The Pi NoIR: inexpensive nocturnal wildlife video

A further quick camera-related post. Andrew Back, an enthusiast for open hardware, has been using a Raspberry Pi (the tiny cheap computer) with an unfiltered CMOS imaging chip to shoot night-time wildlife. In this case it's, so far, mostly slugs and bugs caught using time-lapse photography.

See all the gory detail on the Design Spark blog.

30 October: Andrew continues posting his results on the Design Spark blog. Here's a time-lapse movie of the landscape near Hebden Bridge.

Thermal imaging reveals wildlife secrets

The BBC's new natural history series The Great British Year has shown some fascinating, and very artistic, uses of thermal imagery. (Best if you expand the videos ... but sorry they probably won't work outside the UK.)



And there's a movie showing something of the technology.



Shows you don't have to wander the plains of Africa to get exciting thermal footage, and I have to say it's nice to see something more subtle than the usual blue/red heat pattern. Also worth a read (and with the 'usual' colouring in many cases) is a web page on 10 wildlife secrets revealed by thermal cameras ... even a hot plant!

New IR camera is user-configurable

New near-infrared cameras are few and far between and there is an increasing choice of thermal imagers, even if they tend (with a notable exception) to be very expensive. However, cameras working in the gap between the two are much rarer beasts.

Episensors of Bolingbrook, Illinois have announced a new camera working in the short wave infrared (which lies just beyond photographic/near infrared) and which is intriguing, not just because they describe it as 'low cost' (not sure just how low) but also because of its versatility. Here's a paragraph from their press-release.

The infrared camera company Episensors, Inc. recently launched a new type of portable infrared camera called the Night SWEEP-1 (“NS-1”). Infrared cameras can see light that is invisible to the human eye and provide imaging at night and through obscurants like smoke and fog. What sets NS-1 apart is its portability and customizability, which allows scientists, researchers, and others to utilize the camera in the field, without sacrificing the capability of swapping between short-wave, mid-wave and long-wave infrared focal plane arrays, lenses and other components. Based on a patent-pending design, this infrared camera system is fully customizable. The camera can be configured with a pour fill Dewar or a closed cycle Integrated Dewar Cooler Assembly (IDCA) depending on the customer’s preference.

An excellent technical note on their web site explains the wavelength domain this camera covers. It's notable not just because the user can change the imaged band but that the extended SWIR (short-wave-ir) band, between 1 and 3 µm (1000 and 3000 nm) not only has some haze and smoke penetration ability but also contains a sweet spot where there is some smoke penetration but also the radiation goes through glass. Output resolution is 320 by 256 with plans for 640 by 512. The digital resolution is 14 bit and I assume having a supercooled sensor (that Dewar referred to in the note is a thermos flask of something like liquid nitrogen) will give a low noise floor.

So this camera is a kind of infrared SLR and operates between photographic infrared (which ends around 1500 nm) and the thermal bands and operates using reflected radiation (from the sun for example) while thermal imagers show radiation from the objects themselves. I believe this mid-infrared imaging is sometimes referred to as reflectography and has applications in art restoration amongst other things.

Check out the videos on the web site. They look like photographic infrared rather than thermal but you will notice some smoke penetration. It'll come down to particle size and by configuring the camera the user will be able to balance haze and smoke penetration against things like glass transparency. The nearest I've seen to this in other devices is where a single unit combines two different cameras.

Whether we will see the NS1 on this side of the Atlantic is currently debatable as some of the technology is export-restricted.

Michael Nichols lions

I know from the work of Colin Jackson at the BBC Natural History Unit that you get some fascinating shots using infrared cameras with lions at night. You would imagine that National Geographic would also come up with something impressive when covering the same subject.

Michael Nichols spent months photographing lions on the Serengeti and I'll do no more than direct you to a page of his images (some infrared) on the NatGeo web site ... especially a mesmerising shot of a lion called C-Boy. The accompanying piece appeared in the August 2013 edition of the magazine.

I'll be returning to the annals of National Geographic in future posts as they played a significant role in several historic infrared imaging adventures.

DSLR infrared sensor response

Camera manufacturers tend to be coy about releasing the spectral response of their sensors: they're (logically) more concerned about how the camera as a whole performs than how the sensor might deal with infrared (or UV).

A peek behind that curtain has come courtesy of Christian Mauer of the University of Applied Sciences in Cologne. His thesis Measurement of the spectral response of digital cameras with a set of interference filters (January 2009) is interesting in its own right but if you work your way down to Appendix A page 81 (section A.1.7) you will find the spectral response of a Canon EOS 450D without its IR blocking filter. It shows the usual bump in blue response just beyond 650 nm so that the respective responses of the red, green and blue channels at 800 nm are around 20%, 30% and 40% of the peak green response (at 540 nm) respectively. All channels come together at 20% at 850 nm and the response is monochromatic beyond that.

These figures are actually showing the spectral response of the sensor plus its Beyer filtering, since the underlying sensor is monochromatic and should have a smooth response curve peaking at around 600 nm and slowly dying away to over 1000 nm. However, this explains the strange colours when you take infrared images through a 720 nm filter and why ones through an 850 nm or longer filter are colourless.