Friday, July 15, 2016

A simple tutorial for reflected UV photography III

Well, I thought it was about time to go over my "cook book style" tutorial on UV photography, which I did quite some time ago. I also wrote about the system lens + filter for UV. But meanwhile (2016) things have changed more, even more research has been done, so I thought it would be time for version III. So here it is, all based on my personal experiences, research and, of course, likes.  [last update: 2016-07]

1) get a suitable lens for UV: I made a comprehensive list of lenses tested good for UV here. The EL-Nikkor enlarger lens 5.6/80mm has proven to not only have the highest UV transmission, but also is virtually free of focus shift. That and all enlarger lenses without focusing ability additionally need a focusing helicoid. Alternatively get the Novoflex Noflexar 3.5/35mm lens which also has a very high UV transmission, is virtually free of focus shift and allows close-up shots up to 1:2 (0.5x) without additional tubes or helicoids. Both lenses are ($)$$, easy to find and may be suitably mounted to achieve infinity focus. If you need a wide angle lens, that's a bit more difficult, but there are some. Still the best and the "industry and scientific standard UV lens" is the discontinued Nikon UV Nikkor 4.5/105mm, or the identical, still available from stock Tochigi Nikon UV 4.5/105mm. Also still available from stock are the JENOPTIK Coastal Optics 4/105mm UV-Micro Apo and 4/60mm UV-VIS-IR Apo Macro (both unfortunately having some issues) but all those four quartz flourite lenses are a quite costly in the higher $$$$ range, are a true investment and only fit Nikon cameras directly, others with easy to find adapters.

2) get a suitable filter: The 2" Baader U-filter still today is the best filter you can get, better than 80% peak and 325...395nm transmission band, IR excellently suppressed below 1.0exp-3, which is important for most DSLRs due to their high IR and low UV sensitivity, especially if your camera has the internal filter removed. Be prepared to expose 8-10 stops more (newer cameras 6-8 stops) than normal. My usual setting on an sunny to overcast day is 2...4" @ f8-11 ISO200 using an older type Nikon D70 or converted D200 but 1/2-1/4" @ f8-11 ISO400 on a converted Panasonic Lumix mft camer. Modern converted cameras have lifeview for UV, which also works considerably well in A-mode and using those purely manual lenses. Best is to have that filter built into a filter slider (astro shops, unfortunately not for lenses with rotating front) or a Nikon AF-1 gel filter holder, which needs a 60mm (male) - 48mm(female) and 48mm (male) - 52mm (female) step ring to mount the filter inside and also allows to mount a 52mm sunshade outside. That contraption allows to flip down the filter, adjust focus, take a VIS shot if needed for comparison studies, flip up and take a UV shot. Magnetic filter holding ring sets are a rather new development, which works rather well and saves quite some time. But also screwing in and out of the UV filter works reasonably well if done with care. Should you have a full spectrum converted camera (with clear filter inside), an external filter which compensates that is needed, so as to be able to shoot normal visible photos with it (as before the conversion). I recommend to use an external 2mm thick SCHOTT BG40 or SCHOTT BG39 or  Schott BG38 (in that sequence of usefulness) for that purpose and adjust white balance accordingly. Some companies offer such "compensating filters", but basically it is just the filter glass I have mentioned. Cheap UV filter glass from China is being curretly offered, it quality is not great and transmission overall not as good as SCHOTT or HOYA glass, personally I stay away from that for now. For beginners SCHOTT UG11 / HOYA U340 in 2mm thickness stacked with SCHOTT BG40 in 2mm works rather well with approx 60% peak transmission @350nm as a cheaper alternative. Remember to demand from any UV transmitting filter a IR suppression of at least OD3, better OD4!

3) get a suitable UV enabled camera: My finding is that today converted mft (micro four third) or Sony NEX cameras are so far the best cameras for UV and allow a plentitude of lenses using suitable cheaply avaulable adapters. Their short register (around 20mm) length allow many lenses which a DSLR cannot use. Still the older type Nikon D70(s) is the best value for money for UV as is the D40, since both work off the shelf unmodified. D80 and D200 work well either, but need the internal filter exchanged against a clear quartz glass filter first (use a professional service for that: maxmax and lifepixel in the US. The Nikon D7000 has turned out to be a very useful camera for UV, but needs a converting company, that can deal with the internal IR leakage caused by Nikon's IR shutter monitor (I have reported about that here in detail). CANON shooters - it does not work well with older Canon DSLRs, their filters and CMOS chips do not allow to record UV in an acceptable manner (see the test I have published here; extremely long exposure, high ISO, noisy results), but the newer types, due to different sensor seem to work quite well - I have no personal experience with that.

4) get a suitable UV light source: the sun is of course the best, but not always available. Xenon flashes come next as they have a very similar spectrum than the sun has. Most need the front filters removed, some even need the golden UV suppressing coating on the Xenon tube partially (leave a bit on the back or it does not ignite anymore!!) polished off (using fine Cerium oxide powder). A well known candidate is the good and cheap Vivitar 285HV flash (use 2 or 3 if needed), as it already has a clear tube and a low trigger voltage which is safe for modern DSLRs. Another one would be the stronger Nikon SB-14 hammer head flash, but here the tube needs polishing for higher UV output. Another alternative are modern UV LEDs, built into LED flashlights, here especially the Nichia 365nm types. These are available nowadays easily (ebay, amazon etc.), so are easy to use and not that expensive anymore, but still ($)$$. Stay away from cheap chinese UV torches, not really worth the money and the claimed tech. data often do not hold. There are also more advanced systems available of course, which even use the most recent 4 dice high power UV LEDs but hose are are quite dangerous to the naked eye and should only be used be experienced users and ALWAYS USE EYE PROTECTING UV GOGGLES when working with those. Ethically I find it unacceptable to use with living beings.

5) get a sturdy tripod: you need usually at least 1/2-1/4" / 2...4" exposure time (depending on camera used) in full sun outside, sometimes even longer, which calls for a sturdy setup on a tripod. UV is strongest 90 degrees to the sun where the sky is the bluest; avoid to shoot in bright midday sun, due to high IR content present (although no longer a big problem with the new Baader 2" U-Filter, but still IR leakage may happen in rare cases). Using Xenon flash brings exposure time down to 1/200, but the flash needs to be strong and quite close to the subject, which is not always doable and with living beings I find it ethically unacceptable. A few flashes wilts a flower quickly, so imagine what it does to an animal or insect eye.

6) get a suitable shooting habit: for comparison shots I shoot visual light first and then switch to UV filter and shoot UV with exactly the same framing. Be careful not to move the camera. Should you be using using an older lens which most likely has focus shift, focus closer. This needs to be tested out, my finding is that the f8...f11 position on the DOF scale works best (similar to an IR mark on some lenses) but could also calibrated for that lens (like a IR mark but for UV). Shoot RAW files or high resolution JPEGs. Pro's do RAW, but for first tests JPEG will do. Set camera white balance to 2500 degrees Kelvin to avoid a blown red channel (Nikon only) or use UNI white balance.

7) get the results processed: Upload pictures to your PC and process them. They will look very red (if using Nikon DSLRs, other DSLRS produce blue or magenta looking results), but what you see is UV, depending on camera (and only if a good UV filter with no IR leakage has been used, like the Baader-U) . Then either you process them to black/white or white balance them. Then adjust to taste. UV has no "color" by definition, so you may set what you prefer. I have been using BibblePro  its "click white" operation and the built in denoisifier. Others are more happy to use Nikon NX-D. Today I use Capture One Pro.

8) get help and discuss results: exchange and discuss your results on one of the few UV forums on the net,, and Quite a bit of my old content resides on the Nikon-only forum

This is in condensed form the result of some years of research and testing and of course only reflects my personal opinion as of 2016 - others may think differently. No warranty given or implied for all being mentioned here and you take full responsibility for all you do with that. If you need some rare equipment, let me know, I may be able to help. I have plenty of filters, lenses etc. available for sale, or may be able to direct to a source. I also do engineering and photographic consultation on a professional basis about any UV related subject.

All my works shown here on my BLOG, my site or my site carry my copyright, so if you like to use any of my graphs or any of my pictures, please do ask me for my explicit permission first.

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site

How to stand out in the crowd - R. Hirta shows its ecologic advantage using intense UV reflection

Today a little different topic: I would like to show, how a flower (R. hirta) achives a competitive edge over other flowers (Monardia, Echinacea) by making use of a specific intense UV reflection around 365nm, matched to the insect eyes sensitivity. This will be shown using a flower originating from the USA Prairie, a Black-eyed Susan - Rudbeckia hirta and it will be done in reflected ultraviolet photography using my "work horse" UV filter, the Baader-U filter aside from a visible light shot. Lens was my UV-Nikkor 105mm quartz flourite lens. Light source was sunlight. All shots were done at f8.

[click on image to see a larger one]

Visible light image (400-750nm):  

Reflected UV image using Baader-U filter (320-395nm):  

Diptych of visible image (left) and reflected UV image (right):  

In visible light, all flowers are rather bright to our human eye. But this R. hirta flower in UV (only visible to bees and butterflies) shows a very prominent and bright bullseye pattern, as its petals are very UV bright (around 365nm) and its center is very UV dark, compared to the rather dull UV reflecting Monardia and Echinacea flowers (around 380nm only), hence creating an impressive competitive edge in terms of chances for getting pollinated - and all this gets nicely visible.

Stay tuned, more will follow on that fascinating subject...

Mexican Zinnia - Zinnia haagenea in reflected ultraviolet photography and simulated butterfly and bee vision XXVI

Today first shots of a very decorative summer flower in 2016, Mexican Zinnia - Zinnia haagenea in reflected ultraviolet photography using my "work horse" UV filter, the Baader-U filter as well as in simulated butterfly and bee vision using my proprietary XBV filters. Lens was my UV-Nikkor 105mm quartz flourite lens. Light source was sunlight. All shots were done at f8.

[click on image to see a larger one]

Human vision:

Ultraviolet (UV):

Simulated butterfly vision:

Simulated bee vision:

Quadriptych (left to right, top to bottom): Human vision, UV, simulated butterfly vision, simulated bee vision:

Mexican Zinnia flowers have a very specific UV pattern. Their petals are very UV dark in the middle and bottom, their petal tips, however, are very UV bright (around 365nm outer tip), and all this gets nicely visible, also in simulated bee and butterfly vision.

I have previously written about those Zinnias HERE

Stay tuned, more will follow on that fascinating subject...