Images (c) Dilip Krishnan & Rob Fergus

I was reading through the proceedings of this year’s SIGGRAPH (Special Interest Group on GRAPHics and Interactive Techniques) conference - as I’m sure we have all done at some point in our lives - when I came across a very interesting paper.

The conference generally concerns computer graphics and image analysis however the following title has a very practical application in photography: Dark Flash Photography. No we’re not talking about Joey Lawrence’s promotional images for the film Twilight, but instead a way to take flash photographs without people objecting, or even noticing!

The gist is that you can ‘hide’ the pulse of light outside the visible spectrum thus making it appear as much as 200 times dimmer than a regular flash. This requires an IR enabled camera and suitably modified flashgun. The use of flash for photography can range from an mild annoyance to a dangerous distraction in certain circumstances, which leads to the use of shutter speeds far slower than would be ideal. The dark flash solves this problem but creates a new one.

left to right, IR image, natural light image, combined image, long exposure natural light (for reference)

Capturing light in the IR part of the spectrum doesn’t allow natural looking colours to be recorded. Dilip Krishnan and Rob Fergus solved this problem by taking two exposures, one with the dark flash and one high ISO natural light photo immediately after it. The clever part is that the dark flash image can be used to guide to de-noise the high ISO image far more effectively that any other noise reduction technique. Simply put if you see an edge or spike in the natural light image and there isn’t a corresponding edge in the IR image then the point is probably the result of noise. The actual process is a little more involved, I’d recommend anyone technically minded to have a look at the original paper.

The result is a clean image with natural looking colours. The post processing required is complex, and there times when the approach wont work well if the subject moves between the two exposures (shooting fast paced sports for example). However if you have an IR enabled camera and like black and white images I can see this being a very valuable technique when in many circumstances, and indeed the only real solution to the problem of dazzling people with flash.

MG

I originally got a macro (close up) lens mainly to do jewellery/product shots, I didn’t really intend to do much nature photography with it. A while ago whilst doing some late night internet shopping I had a moth buzzing round the lightshade being a nuisance. I turned the light off hoping it would go away but it just landed on the computer monitor instead. I tried (and failed) to get a shot of it using the monitor as a lightsource (it was too dim). I then decided to have a go with the flash not really knowing what to expect. Considering it was all done with no preparation I was pretty pleased with the result. Here’s the set up if you don’t believe me!

The chance to do some more nature macro photography fell into my lap recently - though I warn you if you are at all afraid of spiders then I strongly suggest you don’t click through to the second part of this post!

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Ok this is the first (and by far the most important) link/piece of advice I can offer for aspiring photographers.

I’ve always hated the look of flash in photos; nuclear white deer in the headlamps subjects in front of an underexposed background. When I started to become serious about photography I did everything I could to make use of available light to take photos including investing in expensive wide aperture lenses and some dicey handheld long exposures. I was totally anti-flash.

I knew that studio photographers used big flash heads all the time but had dismissed this as the preserve of the rich[er than me]. This was until discovering David Hobby’s blog: strobist, which demonstrated what can be accomplished using an inexpensive battery powered flashgun and little bit of brainpower.

This lead me to the following realisation: photography is light. And if you are not doing everything in your power to bend light to your will then you are not realising the full creative potential of a given scene. It doesn’t matter if you don’t have a suite of big mains-powered strobes, the key is to control the light by any means possible, whether it’s changing the colour or firing the flash remotely from an oblique angle or simply bouncing/modifying the onboard flash.

MG