Microscopy – illumination wavelength tweaks to improve resolution

With my UV microscopy, I’ve noticed a dramatic improvement in resolution as the wavelength decreases. A well known effect, but the UV gives a great demo of how big a change can be observed – for example see my work on a test slide here. However converting a microscope to be able to image in the short wavelength UV region is no small task as glass absorbs the light. Is there a benefit to filtering visible light to image in the short wavelength blue region? There certainly is, and again this is well known, and is something I regularly do. However I thought I would share an example to show the effect, and also how to go about doing it in practice.

The test slide was a piperine mounted diatom slide, and the subject a Pleurosigma angulatum that was present on it. I set up my Olympus BHB with a 40x Olympus Dplan Apo UV objective (set the coverslip thickness collar to as thick as it would go, as the sample had a thick coverslip, and this gave the best setting). Camera was a monochrome converted Nikon D800. Light source a white light LED (more on that later). Condenser an Olympus Aplanat Achromat, set to oblique. Single image, no stacking. Everything was kept the same for the images, except a Thorlabs 450nm (40nm FWHM) filter was added above the photoeyepiece for the 450nm image. Images from the white light and the filtered 450nm light were processed the same way, and the full images have been reduced for sharing here.

First the white light image.

White light image

Next, the 450nm light image.

450nm light image

At first glance there doesn’t look to be much between the two images, however going in closer on parts of the images tells a different story. Here are a couple of sets of crops from different parts of the diatom. In each crop the white light image is on the left, and the 450nm image on the right.

Magnified and cropped portions of the diatom. White light on the left and 450nm light on the right.
Magnified and cropped portions of the diatom. White light on the left and 450nm light on the right.

Note, the crops above were taken as screen grabs, and have a slight warm tinge to them as that is how I like my monitor. It is subtle, but there is a slight improvement in resolution as a result of using 450nm light vs the full spectrum of the white light.

For the 450nm image, I used a 25mm diameter Thorlabs 450nm (40nm FWHM) premium bandpass filter, and simply placed it on top of the photoeyepiece.

The filter is dichroic and has a preferred direction for the light going through it. This is shown by the arrow on the side of it. The LED is use is a cool white one I got from ebay and made an adapter to fit my light. This is its irradiance spectrum (measured on my Ocean Insight FX USB spectrometer).

Cool white LED irradiance spectrum

As can be seen the LED gives a broad wavelength range, but actually a nice strong peak at around 450nm. This is why I chose this filter and not a 405nm or 400nm one. Also using 450nm vs 405nm or 400nm is good for normal unmodified cameras as typically the internal filters on them will start blocking light at around 400nm. As a result 450nm is a good compromise – short wavelength, but detectable by normal cameras. Also the Thorlabs 450nm filter I used had a wide bandpass of 40nm, allowing plenty of light through. A 10nm bandpass filter would give a narrower range of wavelengths, but much less total light.

This can also be done (and was done historically) by putting a blue filter below the stage. I prefer to have the filter as the last stage before the light reached the camera though, which is why I put the filter on top of the eyepiece.

Of course a blue LED could be used, but as the white LED had a strong peak, I went down the route of filtering the light rather than having yet another light source.

A simple modification, but a helpful one when it comes to diatom imaging, adding a blue filter can produce higher resolution images for a given optical setup when compared with normal white light imaging. As always, thanks for reading, and if you’d like to know more about my work I can be reached here. Oh, I nearly forgot. Here is the slide I used for the images. While is says ‘Surirella gemma‘ on it there are plenty of Pleurosigma angulatum as well.

Photography – Fuji IS Pro ‘full spectrum’ camera spectral sensitivity

The Fuji IS Pro camera (or to give it its full name the Fujifilm Finepix IS Pro) was a DSLR introduced back in 2007. Based on their S5 camera body (which was based on a Nikon D200) this was advertised as being able to image in the UV, visible and IR and as such was not really aimed at the consumer market but more at the scientific and forensics areas. Indeed it didn’t go on general release and Fuji required buyers to sign a release form saying they weren’t going to use it for ‘unethical purposes’. It followed on from their S3 Pro UVIR version, but even from the beginning it was apparent that all was not well with the IS Pro and its UV sensitivity especially was not that great. I recently got hold of one these cameras and thought it would be fun to measure its spectral response as I have done with my other cameras.

Before we begin with the technical stuff, here’s the camera with a Zeiss ZF-IR 50mm f1.4 lens attached.

Fuji IS Pro with Zeiss 50mm f1.4 ZF-IR lens

Handling it, I like the feel of it. It feels well made and nice and solid. It takes compact flash cards, and has an APS-C sized sensor. Speaking of the sensor, this was a quirky design. A 12.3 megapixel ‘Super CCD’ with two different types of pixels – 6.17 million S-pixels and 6.17 million R-pixels for enhanced dynamic range. The degree to which these are used together can be selected by the user from the menu on the back. Although not a huge resolution, the sensor (when used in the S5) was well regarded by photographers especially with regards to the skin tones it was able to produce.

What’s the spectral response like? Here’s the results of my measurements.

Fuji IS Pro spectral sensitivity curve from 300 to 800nm

First thing to notice is this is barely UV sensitive, and only at the top end of the UV range from about 370-400nm. Below that sensitivity is essentially zero. The sensitivity it has is also mainly in the blue channel. This is different to the Sony, Nikon and Canon cameras I have looked at which have a little more sensitivity in the red and green channels in the UV, and a little more reach at the short wavelength end (for example see here for my Sony A7III data). While the IS pro could be used for imaging in that 370-400nm region, it is not really a UV camera. At the IR end things are better, and it is behaving here as expected for the other cameras which have been converted for multispectral imaging, although with a bit more emphasis on the red channel vs the blue and green channels in the 650nm to 780nm region.

However the really interesting area for the Fuji is how it splits blue, green and red. If you look at the Sony A7III for example, the red channel shows some significant response in the green and even blue wavelengths. Likewise the green channel spreads well into the blue and red channel regions. The Fuji IS Pro has very clean colour channels – while the overlap at their edges they do not spread over wide wavelength ranges, and the red does not bleed across the blue for example. This might account for its ability to capture skin tones accurately. I can also imagine it would be good at blue subjects – the Bluebell test, for example.

This IS Pro cannot be used simply like a normal colour camera given its IR (and the a lesser extent UV) sensitivity. However by using a filter such as BG38 on the front of the lens could be used for normal colour imaging, although the images would probably need to be carefully white balanced to get the best from them. I have also heard that IR photographers like it for the images it produces, so this is something I will try out.

Over the years, camera manufacturers have played around with different sensor technologies and each have their own little quirks and subtleties with regards to how they capture colours. Taking a look at the Fuji IS Pro has certainly been interesting, end despite its relatively low resolution compared with today’s offerings I can imagine it would still earn a spot in the camera bag for certain subjects. As always, if you’ve made it this far I thank you for your time, and if you’d like to know more about any aspect of my work I can be reached here.

Microscopy – latest historical diatom slides

It’s no secret that I enjoy imaging diatom microscope slides. They provide delicate and detailed structures and push me to get better at the imaging process. I tend to buy second hand older ones to image. While there are vendors still making slides, I think the older ones tend to have more character, and many are still surprisingly clear and usable for a fraction of the price of newer ones. Today’s post shows some of the slides to arrive recently and discusses how the images were captured (note that images have been reduced in resolution for sharing here, and all have been tidied up a bit to get rid of dust/dirt from the camera sensor).

The first is a slide with a Triceratum kinkerianum diatom mounted in Styrax.

Triceratum kinkerianum mounted in Styrax

There is only a single example on the slide, so it took some finding as it is very small. This was lit using oblique lighting from below (Olympus Aplanat Achromat condenser) with the condenser set to still produce a bright field image, but one which has obvious side lighting, as can be seen by the shadows in the image. The objective used here was a 20x Olympus Splan NA 0.46, and the camera my Nikon d800 monochrome conversion. White LED light was used. Here’s the slide itself.

Triceratum kinkerianum slide

Next up is a Navicula firma slide. This has multiple examples of the diatom and was again imaged using oblique light from below, and with the 20x Splan objective.

Navicula firma slide

The diatoms are quite large but show some lovely features and will be well worth coming back to at a later date to look at in more detail. Here’s the slide.

Next is a diatom and spicule strew made by Eduard Thum (one of my favourite slide makers). This was also imaged using oblique lighting from below and with the 20x Splan objective.

Diatom and spicule slide by Eduard Thum

This slide is a strew so contains a wide selection of material to image. It seemed to lend itself very well to the oblique lighting, creating a great 3D effect. Here’s the slide.

Diatom and spicule strew slide by Eduard Thum

The final one for today is a Niztschia species slide by A.C. Cole. I spent a bit of time with this one. First a couple of images done with the 20x Splan objective.

Nitzschia slide, strongly oblique lighting
Nitzschia slide, straight bright field illumination

Both the images above where taken with the same condenser with light coming from below – an Olympus Aplanat Achromat. In the first image the lower part of the condenser was moved to one side. A small movement to the side produces oblique lighting and nice shadows, however a larger movement (or closing down the iris further) as done here, produces a dark field effect with a black background. This can be very useful for highlighting features in the diatoms. In the second image the lower part of the condenser was returned to the middle, and normal bright field imaging was done. The resultant image is relatively low contrast, and it is harder to see some of the features of the diatoms. How you light the sample has a huge impact on how it appears.

Next I imaged the same slide with a 40x Olympus Dplan Apo UV NA 0.85 objective. This has a coverslip thickness correction collar, and as the mounting of the sample had suffered over the years, the coverslip had tipped up slightly on one side. So I adjusted the correction collar to it’s max thickness (about 0.22mm). I also used 450nm filtered light to try and squeeze a bit more resolution out, and I set up the condenser for slightly oblique illumination. I did a stack of 7 images in Zerene stacker. This was the final image.

Nitzschia slide, slightly oblique bright field illumination

The higher resolution from using a higher NA objective and 450nm light is evident. The keen eyed amongst you will also have spotted the diatoms have been rotated by 180 degree from the images with the 20x objective. I took the slide off during imaging and must have put it back on the other way around when I returned it.

Stacking diatom images can be a challenge, as when the focus is changed different parts of the structure not only come in and out of focus, but look different as a result of the way light passes through the diatom structure. This can be seen in the video clip below, where I moved the stage upwards as the video clip was captured.

Here’s the slide.

Nitzschia slide

This is an interesting slide, with the label on the back, so effectively the slide needs to be turned upside down to image (in the photo above the sample and coverslip are on the underside of the slide).

There are always plenty of diatom slides for sale on places like eBay, and while some go for high sums of money, others can be had for a few pounds. Some of the historic microscopists were capable of producing fantastic slides and as such these are a great way to get some beautiful slides to image. With imaging lighting is key, and changing the lighting setup can have a huge effect on the final image. As always if you have made it this far thanks for reading, and if you’d like to know more about my work I can be reached here.

Microscopy – Realgar (Arsenic sulfide) diatom mounts

Microscopists have become very inventive when it comes to finding mounting materials to make the subjects they are imaging more obvious. One way of doing this with diatoms is to use something with a high refractive index (RI). While organic based mounts can provide some improvement, some of the inorganic mounts have very large RIs, and as such are able to produce slides with very good contrast. Metal and metal oxide slides are one approach (such as the work by Horace Dall which I have discussed here and that of John Dale, see here). Another approach is the use of arsenic sulfide (known by mineralogists as Realgar). I am currently in the process of writing a couple of research articles, one on metal and metal oxide mounts, and another on Realgar mounts, which I hope to publish later this year. For now though I wanted to share some images from a historic Realgar slide made by Henri Van Heurck.

The slide was likely made sometime around the 1880s, and is a strew of a number of different diatoms mounted in Realgar. I’ll show a picture of the slide later, but for now here are some images from it, captured on my home built Olympus BHB microscope.

Pleurosigma angulatum on the Realgar mounted Van Heurck slide
Pleurosigma angulatum on the Realgar mounted Van Heurck slide, crop from main image
Surirella gemma on the Realgar mounted Van Heurck slide
Surirella gemma on the Realgar mounted Van Heurck slide, crop from the main image

The images above were captured using a 40x Olympus Dplan Apo UV objective (NA 0.85) and with oblique illumination from below. The high contrast the mount provides is evident in the images. They were produced using white LED light and the mount itself is a yellow colour, as can be seen below.

Dr Henri Van Heurck, Realgar diatom slide

Realgar slides are delicate and light sensitive, so effort must be taken to store them in the dark and only expose them to light during imaging. Very often the slides show cracking of the Realgar and this is evident here as well.

It should be mentioned that making the slides is a hazardous process, and should only be attempted by someone familiar with the use of dangerous chemicals. This is probably one of the reasons why the technique is no longer done.

I have a number of Realgar slides in my collection now, and as mentioned above aim to write a paper about these fascinating historical items later this year.

As always thanks for reading, and if you’d like to know more about this or other aspects of my research, I can be reached here.

Microscopy – Diatom imaging with a Watson Holoscopic condenser

A bit of a fun experiment today. The images we create depend greatly on how we light our subject. Changing the lighting can have a drastic impact on the final appearance of the photo. This post shows how using a historic Watson Holoscopic condenser can be used to image diatoms, and how the picture look compared with straight brightfield, and oblique illumination.

The subject was a Darlaston slide with two Amphipleura lindheimeri diatoms present and a two circular diatoms as well. The microscope was my usual modified Olympus BHB. Objective was a 40x Olympus UVFL PL NA 1.3 silicone immersion one with an adjustable iris (the adjustable iris was important for this experiment, more on that later). I used 450nm filtered LED light, and images were captured on my monochrome converted Nikon d800 camera. For condensers I used an Olympus Aplanat Achromat one (normal brightfield and oblique brightfield) and the Watson Holoscopic condenser. For both of these I oiled them to the underside of the slide using immersion oil, and I also used that for the objective. The objective was designed for silicone oil, but I didn’t have any of that, so just used immersion oil. In hindsight apparently 50% glycerine in water might have been a better bet, but for now the experiment was done with immersion oil.

Enough chat, what do the images look like. Note, I’ve reduced the images resolution for sharing here. First with the Watson Holoscopic condenser.

Image of A. lindheimeri using a Watson Holoscopic condenser

Next with an Olympus Aplanat Achromat condenser, in normal brightfield mode.

Image of A. lindheimeri using an Olympus Aplanat Achromat condenser, normal brightfield

And finally, with the Olympus Aplanat Achromat condenser but in oblique mode.

Image of A. lindheimeri using an Olympus Aplanat Achromat condenser, oblique brightfield

The Watson Holoscopic condenser gives dark ground (darkfield) appearance to the image, but for this to happen I had to stop down the iris on the 40x Olympus objective slightly – fully open it didn’t produce a dark ground image as the objective NA was too high. This is why it was important to use an objective with an adjustable iris for this experiment. It was probably just below NA 1.0. The iris on the objective was then left the same for the images with the Olympus Aplanat Achromat condenser. The low contrast of the normal bright field image can be seen, as well as the improvement in 3D appearance with the oblique condenser. In these full size images though the Watson Holoscopic condenser looks to show the features of the diatom quite well.

Crops of the 3 images show a bit more of the detail they can reveal.

Cropped image of A. lindheimeri using a Watson Holoscopic condenser
Cropped image of A. lindheimeri using an Olympus Aplanat Achromat condenser, normal brightfield
Cropped image of A. lindheimeri using an Olympus Aplanat Achromat condenser, oblique brightfield

The benefits of oblique illumination over normal brightfield for the diatoms can clearly be seen in these cropped images. The Watson Holoscopic condenser also seems to be highlighting some of these features, especially at the edges of the diatom and along the central ridge.

What is the Watson Holoscopic condenser? Here’s a picture of it.

Watson Holoscopic condenser

And an excerpt from a 1930’s Watson catalogue which provides some information about it.

This shows why an adjustable aperture on the objective is useful, as with oil immersion objectives is requires an aperture of less than NA 1.0. It should be noted that the condensers were designed to be used with slides of specific thickness (this one being 1.3mm) so the slide used here was perhaps not ideal for this specific condenser.

The objective was quite an unusual one – a 40x Olympus UV FL PL NA 1.3 silicone immersion one with an adjustable iris.

This is designed for UV fluorescence work, (‘UVFL’ on the barrel) so has quite good transmission in the upper UV region. It is also a phase contrast objective (the ‘PL’ on the barrel). It was meant to be used with silicone oil, although I just used normal immersion oil. I should have tried glycerine and water mix, as I have since read that that would be a better match to the silicone, but ‘every day is a school day’ as they say. Although not labelled as such it also has an adjustable iris to reduce its NA. This can be seen by looking through the objective when the knurled iris ring is rotated. This feature makes with useful for dark ground imaging, where tuning the objective NA to the condenser can optimize the image.

Finally a couple of shots of the slide itself. This was picked up on ebay for few pounds (GBP).

The original makes label says W.H. Darlaston of Birmingham, who is a well known slide maker. But is also labelled with T. Frankish, B.Sc, who I am guessing was the owner of the slide.

The Holoscopic condenser is a relatively simple construction, and I am wondering if it possible to make one of these using quartz or fused silica. If so it would be possible to use it deep into the UV which should allow for some very high resolution imaging. But that is for another day. As always thanks for reading, and if you’d like to know more about this or any other aspect of my work, I can be reached here.

Microscopy – Polycistina slide with an unusual feature

I’ve been busy with work, but last night took a break to look at a microscope slide which arrived recently. It was described as a ‘Polycistina’ slide from Barbados and it had an unusual feature on it.

Here’s a couple of pictures of the slide taken using different iris settings on the condenser.

Polycistina slide, condenser iris setting 0.4 – shallow depth of field
Polycistina slide, condenser iris setting 0.2 – greater depth of field

The unusual feature is the one with tendrils, and it has been mentioned that this could be a plant trichome. In the images above, there were two settings used for the condenser iris – the first one was open to NA 0.4, and the second one it was closed down to about 0.2. Everything else was the same between the two images (Nikon d800 monochrome camera, 10x Olympus UVFL NA 0.4 objective, white LED light) although exposure time was increased for the smaller iris aperture. This shows the effect that iris aperture setting can have on depth of field in an image. Closing down the aperture too far though can be a bad thing due to diffraction starting to occur, and also a shallow depth of field helps emphasize the subject. As with many things in life choosing what looks right is a balancing act.

The sample is quite thick, and as the stage was moved up and down different parts of the image came in and out of focus. This can be seen in the video below where the stage was gradually moved up.

It was actually quite interesting to view the slide using a low magnification (4x) objective. The sample was so thick that slight movement of my eyes when looking at it through the eyepieces gave a ‘3D’ image as the features moved differently depending on their depth in the slide.

The slide itself is interesting and the maker even engraved the shape of the unusual feature onto the slide. Unfortunately there is no makers name. The slide itself is very thick.

Label on the slide, showing the ‘feature’ at the bottom right
The sample
The slide

Microscopy continues to fascinate me, providing a window in to the wonderful world of the tiny and the amazing structures that nature can produce. As always, thanks for reading, and if you’d like to know more about this or any other aspect of my work I can be reached here.

UV Microscopy – Thorlabs SLS204 deuterium light

‘Life is not an exact science, it is an art’. A quote by Samuel Butler, and much as though the scientist in me would like to control every aspect of my life and my work, it does not always work out like that. Sometimes we cannot rely on science alone and must resort to gut feelings based on experience and understanding of the problem. In building my UV microscope there have been many challenges – the optics can’t be made of glass, the camera sensitivity needs to be increased, and what to do about the lighting? Having dealt with the optics and the camera, the lighting has been an issue for me lately. At 313nm and 365nm, a mercury xenon lamp is a good option. Nice strong emission lines and focussable. Below 300nm things get tricky. I did build a 254nm source using a low pressure mercury lamp, and that did enable me to get some images with the microscope, but it has it’s challenges. While it has a nice sharp line at 254nm, it does still require filtering to remove other emission lines, and while the efficiency is high for producing UV the overall power is low. Also it emits light 360 degrees, so I can only harness a fraction of what it produces. What I needed was a better light, and this is something that has kept me awake at night for quite a while. In the end I settled on a deuterium light source. Plenty of UV, especially in the 200-300nm range, which was just what I needed, along with relatively little visible and IR light. However what I couldn’t find was a direct comparison with the little 3W low pressure mercury lamp I had. In the end I just had to jump in based on a best estimate and a gut feeling.

The light source I went for was a Thorlabs SLS204 deuterium lamp. The main reason for this being that the fiber port could be removed, and there was a SM1 thread present to allow me to easily attach things like condenser lenses and other optics to focus the beam. Here’s the light source.

Thorlabs SLS204 deuterium light

The fiber port where the light comes out is underneath the protective cover on the right hand side. The cover, and the black circular part which holds the fiber port underneath can be removed to reveal the deuterium lamp and that is where condenser lenses and other optics can be attached. That is a big tick Thorlabs. Couple of things are not big ticks though. The tool to remove that black circular piece is not included with the light, so I’ll need to order that separately (and pay for more postage, grrrr). Also there is no internal shutter for the light, unlike on my Ocean Insight one. As such when the deuterium lamp is on and with the safety cover removed, there is nothing to block light coming from the lamp housing. This could be a safety issue for my application, and as such I’ll need some form of manual shutter or at least an iris to reduce the output. Not ideal.

Enough of my moaning. How does the output spectrum look? As a first look I just put the fiber (with a cosine corrector) from the Ocean Insight FX spectrometer up against the output port of the light. I then also put a Semrock 260nm brightline filter in place, as this blocks most of the visible and even some of the IR to get an idea of how effective it would be. These were the spectra produced.

The light produces the as expected profile for a deuterium lamp. Lost of UV and a strong line in the visible at about 655nm. The Semrock filter does a good job of removing the long wavelength UV and a lot of the visible up to about 700nm but after that doesn’t offer any additional blocking. Will this be good enough on it’s own? I am not sure about that, and that remains to be seen. The good thing is that it lets plenty of light through in the 250-270nm region, and is not a line spectrum like the low pressure mercury lamp. This should help with its use as a source for microscopy.

Is the deuterium lamp the perfect solution? Well, no, unfortunately not. It still requires filtering, and it is not as intense as a low pressure mercury light. However it offers a continuous spectrum with plenty of light in the 250-300nm region and as such is worth exploring, despite the hefty price tag. The next step is to get a condenser lens in there and build an adapter to fit my microscope. The light also might be useful for UV photography in the 200-300nm region, so that is something else to think about in the future.

Science doesn’t always go to plan, and at some point many of us are faced with making decisions based on our best estimates. While this is scary, it is part of science, and is something which needs to be dealt with if you want to make new discoveries. If we knew all the answers there would be no new discoveries. Thanks as always for reading, and if you’d like to know more about this or any other aspect of my work, I can be reached here.

Tasmania – Landscape photography in UV, visible and IR

While we are used to seeing the world in the visible spectrum, moving outside of that into either the Ultraviolet (UV) or Infrared (IR) regions can make scenes look very different. During a trip to Tasmania I took one of my multispectral cameras with me to compared some landscape photography in the UV and IR with visible light images, and these are what I am sharing today.

The comparison images are shown in black and white, to remove the issues of whitebalancing non-visible images. A multispectral Canon EOS 5DSR was used along with an 85mm f4.5 Asahi Ultra Achromatic Takumer (which has quartz and calcium fluoride lens elements instead of glass to allow it to transmit UV). The following filters/filter combinations were used in order of increasing wavelength range;

UV – Baader U

UV/Visible – Chinese BG39 2.5mm alone

Visible – Chinese BG39 2.5mm + B+W486

IR – Hoya R72

First set of images – The view from Ben Lomond.

Note that the visible image here is actually UV+visible as the UV portion of the spectrum was not removed by the BG39 filter alone. However the UV contributes relatively little to the image, so the image should be considered as mainly visible light. In UV the haze is emphasized, making the distant landscape blend more into the sky. It also lessens the appearance of clouds making the sky look more homogeneous and giving more of a feeling of distance to the landscape. The contrast between bright sunlight and shadow on the rocks is also reduced and foliage is darkened. Conversely, in the IR image blue sky becomes darkened, foliage almost white, and haze is reduced.

Next area Stephens Bay in the South West National Park, and about as remote as you can get (which is saying something in Tasmania).

It was quite a dull day when we were there, with no blue skies, but the effect of going from UV to Visible (this time a UV blocker was used in combination with the IR blocking filter) to IR can again clearly be seen. As an aside, this is a fascinating area and hugely culturally significant as there are Aboriginal middens along the beach which are full of shells and date back thousands of years.

The final area for today’s post, the view to the dolorite spires of Cape Raoul from Maingon Bay Lookout at Remarkable Cave on the Tasman Peninsular.

Again these show the expected behavior going from UV through to IR.

Varying the wavelengths we use for imaging has a huge impact on how a scene is rendered, and this is as applicable to areas such as dermatology and forensics as it is to landscape photography. Thanks for reading and if you’d like to know more about this or other aspects of my work, I can be reached here.

Tasmania – UV fluorescence photography of orange lichen

Anyone who has chatted to me will probably have gathered that I have a huge soft spot for Tasmania, as it doesn’t normally take me long to start talking about how amazing it is. In previous visits I have taken my UV camera along to capture some photos there (UV levels are very high in Tasmania which make UV photography easier, but has a nasty habit of burning you if you forget your sunscreen and hat). I’ll share some of the images from these visits in the future as they demonstrate nicely the effects of UV imaging compared with visible light and IR imaging when photographing the landscape. To start things off though, the first post on this topic is something a little different – UV induced fluorescence photography. This uses UV light to illuminate the subject, and the visible light this produces due to fluorescence is then photographed. The subject for this experience was a rock with some of the orange lichen on it. Orange lichen is present across most of Tasmania and makes for striking landscape photos, and it got me wondered what this material looked like under UV induced fluorescence. I am certainly not a lichen expert, so this will concentrate more on the imaging and less of what specifically the lichen is.

The rock itself came from Green Point Beach in the North West of Tasmania (part of the Rocky Cape Group). The rocks on the beach had some damage from regular strong waves, so I picked up a piece a few centimeters across which looked to have recently broken off from the main outcrop. The rocks in this part of Tasmania are old. Very old. They are about a billion years old, and appear to be something like quartz arenite.

Here’s the front of the rock in normal visible light and in UV (365nm LED light) induced visible light fluorescence.

And the rear of the rock, again in visible light and UV induced fluorescence.

The front surface of the rock sample shows the vivid orange colour in visible light. Interesting this lichen also fluoresces orange under illumination by UV light. The matrix of the block itself mainly fluoresces blue, however there are some bright yellow regions as well, perhaps indicating slightly different mineralogy in those areas.

Here’s the rock formation on the beach.

This does raise an interesting possibility – could UV induced fluorescence be used in the image of lichens to help with their identification? Do all lichens which are orange in the visible spectrum fluoresce the same way? This is something I don’t not know, but UV fluorescence is used in many research areas so might be worth trying in the future. It would also make for an interesting form of landscape photography – light painting the scenery with a portable UV light and imaging at night or in twilight.

Technical details. For the fluorescence image the light source was a 365nm LED light which was filtered to remove visible light. the camera was a Canon Eos R7 and a 420nm long pass blocking filter was use to eliminate any reflected UV light. A daylight white balance was used for the UV induced fluorescence image. The lens was a 105mm Rayfact (UV Nikkor) macro lens at f22. ISO 200 was used for the images, and the UV fluorescence image was of course taken in the absence of natural visible light. A black background and sunlight was used for the visible light image.

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

Microscopy – Diatom arrangement and bacteriastrum strew

I try and keep an eye out for old and antique microscope slides as they often provide some really interesting subjects for not much money (in some cases, although it should be said that some old microscope slides command extremely high prices). Today’s post shares two slides, a diatom arrangement by Richard Suter, and a bacteriastrum strew (mounter unknown).

First the diatom arrangement slide by Suter described as being Heliopelta Metii. Here’s the slide, taken with 450nm light and using a 10x Nikon Fluor NA 0.5 objective, cropped slightly to removed the dark corners of the image.

Heliopelta metii arrangement slide

The slide is very clean and all the diatoms intact. A lovely arrangement. And a closeup of part of the slide (just from cropping the original image).

Closeup of the Heliopelta metii slide

The above was a single image, so will be worth coming back to for some stacking at some point with a higher magnification. A very pretty slide and well worth the investment. This is the slide itself.

Heliopelta metii slide by Suter

The second slide for today is a Bacteriastrum strew. These diatoms are fragile and often break up, making them more of an unusual subject to find. First the slide itself (not sure as to the mounter of this one – if you know drop me an email please).

Bacteriastrum strew slide

And some images of the slide, again taken with 450nm LED light and the Nikon 10x NA 0.5 Fluor objective. Shown as full frames (or nearly full frames) and a couple of tighter crops.

Full frame (very slightly cropped to remove dark corners).

Bacteriastrum strew slide, area 1, full frame
Bacteriastrum strew slide, area 1, tight crop
Bacteriastrum strew slide, area 2, full frame
Bacteriastrum strew slide, area 2, tight crop
Bacteriastrum strew slide, area 2, tight crop

Overall these two slides were really pretty and very interesting to look at. It is well worth keeping and eye out for interesting looking old slides, as other they can be cheap way to get some really well prepared subjects. As always, thanks for reading, and if you’d like to know more about my work I can be reached here.