Ed Thompson Infrared Story

Back in September 2016 I wrote about a colour infrared project by documentary photographer Edward Thompson called The Unseen.

Ed has been building up a YouTube channel called Pictures On My Mind and this includes some explanations of the work he did with some of the last remaining stock of infrared Aerochrome, which was basically the same as infrared Ektachrome EIR.

The latest video outlines at length the shooting he did in Pripyat, Chernobyl, and included in The Unseen. This part of his infrared journey started with finding out that false-colour infrared film was widely used in forestry. The normal red look of healthy foliage would tend towards magenta when the foliage was 'stressed' and it was a good way of determining forest health from a distance.

Alongside the Chernobyl video is another one going into more detail about other parts of the Unseen project, but because it includes some nudes (to demonstrate IR's ability to allow you to see a few millimetres under the skin and to echo demonstration shots published by Kodak) this video is restricted and Ed has had difficuly making the most of his whole channel.

This video passes on a couple of interesting pieces of information about Ed's technique. One is that, certainly until he was totally au fait with the idiosyncratic film, Ed bracketed the shots. I always found this was essential for any infrared film but I have come across photographers who are able to get it spot on without bracketing. The other is that he says in the video that he used a visually-opaque R72 filter to get the very deep reds that he achieved. Usually you'd use a minus-blue filter (yellow) with EIR. Those reds are mind-blowing!

Each section of The Unseen represents different applications of infrared photography with others including art investigation and restoration and medical imaging. (In fact the third edition of the standard text, Photography by Infrared, was written by Lou Gibson, who was a pioneer of medical photography.)

So I can recommend Ed's YouTube channel and especially The Red Forest of Pripyat Chernobyl. Enjoy!

Near infrared optical coherence tomography

I recently had a bit of a false alarm, or a false positive in data terms, with my eyes. A routine eye test threw up a structural condition that could result in glaucoma and so I was sent off to visit a specialist eye clinic. As I said, the problem wasn't actually there, but in the course of the test I came across a use of near-infrared light that was new to me: OCT or Optical Coherence Tomography.

The test experience was somewhat like that slit-scan sequence from the movie 2001, with me seeing moving rectangles and triangles expanding and contracting in my field of view. The result was a cross-sectional view of my retinas looking something like this:

This is an OCT scan of the cross-section of a retina at 800nm with an axial resolution of 3µm. Near infrared will easily penetrate a few millimetres into human tissue and by using a pulsed laser and a lot of computing an image of this type (described as being like 'visual ultrasound') can be built up. If you want to see the techicalities (and some maths) then check out the Wikipedia entry. The particular equipment used for my test was by a company named Optovue.

[Image is copyright: GNU-FDL, origin medOCT-group, Dept of Med. Physics, Med. Univ. Vienna, Austria, 2004 via Wikipedia]

Infrared and tissue penetration

A recent article in New Scientist caught my eye. My drug-filled nanospheres heal at the speed of light reports work by a team led by Professor Adah Almutairi at the University of California, San Diego.

Her work explains that by making use of near infrared's ability to penetrate skin and tissue, it is possible to use a laser of the appropriate wavelength to trigger a polymer nanotube to break down and, if it's carrying a drug, to release it. Since the light can be tightly targeted it would be possible to therefore tightly target a release site for the drug. There are other mechanisms for triggering release, such as the temperature of inflammation or even sunlight on the skin. This latter has the neat prospect of a sunscreen that activates when you get into the sun.

While the NS article is very recent, I found a paper from 2011 by Almutairi's team that explains the concept:

Low Power, Biologically Benign NIR Light Triggers Polymer Disassembly Fomina et al
Macromolecules, 2011, 44 (21), pp 8590–8597

You can see the abstract or buy the paper from ACS Publications.

One interesting thing, for me, is the statement at the top of the abstract that "Near infrared (NIR) irradiation can penetrate up to 10cm deep into tissues". Admittedly, from a photographic point of view you need to remember that the IR has to penetrate the tissue and then get back out again, but I believe the figure of 'a few millimetres' has been a good rule of thumb for years. A figure of between one and two cm has been cited from a paper by Gao et al, In vivo cancer targeting and imaging with semiconductor quantum dots from 2004.

So I decided to see what Lou Gibson had to say on the matter in his third edition of Clark 'Photography by Infrared' in 1978. He quotes Balderry and Ewald, in a 1924 paper called 'Life Energy in Theraputics' as saying that sunlight can penetrate up to 25 cm into the body. So that 10cm seems quite reasonable.

Photographically, however, a near infrared photograph will often show veins under the skin, and will almost always give people a 5-o'clock shadow (even some women). This is also, as I've pointed out before, the cause of the alabaster look you can see in infrared portraits. I'll leave you with this image of Jude (a lady with whom I used to work) demonstrating the infrared look, with the added 'bonus' of 35mm infrared film grain.

Near-infrared used for vein visualisation

There's an interesting use of near-infrared detection combined with a kind of augmented reality in a device being trialled by the Australian Red Cross Blood service. Since near infrared radiation (NIR) penetrates a few millimetres into skin you can often see subcutaneous veins in infrared images because the de-oxygenated blood absorbs light at these wavelengths. This device, made by Christie Medical, takes that a stage further by illuminating the area with NIR and then projecting the resulting image in visible light back onto the skin. It's shown in this video ...



More information in this punning post from the Blood Service.