Ultraviolet Light Photography

I'm pleased to introduce another Knowledge Base article. As the title suggests, this on explores the world of UV photography. It's a highly specialised field, and we are fortunate to have amongst us Alex H, who has kindly offered to share his knowledge and experience with us. Thank you very much for the article Alex. Hopefully a few members will be inspired to try something a little different, and see the world through different eyes. Cheers, Frank

Preface

The article below is prepared with users of Minolta and Sony digital SLR cameras in mind, however, the same information can be applied to other camera brands and types. Please also note that everything in this article refers to reflected ultraviolet in the range of approximately between 350 nm and 400 nm. It is not to be confused with the UV-induced fluorescence photography, where the object is exposed to UV radiation and emits light of longer wavelength (usually visible), which are then captured by the imaging device and the ultraviolet is filtered out.

Introduction

Photography in the reflected ultraviolet is uncommon and rather specialized filed, mainly known in science, medicine and forensics. It was pioneered by Prof. R.W.Wood, who in 1903 invented the first UV-pass filter that would block visible light. He was also the first to publish landscape and human pictures taken on film in reflected ultraviolet spectrum. Since then, UV photography found its use in botany, dermatology and forensic applications.


Graffiti in visible (left) and ultraviolet (right)

Many structures and substances reflect ultraviolet light differently than they reflect visible light. Just like when taking pictures in the infrared spectrum, the purpose of UV photography is to get an image of something we can not normally see with our own eyes. Ultraviolet, however, is different from the infrared – even though humans can not normally perceive it, many insects and birds, and even some mammals can see in the near-UV spectrum.


Goldfields

Many flowers show strikingly different patterns when viewed in visible and ultraviolet spectrum – a feature related to pollination by insects. Not surprisingly that the majority of UV-photographs on the web are those of flowers. Photographers using ultraviolet photography for artistic purpose a rare to come by and I personally did not reach that stage yet where one can produce aesthetically pleasing UV-pictures.


Florida hedgenettle flower in visible (left) and ultraviolet (right)

Equipment

Camera:
In the film days things were different. Silver-based emulsions are sensitive to UV in general (hence the need to use UV-cut filters when shooting film), although there are certain films that are especially useful for UV-photography, such as Fujifilm RTP 120 Fujichrome (older version is recommended by B. Rorslett). Any film camera will work when loaded with appropriate film, and equipped with correct lens and filter. It is very different with digital equipment, unfortunately. There are of course specialized cameras designed to record UV-light, but their use is rather restricted to scientific and industrial applications and their prices are beyond reach of most amateurs. Digital cameras available to the public, on the other hand, are not designed to record UV-images. The ability of their CCD and CMOS/NMOS sensors to record ultraviolet light is a lucky byproduct. Unfortunately though, the internal cut filters (ICF) that are placed in front of the sensor to block infrared light (to which sensors are extremely sensitive) are also often very efficient in blocking ultraviolet light as well.


White woolly daisy in visible (left) and ultraviolet (right)

There are very few models of DSLR that can be effectively used for UV-capture without any modifications, as well as several factory-modified cameras sold mostly to forensic investigators, such as Fuji IS Pro and Fuji S3 Pro UVIR. The most commonly used UV-cameras were produced by Nikon. The older models like D70 and D40 had ICF that would pass sufficient amounts of ultraviolet to capture the image. Most of the newer models have very strong UV-blocking ICF that have to be removed and replaced with a suitable UV-pass window made from quartz glass. But the ICF is not the only part of the sensor that can block ultraviolet and influence the resulting image. Anti-aliasing filter, microlenses and colour filters on top of the photodiodes all have a certain impact on the quality of resulting UV image, and those can not be removed and replaced. Therefore, cameras that use the same sensor design (Nikon D80, Sony A100 and Pentax K10D as just one example) can produce somewhat different UV-images.

Out of several Minolta and Sony cameras I tested for UV-photography (KM5D, A100, A290, A500, A55 and A700), all record a UV-image unmodified if the exposure is long enough, but A100 was found to be the best among those I tested. The translucent mirror in A55 is to be blamed for the strange flare and very weak UV-sensitivity of the camera, but I did not dare to remove it. Also, ICF in KM5D has very strong UV-blocking properties, much stronger than that of later (newer) Sony models. Many other cameras, with either CCD or CMOS sensors, can be used for UV even unmodified, but the exposure time under natural lighting conditions such as direct sun are still to long to be practical.



Removing ICF increases the sensitivity of for example A100 to ultraviolet light by 2-3 stops of exposure. However, the camera will require a special filter when used for visible light photography, which has to replicate the properties of the removed ICF. So far I have only tested modified cameras with Sony 10 Mp CCD (used in A100, A200, A230, A300 and A330), 14 Mp CMOS (used in A450, A550, A560 and NEX-3/5) and 16 Mp CMOS (used in NEX-5n, A55 etc) sensors and both perform equally well. Newer CMOS sensors, however, have an advantage of handling high ISO much better comparing to the older CCD sensors, and are therefore my preferred choice for photography under natural light conditions.

Lenses:
The lenses specially designed for UV-photography are usually built using exclusively quartz and fluorite elements instead of optical glass used in construction of regular camera lenses. Such lenses are designed to transmit equally well across a much broader range of wavelength, from below 300 nm and sometimes far beyond 900 nm, while the transmission of regular lenses is optimised only for 400-700 nm range of visible light. The most known example is a long discontinued UV-Nikkor 105 mm F/4.5 lens and its current successor Nikon Rayfact 105 mm F/4.5 PF10545MF-UV lens. Two other currently produced lenses are Coastal Optics UV-VIS 105 mm F/4.0 Apo Macro and UV-VIS-IR 60 mm F/4.0 Apo Macro. Unfortunately, all these lenses are very expensive and designed to be used with F-mount cameras (Nikon and Fujifilm). Other lenses dedicated for UV-photography are very rare and expensive – they were built in small quantities and are more of a collectors items these days.


UV-Daisy

Fortunately, there are other, less expensive options. Many enlarger lenses formerly used for black-and-white printing are designed to pass some ultraviolet light because photographic paper is more sensitive to UV than to visible light. Also, some older lenses with simpler optical design and weaker coatings pass sufficient amount of ultraviolet. All of these non-dedicated lenses have one thing in common – they are not superapochromatic in their design so they will show some focus shift between UV and visible. Sometimes the focus shift is very small and negligible when the lens is stopped down to F8-F11. Dr. K Schmitt recommends to calibrate such lenses for ultraviolet wavelengths, just like many manual focus lenses were calibrated for infrared photography by the manufacturer. All of these lenses are manual focus and often manual aperture, and can be converted to MAF-mount or used with mechanical adapters without compromising their functionality. These are three lenses I personally use extensively and can recommend as a good choice for UV-photography.


UV-Lichens

Novoflex Noflexar 35 mm F/3.5 was found to be good performer for UV-photography by Vivek Iyer. It is an unusual “macro” lens, relatively simple optically, with only four elements in four groups, and a preset aperture. Originally this lens was made for several different camera brands, including F-, M42- and Exacta mounts. Its peculiarity is the focusing mechanism. Besides using normal helicoid, it also works as a variable push-pull extension tube, reaching 1:2 magnification at its maximum extension. Therefore, it is very handy all purpose UV lens, both suitable for general and close-up photography. Its UV transmission is very good, reaching below 350 nm (K. Schmitt). The lens produces nice sharp pictures in UV and has minimal focus shift.


Novoflex Noflexar 35 mm F/3.5 lens

El-Nikkor 80 mm F/5.6 lens is one of the more common and still relatively cheap enlarger lenses. According to the specifications this lens is corrected for 370-700 range. Dr. Klaus Schmitt discovered, however, that this lens transmits much deeper in UV and is a very good performer. It comes in M39 mount and needs focusing helicoid and adapter to be used on a DSLR. It can reach infinity with relatively short focusing helicoid, but I personally mostly use it for close-up and macro. The front filter thread is uncommon, and the simplest way to use this lens is to permanently glue the appropriate step-up ring to it (see picture below). The lens produces nice sharp pictures in UV and has minimal focus shift. Other El-Nikkor lenses can also be used for UV-photography, albeit they show    somewhat weaker UV transmission.


Nikon El-Nikkor 80 mm F/5.6 lens

Steinheil Cassar-S 50 mm F/2.8 lens was also discovered by Dr. Klaus Schmitt. It has three elements in three groups and manual aperture. It comes in M42 mount. Its UV transmission is also very good, reaching below 350 nm. Wide open the lens is somewhat soft and needs to be stopped-down for the best performance. It also displays some focus shift between visible and ultraviolet. However, it is one of the few relatively fast (F/2.8 and faster) lenses available for UV-photography.


Steinheil Cassar-S 50 mm F/2.8 lens

Wide angle lenses are desired by landscape shooters, but their complex design with multiple, often cemented together elements, is responsible for diminished UV transmission and often low contrast. Nonetheless, there are few older wide angle lenses designed for SLR cameras that transmit enough UV to produce sharp and contrasty picture, for example the 21 mm F/4.5 Auto Tamron (in adapt-a-matic mount).


Orange coneflower shot with Auto Tamron 21 mm F/4.5 lens

Other lenses that are suitable for UV but that I have no direct experience with are listed in [URL=http://nikongear.com/live/index.php?/topic/30924-the-uv-sticky-edition-30/" rel="nofollow]UV-Sticky/URL] and are also discussed in details on the pages of Photography of the Invisible World.

Filters:
The most recommended filter for UV is Baader-Planetarium UV-pass filter. Please note that there was an older version of this filter with some infrared leakage, but the recent version is optimized for 320-395nm nm transmission and blocks visible and infrared spectra very well. There are other filters listed in UV-Sticky on Nikongear but they are either discontinued, or not suitable for digital UV photography. Most of the older and generic UV pass filters (like Kodak Wratten 18A) also transmit a lot of infrared light and need to be used with IR-blocking filters to perform properly. Unfortunately, these IR-blocking filters often also attenuate some of UV. Please read this web page for the details.


Viper's-grass

Lighting:
The best source of broadband ultraviolet radiation is the sun. However, when there is not enough sunlight, or in the studio, one needs to use artificial light sources. It is important to remember though that UV light is harmful. Using any artificial UV sources require both eye and skin protection! The continuous light sources for UV are somewhat restricted. Even though there are a lot of UV LED lights advertised online, the majority of cheap ones are too weak for photography. The best ones are high power UV LED based on Nichia chips that emit around 365 nm. Besides the cost, the other disadvantage of UV LEDs is that they produce a relatively narrow band of light resulting in mostly monochromatic images. The broad-spectrum flashes are thus much more useful for illumination of the subject, while UV LEDs can be used to provide light for focusing if the camera has main-sensor live view.


UV-Birches

The photographic flash/strobe produces a broad spectrum output, but most of the UV and IR is normally filtered out either by the coating on the flash bulb or by special filters mounted in front of it. Therefore, any strobe that can use uncoated bulbs can be used for UV illumination. Hand and shoe-mount flashes, on the other hand, often need to be modified. The only dedicated UV flash I know about was made by Nikon (SB-140). Most commonly recommended for modification are Vivitar 283 (NOT to be directly connected to digital cameras without special adapter!), Vivitar 285 (NOT to be directly connected to digital cameras without special adapter!), Vivitar 285HV ("digitally safe"), Metz 45CT and 60CT series (older versions of these flashes have high sync. voltage and SHOULD NOT to be directly connected to digital cameras without special adapter!). I use two Vivitar 285HV modified according to these instructions by Shane Elen. It should be noted that plastic yellow filter and fresnel lens of 285HV do block UV and the best results are only obtained when both are removed and replaced with quartz or borofloat glass (for safety reasons).


UV-Forest

Other Tips

Shooting with long exposures requires ultimate stability, so the heavy tripod and head, and remote shutter release are essential. Macro rails will aid in precise focusing, while the optical viewfinder of conventional DSLRs needs to be closed during exposure to prevent light from leaking through it. Also, some of the lens adapters may leak light through the lens lock, spoiling the image, so they should be tested beforehand.


Sony A100 with El-Nikkor 80 mm F/5.6 lens mounted on focusing helicoid

The importance of correct white balance.

Most of the cameras will produce very red or purple pictures when used with Auto white balance. To produce more pleasing and “uv-correct” results the camera white balance needs to be pre-set using UV-white or UV-grey target. The most accessible and affordable UV-white target is pure PTFE (Teflon), which properties were also discovered by Dr. Klaus Schmitt. Even then, images will often require additional tweaking of white balance in post processing, but the properly set camera will make it easier to set proper exposure and also pre-visualise the image. Of course, since we are already dealing with false colours, every photographer is free to manipulate the image to their liking until they are happy with the result. There are no artificial colour boundaries in the invisible spectrum.


Same picture with “Auto” white balance (left) and after setting the white balance with UV-neutral target (right)

Sources of additional information.

The best sources of information on UV-photography are:
1) The discussion forum and the UV-Sticky on Nikongear. This is the fullest and most up to date resource with many links to other sources, especially in the Sticky. The discussion board itself requires subscription.
2) Bjorn Rorslett's All You Ever Wanted to Know About Digital UV and IR Photography, But Could Not Afford to Ask.
3) Klaus Schmitt's Photography of the Invisible World.
4) Some of the UV-pictures, tests and DIY solutions can also be seen on my personal blog.


UV-Dandelion



Edited by Maffe - 28 September 2012 at 19:23

Thanks Alex H, a very clearly written and illustrated contribution

fem2008 wrote: There a small typo: I think you meant to say Newer here instead of Never? "Never CMOS sensors, however, have an advantage of handling high ISO..."

Typo corrected, thanks!
And btw, the kudos for this article should better go to Dyxum member Alex H than the mod, who just posted it in here

Edited by Micholand - 19 November 2011 at 08:29

Really beautiful!

Just found this thread. Amazing shots!

I don't suppose anyone has sample UV pictures that were taken with an A55? I'm curious to see exactly how much of an effect the translucent mirror has on the images. I ask because I think there could be some advantages of converting an A55 or A33 to shoot UV + IR + full spectrum, etc. using on-lens filters.

translucent mirror in A55 is to be blamed for the strange flare and very weak UV-sensitivity of the camera, but I did not dare to remove it.

Thanks!

Thank you for the article. It reminds me I have still had a UV filter B+W UV403 and MF lens Helios MF 55 mm/f2.

These are my old results with Sony a700, I have to try it again.

1.


2.


3.


4.

Aldaer, those are very good, actually, for the first try!

thank you, Alex H.