UV–A, UV–B, UV–C:

Ultraviolet equipment (lenses, filters, sources) are designed and employed for different purposes, and this is largely dependent on their operating wavelengths within the UV range. Wavelengths are measured in nanometers (one billionth of a meter), with the UV spectrum generally falling between 10 and 400 nanometers (nm). The portions of the UV spectrum the concern our applications with the Nikon UV-105 lens are these three categories: UV-A, UV-B, and UV-C.

Ultraviolet Spectrum Sectors The UV-105 Can Work With * the UV-105 can transmit UV effectively down to 220 nm, most but not all of the UV-C.

Band Wavelength range (nanometers) Name Typical Applications UV-A 400 nm - 315 nm Long Wave Black Lights, concerts, entertainment UV-B 315 nm - 280 nm Medium Wave forensics, medical applications, reptile heat lamps UV-C 280 nm - 200 nm* Short Wave germicidal (253.7nm), sterilization

The long wave UV–A and medium wave UV–B are the types of naturally occurring ultraviolet energy that can be encountered on Earth. The UV–C is encountered only when generated by artificial sources.

• UV–A is associated with aging of the skin by unprotected exposure to sunlight. When the skin cells’ DNA is damaged by UV radiation then Apoptosis (Type I cell death) is triggered and the skin is replaced; malignant melanoma may occur as a result of indirect DNA damage when the damage is not properly repaired. Proper repair occurs in the majority of DNA damage therefore not every exposure to UV results in cancer. While Earth’s atmosphere provides some protection the exposure to both UV–A and UV–B increases by ten percent (10%) for every 1,000 feet rise in elevation. Residents of those areas of Earth where ozone has been depleted suffer from greater exposure hence a higher percentage of skin and eye damage including cancers.

  The Black Light and the Wood’s Lamp are among the more common manmade sources of UV–A, these are used for hobby and entertainment effects with most sources peaking anywhere between 370 to 450 nm. All reptile lamps emit UV–A while some lamps may emit a moderate amount of UV–B too; these are used in terrariums to maintain pet health. While the human eye can not see most of the radiation emitted by a Black Light certain colors and pigments absorb the invisible light then discharge it appearing as a glowing effect. The eerie appearance of posters when observed under UV are one example of this effect. Detergents may contain as much nine percent (9%) phosphorus content, the phosphors absorb UV radiation then expels them as light so that white fabrics shine brilliantly under a Black Light.

• Medium wave UV-B is a higher energy electromagnetic radiation than UV-A hence it can penetrate deeper into the human skin. This increases the likelihood of skin cell DNA absorbing this energy and being modified or destroyed, because of this the letter "B" in UV-B has been associated with "burn" as in sunburn. The ozone layer of Earth’s atmosphere attenuates UV-B however, the amount of UV-B that penetrates the atmosphere to ground level at the equator has historically been about 1,000 times greater than that at the poles. But every one percent (1%) decrease of the ozone layer in the atmosphere results in a two percent (2%) increase in UV-B exposure and a four to six percent (4-6%) increase in carcinoma. Additionally, a correlation between incidence of squamous cell carcinoma of the eyes conjunctiva and exposure to UV–B ultraviolet light has been noted; this can be a local disease process or metastasize to become fatal.

  There are Black Light sources employing MgSrAl10O17, Ce phosphors that emit as low as 310 nm peak. Medium wave UV-B sources cause certain bodily fluids to luminesce, so crime scene investigators and forensic laboratories employ these to detect blood, saliva, semen, and other fluids. Medium wave Black Lights are also used to detect anti-counterfeit markers in currency and have many other security applications including screening for counterfeit currency.

• Most of the natural short wave UV–C radiation emitted by the Sun is absorbed in the Earth’s atmosphere so most human exposure to UV–C will originate in artificial sources including Low-Pressure Mercury Arc Lamps. Short wave ultraviolet radiation can also cause sunburn. Short wave ultraviolet is almost completely stopped by most forms of glass or plastic, so quartz (fused silica) or special glasses must be used in the manufacture of short wave light tubes so that the short wave UV–C radiation can pass out of the tube. Short wave ultraviolet is the most popular illumination source for observing mineral fluorescence and phosphorescence producing this in perhaps ninety percent (90%) of fluorescing minerals.

  A short wave UV–C sterilizing tube lamps emits radiation that is destructive enough to purify water of living contaminants and to sterilize medical equipment. It has a variety of industrial uses and is considered "germicidal."

Sources Light sources that produce UV in quantities to be useful for imaging include: flash, incandescent, fluorescent, or LED's where there are now DUV–LED's made for work down to about 240nm. The best choice of source will depend on the intended application (UV–A, UV–B, UV–C), and whether or not the subject could be altered or damaged by energy radiating from some sources. It is not a simple matter to adapt conventional light sources for use in the UV since commercial lights usually do not emit sufficient UV to provide good results through a UV transmission filter but we do offer specialized portable, handheld or tabletop, and larger installable UV lamps including high-power UV Grid models made by UVP for example.

UVP UV-C lamp shown lighting a mineral sample.	Woods Lamp 365nm UV fluorescent 'Black Light', above and below. Typically used for magnified medical exams.	Nikon SB-140 Flash filter not shown	Hammamatsu Xenon or Deuterium lamp bulbs	Hammamatsu UV LED with Controller

Above: examples of common commercial UV sources (20,556, 39,782, 8,118, 10,722 then 58,009 bytes).
Click on images of UVP, Woods Lamp, and Hammamatsu items to see enlarged views (96,926, 103,757, 278,768 and 189,873 bytes).

The lighting sources for field photography or forensics applications should be portable and able to run off of batteries, or the lighting may be AC powered. To freeze the moment and to minimize exposure time of the target to UV sources we prefer the flash unit, though the best rarely go lower than 300nm depending on the supplied UV filter element. There are light systems made specifically for UV that incorporate excitation filtering; you will find information about suppliers for minerals studies, etc. on the Internet. A shade or reflector should be used to better direct the light onto a target and eliminate stray UV light.

Of course safety gear (goggles, etc.) will also be associated with the use of most light sources. So you may want to organized a 'UV Kit' and keep it cased and ready to go.

Techniques in order to obtain the best results when working in the UV one should first understand:

Induced Light Emission: when materials are exposed to ultraviolet radiation then that target may luminesce, emitting radiation at longer wavelengths. Some of this can be seen with the naked eye (visible spectrum) or may extend into the infrared. There are two types of luminescence:
• Fluorescence a form of luminescence where the emission of longer wavelengths ceases almost immediately after the excitation source of UV is discontinued.

• Phosphorescence a form of luminescence where the substance will continue to emit (luminesce) for some time after the removal of the excitation source of UV.

Induced Light: this techniques is commonly used for studies of visible or IR fluorescence or phosphorescence and relies on two filters: excitation and blocking filters*. This requires the target be illuminated by a light source that incorporates an excitation filter so that it emits UV light but no infrared or visible. For example this may be a Kodak Wratten 18A filter that appears black and opaque to the naked eye. The camera (or sensor) that is focused onto the object of the study will incorporate a lens that has the capability to pass UV light. The lens will have a filter (Kodak Wratten 2A for example) that blocks UV light but will pass visible fluorescence. So when the target is excited by the light source then the visible or IR fluorescence or phosphorescence will be seen, and the image can be recorded by film or modern digital cameras.

* The same filter might be used as either an exciter or as a blocking depending on it’s placement within the system. For example the Kodak Wratten 18A when attached over a flash becomes an excitation filter, or when over the camera lens then functions as a blocking filter.

When working in the UV then the best results will be obtained when working in a dark room, an environment where any source of light in the visible or IR can be shielded or turned off just prior to taking the exposure.

Filters Filters are used to block portions of the spectrum that we do not wish to use, so keep in mind that filters take away but can not add anything.

The UV Transmission Filter that was formerly made by Nikon and provided with the original UV-Nikkor lens (below) is satisfactory for most applications however, this filter has been discontinued. However, over the recent years newer technology filters have been devised that not only block visible light but also block infrared leakage. Among the newer filters recommended by and sold by Company Seven are:

• Baader Planetarium U-Filter (shown at right), sometimes referred to as the 'UV' or 'Venus Filter' this is suitable for work in the UV-A. The BPU2 filter is a ultraviolet (UV-A) bandpass filter made so that only light in the 320 to 390 nm portions of the spectrum are transmitted; it will effectively block all else spanning 200nm to 1120nm. This U-Filter transmission peaks with 85% transmission at 350nm with a 70nm bandwidth, and with a 5 stop reduction in the IR portion of the spectrum.

  This filter is offered only in 2 inch filter thread, so to adapt the U-Filter onto the UV-105 lens we recommend you also order Company Seven’s custom machined Mark 1 adaptor ring. Note there is no vignetting since the diameter of the front lens element is far smaller than the diameter of the U-Filter; you can see this in the images and optical profile drawings above. The filter can be accommodated by most of our systems too.

The Baader U-Filter are visually opaque filters, these reject visible light and most infrared too. As typically employed the UV Transmitting Filter is installed into a filter holder (or cell), then this assembly is attached to the front hinged flap of a camera lens or in-line with our microscopes. To focus visually one slides the filter out of the way, then once focus is achieved the filter element is moved over the lens to block the visible and most IR light. For infrared photography a suitable optional filter (R60 for example) would be used in place of the UV transmitting filter. Of course if one is imaging in real time with a CCD system that displays an image on a screen then one could focus by that aid.

Film, or CCD, or ? Cameras:

Our Nikon 105mm UV lens is suitable for imaging with film or with suitable CCD detectors, or it may be incorporated into a specialized instrument (Radiometer, etc.). Any consumer film or digital camera and film can pick up visible fluorescence, phosphorescence, and tenebrescence. Most film cameras could do well when working into the UV when using specialized films, most notably Eastman Kodak 103-0, but many people have obtained results with artistic and or scientific value using certain conventional black and white films too. Unfortunately, the availability and variety of films is fast diminishing as the photographic industry transitions from film to digital cameras. Of course the digital cameras provide the user with 'instant gratification'; the capability to see their results immediately and not have to pay for and wait for developing.

Ilford HP5 Plus Film black & white print emulsion.	Fujifilm RPT 135 Film tungsten color slide emulsion.	Kodak KAI series Charge Coupled Device (CCD)

Above: some of the films and an example of a CCD detector for UV work (183,056, 168,442, 140,981 bytes).
Click on images to see enlarged views (218,292, 260,322 and 300,006 bytes).

The earlier generations of DSLR cameras (including the Nikon D1, D2, D70, D200) employ a charge coupled device (CCD). Depending on the camera model a CCD based DSLR may have enough sensitivity around and below 400nm to be useful in areas beyond fluorescence in the visual spectrum.

The only company that marketed production DSLR's engineered specifically for work from the UV and into the IR was Fujifilm who in August 2006 introduced the FinePix S3 Pro UVIR and later the FinePix IS Pro, DSLR cameras with factory engineered modifications of hardware and firmware geared especially for law enforcement and scientific applications. These were the world's first production DSLR cameras capable of taking photographs, depending on the lens and filter attached, in the ultraviolet, or visible, or infrared light portions of the spectrum spanning from 350nm (380nm for the IS Pro) to 1 micron.

Right: The Fujifilm IS Pro may be the last 'production' digital DSLR optimized for UV/IR applications.
Shown at Company Seven with our optional Nikon UV-105 F4.5 lens and battery pack (46,598 bytes).
Click on image to see enlarged view (301,963 bytes).

Among the most noteworthy features of these UVIR cameras are their compatibility with most Nikon F mount autofocus or manual lenses as are modern Nikon DSLR's, including the UV-Nikkor and Nikon UV-105 lenses. The S3 Pro UVIR and IS Pro have since been discontinued.

Just as the CCD based systems grew in pixels to cross the ten megapixel threshold thereby becoming truly attractive for the masses, the DSLR makers transitioned to the complementary metal-oxide-semiconductor (CMOS). The recently developed CMOS requires less power than the CCD hence longer battery life. Unfortunately, the CCD cameras are more sensitive to UV than most current CMOS as these arrays have been engineered to reduce their sensitivity to violet. The changes of sensitivity for the CMOS came about in part so that the detector will be less sensitive to false color (chromatism) that may originate from simpler lenses that will tend to show violet halos surrounding contrasting features; why make the lenses better (and more costly) when the detector can be made to not see some of the problems? While some CCD based cameras have been shown to capture UV down to below 365nm, most drop off approaching 400nm or just below that. The CMOS based Nikon D700 for example incorporates UV cut filters so that light at about 420nm and below is not registered by the CMOS. By 2011 almost every new DSLR in production incorporates either a window (on CCD) or CMOS sensor made to effectively block UV starting at about 420nm and below. So there are few suitable consumer digital cameras to be found new or used that can record the ultraviolet spectrum therefore, there is no practical reason for most mere mortals to pay any premium for these esoteric UV-capable lenses.

As further evidence of the above statement consider the Nikon L37c filters that were in production until the DSLR's came to dominate the camera market. The L37c filter absorbs ultraviolet wavelengths below about 370 nanometers thereby preventing 'blue blur' of the image mostly caused by atmospheric haze, hence the designation 'L37'. The 'c' suffix indicates the front and rear of the filter has NIC antireflection coatings (the same multi-coatings as on Nikon lenses) to prevent causing reflections or ghost images. So well has the ultraviolet been blocked by modern digital cameras that Nikon no longer offers the L37c filters, instead they now offer multicoated Nikon 'Neutral Color' filter that is similar in it’sprotective aspects to the L37c type of filter but the NC filter does not cut out longer ultraviolet wavelengths.

For our industrial and research clientele Company Seven and other companies too do offer digital cameras made specifically for work into the UV. These tend to be monochromatic cameras with comparatively small detector arrays than those found in most consumer DSLR cameras. These UV-capable cameras can usually be provided with a threaded lens mount or a bayonet that will accept most popular formats including the Nikon F-Mount.

Left: one of our megapixel CCD cameras incorporating a 2/3 inch diagonal format detector, shown alongside Quarter coin for scale (31,561 bytes).
Click on image to see enlarged view (205,738 bytes).

However, the immediate future does not look good for the hobbyist who seeks to explore UV digital imaging; they will be left searching out used DSLR CCD-based cameras or old stocks of suitable film.

Please contact Company Seven for advice that may be more specific to your requirements.

Nikon 105 UV Lens Development And Marketing:

as explained in our discussion of Nikon history, the 1970’s and 1980’s were amazing decades for optical developments. Most of the innovations in camera lens technology over this period could be attributed to improved performance of computers used to model the optical designs, computer assisted manufacturing machines, and to the advanced glass types developed and with consistently higher purity (homogeneity, etc.) that would permit engineers to push the boundaries of lens tech.

Right: UV-Micro-NIKKOR 105mm lens prototype, Serial No. 252208. Shown about life size (68.5mm / 2-11/16 inch diameter). Image size 77,272 bytes.

The team at Nikon that developed what would initially be known as the UV-Micro-Nikkor 105mm f/4.5 lens was led by Wakamiya Takakazu, he was assigned to the Optical Section 1, Optical System Department. The UV-Micro-Nikkor 105mm f/4.5 was not the first UV lens to be made by Nikon, before it were the 55mm f/4 UV Nikkor Auto lens (closely resembling the 55mm f/3.5 Micro) introduced in 1965, that would be followed by other 50mm to 55mm UV lens models. Some twenty years after their original UV lens was introduced, the UV-Micro-Nikkor would be developed. The prototype lens is S/N 252208, designated “105mm f/4.5 UV-Micro”, and this was completed early in 1984. This prototype was based on a modified production Nikon 105mm f/4 Micro Ai-S lens, a five element design in three groups that later was refined into a six element arrangement. The changes to make the 105mm a UV-Nikkor were radical including an optical arrangement that in no way resembled the original conventional Micro lens furthermore, all six lens elements of the UV-Nikkor final design are made of very costly synthetic materials. Finally the conventional multilayer antireflection coatings would inhibit the UV transmission, and so several of the six air-spaced components are coated with a synthetic material to reduce reflections; the resulting overall transmission is approximately 70%.

The first production model was designated “UV-Micro-Nikkor 105mm f4.5”, this was announced in April 1985. These could be ordered in most Nikon markets, including in the United States through Nikon Inc. but only by special order as Product No. 1453 NAS. The UV-Nikkor 105mm f/4.5 lens bears the international Nikon Product Code JAA62001: