Article

Infrared

September 22, 2022 by David

Until James Clerk Maxwell worked out his famous equations of light in 1865, no one had any inkling that there were invisible wavelengths of light beyond our human perceptions.

Thanks to Maxwell, we now know the electromagnetic spectrum stretches from enormous miles-long radio waves, through microwaves, infrared below the visible light band, to ultra short wave ultraviolet, X-rays and gamma rays above, yet we can only perceive the tiny sliver of the spectrum we call visible light. We were shut off from the full richness of the spectrum until we invented detectors that see where our eyes cannot.

Image source: https://gamma-sci.com/2021/07/02/electromagnetic-spectrum-101-radio-microwave-and-infrared/

One of those detectors is the humble sensor in our cameras. Our cameras are sensitive to near infrared radiation as well as visible light and need IR blocking filters to constrain their response to the visible band.

Image source: http://www.astrosurf.com/luxorion/photo-ir-uv.htm

Fortunately for photographers interested in infrared photography, a number of entrepreneurial souls provide services to remove or replace these filters. I recently had my Fuji X-T1 converted by Alan Burch of Infrared Camera Conversions, based on the Isle of Wight (cost around £300 incl shipping). Alan removed the IR blocking filter and replaced it with a visible light blocking filter below the 720nm wavelength. This conversion makes the camera perfect for B&W infrared photography.

Many companies offer a variety of services, including completely removing the blocking filter and replacing it with plain glass for “full spectrum” conversion, or replacing it filters that block visible light below the 320nm to 830nm wavelengths. The shorter wavelength filters let some visible light in, allowing various flavours of “false colour” photography, while the longer wavelength filters are best for black & white. If you choose full spectrum, you can use external filters on the lens to tune the camera’s sensitivity.

My X-T1 was turned around in a few days seemingly unchanged – until I switched it on and looked through the viewfinder. Instead of the usual colourful view, the EVF now showed a reddish-purple monochrome view – my XT-1 was no longer a colour camera. I set the film simulation to B&W to banish the red colour cast and was ready for test shooting.

In most regards, the camera behaves exactly as it did before. Autofocus is impeccable, exposure works as normal. I do need to keep a close eye on the preview histogram, to make sure the highlights don’t blow – infrared doesn’t seem to have quite the highlight range of the stock camera, but in all other regards it is works as normal.

One thing to watch out for with infrared converted cameras is lens hotspots. Some lenses are prone to create a lighter patch in the centre of the image. This is lens dependent, so test your lenses carefully at different focal lengths and apertures. There are online databases that collect information on lens suitability for infrared but your particular lens may deviate from the reports, so check carefully. If a lens has a problem it will be completely obvious!

Infrared B&W photographs can be beautifully contrasty and punchy and the brilliant thing is that infrared works well at times of the day or in weather where photographers are reluctant to work because of harsh light or unflattering overhead light at noon. An infrared camera provides you with photographic opportunities where and when you would normally put away your camera and catch up on some sleep.

The downside (in my opinion) is that it is easy to get carried away with the most obvious feature of IR B&W (bright white foliage) and end up with a string of photos that are a compositional mess. IR is not an excuse to avoid careful composition and judging tones carefully!

More infrared images in: my galleries

More links

https://gamma-sci.com/2021/07/02/electromagnetic-spectrum-101-radio-microwave-and-infrared/

https://en.wikipedia.org/wiki/James_Clerk_Maxwell

http://www.astrosurf.com/luxorion/photo-ir-uv.htm

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