Second in a series about Infrared Photography
The first post is: About Infrared Photography
So now you know what Infrared Photography is, and what it’s good for. How do we do it??
History – Infrared is So Much Easier Now
Before digital cameras we had to use special infrared film. This was nasty stuff. Expensive, hard to use, very grainy and you had to load it in the dark! Worse still, to get the full IR effect, you had to cover the lens with a black filter. (*) So with an SLR you couldn’t aim! You had to experiment with the focus, which meant waiting for developing. That was black and white. Color was even more expensive and tricky.
That was then. Now, digital cameras make it much easier. Camera sensors are inherently very sensitive to near infrared. Except for one big problem. In order to get a realistic color picture, the digital camera has to mimic the sensitivity of our eyes, which means they have a filter that cuts out the infrared. So the camera can no longer see IR. (** See below)
Modify (Ruin?) Your Camera
The filter that cuts out the IR can be removed! This is operation is not for the faint of heart. I have done it a few times, sometimes successfully! There are vendors who will do it for you. For example, www.lifepixel.com. Or, you can find instructions on how to convert certain cameras to IR. Try Googling “IR conversion” and your camera’s name. Or find some instructions and buy the appropriate camera used.
You (or a tech) replace the IR blocking filter with a filter that lets IR pass through. Choose a filter that cuts out all visible light (it looks black), or one that passes red along with IR. You can buy various IR filters; a popular one is called IR-720, from several makers. Ordinary Red filters, including #25 and #29, let IR through as well as red light. You can buy filters of the right size and shape from lifepixel. Since I am cheap, I cut them out of a standard round filter that I already had, using a diamond bit on a Dremel tool.
I prepared one camera with a red #25 filter (which passes IR), and one with a black IR-only filter.
Here is a picture from each, normal color, IR only black and white, red+IR right from the camera, and one I’ll explain soon.
The IR-only camera gives black and white images. I love the dramatic look of IR black and white.
But I often prefer the red+IR camera because it gives me IR images in color.
Color infrared? In order to make normal color images, digital sensors have an array of tiny color filters right on the sensing layer. These are the 3 primary colors of photography, red, green, blue. You can’t remove this filter. It turns out, luckily, that the blue and green filters allow infrared to pass just fine. So the camera with the red filter records red as red, and IR as blue/green or cyan. Real blue and green do not show up.
As you can see, straight from the camera, my infrared color images look pretty ugly. Foliage is bright blue-green. The sky is dark red or pink. Stones and concrete are gray. Clouds are white or pink. In post processing, if I swap red for blue and keep green green, I get a very deep blue sky, and foliage that is yellow, red, or bright green. Here are more examples.
Replacing the IR cut filter in a digital camera of course voids the warranty, so waiting for it to run out makes sense. This is an excellent use of an old obsolete camera. Now that cameras have mated with computers, their digital camera offspring become obsolete almost as fast as computers do. You don’t need the latest high performance camera for Infrared anyway, because you won’t be able to take advantage of the latest automation and other capabilities. I use two Nikon D50’s.
After you replace your older camera’s IR cut filter, there is still more to getting good infrared pictures.
Camera lenses are not normally designed for infrared, but some can work in IR. If you have ever looked through an old fashioned magnifying glass, you may have noticed that a simple lens like that makes red, blue, or purple color fringes around bright things. It focuses light of varying colors differently. It’s called chromatic aberration. Camera lens designers use multiple pieces of glass working together to avoid this problem. They also use special glass coatings to avoid reflections.
But the designers don’t care about infrared. (***) So most camera lenses make a blurry IR image, possibly with color fringes. And the anti-reflection coatings sometimes don’t work at all in IR.
To get a good IR image with my obsolete, IR converted DSLR I do the following.
Choose the right lens
Lenses range from very good to useless in IR. Old ones seem to work best. I list the lenses that I use below. If you search the Internet for which lenses work best in IR, you find much talk about “hot spots”, that make lenses bad choices for IR. A hot spot is a big spot where the image is brighter. Lenses also have different amounts of aberrations in IR and different focus shifts. It really is hit or miss.
I also find that many lenses actually block most of the IR. I have one that blocks all of it! I think it’s the coatings. I found no mention of this in my Googling. Modern complex multicoated lenses are most likely to block IR. Old, manual focus, non-zoom lenses work better. These are what I use, both from approximately 1970:
Nikkor 28mm f3.5 Nikkor 50mm f2
They are both excellent IR lenses if you stop down to f 8 or f 11. They have old style single layer coatings. I’m looking for a good IR telephoto lens, but haven’t found one yet. The Nikkor 55mm f2.8 micro (macro) is a great lens free of aberrations, with very small focus shift, but it blocks too much IR to be useful in IR.
Use a small f-stop
Practically all lens aberrations (imperfections) improve if you close the lens down. This is important because lenses have worse aberrations in IR than visible light. I use f8 or f11 whenever possible. I can’t get a satisfactory image at f4 or wider.
Use a lens hood
This is especially important since the anti-reflection coatings don’t work well for IR light. Also avoid putting the sun in the picture.
Autofocus may not work; I don’t use it. Most modern autofocus lenses are not good for IR anyway. I use old manual focus lenses and adjust the focus myself. This is very easy in landscape and aerial photography because everything is at infinity, so Autofocus is not needed.
Old manual lenses often had an IR focusing mark. You were supposed to focus by eye, and then shift the focus ring over to the IR mark, when using IR film. I use the same method, but I had to make my own IR marks based on experiments to get the best focus. My marks are much farther over than the factory IR marks.
Fortunately, digital cameras make it easy to test out different focus adjustments and narrow down to the best. Here is an example of the focus shift, taken from a tiny part of the picture of the house above. First, normal color, then IR color with the exact same focus setting, then IR color with focus adjustment. You can see how important the focus adjustment is.
All of my Infrared Images were made this way, with the 28mm or the 50mm lens.
I hope this post encourages you to try IR photography. Please write some comments about your progress. If you find a good lens or a good technique, please share the info.
That’s all for now.
* (Incidentally, You can also use an opaque IR filter on an unmodified DSLR. Put it on a tripod, aim, put the filter on, and expose for a second or more in bright daylight. This can produce an IR image.)
** (Also, black and white video cameras can see IR and visible light. They often have an invisible IR lamp for night surveillance. These are popping up everywhere, so be careful what you do in the dark. They are very affordable. See http://www.supercircuits.com/Security-Cameras/Infrared-Security-Cameras/ )
*** An exception is the Coastal Optics 60mm APO, but it’s priced way, way out of my range.