use of standard optical elements in the microscope and standard prepared slides for imaging diatoms, and enables improved resolution compared with white light and even 450nm light. Downsides – well you’ll need a UV sensitive camera with the internal UV/IR blocking filter removed. The LED source I have is plenty powerful enough and was cheap – about 25GBP – however with cheap often comes ‘nasty’ and one quarter of the LED has already burned out after a few uses. Brightness is also not very stable, making capturing images for stacking a bit more annoying. Caveat emptor….. A more expensive UV LED setup like the types that Thorlabs make should improve the issue with brightness variation, but at a much higher cost. I could also make one myself, and may do that if I have the time and/or the inclination. I will certainly persevere with 390nm light though, and a replacement torch is on its way. If this new one burns out I’ll get some better LEDs and modify them myself.

As always, thanks for reading and if you’d like to know more about my work, I can be reached here.

International Society for Diatom Research – the benefits of societies

Yesterday I found myself in need of an article published in the journal Diatom Research. As I do not have academic access to this journal, it was going to cost me a significant amount to download and read it (45GBP for 48 hour download access). I mentioned this on the Diatom Images Facebook page, and someone mentioned I should check out the International Society for Diatom Research, and think about becoming a member. Membership allows free access to the journal Diatom Research. And get this, annual membership is 40GBP. So by becoming a member for the year it costs me less than the prices of accessing one article from the journal, and I get as much use as I need from it, and it puts me in contact with folks with a similar interest. Win win (or should that be win, win, win).

After 2 years of doing my diatom photography, this was the first time I had heard about this group. If in doubt, ask about…..

Microscopy – when does editing images become too much?

Today’s post poses a question. When does the editing of images become too much? When doing microscopy, images have to be edited. Dust on the sensor needs to be removed, the background needs smoothing, noise needs reducing and images need sharpening. The question here though, is what is acceptable editing and what isn’t? A somewhat philosophical issue, but something I found myself thinking about with an image recently. Here’s the image, a Brightwellia coronata diatom from a strew slide of Totara, Oamaru, New Zealand, made by Ray Parkinson (reduced in resolution from the original 3500×3500 image for sharing here).

Brightwellia coronata diatom from Ray Parkinson slide of Totara, New Zealand

The image above was taken using my Olympus BHB microscope, using 450nm LED light, and a 63x Leitz Pl Apo NA 1.40 oil immersion objective. Brightwellia coronata is a beautiful diatom, and one which is very difficult to find undamaged. I have various strew slides from Oamaru which have broken ones on them, and some which are almost but not quite intact. A few days ago I was looking through this slide from Totara, as I’ve been having some good luck with strew slides recently. After looking through most of it, and seeing fragments I saw what looked to be an intact one, buried in the middle of a load of others. This was what I saw with a 10x Nikon Plan Apo NA 0.45 objective – the B. coronata is in the middle of the image.

Totara strew slide by Ray Parkinson

As can be seen from the image above, its a busy slide and with quite a bit of debris across it. In addition to what looks to be a small B. coronata in the middle of the image, there are a couple of larger broken ones to the left and lower left of the one in the middle. In this low magnification image the main one looked to be intact, but there was some dirt at the edge of it at the 8 o’clock position. When I did a high magnification image of it using my 63x Leitz Pl Apo NA 1.40 objective, the piece of dirt was just covering the very edge of the diatom. Removing most of the dirt which wasn’t over the diatom was simple enough using the stacking software (Zerene) and blank image. However I started wondering, can I remove that piece of dirt in Photoshop by cloning a short section of the edge of the diatom that I can see and pasting it over the bit where the dirt was? Below are three crops of the area in question from the stacked image to show what I mean.

First is the stacked image from Zerene, the bulk of the dirt which is not on the edge of the diatom has been removed. It obscures the very edge of the diatom’s rim over roughly 3% of the overall circumference.

Dirt on the edge of the diatom

The diatom underneath did not look to be broken, it just looks like the piece of dirt is laid on top of it. The next image is with a section from the rest of the visible edge of the diatom cloned and pasted over this bit with the dirt and smoothed out (and I’ve removed some dust on the sensor – the circle at the lower right of the image above).

Image after removing the dirt on the edge of the diatom

I then went through the final editing (removal of dirt from the sensor, denoising, sharpening, smoothing, contrast etc), and ended up with the image shown at the beginning of this article. The crop of the area of interest after all this is shown below.

Crop of the final image

And this is where I come back to my original question? When does editing of the image become too much? As a matter of work flow, I play around with brightness, contrast, sharpness etc all the time. I clone out areas where there is dust on the sensor, making a best judgement as to what to replace it with by looking at the surroundings. I remove dirt and other diatom fragments from the background of the image, and smooth it out so it doesn’t detract from the main subject. However what I don’t do with a broken diatom is replace parts of it to make it look whole again. At the end of the day I am trying to image what is there. This case is a bit of a middle ground. The diatom did not look broken from what I could see, and the dirt was covering a small part of the edge of it. I made a judgement call as to what the bit that was covered would look like and replaced it. It certainly makes the image look nicer, but is it still relevant as an image? This is one of those images where I could argue either way. If I were to put this image in an article I would feel the need to disclose that it has been edited (and how it has been edited), but this is just how I work.

Before I wrap up, here’s the slide.

Ray Parkinson strew slide from Totara, Oamaru, New Zealand

Image processing is a necessary part of dealing with microscope photos. What we deem as acceptable comes down to a number of factors including our own personal preferences and where the final image will end up being used. I hope you found this interesting, and if you’d like to know more about my work I can be reached here.

Microscopy – Beck quartz condenser, NA 1.25, water immersion

Bit of an update today on a new piece of equipment for my UV microscopy work. A few days ago I was at a Quekett Microscopical Club meeting, and one of my microscopy friends approached me and offered me something they had recently got as part of a consignment of microscope parts – a condenser made by Beck and described as ‘Quartz condenser, NA 1.25, W.I.’. I nearly fell off my seat, as quartz condensers are rather rare. Anyway I jumped at the chance to have it, and this post shares some initial images of it, and shows the transmission through it in the UV.

Here’s the condenser.

It came in a mount which is slightly too big for my Olympus BHB but the condenser itself unscrews from the mount and is RMS threaded as shown below.

Last year I had a condenser holder made which is RMS threaded and fits my microscope, so this will fit just fine. It also has a small diameter so will fit through the hole in my stage.

Why the excitement? Normal glass blocks UV, especially the shorter wavelength end of the UV spectrum below 365nm. As such it is no good for imaging at 313nm or below. Quartz however lets UV through and is good with light down to at least 250nm. Unfortunately quartz condensers were both rare and expensive when originally made, and as far as I am aware no-one currently makes them, which makes finding them a challenge. While I keep an eye out for them in the usual places, finding them is uncommon, and usually needs an element of luck (as was the case this time). This one has ‘W.I.’ written on the side, which means it is designed for use with a drop of water as the immersion fluid, although for low NA applications (when the objective is below NA 1) it would probably be fine to use it dry.

As I had not seen one like this before, the first thing I did was measure the transmission spectrum through it using my Ocean Insight FX spectrometer, and got the following.

Transmission through the Beck quartz condenser between 280nm and 420nm

As expected, the transmission through it in the UV was good, not dropping at wavelengths below 365nm as would be expected for a normal glass one.

I have not seen one like this before, but I suspect it was originally designed for fluorescence work rather than UV microscopy (as mentioned for a couple of quartz condensers in this Beck catalogue) and is probably a simple Abbe construction. Simpler is normally better when it comes to UV.

Joining a club such as the Quekett is a great way to meet very knowledgeable and passionate folks, but also to find historically interesting items which you may otherwise never get to see, and I can well recommend it. I now look forward to trying this out for my UV microscopy work. As always, thanks for reading and if you’d like to know more about my work I can be reached here.

Microscopy – Mystery of the Leitz 50x Pv glycerine immersion lens solved

This is something which goes back to my early days of exploring microscopy in 2020. I bought a slightly mysterious lens, a 50x Leitz Pv NA 1.0 glycerine immersion objective, which has designed to be used with a 0.18mm thick quartz coverslip. I originally wrote about this here. At the time when I tested it I was slightly surprised to find that despite being designed to be used with glycerine as the immersion fluid and for use with a thin quartz coverslip, the UV transmission was not like a Zeiss Ultrafluar. Although offering some UV transmission especially at 365nm, it dropped at the shorter wavelengths and was blocking the light by about 320nm. At the time I didn’t expect this, as I had thought it would transmit further into the UV, however the objective had some unusual markings on it, and I wondered if this was a prototype, mock up or master copy for the factory perhaps just fitted with glass elements. Since then I have always kept a look out for another copy of the lens to test for transmission and compare with my original copy. However this is a rare objective, and it was nearly 4 years before I saw another one for sale. Today’s post shares the results of my transmission testing of this new copy, and discusses the implications of my findings.

Here are the two copies of the objective. My original one with ‘Muster-fasserei’ written on the side on the left, and the new copy on the right.

Two 50x Leitz Pv NA 1.0 objectives

And the back side of the objectives.

Two 50x Leitz Pv NA 1.0 objectives, back side view

There are some differences in style and labelling of the two objectives, but overall they should be the same – 50x magnification, phase contrast (Pv), NA 1.0, glycerine immersion and for use with a 0.18mm thick quartz coverslip on a 170mm tube length microscope. Except, according to the original Leitz literature, they were actually meant for a microscope, but a ‘microspectrograph’. However they do work as normal microscope objectives with a phase contrast ring in them.

So, the six million dollar question, how does the UV transmission of the two version compare? To check this I measured both of them using my Ocean Insight FX spectrometer and got the following graphs.

Transmission through the two copies of the 50x Leitz Pv objectives

What does the graph above show? There are the two copies of the objective. The transmission through the original one with ‘Muster-Fasserei’ in blue, and the new copy in red. The transmission spectra for the 2 objectives are almost identical and certainly close enough for me to be happy that there are no major differences between them in terms of construction. Both have good transmission at 365nm, and then dropping in transmission below that, with them being essentially opaque by 320nm. Below 320nm we are down in the noise and although it says about 3% transmission this is just a quirk of the measurement process.

Where does this leave us? My original ‘Muster-Fasserei’ copy has the same transmission as the other copy, so optically I am happy that this is the same as the production copies. They have good UV transmission above about 350nm, but poor transmission below that, so they are not true UV lenses like Zeiss Ultrafluars or the Leitz UV objectives, but then they do not claim to be. Glycerine immersion normally would indicate UV work, and the 0.18mm thick quartz coverslip would also back that up. Now though I come back to the entry in the Leitz catalogue which described the objective for being for a ‘microspectrograph’. I suspect the use of glycerine as an immersion fluid was to reduce fluorescence as it is low fluorescence fluid. Also the quartz coverslip will be lower fluorescence than a glass one (I’ve looked at fluorescence of glass and quartz/fused silica here). Minimizing fluorescence of components in the optical train will be very important for a spectrograph which will be measuring light intensity. These were therefore probably designed to be used in a setup where low fluorescence was important, so perhaps for use with light with wavelengths from 350nm and up.

Answering questions about older microscope equipment can be a real challenge. Documents do not always exist online, and personal knowledge of folks who might have used or worked on older equipment is unfortunately disappearing rather too rapidly. This has taken a few years to get an answer but I feel I know more about them now than I did before, and as a scientist that is very important to me. As always, thanks for reading and if you’d like to know more about my work, I can be reached here.

Microscopy – A diatom wish list

Firstly, apologies for not posting a lot recently. My wife and I had a holiday in Tasmania in January, and I am still going through the photos from that (it’ll be done by the end of the month, fingers crossed). I have done a bit microscopy in my down time though, and it got me wondering, what would be my wish list for diatoms to image? I’m sharing some thoughts on this today, some of my wish list I have and others that I have yet to image. These images were done using my modified Olympus BHB microscope, and have been reduced in resolution for sharing here (the original are much higher resolution).

EDIT, 18th March 2024. I have managed to find an example of one of the diatoms am looking for – Truania archangelskiana – on a strew slide I had, so have included an image of that now.

I’m going to start with ones on the wish list that I have managed to find. Firstly one of the structurally prettiest diatoms I have imaged so far, Cerataulus subangulatus from the Oamaru deposit.

Cerataulus subangulatus

This was a slide made by Emiliano Bellotti and has a single example on slide. A beautiful structure as well as being a challenge to image.

Next we have Brightwellia Coronata, again from Oamaru.

Brightwellia coronata

This was on a strew slide from Allans Farm, Oamaru by Bernard Hartley, and is the most complete one I have found in the slides I have. It seems to be very prone to breakage, and finding a complete one is a ‘challenge’, although many Oamaru strew slides will contain fragments of them.

Next is Hydrosilicon mitra.

Hydrosilicon mitra

The slide maker here is JA Long, and the location is given as New Hebrides. It’s quite a rare diatom and extremely fragile. This one is the best I have with only a few broken ribs.

Next is Monopsia mammosa, another one from Oamaru.

Monopsia mammosa

Another slide by JA Long, and I do have second example of one which is more broken up. This has a couple of cracks, but that is about it.

This one I only imaged a few days ago – Actinoptychus affinis from Java.

Actinoptychus affinis

This was a slide by Samuel H Meakin, and is almost complete apart from a bit of the edge missing. I love the patterning on this one.

Now for Triceratium nitescens on a slide by the maker RI Firth.

Triceratium nitescens

A beautifully shaped diatom from Barbados and one I was really happy to be able to image (the slide says ‘very rare’ and I believe that is true).

Now we get into ones that I am still actively looking for examples of, because I either only have a fragment of it, the one I have is not ideal for some reason, or ones which are so unusual I have only seen pictures of. To start with Charcotia decrescens from Antarctica.

Charcotia decrescens

This one is on a strew slide by Klaus Kemp, and is actually pretty good. I’m being picky here, it was at quite an angle in the strew, and made imaging difficult, so is one I keep an eye out for. I think it is also known as Chacotellia decrescens, and Actinocyclus actinochilus.

The next is one I only have a fragment of – Biddulphia pedalis from Oamaru.

Biddulphia pedalis

Another slide by Samuel H Meakin, I have seen fragments of it, but so far have not tracked down a whole one and it seems to be quite a rare diatom. Also known as Grovea pedalis. Lovely details on it though. The image above was done using 365nm light and the short wavelength makes all the small features really pop.

The last one I do not have a individual sample of, but I have managed to find it on a strew slide by Bernard Hartley. It is Truania archangelskiana, and is shown below.

Truania archangelskiana

Reported locations for this one include Singiliewsky and Inza, Russia and Eidsbotn Fjord, Devon Island, Nunavut, Canada (seen here). An image of one can also be seen on the Photomacrography forum, here. A striking looking diatom and well worth looking out for for imaging.

I find imaging diatoms fascinating and rewarding, and never cease to be amazed by the varying forms. There are loads I could have listed here, but this gives a nice cross section of some of the more unusual ones. I hope you enjoy these images, and if you have any slides of these you would be open to finding a new home for, I can be reached here.

UVA and UVB Video microscopy of titanium dioxide (TiO2) particles in sunscreen films

Firstly, a belated Happy New Year to everyone. I wish you all the best for 2024. I start the year with some microscopy work, but something a little different to the diatoms I regularly share. My day job is in the field of dermatology, and the initial reason I built my UV microscope was to be able to image sunscreen (SPF) products. Specifically to be able to image UVA and UVB sun filters separately and see where they are in the cream. While most of my imaging is done using photographs I do occasionally do video work. This post shares some really funky videos looking at titanium dioxide (TiO2) particles in a partially dried sunscreen film, with the videos being recorded both using UVA – 365nm light – and UVB – 313nm light.

The product contained titanium dioxide (TiO2) particles as the UV blocking ingredient. The slide was prepared and the product allowed to dry slightly before imaging. Imaging was done using my modified Olympus BHB microscope with a 100x Zeiss Ultrafluar NA 0.85 objective lens, and using two different UV wavelengths – 365nm (UVA) and 313nm (UVB). This is not fluorescence imaging, this is direct imaging of the UV at the different wavelengths.

Two videos to share. First, captured using UVA light.

UVA video of partially dried sunscreen film

What are we looking at here? The video shows a partially dried down film of a sunscreen cream. There are regions where there are still droplets of oil from the topical emulsion before the droplets have chance to coalesce. Inside the oil droplets there are particles which are moving – these are particles of TiO2. Some of these particles look white and some look black in UVA, i.e. some are absorbing the UVA and go black, and some are reflecting or scattering the UVA, and look white. Whether they absorb or scatter a given wavelength depends on their particle size. However the really cool thing is that they are moving and moving quite a lot. What’s causing this? I’m shining UV on the slide with the product film and some of that is being absorbed by the TiO2. As a result it will warm up and start to move – Brownian motion – bouncing into other particles and transferring energy causing them to bounce around. As a result UV energy is absorbed resulting in particle motion.

With my microscope I can image other UV wavelengths. By swapping filters and imaging at 313nm I got the following video.

UVB video of partially dried sunscreen film

Same region of the product film, but now we have a video of how the sample looks using UVB light of 313nm. The video is much grainier as the camera is less sensitive at that wavelength, so the ISO needed increasing to be able to capture video footage. The particles look different now – most look black showing that most are now absorbing the 313nm wavelength light rather than scattering it. This is to be expected for TiO2 particles as the absorption of light is wavelength dependent. The motion is still present. The particles are typically sub-micron in size, but are probably aggregations on individual TiO2 particles as the smallest ones would be too small for me to resolve on my microscope.

Before I wrap up, I want to revisit the second video. Excuse me while I geek out for a moment. This was imaged using 313nm light and through a high magnification microscope objective. The camera was a monochrome converted Nikon d800 prepared by MaxMax in the US. Even though monochrome conversion improves sensitivity at 313nm, I was amazed to be able to capture live video of the behavior of this sample and how it looked in the UVB region.

It’s funny, when I first looked at these samples the movement I observed reminded me of cells moving around. However as I mentioned above, this is about energy transfer and heating of inorganic particles. The motion, while cool to see, is actually a problem for capturing images. Often my exposure times for capturing UVB microscope photos are of the order of half a second or more. Movement of the particles causes blur and reduces the resolution achievable. As always it is important to understand the techniques you are using when trying to understand what it is they are telling you.

I’d like to thank DSM-Firmenich AG for supplying the sunscreen sample to image, for funding some of my UV microscopy research and for giving me permission to share these videos. As always, thanks for reading, and if you’d like to know more about my work I can be reached here.

Latest publication – Microscopy of metal and metal oxide coated diatoms

This is a nice way to end 2023 – a new publication of an article which was a fairly major piece of work this year. This one is the about the use of metal and metal oxide coating for diatom microscopy, and looks at the slides and techniques of making them from the very earliest examples to the modern day. It has been published in the Quekett Journal of Microscopy. I even managed to get one of my images as the cover art of this edition.

Shown below are some extracts from the article and the cover page.

Please excuse the relatively poor quality of the scans, my home scanner is not the most up to date. The hard copy in the Journal is much better.

It was as pleasure working on this one, as I find the approaches used to improve diatom visibility fascinating. Sourcing the slides was the biggest challenge as these are unusual items, but I wanted to write something to show the wider world some of what these amazing slide makers have produced.

More to come in 2024 as I have a few papers already in the pipeline. As always, thanks for reading, and if you’d like to know more about my work I can be reached here.

All the best for 2024 everyone!!!

Microscopy – Various diatoms, seasons greetings and 2024 plans

Firstly, seasons greetings to you all. I wish you the best for Christmas and the New Year. Today’s post is a chance for me to share some of my recent microscope images and also my thoughts on where my research will take me in 2024.

I am pretty certain that most of you come here for the pictures (rather than my deep and meaningful conversation), so lets jump straight into the images. All of these were done on my UV modified Olympus BHB microscope, but mainly with 450nm light rather than UV (easier to use with some of the slides). Camera for these was a monochrome converted Nikon d850 from MaxMax, and stacking was done using Zerene. Images have been reduced in resolution for sharing here. First up, a favourite of mine and a diatom that I’ve been on the look out for an intact copy of for a while – Hydrosilicon mitra, imaged using a 63x Leitz Pl Apo NA 1.40 objective and oil immersion, with oblique lighting.

Hydrosilicon mitra

And the slide.

Hydrosilicon mitra slide

I believe the maker for this is JA Long, and there is a single example on the slide. Location for it – New Hebrides. The image was quite low contrast, as the mountant didn’t look like a high refractive index (RI) one. I have a couple of examples of this diatom but they have much more damage than this one does. I suspect this is a particularly delicate one to mount. A very unusual looking diatom.

Next up is Porodiscus hirsutus from an Oamaru strew slide by Mike Samworth. Again imaged using a 63x Leitz Pl Apo NA 1.40 objective with oil immersion, this time with bright field illumination.

Porodiscus hirsutus

And the slide.

Porodiscus hirsutus slide

A fabulous looking diatom with lots of interesting structures in it.

Next up two slides by ECP Bone. Both using the 63x Leitz Pl Apo NA objective with oblique lighting.

Dictyoneis marginata var. janischii
Pinnularia lobata

And the two slides.

Dictyoneis marginata var. janischii slide
Pinnularia lobata slide

Both of these are well made slides, each with a single example from Oamaru. Note that the Pinnularia lobata slide actually has the name Pinnularia excellens. This looks to be an error as the diatom looks more like the former than the latter (this happens more than you might expect due to the difficulties in identifying diatom species and the changes that have occurred with the names over the years).

Finally for today an image from a Watson ‘Amichian test slide’ using darkground illumination (Reichert Neo 1.42/1.18 darkground condenser and 100x Leitz Pl Apo NA 1.32-0.60 condenser, both with oil immersion). For this one I went into the UV and used 365nm light.

Watson ‘Amician test slide’

And the slide.

Watson ‘Amician test slide’

The ‘Amician test’ is a test for resolution, and uses a Navicula diatom. However it is quite a mysterious test, and although this one says Navicula rhomboides, there is come controversy of which species was used for Amici’s original slide. Perhaps this will be something to write more about in the new year. Which leads me neatly on to the plans for 2024……

I like to have a few papers or articles which I am working on at any one time. A couple of papers are already planned for 2024. Firstly, some initial results on a new darkground condenser I’ve been working on. It is early days, but might be a neat idea for my UV darkground imaging where there are limited options available to buy (and by limited I mean as rare as hens teeth). Also building on an article I’ve recently written for the Quekett Journal of Microscopy on metal and metal oxide coated diatom slides, which looks at examples from their inception to now, I’d like to do a similar one from slides made using Realgar (a high RI material based on Arsenic Sulphide). This one needs a bit more thought, and ideally I need to get access to a 2d or 3d confocal Raman mapping device for a day to take a look at a slide in more detail, and try and understand more about what is going on chemically in the mountant. A work in progress.

Given I am now building up quite a catalogue of high resolution diatom images (the ones I have shared on this site are generally low resolution to I don’t exceed my storage capability) I’ve had a couple of people ask me if I am going to write a book or do something else with them. I’d like to do a book, but I know how much work they are. I think a mix of high res photos and some details on the slides, but combined with some essays on microscopy would be a good thing to do – a mix of art and science, and along the style of some of the early microscopists. Perhaps this can be my legacy to the microscopy world.

Anyway, as always, thanks for reading, and all the best for Christmas and 2024 whatever you are up to. If you’d like to know more about my work, I can be reached here.

Microscopy – Diatoms from Toome Bridge, Ireland

You can find find diatoms pretty much anywhere, but the range present at one location can be very different to other places. Toome Bridge (now called Toome or Toomebridge) in Ireland is a place which seems to have an amazing array of photogenic diatom species in the diatomite that is mined there. I have a couple of strew slides from that location and today’s post will show some images from one of those.

This slide was made by Neville Bradpiece, with diatoms mounted in Sirax. Apologies, but I don’t have names for all of these different species, but I have added names where I can. Some of the images have been reduced in resolution for sharing here. To start with, the eye…..

The image above has two diatoms in the centre, a circular one on top of a lens shaped one. This reminds me of an eye looking back at me through the microscope. Next is a tiny one, being only about 20 microns across.

This one was tiny, being only about 20 microns across. Next is I think Navicula radiosa. I was using 365nm UV illumination for this slide, and a 63x Leitz Pl Apo objective with an NA of 1.40. Hence very high resolution.

Below is part of a Pinnularia.

Going in close to this I got the following.

Based on the analysis in ImageJ, the spacing of the poroids here is about 190nm. Theoretical resolution with 365nm light and the NA 1.4 objective is about 130nm so this could well be correct, and it matches with SEM data I have seen for this species.

The one below is a Gomphomena.

The last one from this slide is a Cymatopleura elliptica.

Here’s the slide.

This slide caught my eye as it uses the mountant Sirax, and it mentions the very high refractive index it has (1.8). Sirax seems to be good for UV imaging as it is a high RI mountant which does not block the UV, hence I can get good contrast AND good resolution when using 365nm light. Note yet another spelling on the label – this time Toom Bridge. The images shared here scratched the surface of what was on the slide. I images upwards of a dozen different species from the slide, and that was not all of them. The more I looked the more I saw.

Strew slides are often overlooked in favour of slides with single species on them, but they can provide literally hundreds or thousands of diatoms to image, and are often cheaper than single species slides. This one cost me about £10, and I feel like I got an absolute bargain with it.

As always, thanks for reading and if you’d like to know more about any of my work, I can be reached here.