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Finally, after years of having my filters attached to a cardboard/tape roll, I mounted them in appropriate filter rings. This improves versatility a lot. I took a UV, VIS and IR image of a plant to test multispectral stacks. The filter rings allow me to change my filters without moving my camera (at least, reducing the forces on the lens). I didn't refocus, and I didn't align the images, so enjoy some chromatic aberration. The paper tissue was used as a white balance target. UV, VIS and IR images white balanced in-camera, stacks white balanced in Photo Ninja (it provides better results than IrfanView). This time I worked with .tif files, so the quality should be better. Camera: full-spectrum Canon EOS M; Lens: Soligor 35 mm f/3.5. Filters: UV: ZWB2 (2 mm) + Chinese BG39 (2 mm); VIS: Chinese BG39 (2 mm); IR: Hoya R72. UV (f/8, ISO 100, 8 s exposure): VIS (f/8, ISO 100, 1/125 s exposure): IR (f/8, ISO 100, 1/60 s exposure): TriColour (IR = red, VIS = green, UV = blue): IRG: GBU: Notes: - My Chinese BG39 is not the best filter to cut UV/IR, because it doesn't cut UV at all (at least, most UV) and it suppresses the reds too much. But this is what I have at the moment. - IRG and GBU should be quite known abbreviations here, but to recap: An IRG image has infrared in the red channel, red in the green channel and green in the blue channel; A GBU image has green in the red channel, blue in the green channel and UV in the blue channel.

I brought home this bunch of flowers including this lovely smelling Oriental Lily. I photographed it under a cool white LED & some different UVA LEDs., with my converted Sigma fp, with Canon 40mm pancake lens, with the Baader U filter. Oriental Lily, under a Cool White LED light, CWB. Oriental Lily, under a 365nm LED torch, CWB. Oriental Lily, under Quad UVA LED lights, CWB Oriental Lily, under Quad UVA LED lights, CWB Plus an extra 365nm torch,

Sulley (James Patrick Sullivan) is the blue monster in Monsters & Co. I had a peluche of him when I was a child, which then became one of Sugar's many toys (our dog). It was very well-made, and resisted for months, until one week ago Sugar was able to tear his head open. He managed to tear apart one of his eyes clean, and I kept it. I imaged it in visible light, IR TriColour and UV BiColour. Gear: Camera: Full-spectrum Canon EOS M Lens: Soligor 35 mm f/3.5 Filters: IR: Hoya R72 UV: ZWB2 (2 mm) + Chinese BG39 (2 mm) No filters in the visible light image Channels: IR: Red: 940 nm Green: 850 nm Blue: 730 nm UV: Red: 365 nm Cyan: 340 nm The light sources were all LEDs. Visible light. f/8, ISO 100, 1/2 s exposure IR TriColour: UV BiColour: Notes: - All images taken at f/8 and ISO 100, with varying exposures; - I set the camera to auto exposure, as it is easier and faster to work this way. If I understand correctly, IrfanView white balances images by re-weighting the channels, and this is why it can't set a UV WB. It doesn't create non-existing channels (this reminds me of this conversation). This "feature" is actually very useful when doing TriColour images, as it compensates for the different exposures of the channels, without altering the colors; - The UV BiColour image doesn't look very good for two reasons: the first one is that running my 340 nm LED at 100 mA produces very little light, and considering I used ISO 100 and f/8, that meant 20 minutes of exposure, and they weren't even enough. This resulted in a very dark image that needed to be lifted up by several stops. The second reason is that, for reasons unknown to me, the program I use to stack the images (ImageStacker) doesn't work properly if one of the images has been processed in Photo Ninja. I had to process the dark 340 nm .CR2 image using Windows Photo editor (it handles raws, surprisingly), and this may have impacted the quality a bit. Also, the LEDs weren't in the exact same spot, and the shadows on the paper tissue below show this. - The three images (not the single channels, but the finished images) were not taken exactly in the same spot, and cannot be stacked. By changing the filters I couldn't keep the camera still, and it moved a bit. I will try to improve my technique. I have to make the tripod sturdier, and when I will have better filters (that actually screw on the lens) and a nice collection of light sources as well as filters, I will be able to do more. For now, not too bad.

I came across this from the National Optical-Infrared Astronomy Research Laboratory and thought others here might enjoy it: "Detailed new images of Jupiter captured in different colors of light reveal a multitude of atmospheric features" The detailed images can be viewed by selecting from the column of thumbnails on the right. https://noirlab.edu/...ws/noirlab2116/

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:

I took advantage of the long winter nights to do some fluorescence photography. Here are some results of UV- and Visible-Induced IR fluorescence, done in tri-colour. I’ve also included standard visible and a few UVIVF images for comparison. (There are some more tri-colour IR Fluorescence images, using rock samples at https://www.ultravio...__fromsearch__1 ) The Tricolour channel assignments are: Red Channel: 1000nm Green Channel: 850nm Blue Channel: 750nm Light Sources: UV: Nemo Torch Visible: Lumitact LED torch. Narrower-band Excitation My available UV light sources and filters did not allow for excitation using a narrower band of the UV spectrum, but this was possible using visible light. This set of images includes Visible-Induced IR Fluorescence excited by white, blue (470nm), green (520nm), and red (635nm). Apart from colour cast, there is not a lot of difference, and so all later Visible-induced IR Flourescence images use just white excitation. The blue and red colour casts on the blue- and red-excited images cannot be due to any form of blue or red visible light leak: blue and red in the image is caused by transmission through 750nm and 1000nm bandpass filters and there is no reason why blue light would leak only through the 750nm filter and red light would leak only through the 1000nm filter. Orchid: Visible..........................................................................UV-Induced Visible Fluorescence UV-Induced IR Fluorescence Visible (White)-induced IR Fluorecence......................Visible (Blue)-induced IR Fluorescence Visible (Green)-induced IR Fluorecence.....................Visible (Red)-induced IR Fluorescence White Balancing How do you white balance images like this? I started off with using WB based on a white section of a rock, but this often just gave visually uninteresting so I started WBing against elements of the image. This example shows the differences this can produce. Lily Visible....................................................................................................................UV-Induced Visible Fluorescence Visible-Induced IR Fluorescence: Rock WB method:..................................................................................................WB against dark area at top-left: WB against leaf: UV-Induced IR Fluorescence: WB against leaf: Forsythia: Visible: UV-Induced IR Fluorescence:................................................................................Visible-Induced IR Fluorescence: Flaming Katy: Visible:..................................................................................................................UV-Induced Visible Fluorescence: UV-Induced IR Fluorescence:...............................................................................Visible-Induced IR Fluorescence: For both of these images, saturation has been increased and WB was against the leaf. Winter Aconite: Visible: UV-Induced IR Fluorescence:...............................................................................Visible-Induced IR Fluorescence: Chrysanthemum: Visible: UV-Induced IR Fluorescence:.................................................................................Visible-Induced IR Fluorescence: Visible:...................................................................................................................UV-Induced IR Fluorescence: Jasmine: Visible: UV-Induced IR Fluorescence:................................................................................Visible-Induced IR Fluorescence: WB was against the stamen tip. Snowdrop: UV-induced Visual Fluorescence:.........................................................................Visible-Induced IR Fluorescence: These imges were WBed on the light part of the petals. Daffodil: Visible:..................................................................................................................UV-Induced Visible Fluorescence: UV-Induced IR Fluorescence:...............................................................................Visible-Induced IR Fluorescence: WB was against the stigma tip Tulip: Visible :...............................................................................................................UV-Induced Visible Fluorescence: UV-Induced IR Fluorescence:.............................................................................Visible-Induced IR Fluorescence: These last two images were WBed on the stigma. And now something completely different – Sugar Cubes: Visible:..............................................................................................................UV-Induced Visible Fluorescence: UV-Induced IR Fluorescence:...........................................................................Visible-Induced IR Fluorescence:

In this post I bemoaned the demise of my full-spectrum Sony A6000: https://www.ultravioletphotography.com/content/index.php/topic/4465-aaaaagh-im-full-spectrum-camera-less/page__gopid__44120#entry44120 I decided to buy a replacement from infraredcameraconversions.co.uk (Alan Burch), and took the opportunity to upgrade to a Sony A7R. I was excited at the prospect of having a full-frame full-spectrum camera and the prospect of post-processing being slowed down by having even more megapixels to move around and manipulate. The A7R arrived yesterday. Initial tests showed it worked fine in IR and with a Baader U. But when I used my UV bandpass filters it was clear that the camera could not reach deeply into the UV. At 345nm it semed about half as sensitive as the A6000, and at 320nm about 1/6 as sensitive. This makes it unusable for UV TriColour as the sensitivity of the A6000 at 320nm is already pretty low. Not clear what the reason is. The A7R is unusual in not having an Anti-Aliasing filter, and so the sensor cover plate may have ben modified in some way to compensate. Also Alan says the A7R sensor has an AR coating (which may be another result of having no AR filter). So sadly I am returning the A7R and getting another A6000. It's a bit boring having two A6000s (assuming I get the old one fixed), but at least I know it works down to about 305nm. BTW - I have updated the other post on the problem with the A6000. This may be of interest to you if you are using a Sony A6x00 camera.

Here's a tricolor of snow on a window. The filters are: 780BP30 - red channel 1064BP25 - green channel 1500 long pass (but probably 1500-1550 effectively because of the camera gain fall off) - blue channel The color channels are BGR essentially because it made the snow stand out better. Alternative is to have magenta cyan snow in RGB. visible: Individual frames: 780nm ("red") 1064nm ("green") 1500nm ("blue")

I had this thought for a while. We have already briefly talked about this in the past (below are some links), but I never saw an actual experiment about it (if someone already tried this and posted it on the forum, please link your experiment). So, to put it simply, our cameras have a limited but non-zero ability to distinguish different wavelengths in both UV and IR, which appear as different colors, and this is especially apparent when an image is properly white balanced. In UV, the usual color palette (after a WB) starts with blue at the longest wavelengths (usually near 400 nm, depending on the filter being used), then violet/lavender, then white (at a precise wavelength), then a greenish yellow, and usually around 340 nm there is green, but in real world photos UV-green is almost never seen, unless you have very specific materials such as ruby. If you are interested in a discussion about UV-green objects, read this nice talk members had. In IR (using a 720 nm filter, like Hoya R72 or similar), the palette is quite similar: we start with a yellowish/orange at the 700 nm edge, then yellow, then white, then cyan/blue. I just talked about this here. This means that, both in UV and in IR, the shortest wavelengths appear yellow, and the longest appear blue. But there are really two channels, as Andy showed here. In particular, there isn't the equivalent of a green channel. We have yellow and blue, two complementary colors, they give white when mixed, but that's it. The fact that we have two channels only also explains why there is always a neutral wavelength which appears white. I read on Wikipedia that colorblind people also experience this. BGR images (images in which the red and blue channels have been swapped) map longer wavelengths as red and shorter wavelengths as cyan. This is, to an extent, something similar to a true tri-color image. Regarding true tri-color images, I recently experimented with this technique in IR here, and before me Bernard Foot did the same in both UV and IR. I suggest you to see his work if you are interested in the technique. This images have actual three channels of information, and so it is possible to see red, green and blue objects in the same image, although green seems to be the rarest color. My experiment is to compare a true tri-color image, which was made as described in my initial post, and a simulated version done with more usual methods. Cameras are much less sensitive to wavelengths above 900 nm than to those below, so I needed a light source heavily weighted towards longer wavelengths, and running halogen lamps at low voltages didn't provide enough light. So I used my DIY incandescent lamp (this one), to provide enough light for my purposes. I ran it at about 30 W of power. The resulting images had too much noise and were quite dark, so I took 199 of them, and did a mix of stack/average (sum/50), to have an image 4 times brighter and 50 times less noisy. I did an in-camera white balance before taking the images, and used a Hoya R72 filter. This was the result: Not the best image in the world, but nice enough. The green color cast and the vertical stripes are a result of the noise at low brightnesses. Then I re-white balanced it, swapped the red and blue channels, and increased saturation to the max twice. ...and this is the final result: I got blue water and some reds. Then I did the proper tri-color version, and this is how it looks like: This is the visible light reference: For sure, the two images are not identical, but are quite similar. Also, on the Rubik's cube, the green squares became orange and the blue ones became yellow in the tri-color image. I think I can see a slight difference in the simulated tri-color image too: Visible reference: True tri-color: Simulated tri-color: Isn't the square in the corner a bit redder? I may be overseeing stuff, but I have this impression. Conclusion: in IR (probably also in UV, but I only checked in IR), doing a BGR channel swap on a white balanced image can give a clue of what a true tri-color image would look like, although a true tri-color image can only be done using three filters or three light sources and combining the resulting channels properly. Other occasions in which members, including me, talked about this (I may miss something): https://www.ultravio...dpost__p__39254 https://www.ultravio...dpost__p__36801 https://www.ultravio...dpost__p__25092 (the post contains some links).

I started this new topic since I thought the previous one was already complete, being my first attempts only. I have taken other images, and I am posting them here. This is the first topic: https://www.ultravio...t-tri-color-ir/ As a reminder, the camera I used is a full-spectrum Panasonic DMC-F3, I used a Hoya R72 filter for the IR images and a white LED for the visible light references. Some tri-color images have been white balanced, I will say that for every image. Note: sometimes my camera doesn't autofocus, and usually (ironically) the IR images are sharper than the visible ones the camera was designed to take. Channels: Red: ~940 nm; Green: ~850 nm; Blue: ~730 nm. Visible reference: Tri-color IR (original): I don't think I need to say this, but to be clear the brands shown are just random and there isn't the slightest intent to advertise them. The first bottle from the left is water, the third one is denaturated alcohol 90°. They both appear bluish, but the alcohol is greener. Pens, assorted colors. If the colors aren't clear, from left to right they are BLUE RED BLUE GREEN GREEN BLACK BLACK BLUE RED BLUE. Visible reference: Tri-color IR (original): Full-size crop: Some inks became transparent (red), others orange (blue), others red (green) and the black pens remained black. Black pen ink becomes transparent to IR when thin (see my pen ink filter). Rodolfa Visible reference: Tri-color IR (original): Amethyst (I am 99.9% sure it is that) Visible reference: Tri-color IR (white balanced): Various minerals The rock/mineral below has a quite strong orange fluorescence under 365 nm UV. Visible reference: Tri-color IR (white balanced): Visible reference: Tri-color IR (white balanced, almost identical to the original): The middle specimen is actually green: Visible reference: Tri-color IR (white balanced, similar to the original): The middle specimen is actually blue: Bonus: a failed attempt. I tried to photograph an orange, but it slowly settled down and thus moved a bit. I processed the images anyway and this is the result (crop): Thoughts and conclusions: White, red, orange and yellow plastics come out usually white; Blue plastics are usually yellow; Green plastics and dark blue plastics are usually orange/brown; Black plastics are often black. Most minerals don't have strong IR false colors. Except for one strong yellow, all I got were shades of orange and pink, and a very pale blue from the amethyst. I think I will take other images, probably 3-6, and I will post them here. If you have any suggestions (I am running out of ideas!), please share them here.

Inspired by Bernard's excellent work, I wanted to try full color/tri-color IR too. I didn't use three separate filters, but three separate light sources. More below. I have a wide range of IR LEDs, currently seven between 730 and 1050 nm, but only three of them are usable as of now, since I didn't attach the others to a heatsink yet, and thus they would overheat. Those three LEDs are the most common IR LEDs you can find online, emitting at 730, 850 and 940 nm. Their peaks are roughly evenly spaced, and thus they are suitable for tri-color photography (one can use any combination he/she likes, but evenly spaced filters/light sources are better in my opinion). The LEDs are the "10 W" type, with 9 chips in a 3S3P configuration and a maximum rated forward current of 900 mA. They probably emit 1-3 W of light, not more. I may one day write a topic about my LEDs in detail. I ran all of them at full power. The target was water. People who read my posts for a while know that I like seeing the absorption of water in the near-infrared spectrum (possibly, one day, even in SWIR), and since I know that water appears noticeably darker at 940 nm by experience I wanted to combine three images to make it appear blue. I used my full-spectrum Panasonic DMC-F3, an Hoya R72 filter to prevent any possible (but unlikely) contamination by visible light, and to prevent movements between the images I mounted the camera on a tripod which I attached to the floor with bi-adhesive tape. Since I didn't care about colors in the single images, and I would have needed to convert them to B&W anyway, I directly shot them in B&W in-camera. To have uniform exposures between the images I put the camera on auto ISO mode, and it worked very well. I put a paper tissue in the background to have a white target. Normal copy paper would have worked as well. The water thickness was 28 mm, and the LEDs were ~50 cm (~20 in) from the container. I mapped 730 nm as blue, 850 nm as green and 940 nm as red. Images settings were f/2.8 for all images, and 1/30 s ISO 80 for 730 nm; 1/30 s ISO 100 for 850 nm; 1/8 s ISO 320 for 940 nm. Combined final image (just the three channels stacked, no white balancing, no alignment, no post-processing): Increased saturation: Any suggestion is welcome.

Some of my UV / Protection Filters don't cut UV, why ? So I purchased a new release Manfrotto Outdoor UV Filter. https://www.digitalc...-uv-filter-77mm I was disappointed again that this one didn't cut UV either....? First image is of todays full sunlight. Second image is with the Manfrotto Outdoor UV Filter.

Foot, Bernard (2020) Cydonia oblonga Mill. (Rosaceae) Quince. Flower photographed in visible and reflected UV light together with UV Stereo Anaglyph and TriColour RGB Stack. https://www.ultravio...oblonga-quince/ Location: Date: 16 March 2020 Cultivar Reference: 1. Wikipedia (28 Mar 2020) Quince. Wikimedia Foundation, San Francisco, CA. Visible Light UV Light UV Stereo Anaglyphs UV TriColour Blue Channel = 315nm CWL, Green Channel = 345nm CWL, Red Channel = 380nm CWL

Visible: UV: UV Stereo Anaglyph: UV Tri-colour [blue = 315nm CWL; Green = 345nm CWL; Red = 380nm CWL):

Foot, B. (2020) Malva sylvestris L. (Malvaceae) Common Mallow. Flowers photographed in visible and ultraviolet light with UV anaglyph and UV Tricolor Stack. https://www.ultravio...vestris-mallow/ United Kingdom 04 Nov 2019 Wildflower Synonyms: Malva ambigua Guss. Malva mauritiana L. Malva erecta C.Presl Malva gymnoscarpa Pomel Other Common Names: Common Mallow Cheese Mauve des bois References: 1. Wikipedia (02 Apr 2020) Title_of_Wikipedia_Entry. Wikimedia Foundation, San Francisco, CA. https://en.wikipedia...alva_sylvestris 2. Foot, B. (29 March 2020) Making Stereo Images. UltravioletPhotography.com Visible: UV (Baader U, flash): UV Stereo Anaglyph: UV Tri-colour (Blue = 315nm CWL; Green = 345nm CWL; Red = 380nm CWL):

One of my projects this year is to try some full-colour IR work, by taking 3 shots with different band-pass filters and then using those as colour channels as follows: Blue Channel: CWL = 750nm approx Filter = R72 + Midwest Optical BP735 Green Channel: CWL = 850nm aprox Filter = Midwest Optical BN 850 Red Channel: CWL = 1000nm approx. Filter = MidWest Optical LP1000 I'm waiting for the sun to return to try this out on landscapes - my initial trials on things like flowers and other stuff indoors has not found much by way of colour across this part of the spectrum unless I really wind up the saturation. But there is one area where I have found colour - the sky comes out a lovely blue. This is illustrated nicely in the following photograph, taken in December - saturation has not been increased. there is some colour banding in the fence shadow at bottom-right and on the tree just to the left of the main tree - this is caused by the shadows moving between the three colour separation exposures. I also took some visible shots, which looked quite similar apart from the colour of the grass! Camera was a full-spectrum modified Sony A6000, with a Canon EF 28mm / f2.8 lens.

Not the first time this has been tried, but I attempted to make some wavelength-dependent false colors by taking three photos using a 780BP30, an 830PB40, and a 1064BP25 filter and putting the resulting images in the blue, green, and red channels respectively. The camera used was the TriWave, which is monochrome and has no Bayer filter to distort the results. Lighting was a halogen light with some kind of shield over it. The physical setup looked like this. I have the TriWave attached to an iris, followed by a 100mm lens with a NIR/SWIR AR coating from Thorlabs, and then a sliding filter holder that lets me easily swap filters without messing up the image. The experimental subject was this jalapeño: The filter spectra (supplied by Omega with the filters) were: The three unaltered images came out like this: Gain of the camera went down over the range, so I adjusted exposure time by roughly one stop for each image. 780BP30 (blue channel) 830PB40 (green channel) 1064BP25 (red channel) I took one additional image at 1500nm long pass (the end of the camera's range). This wasn't used for anything, I was just curious and it was the last filter in the filter holder, so I took it "while I was there anyway." I put the images in the three channels and got this: Then I whitebalanced off the paper in the background using PhotoNinja and trimmed the histogram for better contrast:

Inspired by a couple of threads on here (namely Bernards great examples, looking at using 3 filters to cover the UV range - https://www.ultravio...dpost__p__30286, and Andys post about the limited range of colours in a typical UV image - https://www.ultravio...dpost__p__30024), I've been thinking about using multiple filters to cover the UV range, in combination with a monochrome camera, and assigning the image from each filter a different colour. Then the images would be combined to make a composite UV image with a wider range of colours, than one done with a single wide band UV filter, and converted camera with the Bayer filter still present. This thread will cover my work on this, as it may be of interest to some on here. It's going to be a work in progress, as I have discovered it's a lot more complicated to implement than I initially thought, and I need to do a lot more work on it to get it to where I am happy.

I found this to be an interesting series, which seems to be the reverse of what I typically see. It seems the petals get darker into higher UV (closer to 390nm) and lighter in deeper UV (Closer to UVC). Visible reference image of the Sunflower: All the below monochrome images are captured off the back of the KSS Imager with quartz 60mm lens, using a stock GM5 camera with Olympus 30mm f3.5 Macro lens. UVC image of sunflower using single 250nm UVC light with just 253.7bp25 filter: All the following images were captured using 2 ExoTerra UVB 26W bulbs. Since the Monochrome imager down converts the high UV energy to green light, it doesn't seem to pass 600nm+ light. So I don't need to use an IR blocker filter with my filters that leak IR. 303bp10 with 2mm U340 filter (seems to be the best to reduce the off axis dichroism): 313bp25 filter (clear slide filter inserted): 335bp10 filter (clear slide filter inserted): 370bp15 filer (clear slide filter inserted): 390bp25 filter (clear slide filter inserted): 405bp10 filter (clear slide filter inserted):

Warning, do not use 250nm UVC lights unless you take proper precautions. Image only in controlled room, away from pets, kids, loved and non loved ones. Best to image in dehumidified area, winter months work, to reduce air moisture. Ozone will build up quickly when working with UVc lights. Ideal to have a room vent. Tether your camera to a computer located in an other room to work with camera settings and images. This can be done with 25 feet long usb cords. I imaged a white flower using both the Sirchie Monochrome imager, coupled to my GM5 camera and using my EM1 just to compare the UV reflectance. I have also included some fluorescent images as they seem the most fun. Although the UVC and UVB do show some petal damage or something not visible in the visible or upper UVA range. Also it looks like the Sirchie phosphor screen may be sensitive from 200nm to 500nm, as I do see an image using the Lee 729 filter used for IRchrome imaging. It gets very glowly the higher you go, But didn't test the absolute upper cut off. Visible image of Flower: 253bp25, using single UVC light: 303bp10 +330WB80 improved filter, using two UVB lights: 313bp25 +330WB80 improved filter, using two UVB lights: 370bp15 +330WB80 improved filter, using two UVB lights: 390bp25 filter, using two UVB lights: 405bp10, using two UVB lights: Lee729 with KG3 2mm using two UVB lights: The following images for comparison using EM1 full spectrum camera with UAT lens at F8 with two UVB bulbs Visible: U330wB80 filter only (UVA): U330WB80 + 313bp25 (UVB): Then for some fun here is the UV induced images using two 365nm lights with ZWB1 filters, Using the UAT at F8 on the Full spectrum EM1 camera: UVIVF (using Sigma SD15 filter to block under 405nm and over 680nm): UVIVIRF (using just a Tiffen 2A filter on the camera): UVIIRF (Using as LP 720nm filter on camera): Here is a better IR induced fluorescence image using a 405nm light and the LP 720nm filter 405 IIRF: 313bp25 +330WB80 improved filter, using two UVB lights:

SAFETY WARNING: UV-C is dangerous to your eyes and your skin. UVP DOES NOT SUPPORT USING UV-C ILLUMINATION. [UV SAFETY] UV-C Light Dangers Warning, do not use 250nm UVC lights unless you take proper precautions. Image only in controlled room, away from pets, kids, loved and non loved ones. Best to image in dehumidified area, winter months work, to reduce air moisture. Ozone will build up quickly when working with UVc lights. Ideal to have a room vent. Tether your camera to a computer located in an other room to work with camera settings and images. Thus can be done with 25 feet long usb cords. Andy requested a fun series of UVC, UVB and UVA images. So I photographed an Acorn yesterday next my dried up Kiwi berries, that I imaged last week and still need to sort. This was imaged differently. Here I am using the 60mm f3.5 KSS quartz lens set at F4 on the phosphor imager. I have then converted the back with a set ring to mount my Olympus 30mm Macro lens which is set at F5.6 on my Panasonic GM5 camera (stock not converted). The camera was set to ISO 200 and all photos were taken in Monochrome mode as the back imager is just green anyway, so might as well be monochrome. For the 253nm UVC images a 250nm UVC sterilizing bulb was used. 253.7bp25 only: For all the rest of these images a single UVB ExoTerra 26W bulb was used. 303bp10 + 330Wb80 improved: 313bp25 +330Wb80 improved: 335bp10 + 330Wb80 improved: 340bp10 + 330Wb80 improved: 370bp15 + 330Wb80 improved: 390bp25 only: Now for the fun part you can do this a home as well. I aligned the images using hugin and then color stacked them using Gimp in the color compose tools. These are my fun ones to compare: 254R_303G_370B 254R_313G_370B 254R_335G_390B 303R_370G_390B 313R_370G_390B 335R_370G_390B: There is almost no change in the dried fruit, but the color composite allows you to really see the differences in the Acorn. I will have to get some flowers or test this better with some fruits. A color image of the test acorn for comparison with GM5 Olympus 30mm at F8 ISO200: Filter information updated to all stacked filters used.

My flower seemed to be stimulated by the UV light. But I thought I too would try the UV color composite test. Here is my series, I am using Full spectrum Olympus EM1 camera. The Pentax UAT 85mm lens at F11. I am using a ExoTerra UVB light bulb on the left, a Lucky Herb UVB bulb on the right and a 302nm bulb in front of the tiny flower. Visible of flower: 303bp10 with 330WB80 filter: 313bp25 with 330WB80 filter: 335bp10 with Baader Venus U filter: 370bp15 with Baader Venus U Filter: 390bp25 filter Baader Venus U filter only: 330WB80 Filter only: Now the fun part. These were aligned using Bernards method with the command prompt and then color composite in Gimp. These are my favorite with Blue as 390nm and 370nm as Green: Red channel 335, Green 370, Blue 390nm Red 313, Green 370, Blue 390nm This is the typical range that I don't really like the output of Blue 335nm, Green 370nm, Red 390nm:

*** Updated 04 Nov 2019 *** - Added notes on aligning the images using Hugin. This article now describes my "production technique", which is now reasonably slick and which I follow for all my images.. *** Updated 22 Sept 2019 *** - Updated the notes on technique in the light of suggestions made by other forum members, added some now photos made with the new twechniques, and removed some of the original photos. *** Updated 11 June 2020 *** - Updated the notes on technique to add a requirement to use fixed Tone Curves. Modified text to indicate that in-camera White Balance setting is irrelevant. Simplified Exposure Factors for the three filters.Updated notes on Focus Shift. Following some discussion elsewhere in this forum I decided to try making full/false-colour UV shots by making three colour separation images in different parts of the UV spectrum, colouring them red, green, and blue, and then overlaying them. The same way you could make visible light images in natural colours by making red, green, and blue separation images – but doing it in the UV region instead. There were a number of potential issues that might lead to failure. But actually – it works! Here are some of my early results - notes on the technique are provided at the end. Nearly all of the subjects have 3 images - Visible, followed by standard Baader U, followed by False-Colour UV. (Here are the images added 22 Sept 2019) This is a comparison between different white papers. Pinkness indicates absorption of the shorter UV wavelengths. All exposures were the same, so brightness of the image gives an indication of total UV reflectance. The Glossy Photo Paper looks good in terms of neutral tone, but is surprisingly dull: Now some flowers: In this shot, the blue/cyan colouring in the Full-Colour UV shot shows that there is more reflection of the shorter wavelengths than the longer wavelengths: Cyclamen: A variety of plastics: Printed card packaging: And finally some outdoor shots. Saturation and contrast increased: In this shot notice how much bluer the shade is than the sunshine - showing the higher scattering of shorter wavelengths which is then illuminating the shade: And here the progressive move to blue in the distance indicates the higher scattering of shorter wavelengths. And comparing the UV shot with the visible shot, the hgh level of scattering in UV compared with visible is obvious: (The rest of ther images remain from the original Post) In this first trio, the False-Colour image looks a bit like a visible image. But compare the car wheel, bike frame, tail lights, and garage door surrounds with the true visible image: Here I used a panorama for the False Colour image, and bosted the saturation. Here is another panorama - the False Colour image required 27 changes of filter and exposure, so plenty of opportunity for screw-ups! Saturation boosted again. Now some glazed pottery: At last some flowers - starting with our good friend the Autumn Hawkbit: Sweet pea: Now three flowers whose names I can't remember: Here's a reminder not to take UV photos through glass. Open window on the right, triple-glazed window on the left. The colour tells us what we already know - the shorter wavelengths (blue) are absorbed far more strongly: Why bother? Well, to see what happened. And to make use of the shorter wavelengths in UV. Because cameras are far more sensitive to longer UV wavelengths than shorter ones, and there is less shorter wave UV light around, most UV images are really only showing the longer wavelength end. By making separate images in different areas of the UV spectrum, the weaker short-wavelength images can be boosted to have equal weight to the longer wavelength image. Apart from the ability to create full colour images, this should also add detail into the black areas of UV shots where there may be no longer-wavelength UV but there may be shorter-wavelength UV which is not bright enough to get recorded. Equipment I only have some basic kit – a full-spectrum Sony A6000 with the following UV-friendly lenses: Soligor 35m/3.5 (Enlarging Lens) Cassar S 50mm/2.8 Focotar-2 50mm/4,5 (Enlarging Lens) Metal El-Nikkor 80mm/5.6 (Enlarging Lens) Metal El-Nikkor 105mm/5.6 (Enlarging Lens) These perform reasonably well and can record images using the 315BP25 flter at the exposure factors identified above. Filters. The plan was to obtain 3 filters that would transmit different bands in the 320-400nm range. I described my intentions to Bob Johnson who owns the business at http://www.ebaystore...AG-EBUYER-STORE . He thought this was an interesting project, and offered to construct some filters that would do the job. In the event, he constructed 5 different "UV False Colour" filters, and I bought three of them: 315BP25, with a peak transmission of about 75%. Peak Transmission wavelength is 323 nm - the transmission cure is not a bell curve. 345BP20, with a peak transmission of about 78% 380BP25, with a peak transmission of about 50%. All the filters have blocking of OD 6. This is a high blocking factor, but I was worried it might not be enough for the 315 nm filter if the sensitivity of the camera was so low at this wavelength that very long exposures might be needed and so even very, very low IR or visible leakage would ruin the image. Fortunately this concern turned out to be unfounded: the sensitivity of the camera/lens around 320nm is indeed low, but nowhere as poor as I thought it might be. Hot-spotting Problem The 380nm filter and, to a lesser extent, the 315nm filter caused problems with several of the lenses which results in various manifestations of hot-spotting or light patches. I'm guessing it is caused by light reflecting off the lens or diaphragm and being reflected back into the lens by the mirror-like coating on the filter. In daylight. these seemed to be no consistency of cause in terms of light direction or aperture. With flash, the problem was noticeable on the Cassar when getting close to the Macro range with the lens not reversed. The problem can generally be avoided by using a small-diameter lens hood of appropriate length. For the Cassar S, 2.5cm M42 extension tube screwed to the front of the filter works well for distances > 1 metre: longer tubes can be used for close-up work or longer focal-length lenses. White Balancing Setting The camera's White Balancing setting is irrelevant as all work is done using RAW files from the camera. Exposure Factors To balance exposures through the three filters I derived exposure factors for each filter such that a PTFE tile would appear white in the final result. I derived these exposure factors by seeing what exposures through the three filters would result in a similar histogram. The histogram has to be within the boundaries so that there is no clipping at either end. It has been suggested that the camera is set to monochrome for this so that your don't have to worry about the three separate colour histograms. The following standardised exposure factors (normalised for 380BP25 = 1) worked for me, using a full-spectrum Sony A6000. Final White Balancing to take account of the different lenses being used and different daylight conditions is achieved later at the Final White Balancing Stage: 380BP25 Daylight: 1 Flash: 1 345BP25 Daylight: 2 Flash: 2 315BP25: Daylight: 64 Flash: 48 For daylight images, the exposure was adapted by varying the shutter speed. For flash images, the exposure was varied using a mixture of varying the ISO setting and using multiple flashes per image. Setting up White Balancing Exposures of PTFE white tile were made correspoding to the above exposure factors, and reference grey images were made using the overlaying process described below. These resulted in plain grey images. These were then white balanced in RawTherapee and the white balancing parameters saved as white balancing profiles for the various lighing types. Making the exposures The first exposure used the 380PB25. In daylight the auto-exposure would provide the correct exposure for this filter, and then the above exposure factors would be applied to get the exposure for the other filters. (On the Sony A6000, I need to add 2 stops of exposure compensation to the auto-exposure to get decent UV results.) When using flash, the exposure for the 380BP25 was found by trial and error, and the exposure for the other filters was modified by increasing the camera's ISO setting and using multiple flashes. This resulted in high ISO settings for the 315BP25 such that the images were noisy – but this is not noticed when the image is overlaid on the better quality images from the other filters. Focus Shift Both the 345BP20 and 315BP25 filters cause focus shift compared to the 380 BP20. The 315BP25 focus shift is more significant than the 345BP25, and increases with lens focal length. The 315BP25 focus shift requires the lens to be racked out (i.e. moved away from the sensor), which you would probably expect - but the 345BP25 focus shift sometimes required the lens to be racked in. When working outdoors it is relatively easy to focus the images through the 380nm and 345nm filters. The 315nm image may be very dim, but focussing can normally be done using the ground/sky boundary. When working close up with flash, the 380nm and 345nm images can be focussed using a UV torch, such as the Convoy S2+ with Nichia UV LED. But this cannot be used for the 315nm image, so I have experimentally developed a series of charts showing how much to turn the focussing helicoid to get the 315nm image in focus for the various lenses and subject distances. This refocussing requires a stage to scale and align the 3 images in post-processing Preparing the Images for Overlaying Each of the RAW colour separation images is pre-processed (I used RawTherapee) to set the colour management to No Profile and remove White Balancing. A standardised (e.g. "Linear") Tone Curve must also be applied - it does not matter what Tone Curve is used, as long as the same one is always used. (The Tone Curve maps input pixel brightness to output pixel brightness). RawTherapee, for example, by default applies the Tone Curve derived from the JPEG embedded in the RAW file. But this Tone Curve varies between the three colour separation images and from subject to subject.) Failing to do this will result in inconsistent colour balancing and may cause anomalies - such as sky and other bright areas to become pink. The images are then saved as TIFFs. Aligning the Images Refocussing for the different filters results in the images having slightly different magnifications. It is also possible that the camera was moved between exposures. Because of these factors, an aligning stage is required.It is possible to do this manually using software such as GIMP, but that can take a lot of time and patience. Fortunately, the alignment can be done using another piece of freeware, Hugin. The alignment can be done by opening a cmd.exe window and running a command line. The generic structure of the command line is: "{Pathname to Hugin Alignment executable}\align_image_stack" -a "{Pathname to output folder}\{Prefix for Output filenames}" "{Pathname to folder holding the input files}\*.tif" -m The quotes are required. As an example, the command line might look like this.The same folder is being used for both input and output. The output consists of one file for each inout file; the filenames are of the format Aligned0000.tif : "D:\Program Files\Hugin\bin\align_image_stack" -a "C:\Users\Bernard\Desktop\UV Colour\Align\Aligned" "C:\Users\Bernard\Desktop\UV Colour\Align\*.tif" -m These three aligned images are then used for the rest of the procedure. The Hugin tool sometimes cannot align the 315nm image with the others, where the correction for focus shift has caused significant scaling of the 315nm image. In this case, Hugin can be used to align the 380nm and 345nm images, and elignment of the 315nm image must be done manually. Overlaying the Images. I used GIMP to do this, but other software products are available. Each of the three aligned TIFF images is loaded as a layer, 315nm as the background, then 345nm, then 380nm. You do this by dragging one image into the GIMP window, then the 2nd, and then the 3rd. It saves you a bit of time if you drag the images in the order 315, 345, 380. Then the images need to be converted to greyscale (Image>Mode>Grayscale). The colour image can then be created created using Colors>Components>Compose: if you dragged the images in in the order 315, 345, 380 then you can simply accept the proffered order for the R, G, and B components. (Thus assumes you wanr to mimic the visible spectrum by using the shorter wavelength component (315BP25) for the blue channel, the mid-wavelength component (345BP20) for the green channel, and the long-wavelength component (380BP25) for the red channel. No reason why a different colouring protocol couldn't be used, but then you need to change the allocation of images to the RGB layers.) The resulting full-colour image should then be saved as a TIFF. Final Colour Balancing The full-colour TIFF is then opened in RawTherapee, and the appropriate white balancing profile (as described above) is applied.If you used a linear Tone Curve earlier on in the process your results at this stage may be flat (i.e. low contrast). In that case you can modify the images to correct that at this stage - e.g. by applying a Tone Curve of a standard "Leaning-S" shape to boost contrast of mid tones.) If you want to save the result as JPEG, do that conversion here and not earlier in the process: it's better to do all the intermediate processing using TIFF. I find that outdoor shots show very little colour, so for these I may boost the colour saturation and contrast to get a more interesting result. Restrictions Because this technique needs multiple exposures, sometimes with exposures of 30 seconds, you are limited to static subjects. Waving vegetation, insects on flowers, and moving people and vehicles will all cause colour fringing or random colour blobs. The smallness of the filters may prevent use with some lenses - such as wide angle lenses (less than 35mm focal length on an APC-C sensor) or where the front element is deeply recessed (e.g. with some of the UV-friendly 35mm lenses, such as the Prinz Galaxy.)

EDITOR'S NOTE: Posts within the topic Modelling UV camera response from Bayer filter meaurements about using narrowband UV-pass filters to make RGB stacks were moved here to their own topic in the Filters section. All this gets me thinking of three narrow band UV filters, shot separately. Low, medium, and high UV-A bands. Say, 330BP15, 360BP15, and 380BP15, just as a rough idea. Those bands are in no way thought out, they could be adjusted for peak and width to whatever one thinks is best, but I might tend to keep them a bit separated rather than overlapping. This would do well to have a deep reaching UV transmitting lens to eliminate any lens transmission curve slope that would truncate or basically remove transmission from the lower range bandpass filter. We have the sensitivity drop off of the sensor, so a monochrome UV conversion would do well for this set up also, however it could still be done with a standard full spectrum conversion. Whether we use a monochrome UV camera or not, we still have a drop off in sensitivity to UV with the sensor. Given the sensor sensitivity drop off, each shot would have a different exposure time to adjust for the sensitivity of the individual bandpass. I think the separate exposures give us something unique compared to a single UV filter shot, because given the sensitivity drop off, our UV shots may be heavily weighted in the upper range of UV-A. Assigning each band to RGB, in whatever arrangement one desires, might be interesting... other than just the laborious nature of shooting three shots. I am sure it has been done, but I don't recall seeing such, and it would require some special and expensive filters, especially if you use something as large as 52mm filters. I have of course seen it done with the IR range... Just an idea. Tri Color UV, or TrU Color? ;) Well then, OK, skip the names, but the idea that the lower, middle, and upper bands would all have optimal exposure times for their own sensitivity should produce more presence in a composite mix than seen with a single broadband UV filter shot, as well as great flexibility with color arrangement. The Sparticle shows green, yellow, lavender/blue (basically), but have you ever seen the 340nm green in reflected shots? I don't know, but lets say that the idea produces a stronger 340nm presence... ...and lets say that we apply the three color bands, green, yellow, lavender/blue, in whatever arrangement to RGB. Just imagine the possibilities.

Blum, A.G. 2013. Trifolium arvense L. (Fabaceae). Rabbit-foot Clover. Flowers photographed in ultraviolet, infrared and visible light. Composite multispectral stacks also presented. http://www.ultraviol...ts-foot-clover/ Updated: 10 Jan 2018. Set 2 is in next post. Comment: The soft pink Rabbit's Feet flowers give some roadsides a delightfully furry look when at peak bloom on Mount Desert Island. This species is non-native to the US. Like others in the Trifolium genus, the T. arvense flower is UV-absorbing. Reference: 1. Mittelhauser et al. (2010) Rabbit-foot Clover, page 190. The Plants of Acadia National Park. The U. of Maine Press, Orono, ME. 2. Newcomb, L. (1977) Rabbit-foot Clover, page 60. Newcomb's Wildflower Guide. Little, Brown & Co., New York City, NY.
 Set 1 Southwest Harbor, Maine, USA 20 July 2012 Wildflower Equipment [Nikon D300-broadband + Carl Zeiss 60mm f/4.0 UV-Planar] Visible Light [f/11 for 1/6" @ ISO 200 with onboard Flash and Baader UVIR-Block Filter] Ultraviolet Light [f/11 for 8" @ ISO 200 in Sunlight with Baader UV-Pass Filter] Infrared Light [f/11 for 1/4" @ ISO 200 with onboard Flash and B+W 092 IR-Pass Filter]