Black light experiments

So when a client, and it has to be said, on a somewhat dodgy phone line said we want you to film some dancers in back light I thought ‘well I can do that, not too tricky’. I was just filming a spot for BBC World wide to promote Bake Off which was a heavily back lit promo, as you can see from the picture, so was smugly confident.

Behind the scenes on a trail for Bake off
Behind the scenes on a trail for Bake off

It was only a day or two later that I had another call and realised my school boy error of not listening properly – it was actually black light, or UV as it is more frequently referred to. This was not something that I had an enormous amount of experience in and was further complicated by the fact that it had a very short run time, was to be delivered in a VR environment at 360 and, as the producer said ‘did I mention we are shooting in Russia?’ I have been sworn to secrecy and therefore can’t talk about the client, dance troop or subject but if you’re interested I can talk about the tecce bits. We shot on the RED Dragon as with 360 you really have to shoot in a minimum of 4K and used stills lenses so that we had coverage across the large Dragon sensor. There was no focus pulling so these lenses worked well. We tested a range of focal lengths. With 360 you normally use a fisheye and an absolute minimum of 5 cameras but as this was essentially a stage show which was to be keyed into a Virtual Reality environment we thought that it might read better it we shot the scene ‘flatter’. The fisheye lenses did not really work well for this shoot as it meant being very close to the show and the perspective felt ‘wrong’ even after flattening the image. We ended up using a Nikkor 24mm for the overall performance and swinging onto a 50mm for some elements which seemed to give us the best overall coverage. The real lessons for me came in gaining a better understanding of how the reflected black light, or UV light, reads on the digital sensor. The low cut filter already on the RED Dragon was pretty good, in fact, compared to the old RED ONE it was amazing but just to be sure we also added a Tiffen 4×4 UV filter. The idea is that you need to completely cut any sensitivity to the physical UV light (frequencies below about 400nm) and so all you record is the reflected light which is within our visual register.

We had one day of testing before heading to Russia and this is what we discovered, UV light that reads as blue will never get above about 15% on the waveform. All that happens is that you start losing detail but the level remains stubbornly low. I had expected it to be low as it is essentially only one channel but was worried by exactly how low it was. I tried chucking more light at it but although this made a difference visually, ie some of the detail just started burning, the levels just stayed low. Other colours that combined different channels gave a higher turnout on the waveform but still was visually burning out at 35%. Here’s a picture of the monitor screen that shows the waveform and the visual appearance of the dancers.

The shirts are burning but the waveform shows very low levels
The shirts are burning but the waveform shows very low levels

We used 40W florescent tubes for the bulk of the lighting that was floor mounted. To try and spread the light from above we had a 400w UV softlight. This filled in the shadows above but did little else. I’m pleased to say that the film has now gone through post and the everyone is very happy. There certainly was an element of me that was still convinced that these levels would cause problems with the post process but much to my relief it was unfounded. As I’ve always said, one of the things that I love about this job is that there are always new things to learn and puzzles to solve, long may it continue!

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