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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The above image was shot during a talk I gave to the University of York photographic society (thanks to Jens for letting me volunteer him for this demo). The topic was light, more specifically how nothing to do with light (and therefore colour) is absolute - it’s all relative.

The rim light coming in from the right has a strong yellow coloured gel in front of it but what if you don’t happen to have a yellow gel handy? Well all is not lost, provided you have a blue gel. By putting a blue gel on main light, the rim light - despite being white* - is yellower than the main light:

White balance is the process of picking an arbitrary point on the spectrum and declaring it to be “white” (something our eyes do without us realising). By choosing the white balance in order to make the blue light white, the colours shift accordingly and we end up with this:

which is surprisingly like the first shot (especially since I grabbed a yellow and blue gel that looked about right, without actually testing!)

Ok, so this isn’t the most useful technique in the world, after all if you one colour gel you’re likely to have others as well! But what about if you can’t gel one of your lightsources, what if one of your lightsources is the sky?

MG

_{*as in the colour of daylight. Residents of another planet would probably have flashes which produce a different colour light as “white”.}

This headshot of Oliver, editor of law journal Ebor Lex, done in a standard meeting room in a very short timescale. I thought it would be an interesting subject for a “stream of consciousness” post showing every shot that was taken during set-up and and trying to explain what was going through my head at the time. This is not supposed to be a perfect example of how it should be done, merely a record of how it was done.

It’s important to have some idea what you’re trying to achieve before you start so I decided I wanted something edgy, like this shot but with a more traditional background. That look was achieved by having a pair of softboxes very close to the subject, angled slightly toward the camera so I started off with the lights in that position.

No light meters no modelling lamps, what follows is exactly what I saw on the back of the camera at each stage…

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I was going to call this post something like “and ace up your sleeve” but yeah, it’s a shot involving cards that I thought would make a good behind the scenes post.

Lighting plays a key role in determining the mood of a photo such as this so that’s the first thing to sort out before the shoot begins.

To give a contrasty yet flattering look I decided to go for a strong directional yet soft light for the model. The background was hit with a spotlight on the curtain - to compliment the theatrical setting. Read the full post for more details setting up lighting in two planes:

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