Attempting Infrared Photography.
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What it is.
I’ve been trying a new (new to me) photographic technique recently. It is referred to as infrared photography. Most of the people who end up reading this post will probably know that what we see as white light is actually composed of a number of different colours. You can see those colours every time you see a rainbow.
When you see a rainbow the colours you see go from red at one side, to violet on the other. Beyond red is a part of the visible spectrum (of electromagnetic waves) that our eyes cannot see, called infrared (strongly heated metal, like the heating element of an electric stove produces lots of infrared). For the curious, beyond violet is ultra violet which can cause sunburn and eye damage if you go out into the sun unprotected. But to avoid misunderstanding, the infrared photography I am discussing is not thermal imaging, which is photography or videography of radiated infrared. What I am discussing is reflected infrared light.
It is the reflected infrared light that photographers are usually interested in, either trying to block it out completely or to make use of it to provide some very interesting photographs.
The visible spectrum, what you can see in a rainbow, runs from 400nm to 700nm approximately. If you want the gory details, see here. The part of the infra red spectrum that photographers are interested in runs from beyond 700nm to approximately 1400nm. This is sometimes referred to as near infra red.
Why I want to do IR.
My primary reason is because of the surreal, false colour images you can get with IR. Unfortunately I have not yet been able to produce any false colour image that I like, either I am not finding the right scene to photograph or I am not doing it correctly or I don’t have the right equipment. I have taken the liberty, for demonstration purposes of hunting for an example image and found the image below. It was taken by Talke Photography, who I found on Flickr.
This is a great example of false colour IR photography and has the additional benefit of being copyrighted under a creative commons license which allows me to use it as long as I attribute the photographer. I could not easily find a way to contact the photographer, so I haven’t been able to specifically ask permission, but the license he uses allows me to use the image without specifically seeking permission.
If you would like to see some more examples of false colour IR photographs, the new Google image search works really well.
As you can see, when properly processed, the images have a surreal but dramatic colour that is attention grabbing and very interesting. It is not straightforward to get the picture to this stage because, regardless of which method you use to take the photo, quite a lot of processing is necessary.
As I said before, while I am not getting false colour images to suit my demands, several of the images I have gotten work well in black & white. Characteristic of black & white IR images are supposed to be white foliage, as leaves reflect infrared light, and black water as still water absorbs infrared.
I am not sure though, what is causing my failure to get the false colour images I want. It might be a failure of technique, or I am choosing the wrong scenes to photograph. Or it may be that the filter I have isn’t the correct one.
The electronic sensor in digital cameras is very sensitive to infrared light. In order to prevent this from causing problems with colour rendering (causing the black of some fabrics to render as a purplish/reddish colour, for example) it is necessary to build in front of the sensor a filter to prevent most of the IR light from reaching the sensor.
Over the course of the last few years those filters have gotten stronger and stronger and it now seems like the camera I have is not suited for this particular type of photography as a result of that filter blocking almost all IR light. This is just speculation though, I may be doing it wrong.
Equipment and technique.
If you do not have a camera specifically altered for IR photography (by the removal of the built in filter to block infrared light) you will need a special filter for your lens. I have a Marumi HB700 (because it is the cheapest). This filter blocks visible light to permit only infrared light to reach the sensor. The filter you will hear referred to most often though is the Hoya R72. The Hoya is quite expensive.
As you might infer from the names of the filter IR cut off frequency for the Marumi is 700nm and below and for the Hoya it is 720nm and below. This means that light above ~700nm (699-390nm, which is visible to the naked eye) is mostly blocked.
It is a bit of a kludge (scientific term) because as a result of having a filter in the camera which blocks most of the IR light and a filter in front the lens that blocks most visible light very little light (IR or visible) gets to the sensor and exposure times are fairly long. A tripod is a necessity.
Additionally, to minimize exposure time and the effects of movement in the scene if you are using a filter in front the lens like I am, it is probably best to photograph at midday or the peak of daylight to shorten exposures as much as possible.
Generally speaking, the camera works the same way even if you use a filter. It should automatically set the exposure correctly and also autofocus even though you won’t be able to see through the viewfinder (my comments are specific to digital SLRs). If the camera has a live view feature where it displays the scene on the screen at the back, then it is possible to compose the image even with the filter on.
As the IR filter lets through very little visible light, if you don’t have a live view feature you will be required to compose the picture before attaching the filter.
The other possibility, which is considerably more expensive (unless you are willing to DIY and risk permanently damaging your camera) is to buy a camera with the internal filter already removed, or to send an existing camera to one of the services (here and here) which will perform the necessary surgery. You can also purchase a pre-converted camera sensitive to IR.
The major benefit of these cameras that have the IR cut filter replaced is that you can handhold, see through the lens and switch lenses without worry. Of course, you pay for the privilege.
One last thing that I feel important to mention is the issue of white balance. You cannot judge whether you have the correct white balance merely from the picture as you might in ordinary circumstances. It is necessary to set a custom white balance based on the green of tree leaves or grass, after placing the filter on the lens.
The other aspect of technique involves post processing. Most of the time the image out of the camera is not aesthetically pleasing. It will have a heavy red/magenta cast. I have seen at least one image where the heavy red cast is actually pleasing, but I suspect that most of the time it won’t be. This is where it gets (even more) complicated. To achieve the false colour look of the image at the top (Eiffel Tower) you have to swap the red and blue channels in photoshop or its equivalent.
I don’t want to go into the process of doing this as I am not sure that I can explain it correctly. This is the best guide I have been able to find that outlines the whole process. I believe that the post processing is simple enough to be achieved by someone with moderate expertise handling post processing software.
My experiment with this technique is, of course, nowhere near concluded. When I get the false colour image I have been looking for then I will conclude that I am proficient. Until then I will continue to experiment.
I think my major problem so far has been finding the right scene to photograph and I am now fairly certain that I have the right scene in mind. Unfortunately I have not yet been able to visit the scene as either I don’t have the time when the time is right (midday) or the weather has been cloudy when I need a bright blue sky. Ah well, soon enough I suppose.