Playing with infrared light

Word of warning, this post is a bit different from the normal stuff here and is a bit photo techy but hopefully most folk can still get something from it.  

Some weeks ago I had my, somewhat underused, Nikon D7200 converted to Infrared photography for a project I had in mind. Now when I say ‘converted to infrared’, that’s slightly misleading because I has it really has been converted from ‘not infrared’ to ‘everything’.  By which I mean the infrared cut filter that sits on the sensor was replaced with a ‘whole spectrum - astro’ cut nothing bit of optical glass.  That means the cameras CMOS sensor will record everything it’s capable of and that basically means a wide swathe of wavelengths from infrared, through the visible light  spectrum and into ultraviolet.  You can get a number of different replacement sensor filters for infrared photography but this whole spectrum conversion will suit my needs for the original project and can still be used for pure IR, no visible spectrum, work by putting an IR only (e.g. Hoya R72) pass filter onto the lens. Plus, it is still nominally capable of being converted back to a normal visible spectrum camera by putting a UV + IR cut filter back onto the front of the lens.  Though I’ll admit that it is a crazy thing to do to remove the IR & UV cut filter on the sensor only to put another one back onto the front of the lens!  

The original project, which will be done at night with the aid of infrared flashguns for illumination, is a bit on hold due to COVID 19 restrictions but I do hope to get back to it.  However, today I wondered how a whole spectrum camera thing would work during daylight because it’s going to record both visible and infrared.  How’s that going to look?  Well, I gave it a try and here are the results.  

First off, in open sunlight things are not too interesting.  This is a straight out of camera colour image:

OK, so its just a test shot across a wild meadow and looks a bit weird.  Lots of normal visible light colours in there but with strange cast of orange through pinkish red instead of green on the vegetation. That’s the infrared being thrown off the foliage (grass & trees) but largely an effect of the camera’s white balance that is adjusted for IR.  Convert the image to black & white and some of the IR comes through placing a bit more emphasis on the foliage:

This gives us a slightly different IR view that is a little off of what we might expect but it isn’t that unusual.  However it’s different in a much darker woodland setting where the shade reduces the natural visible light.  Additionally, foliage gives off a lot of infrared (visible light is adsorbed, and IR is radiated by the leaves).  Now we get a very different colour image that is heavily red biased - which I find a bit unpleasant but the B&W version sorts that out and becomes much more interesting. Try the two of the nettle patch below. 

Here is ivy growing on a scots pine tree trunk:

A lone (and late blooming) bluebell in the shade: 

And, finally, just walking in the woods in infrared B&W

I think in all the above you can see the difference with the foliage on the B&W images coming through quite dramatically.  I like this effect in B&W but I’m not a fan of the colour images (though the false colour can be improved with post processing).   

All images taken on a whole spectrum converted Nikon D7200 with a 16-80mm f/4 lens (the original colour images are using a custom white balance setting provided by the company that did the conversion - all the normal white balance settings provided with the camera come out very bright red).  There is a fair bit of post processing in Lightroom to convert to B&W but it’s all quite straightforward.