BeyondVisible
Nikon SB-140 Clone: Modified Nikon SB-14 Flash for Ultraviolet, Infrared and Luminescence Photography

Shane Elen

Disclaimer: Modifying your flash in this way should be left to qualified professionals as the procedure can be extremely dangerous due to high voltages and the pressurized flashtube possibly resulting in injury, blindness or death so PROCEED AT YOUR OWN RISK.

(Left to right) Dedicated UV Enhanced SB-14 (Stage III), UV Enhanced SB-14 (Stage II - Nikon SB-140 clone) and standard Nikon SB-14

• Simple - Bjørn Rørslett, involves a 10 second modification to an obsolete Nikon SB-14 Speedlight requiring the obsolete (currently difficult to find and outrageously expensive) Nikon SW-5UV filter attachment.
• Mildly difficult - Regit Young, describes the modification of the affordable and available Vivitar 285HV through the removal of the manufacturers UV absorption filter and the grafting on of an affordable UV transmission filter.

I respect the work and acknowledge the wealth of information they have posted on the net as they have made UV photography more possible for amateurs. They were very helpful in providing additional information when I requested it. In addition, I would like to thank Don Klipstein and his website for valuable flashtube information.

There are pros and cons to each of these modifications. The lightweight portable Vivitar 285HV is readily available for a reasonable price. All Vivitar 285HV models have a low 6V signal voltage (pers.comm. Vivitar) and are probably fine for most digital cameras. The xenon flashtube is uncoated and removing the yellow filter enhances the UV output. The SB-14 can be modified several ways. Just adding an SW-5UV filter results in a useable but relatively low UV output due to the yellow coating on the flashtube. The SB-14 is relatively scarce but can be had for around $125 used. It is also heavier than the Vivitar and requires an external battery pack. The UV output of the SB-14 can be boosted by two different methods, one electronic and the other mechanical (authors method illustrated below), both require dismantling the flash unit. Electrical modification to boost the overall flash output, and subsequently UV output, will shorten the flashtube life whereas the mechanical modification could result in a broken tube. If either of these happen you have produced a paperweight as the flashtube is non-replaceable due to obsolescence. Naturally combining electrical and mechanical modifications would be UV advantageous and hopefully this will result in my UV modified SB-14 Stage IV version (currently I am on the Stage III version). When I started this project several years ago I shot the following photos but didn't really envision this webpage or I might have actually broadened my depth of field and got them in focus.

My first attempt, which I refer to as Stage I, is the method proposed by Bjørn Rørslett. It comprises of an SB-14 with an SW-5UV flash adapter fitted to the front. This functions OK but is hindered by the UV absorbant coating on the xenon flashtube. Note that the SW-5UV is precariously mounted in this photo as I accidentally trapped the safety chord beneath the adapter. It could have easily fallen off and broken!

Fig.1. Transmission characteristics of the SB-14 plastic diffuser window.

Fig.2. The SB-14 with an SW-5UV flash adapter mounted.

Fig.3. The Nikon SB-14 plastic diffuser window spectrum overlaid on the Nikon SW-5UV spectrum. It can be seen that there is going to be some UV loss with this combination.

Fig.4. This is the transmission characteristics recorded through the plastic diffuser window and the SW-5UV combined. Now the amount UV loss can be seen.

These spectra represent the transmission of light through these materials recorded with a spectrophotometer and are not the actual spectral light output from the SB-14. They represent the best possible results if the SB-14 flashlamp had a uniform emission of light from 200-1000nm. Real world flash output measurements would not be as good, especially in the case of an unmodified SB-14 flashlamp tube, in which the yellow coating absorbs a considerable amount of the UV. Unfortunately the response time of the spectrophotometer that I have is not fast enough to measure the true flashlamp output but these spectra will indicate the potential of certain filter/window combinations.

My Stage II version required modifying the flash with a non-coated Xenon tube and adding the SW-5UV in front of it. This was accomplished by polishing off the majority of the yellow coating. Although the combination of the SB-14 plastic window and the SW-5UV adapter will exhibit the same transmission potential as shown in fig.4, the actual UV output will be improved (over the unmodified SB-14) due to the removal of the yellow coating on the flashlamp.

While this modification improves the ultraviolet output the gain is not a high as the Stage III modification, however this flash can be used for ultraviolet, infrared and visible work, when fitted with the appropriate flash adapters.

Fig.5. The SB-14 prior to modification. Note the yellow colouration due to the UV absorbant coating on the flash tube.

Fig.6. After modification. Note the absence of the yellow coating on the flashtube.

Having taken care of the UV absorbant coating on the xenon flashtube I thought I was all set until I considered the assumptions I had made for Stage II. I had assumed that the plastic diffuser window on the SB-14 was the same material as the SB-140, and that it would have good UV transmission. Although I have been unable to verify the first assumption I believe that it is the same material, however I was surprised by my findings for the transmission characteristics of this plastic. The plastic does transmit UV down to 250nm but only at 55% transmittance throughout the LWUV region. Adding an SW-5UV in front of this reduces this further to 47%. Hence Stage III, remove the plastic window and replace it with filter material of the same characteristics as the SW-5UV. This should theoretically result in a 90% transmittance for LWUV, doubling the ultraviolet throughput.!! While this appears to result in an increase in infrared output, the ultraviolet output increases proportionally and so the UV : IR ratios are about the same. One other possible consideration before moving onto Stage IV, might be to sandblast the UV window to induce some diffuse characteristics to the UV window but this appears to be unnecessary. Unfortunately, unless the flash is used in a macro setup, the gain accomplished by replacing the plastic window with the UV transmitting glass is offset by the increased spread of light resulting from removal of the focusing element (plastic window).

The advantage of this modification is higher UV output, while the disadvantage is that it can only be used for ultraviolet work - small price to pay.

Fig.7. The SB-14 with a UV window replacing the plastic window in front of the non-coated Xenon flashtube.

Fig.8. Throughput of SB-14 Diffuser Window with an SW-5UV attached compared to the Dedicated UV Enhanced SB-14 in which the Diffuser window is replaced with UV glass. The Dedicated UV Enhanced SB-14 exhibits twice the UV throughput potential.

Still under investigation - electronic modification by either adjusting the flash duration and/or using a bigger capacitor. The downside would be a shortened flash life so maybe I am satisfied with Stage III for now.

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© Shane Elen 2006. Last updated Jan 9th, 2012.