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I like the fan shaped round reflector. No plastic diffuser to filter out UV. Price is great. Not a fan of the battery arrangement. Don't some of the Godox work well for UV? Anyone think this one has potential? https://www.dpreview.com/news/3602160276/godox-s-lux-senior-is-a-larger-more-powerful-flash-with-a-retro-inspired-design Thanks, Doug A

Hi Everyone, my first post on this forum, thanks for all your posts that have been very inspiring and special mention to Iggy and Enrico for many tips on camera and lenses that I ended up using. I am a biologist working on butterfly genetics and my team got interested in the study of UVA-iridescence, we published that work here: https://doi.org/10.1073/pnas.2109255118 (this article will be open-access shortly, in the mean time you can browse the main findings here : https://twitter.com/evolvwing/status/1480660574614740994 ) At that time I was happy enough with a reverse-mount El-Nikkor 50mm mounted on belows, and also used a Nikon CFI Plan Fluor ELWD 20x 0.45 DIC L Ph1 DM at some point. I now managed to put my hands on a Mitutoyo M Plan Apo NUV 20× / 0.42, and I was very impressed by the Working Distance and transmission for my specimens. I have not tried it with stacking yet, and should get more tonal range with better light sources, but this is very satisfactory already. I was also very happy to see no vignetting using the El-Nikkor 105mm f/5.6 as a stacking lens, although of course you would need a longer lens if you use sensors larger than the Lumix micro4/3 format. Dimensions : each scale on the image has a vertical width of 80 um. Note: careful on eBay, most items sold as Mitutoyo M Plan Apo NUV 20× appear to be counterfeit. I have a certificate on authenticity on mine, and I cannot comment on whether the imitations are decent for this purpose. Arnaud Diagram legend # Lens unit "Micro-UV" 1 Rubber End Caps 32mm(1 1/4-inch) ID Vinyl Round uxcell / Amazon 2 Mitutoyo M Plan Apo NUV 20× / 0.42 ebay 3 SM1A27 Adapter with External SM1 Threads and Internal M26 x 0.706 Threads Thorlabs 4 SM1 female to M28.5x0.6 male thread adapter rafcamera / ebay 5 U Filter (Venus and Ultraviolet) - 1.25" Baader Planetarium hidden / 6 Baader Double T-Filter Holder 1.25" Adapter # T2-31 Agena Astro 7 Female to Female Double Dual Inner Thread M42 and M42 mm Lens Ring Adapter Amazon 8 M34.5x0.5 male to M39x1 male thread adapter rafcamera / ebay hidden M39 39mm to M42 42mm Adapter for 39mm Enlarger Lens /42mm Focusing Helicoid ebay 9 EL-Nikkor 105mm f/5.6 ebay hidden M39 39mm to M42 42mm Adapter for 39mm Enlarger Lens /42mm Focusing Helicoid ebay 10 M42-M42 Focusing Helicoid Adapter Pixco 11 M42 Lens to M4/3 Focusing Helicoid Adapter Fotasy

Casswell, T. (2022) Gazania rigens (L.) Gaertn. (Asteraceae) Gazania. Flowers photographed in ultraviolet, infrared and visible light. Also with multispectral stack. LINK Location: 17 June 2022 Australia Collected from a street garden adjacent to the beachfront at Coolum Synonyms: several -- see Reference Other Common Names: Treasure flower Comment: This species is recognized as a weed in some areas of Australia, however it is widely used for a groundcover in suburban street gardens, median strips, traffic islands, etc in south eastern Queensland due to its hardy nature and prolific flowers in a variety of colours blooming nearly all year round. Two samples were taken and placed in a water filled vase approx 20 min after collection. Each was imaged using Baader U, Kolari U, Kolari Hot Mirror V2 & a generic 650nm infrared filter. All eight image runs were focus stacked. An attempt was made to combine infrared (R), visible (G) & UV (B) into a multispectral image (mantis shrimp vision?), which proved difficult due to the dynamic nature of the flower given its circumstances. Reference: 1. Wikipedia (18 June 2022) Gazania rigens. Wikimedia Foundation, San Francisco, CA. Equipment: Converted Canon EOS R5 EL-Nikkor 105/5.6. Baader U, Kolari U, Kolari Hot Mirror V2 & a generic 650nm infrared filters Technique: UV, visible & infrared colour balanced using a white PTFE sheet with exposure dialled down to avoid any RGB channel clipping. Focus stacked using Helicon Focus 8. ISO100, f/11 for all shots. Multispectral - aligned using PT Gui with manually placed control points Yellowish White Sample: Visible light, t = 1/100s UV (Baader U), t = 5s UV (Kolari U), t = 5s (some highlight clipping) 650nm Infrared, t = 1/80s Multispectral using the Kolari U for UV (blue channel) Yellow Sample: Visible light, t = 1/80s (slight overexposure) UV (Baader U), t = 8s UV (Kolari U), t = 8s 650nm Infrared, t = 1/80s

Speaking of taking pictures of Dandelions, do you guys know of any way to keep the dandelion open even after I pick it? Mine basically closed up completely like two hours after I tore it from the plant.

There is a possibly interesting M42 bellows up on eBay: https://www.ebay.com/itm/403327409189 It has a lot of possible adjustments like a view camera. I have no idea about how stable it is. Setting the adjustments in an optimal way will be a challenge. I decided to pass this as I have tried doing some macro work with a tilt adapter that works with my mirrorless camera. It was quite tricky to get good working positions and I prefer working with focus stacking instead.

Recently I tried to get some order into older images, which of course is a daunting task. However once in a while one discovers hidden treasures. One of these would be the flowers of Malva moschata Musk Mallow, Malvaceae. This is a species becoming increasingly naturalised on open grasslands and road verges in the lowlands. Flowers are pink or almost white. The stamens are connate and form a column in the flower centre through which the styles emerge. (Fuji S3Pro, UV-Nikkor 105/4.5, UV/IR blocking filter + BG-38) In UV the corolla is bright blue with black veins and the centre is dark as would be expected. (Nikon D3200/built-in Baader U, UV-Nikkor 105/4.5) The standard UVIVF capture shows the usual lint issue on the corolla and that something is going on in the centre. (Nikon Df, Laowa 100mm f/2.8 macro lens, NEMO torch) Time has come to increase magnification, to 5X. Still UVIVF. (Nikon Z7, Laowa 25mm f/2.8 at 5X, NEMO torch) Being ever so curious, I went all out to 20X magnification and got this, (Nikon Z7, Mitutoyo 20X/0.42 objective on an infinity-focus system, NEMO torch) The fact that some pollen grains fluoresce brightly, others don't, may indicate that the strong fluorescence is a result of pollen damage.

Remembered an old Ponder & Best /Vivitar 105mm F4.5, three element enlarging lens in storage. Paid $10 for two of them with a load of photo stuff I purchased. Diagram shows 3 air spaced elements. There is a very slight yellowish coating. Lens seems to record UV yellow as well as the El-Nikkor 80 & 135 and the Igoriginal 35mm F3.5 lens. With 3 elements, I'm not sure if it is as sharp. More testing required. Custom WB camera preset, based on block wrapped in plumber's tape . Silkypix Raw converter used to slightly adjust WB and increase color saturation. Adobe Photoshop Elements 11 provided slightl cropping, resizing, and sharpening. Camera: Pentax K-1 full frame modified by Kolari Vision for full spectrum Lens: Ponder & Best/Vivitar 105mm enlarging lens on Pentax bellows. Filter: Igoriginal supplied ZWB-1 2mm and BG39 2.3mm Exposure: F11 3 seconds at ISO 400 in sunlight Comments welcome. Thanks for looking, Doug A

One of my first reflected UV shots with UV modified Pentax AF540 flash. Pentax K-1, Pentax bellows with 3 extension tubes, Nikon El-Nikkor 135 f5.6 enlarging lens. Bellows has a handy internal filter thread to allow filters to be mounted inside it. Used the Ioriginal supplied ZWB-1 2mm/ BG39 2.3mm filter stack. The flash was placed less than 2" from flower. Flash had 2 2mm filters, probably ZWB-1, borrowed from 2 NEMO torches. The extra 4mm of flash filtration is required to squelch leakage. Exposure f16 1/200 ISO2000. This flower is very small at about 10mm. Magnification is close to 2x life size. This image was slightly cropped for composition. Lens was used at f16 and would probably perform better reversed. Unfortunately, I don't have the necessary adapters to do that yet. I may wait to do this since the 135mm lens really is too long of a focal length to work comfortably on the bellows at these magnifications. Looking for an El-Nikkor 80mm for these applications. Any suggestions welcome. Thanks for looking, Doug A

The Kyoei 35 clone on extension tubes leaves little working distance. Want to try the original chrome Nikon El-Nikkor 105 enlarging lens. Before buying and lashing up a helicoid, I'll try my Pentax K mount bellows. Just need to order a K to m39 adapter. I recently saw a comment saying bellows may not be opaque to UV light. Has anyone encountered this problem? Also wondering if UV intensity falls off with extension, at the same rate as visible light? Thanks, Doug A

I have been playing around with connecting my spectrometer in line with a microscopy and had my first success. The spectrometer is connected to the eye piece using an adapter I made which runs to two channels. The red is a spectrometer with grating #1 and can see from 175nm to 869nm. The blue curve is a spectrometer that can see from 500nm to 1150nm. For this I have a piece of paper on my microscope as a control with green highlighter on it. Here is image taken with 10x and lodestar X2c cammera; The bright purple is the reflected 365nm filtered convoy off just the paper. the bright streak is green highlighter marked on the paper. This is the resulting spectrum grab screen shot from the raw data: This actually follows in the focal plane. I loose signal when out of focus and its back with in focus. So I am paralax. I should now be able to see the spectal output for specific cells. Great first steps.

Safety note - this talks about high intensity UVB light sources. Please do not attempt this type of work yourself without taking the correct safety precautions. Over the last year I've been building a UV transmission microscope to help with one of my projects. One area that needing modifying was lighting, as I wanted to have a good light source in the UVB region at 313nm. As a basis for it I decided to use a mercury xenon light and a small Zeiss 50W came up for sale on ebay so I snagged that. Here's how it looks. In the exit port is a metal tube with a lens at one end to focus the light. This tube and lens can be moved back and forth by turning a black knob on the side of the light. Problem is the original lens is glass, so no good for UVB as it was blocking everything below abut 320nm. It was a non standard diameter so I couldn't find a fused silica replacement. In the end I had a new tube made, threaded on either end for Thorlabs SM1 tubes, and got a Thorlabs 20mm focal length aspheric fused silica lens as a replacement. Original and new tubes shown below. When I originally used this light for UVB imaging I used it without any lens, so obviously lost a lot of light. As a quick check I did some irradiance measurements without the tube and lens, and then with the new tube and lens in the focused position and in the defocused position. In the focused position the irradiance at the brightest area was about 600x that when no tube and lens was present, and at the defocused position, it was still about 30x more intense than without the lens. Interestingly in the focused position it actually produced a slightly fuzzy image of the two electrodes in the mercury xenon bulb and the arc between them when shone at a surface. The image below was taken using a 313nm Edmund Optics OD4 bandpass filter in combination with a Hoya U-340 4mm filter, using a monochrome modified Nikon d800 and Rayfact 105mm UV lens. The light was shone at a piece of white paper inside a box painted with Semple Black 3.0 paint and it was the image projected on this paper that was imaged. In the image above, the lamp is orientated vertically and the electrodes at the top and bottom of the image. This was about as sharp as I could get it, as I'm limited with how close I can get the lens in the tube to the bulb without touching it. More funky was that using that camera and lens I was able to capture UV videos at 313nm and 365nm using EO bandpass filters in combination with Hoya U-340 4mm. They show the arc flickering and moving about slightly on the electodes. I've uploaded these to youtube, and the links are as follows; 313nm video - 365nm video - The increase in brightness will be useful for my work, but it could actually be too bright now and damage the samples. I will be trying it in the defocused position, as even that should be significantly better than with no lens. I also may get some fused silica diffusers from Thorlabs and mount those at the other end of the tube with the lens on it, to help make a more even light source for microscopy. As mentioned at the top, work like this can be extremely hazardous, producing very very intense UV light down to and below 300nm. Do not attempt this yourself without an understanding of the hazards involved and how to protect yourself from them.

I have purchased a cheap Chinese 4x Microscope Objective Lens. This covers 8mm x 6mm on a full frame camera & is a very simple set-up with a 160mm x M42 tube length & the camera on a focusing rail. Soon I will try it out for UVA photography & UVIVF. First some baby steps. The first photo is of an 8mm section of a steel ruler. The second photo is a 8mm section of a leaf with back lighting.

Not long ago I discovered that there are red flowers which appear false yellow in UV. Before that I thought only yellow flowers could be UV-yellow. Today I found another example. It is likely that this flower has already been covered in the botanical section, but I don't know its name. Visible references, taken with a Samsung Galaxy A40: f/1.7, ISO 50, 1/100 s exposure f/1.7, ISO 64, 1/100 s exposure UV, with a full-spectrum Canon EOS M, Soligor 35 mm f/3.5 and Chinese BG39 (2 mm) + ZWB2 (2 mm): f/4, ISO 100, 2 s exposure f/8, ISO 100, 30 s exposure The yellow is not as intense as a dandelion, but it still shows up nicely. Also, there is some lavender inside, so this flower has two UV colors in it.

'That lens' in this case being the 60mm f/4 Macro Novoflex, which I purchased on a whim after reading Ulf's lens post. My aquatic plant project has commenced and field studies are underway. This season will be even more hectic than the earlier years. Duckweeds are early entries as they come out of hibernation. Today, I sampled a population of Red Duckweed Lemna turionifera Landolt which is a neglected and frequently overlooked member of our native aquatic flora. It belongs to the cryptic species complex around L. minor Common Duckweed and is not easy to identify. As the specific epithet 'turionifera' implies, this species survives the cold winter by forming special buds, or turions. They are filled with starch and pigments and sink to the bottom to overwinter there. M y thought was that UV might show additional detail as the pigments possibly could lead to some UV "colouring". So I examined a specimen under UV, using the Nikon D3200 with its built-in Baader U, and the 60mm f/4 Macro Novoflex on a suitable Novoflex bellows. The rig was set up for 3.5X magnification, and UV provided by 2*Nemo torches. Here is the result. Zerene Stacker, 80 frames. The scale bar is 1mm. The plant moves a little around during the UV exposures thus clinical sharpness is hard to get. But one gets the picture as it were. The turions are very easy to observe, being rendered UV black (any false green therein probably is an artefact of the stacking process so should be ignored). I need to repeat with other populations to see whether the UV signature is a reliable means of identifying this species.

Hello from Moscow! I am a photographer with a long history of museum work. I'm also interested in scientific photography, especially macro photography. In recent years, I have also been restoring historical photographs including the earliest ones such as daguerreotypes and talbotypes. Now we are dealing with the problem of visualizations of photographic images on damaged photos. Interesting results were obtained when using transmitted IR for photographic negatives with different spots and now we want to continue these experiments in the UV spectrum. I hope that my experience in such work and the knowledge of the members of this forum will be mutually useful. Good luck to everyone!

In the post at https://www.ultravio...__fromsearch__1 David describes how he fits an SvBony meniscus lens behind his main lens to get a wider angle of view and a brighter image on his M4/3 camera. (This is a home-made, dumbed-down version of the focal reducers sold to allow SLR full-frame lenses to be used on mirrorless cameras with smaller sensors while retaining their full-frame angle of view. These devices start at £80: they have more sophisticated optics which should give better image quality but will almost certainly reduce UV transmission.) This was an interesting and potentially useful development, and I wanted to see if David’s invention would work on the slightly larger APS-C sensor. At the same time I thought I’d try out another solution for widening the angle of view – wideangle converters that screw into the front of the prime lens. I had one in the back of a drawer from my Hollywood days when I used 8mm cine cameras. This multiplied the prime lens focal length by a modest 0.7x. I also got a Lazer Titanium 0.42x version off ebay for the grand sum of £1 (although postage cost several times as much). These devices have “macro” in the name because you can unscrew them and use the rear lens as powerful close-up lens. You just know these devices are going to be great performers because they are engraved with terms like “High Definition” and “Professional”, are from brands famous for optical excellence (like Opteka, Sunagor, Kepcor, Seimar, …), cost as little as £10 new, and are intended for use on camcorders. (There are some exceptions – Schneider Kreuznach produce some costing up to multi-£000s.) Here is a review of these three devices. All testing (unless stated otherwise) was done using a Baader U. Lenses used were the Focotar-2 50mm f/4.5, IgorOriginal 35mm f/3.5, and Lithagon 28mm f/3.5, all at f/11. Angle of View The following images illustrate the increased angles of view when using a Focotar-2 with the three devices. The angle of view of the Focotar-2 on its own is indicated by the red box. What is also immediately apparent is the barrel distortion introduced by these devices. The angle of view using the SvBony is similar to that using the Sunagor. SvBony: Sunagor: Lazer Titanium: Image Quality In these images, the ruler was laid diagonally across the frame from frame centre to extreme corner. Image cut-off can be seen in some images – this is discussed later. The reduction in image quality is obvious, and as a result I don’t expect to be using any of these devices in real life. Interestingly David’s experience was that the SvBony improved the image quality of the Cassar S. Focotar-2 50mm: IgorOriginal 35mm: Lithagon 28mm (Edited: original post had a repeat of the IgorOriginal image): UV Reach UV reach was tested by measuring exposure factors for each device on the Focotar-2 using three UV bandpass filters. The lower the exposure factor, the better. All of these devices will be fine with a broadband UV filter like the Baader U. The SvBony performance with the 315BP20 is adequate for it to be used with applications such as TriColour. The (Lazer) Titanium could be used at a push, if enough light is available. The Sunagor, on the other hand, would be totally unusable. Effect on Exposure David’s experience with the SvBony indicated that up to 2 stops could be gained. I did not see this benefit, although there was some speed gain using the SvBony on the Focotar. I also did a quick check using the Lithagon lens, and here the speed gain was almost negligible. The screw-in wideangle adapters had a negative impact on exposure – presumably simply because of absorption by the additional glass. Image Cut-off/Vignetting None of the devices caused any image cut-off when used with the Focotar-2. With the wider angle lenses, the cut-off is on a knife-edge. For example, if you use the 28mm Lithagon with no filters attached, there is no cut-off using the SvBony, and very little when using the Titanium. However, when you add the Baader U you get significant cut-off. Even focussing for different distances can cause cut-off to appear. My environment probably makes this situation worse. I have 48mm-49mm stepping rings on each side of the Bader U, making it quite deep. And with the Sunagor and Titanium (where the filter fits between the device and the prime lens), there is an additional 52mm-49mm stepping ring in front of the filter and, in the case of the Lithagon, a 49mm-52mm stepping ring behind the filter. The impact of these can be seen in the ruler images earlier on. To illustrate this further, here are comparisons for the Lithagon with the SvBony and Titanium: Lithagon + SvBony, Baader U: Lithagon + SvBony, No Filter: Lithagon + Titanium, Baader U: Lithagon + Titanium, No Filter: "Macro" Capability Here is what you get from the "macro" function of the Titanium and Sunagor, by unscrewing them and using the rear element as a strong close-up lens. These images were made using the Focotar-2 focused on infinity. No need for any comment! Sunagor: Titanium:

Hello 
 I still doing my first test with UV, starting in our wild Garden 
 We have quite some Ficaria Verna and on the weekend we had sun the plant was used in former times in the seafaring as a vitamin C donor, i tried the leaves in salat it is quit bitter 
The plant appears to the human eye yellow, with UV light it looks l much darker in the middle section I used a Baader Filter and a Kyoei Acall Kuribayshi 35mm and a helicoid on a sony 7II full spectrum. For post I use Capture one for for Sony I am happy for any advise or critic best regards Wolfgang

Any suggestions on tags? Today I photographed some bees busy pollinating some dandelions (I think they are dandelions, but there are so many species all very similar...). I had to use high ISOs to keep the shutter speed fast, as bees move around quite a bit as they do their job. The camera was my Canon EOS M, the lens was the Soligor and the filter was my usual one, ZWB2 (2 mm) + Chinese BG39 (2 mm). Most photos were taken wide opoen at f/3.5, some were taken at f/5.6 but I don't know which they are as the camera doesn't know the lens aperture and writes f/0 as a "null" value. ISO 25600, 1/100 s exposure. ISO 25600, 1/40 s exposure. ISO 25600, 1/40 s exposure. ISO 25600, 1/100 s exposure. ISO 25600, 1/100 s exposure.

Lenses used in this test: EL-Nikkor 50/2.8 N (plastic version, enlarger) EL-Nikkor 80/5.6 (metal version, enlarger) EL-Nikkor 105/5.6 (metal version, enlarger) Leitz Wetzlar 50/4.5 Focotar-2 (enlarger) Sigma 24-105/4.0 DG OS HSM Art Steinheil München 50/2.8 Cassar S The information below is generated using a 35mm transparency as the target. This is one of a set of 3 made by Leitz back in the day to check slide projector set-up and performance, and includes some bar patterns providing a lines/mm scale. These slides are being passed on to Ulf, so they may reappear on UVP in the future. I used this transparency as a target for 1:1 macro shots in a bellows-based slide copier. Tests were made for the lenses I use for UV macro. Also included are two lenses that I use in visible macro work but which are not very UV-friendly - an El Nikkor 50mm f/2.8 N (the newer plastic-fantastic version) and a Sigma 105mm f/2.8 Macro lens. The numbers from the lines/mm bars would not tell much of a story as they are similar for all the lenses, so I am providing extracts from the images. With a few exceptions, all the lenses performed very well. This includes the Cassar S 50mm f/2.8, which fared badly in the lens resolution measurements using a target at portraiture distance. This is probably because at 1:1 magnification the angle of view is about half of a landscape shot, and so you are enjoying the central resolving power of the lens and losing the poor image quality towards the edges. ISO 100 and flash illumination was used throughout. Visible - 1:1 Magnification The visible shots were made on a full-frame Canon EOS 6D II. Aperture was f/8, the usual sweet spot for IQ. This is what the target looks like: Results for 50mm Lenses (Left-to-Right: Cassar S 50mm f/2.8, Focotar-2 50mm f/4.5, El-Nikkor 50mm f/2.8 N plastic version. Top Row is at centre of frame, Bottom Row is at the corner of frame.): Results for longer lenses (Left-to-Right: El-Nikkor 80mm f/5.6 metal version, El-Nikkor 105mm f/5.6 metal version, Sigma Macro 105mm f/2.8. Top Row is at centre of frame, Bottom Row is at the corner of frame.): The Cassar S performs well. There is a small amount of flare, and slight softness at the corner. The El Nik 80 and 105 (both older, metal versions) also did well. The Sigma Macro lens is probably the best - as it should be, as this is what it is designed for. The real surprise is how poor the El Nik 50 N was, as I have always been impressed with its image quality in macro work. But I have always used it at magnifications greater than 1:1, so I tested the 50mm lenses at a greater magnification. Visible - 3.3:1 Magnification This is what the full images to test centre and edge looked like: Centre and Edge results for the 3 50mm lenses(Left-to-Right: Cassar S 50mm f/2.8, Focotar-2 50mm f/4.5, El-Nikkor 50mm f/2.8 N plastic version. Top Row is at centre of frame, Bottom Row is at the corner of frame.): Now the El Nik 50 N is cooking with gas! The Cassar S is also good apart from a touch of flare. UV - 1:1 Magnification These shots used a Baader U filter. The camera was a Sony A6000 with an APS-C sensor. Aperture was f/11, as optimum aperture is smaller in UV. The full image looked like this: Here are the results. Only one image per lens (Left-to-Right: Top Row: Cassar S 50mm f/2.8, Focotar-2 50mm f/4.5, El-Nikkor 50mm f/2.8 N plastic version; Bottom Row: El-Nikkor 80mm f/5.6 metal version, El-Nikkor 105mm f/5.6 metal version): All lenses performed very well, and it's difficult to see the differences. The Cassar S and El Nik 50N are slightly soft, but it's pretty marginal. The El Nik 50N image is dimmer, reflecting its poorer UV transmission. IR - 1:1 Magnification These shots used an R72 filter. The camera was a Sony A6000 with an APS-C sensor. Aperture was f/5.6, as optimum aperture is larger in IR. The full image looked like this: Here are the results. Only one image per lens(Left-to-Right: Top Row: Cassar S 50mm f/2.8, Focotar-2 50mm f/4.5, El-Nikkor 50mm f/2.8 N plastic version; Bottom Row: El-Nikkor 80mm f/5.6 metal version, El-Nikkor 105mm f/5.6 metal version): The El Nik 50 N is softer than the others, which are all pretty similar. Overall, the IQ is poorer than in visible and UV, and there sems to be more sensor noise. Note that the El-Nik 105 element was from an image at only 2:3 magnification and so has been enlarged more the other elements.

Over the past year I've been working on a bit of a side project - learning about microscopy and building a UV transmission microscope. The goal was to build a transmission microscope which could be used down to and below 300nm. When I started on this project I had no idea what how complicated it would be. Lenses in the body of the microscope needed changing for UV fused silica, I made a UV condenser at one point from a half ball lens before being able to get some proper quartz condensers, the light source needed an internal lens removing, in the binocular head a prism needed cutting in half and a fused silica block had to be made to the right size to replace the glass part. This list went on and on. There's a bit of an update on the background to the build here - https://jmcscientifi...-silica-optics/ Recently I put everything together and tried it out. The test subject was a sunscreen cream which is an oil in water emulsion (like mayonnaise) and only contained a UVB absorbing component in the oil phase. This was imaged in visible light, at 365nm and 313nm and gave the following images. Visible light 365nm 313nm The big circular feature in the middle of the image is an air bubble in the sunscreen formulation. Around it is a dense structure of oil droplets in a water based continuous phase. The visible and UVA region look similar (as should be expected). The interesting parts of the image are the light regions to the top and bottom right of the air bubble. When imaged in UVB, these go from looking lighter than the surroundings to looking darker, and I suspect these are more oil rich than their surroundings. As the oil has the UVB absorbing component they should be darker. There's a summary of the work here - https://jmcscientifi...mages-it-works/ As it stands at the moment I can image down to 313nm. The microscope itself would be good down to about 250nm but this would require different light sources and camera as even at 313nm it is at the limit of my cameras sensitivity (and blocking capability of my filters).

I do a lot of UV macro photography, using various known UV-friendly vintage lenses and bellows. I've got a couple of specialised macro lenses, but haven't used these for UV because they're not on the list of UV-friendly lenses. So I thought I'd give them a try - perhaps I've been doing them an injustice and they could be giving me better results. The macro lenses are: A modern Sigma 105mm f/2.8 macro lens. A quick sense-check showed it could make images through a Baader U, but couldn't squeeze anythoing out of a 345BP25 filter. A vintage SMC Macro-Takumar, 100mm f/4. Actually Pentax are a bit naughty calling this a Macro lens, as its maximum magnification is 1:2. The sense-check showed this could make images through a Baader U and the 345BP25, but failed to produce anything through a 315BP20 filter. So these lenses could be used with the Baader U, but clearly have less UV reach than UV-friendly lenses which can get images at 320nm or even 315nm. However, this might not be a problem with a broad bandpass filter like the Baader U, because even with a UV-friendly lens the image is formed mainly by the longer-wavelength end of UVA because of the nosedive in sensor sensitivity and lens transmission with shorter wavelengths. Cue for a test .... The images below compare these lenses with the UV-friendly El Nikkor 105mm (metal). All exposures were at an indicated f/8, ISO 100, flash lighting, and a Baader U. The images are all focus-stacked using Zerene. Both of the macro lenses made good images, but there is definitely something missing compared to the ElNik - especially with the Sigma. In terms of image quality there is no obvious benefits of the macro lenses over the ElNik. So my conclusion is that there's no point using these specialised macro lenses and to continue using the UV-friendly lenses with bellows. (Actually, it might be worthwhile using the Macro-Takumar on the odd occasion when it's not practical - or I can't be bothered - to use the bellows and magnification of 1:2 is adequate). Here is the reference image using the ElNik 105. Magnification is about 1:1: Here is the Macro-Takumar image, using the ElNik white-balancing. Bellows were used to get a magnification of about 1:1 : And this is the Sigma Macro image. Magnification 1:1, using the ElNik white-balancing: Here are some cropped/enlarged images to judge image quality. First the ElNik: The Macro Takumar, using bellows to get 1:1 magnification: Now the Macro Takumar again, but from an image at the lens's maximum magnification of 1:2 without the use of bellows: And finally the Sigma Macro:

In a couple of recent posts I presented some experimental results about how the point of focus (i.e. at the subject, in front of the lens) of the Cassar S and El Nikkor 105mm lenses changed with different wavelengths from UV to IR. In this post I am presenting experimental results about how the focal point (i.e. behind the lens) changes over the same frequency range. This is probably a better metric, and easier to understand. A couple of differences in how the information is being presented here compared with the earlier posts: Results for the 2 lenses are being presented in the same post to make it easier to compare. Each graph now covers the whole spectral range, rather than having separate graphs for UVA, Vis, and IR. The vertical y axes in the graphs have the same scale for both lenses to allow comparison, but the horizontal x axes may have different scales. The filters used for the different measurements were: UV: 315BP25 345BP25 380BP20 Visible: Midwest Optical BP470 (Blue) Hoya X1 (Green) Hoya R25A (Red) IR: Hoya R 72 + MidWest Optical BP735 MidWest Optical BN850 Midwest Optical LP1000 1. Change of Focal Point against Wavelength for various Lens-Subject Distances In these graphs, wavelength is on the horizontal x axis, focal shift (in centimetres) on the vertical y axis. The different curves are for different lens-subject distances: the values of these lens-subjct distances are different for the two lenses. The Cassar generally has a lower focal shift than the El Nikkor, except at very close up and at 315nm, where it goes a bit wild. However, the Cassar S focal length is half that of the El Nik 105, so changes in focal point have a greater effect. One of the strange things about the El Nik 105 is the 345nm measurement. At this frequency the focal shift is negative (i.e. the focal point is closer to the lens), whereas for all other measurements it is positive. This is not an error of measurement, it is really happening. 2. Change of Focal Point against Magnification for the various Wavelengths These graphs effectively take account of the difference in focal length of the two lenses by relating the focal shift to image magnification/size: magnification=0 represents a subject at infinity. Magnification is on the x axis, with high magnification to the left. The y axis shows focal shift in cms. The differenrt curves are for the different wavelengths. Both lenses perform well in the visible region that they were intended for. Looking at the full wavelength spread, the Cassar is better at lower magnifications (larger lens-subject distances) and the El Nikkor is better at higher magnifications (i.e. closer up) - this reflects the purposes that the lenses were designed for. Both have problems at 315nm - especially the Cassar S. Both lenses perform well in the visible range. The x axis scales are slightly different in the two graphs. 3. Change of Focal Point against Lens-Subject Distance for the various Wavelengths These graphs show how the focal shift changes at different lens-subject distances. (Note that the x axis scales are different in the two graphs.) Lens-Subject distance (in cms) is on the x axis, and focal shift (also in cms) is on the y axis. The various lines are for different wavelengths. The Cassar S looks better, but again its shorter focal length means that focal shift will have a greater effect on sharpness. The Cassar 315nm curve goes ballistic at arround 15-18 cm lens-subject distance: the El Nik 105 graph does not cover the range below 20 cm, but it too is showing signs of reaching for the sky. These graphs again show how the performance in the visibile range is good for the two lenses.

This is a companion post to the recent one about El Nikkor 105mm focus shift, this time looking at the Cassar S 50mm lens. What these graphs show is how much the point of focus (i.e. in front of the lens, at the subject) changes for different wavelengths and different distances from front of lens to subject. As pointed out in the other post, a better metric would be how the focal point (i.e. behind the lens) moves. This is a bit trickier to do with my limited resources, but I may get round to it. Anyway, you may find the information below of interest. With the simple set-up I was using (observing how the point of focus moved along a 30 cm ruler at 45 degrees to the lens axis) I was limited to maximum subject distance of about 115 cms. All the graphs below relate to the Cassar S - if you want to see the El Nikkor curves, they are in the other post. UV In terms of the distance by which the point of focus moves, the Cassar S seems a lot worse than the El Nikkor 105. But when you relate the focus shift to magnification, the 2 lenses look comparable at 380 and 345nm, but the Cassar seems to have more of a problem at 315nm. Visible In visible, the shift in point of focus is a lot more controlled as you would expect. The amount of shift is comparable to the El Nikkor, although when related to magnification the Cassar S is slightly better. But it looks like the Cassar S might be worse at greater subject distances than the ones I measured. But to be honest I can't see any point in using either of these lenses for photography in the visible anyway (except for convenience when doing UV vs. Visible comparison shots) as modern lenses are far better. IR In the IR, the Cassar has significantly more shift in point of focus than the El Nikkor. However, again I can't see any role for the Cassar in IR photography - my Canon EF 50mm f/1.8 performs far better. But the El Nikkor I do use for IR, as my modern 105mm lenses (Sigma 24-105mm and Sigma 105mm Macro) have hot-spot problems. Full Spectrum This illustrates quite well how the focus shift is controlled within the visible spectrum for whch the lens was designed, although there are indications that the situation might not be so good at greater subject distances. (NOTE: this graph has been corrrected. The original version had incorrect values on the y-axis.)

In another post there was a discussion about focus shift of the El Nikkor 105mm in the UV. I thought I'd spend some of my lockdown time in getting a feel for how significant this is. Graphs below. I used my tri-colour UV filters (380BP20, 345BP25, 315BP25) and compared how the point of focus moved from the point of focus with visible light for subjects in the range of 24-105 cm from the front of the lens. What surprises me is: how significant the focus shift is. that the 380 and 315nm filters both focus further away, but the in-between 345nm filter focusses closer. the odd shape of the 315nm curve at the 102 and 145cm distances. Initially I thought I'd screwed up the measurements, but I was able to repeat the results.

In another recent post there was a discussion about how some lenses perform in UV macro work. The discussion initially commented that the metal El Nikkor 105mm did not perform as well as the Cassar S 50mm because (a) it suffered from focal shift, and (b) even when re-focussed at 345nm it didn't seem able to produce a particularly sharp image at that wavelength. Birna had been looking for a shorter focal length lens for macro and so was interested in the Cassar S, but in the end decided that the Ocean APO (I think it was) performed better. It so happens that last year there was a discussion about lenses with a good UV reach, and in the data provided one of the best was the Soligor 35mm f/3.5 enlarging lens. I was keen to get one of these, but they are pretty rare - but the wonderful Timber took pity on me and generously gave me his copy. So I though I'd do a quick comparison of the Soligor with the Cassar S and El Nik 105 - results below. The main caveat to make is that because the Soligor is a short focal length lens it gives very little working space between lens and subject, so it's quite difficult to position the lighting. But for Birna, who needs a short focal length lens, this Soligor might be the answer. Another comment to make is that I had to ramp up the contrast significantly for the Soligor and quite a lot for the Cassar to match that of the El Nik. This first image is of the centre of a Forget-Me-Not, which is a flower about 5mm across. It was actually a bad choice for the test, because the centre renders very dark in UV. In this image I had the bellows at full extension. The images have been cropped to the same extent (to about 25% of the whole frame) so that you can see the relative image size produced by the three lenses. In the second image the bellows extension has been adjusted for each lens so that they give the same magnification. The third image is a full bellows extension comparison (like the first image) of printed text: And ther last image is like image 2, i.e. bellows extension adjusted to give similar enlargements, but using the text as the subject: The Soligor appears to be the best performer of the three lenses.