One of the neat features of the Nikon D70 is that it is probably one of the last DSLRs that can be feasibly used for infrared photography. Digital sensors are very sensitive to IR, but the designers put filters over the sensor to prevent that invisible light from messing up the image. As manufacturers introduce new models, the “hot filters” are getting better and better at blocking IR from the sensor.
BTW, when we talk about infrared photography, we’re really talking about near infrared. Normal sensors are not able to image heat or see in the dark without artificial IR illumination. Visible light ranges from violet (around 400nm wavelength) to red (around 700nm). Mainstream infrared film (and digital) is sensitive up to 900nm or 1000nm. Radiation from heat doesn’t start until around 3000nm.
When you shoot IR, you are focusing (sorry) on the wavelengths of light from around 700 to 1000nm so you filter out the visible light with an IR filter. IR filters appear completely opaque to the eye, making direct composition impossible with an unmodified DSLR.
I’ve shot with the most popular black and white infrared film (now discontinued), Kodak High Speed Infrared (HIE), and really liked the unique characteristics of that film. The two major characteristics (besides its IR sensitivity) were its lack of antihalation backing and its very pronounced grain. The missing antihalation layer meant that the light from a highlight area of a scene could go through the film, reflect off the camera’s pressure plate, and add additional diffused exposure to the emulsion, causing the highlights to glow.
HIE was pretty difficult to use. It required special handling in your camera and darkroom, and the results could not easily be predicted, since you were dealing with invisible light and had no feedback.
Well, you can mimic the look of the HIE process in digital with less effort and instant feedback. There are lots of web references by people who are doing this with many unique processes and helpful pointers. I’ll discuss here the steps I took with the IR shots in my Angkor Wat Infrared gallery and use the photo “Angkor Wat from Phnom Bakeng” as my example.
Plate 2 is the view in visible light right before the IR shot. The sun had already set and the sky was completely overcast. In addition there was a pretty heavy haze. Compare with Plate 3 below to see the absence of haze on the IR shot.
Plate 3 is the unedited photo in IR. Note the required exposure increase. (1/125s @ 2.8 vs. 20s @ 5.6.) That’s about a 9.5 stop increase, and is pretty typical with the D70. Of course, in the daytime with an ISO bump to 800 it is still marginally hand-holdable, but this post-sunset shot required a tripod (actually a rock…).
To shoot IR, you’ll need a camera with some IR sensitivity, a filter, and probably a tripod. You can check the web to find out about your camera’s usefulness before you invest in a filter.
There are a number of filter options. As you go from red to infrared, you’ll find the following Wratten filter numbers: 25, 29, 70, 89B, 87, 87C, 87B, 87A. I use the Hoya R72, which is equivalent to the Wratten 89B. The R72 filter is the first in that sequence that is visually opaque, but it still transmits a significant amount of red light. That’s why the unprocessed shots are red. Stronger IR filters reportedly produce nearly monochromatic images and give a stronger IR effect, but they also require more exposure.
Since I bought the filter to fit on my primary lenses I used back when I shot 35mm film, I have to use a step-down ring to use the 62mm filter on my 18-70. At its widest setting there is serious vignetting. Not a great idea, and very tough to hide. It’s useless on my 12-24. I used my 180/2.8 for this example and I had to hand-hold the filter on the end of the lens since it’s way smaller than the 180’s 72mm ring and I don’t even have a step-down for it. The filters are very expensive, so get the largest one you will ever need and then buy step-up rings for your other lenses.
A tripod is really necessary for IR photography, but this particular shot is the only IR photo I took in Cambodia that wasn’t handheld. Bad practice, but I took multiple shots of each to have a better probability of getting one sharp.
When you’re shooting a DSLR, you are shooting blind just like with film, so that’s another reason to use a tripod. You can frame with the filter off, and then add the filter for the IR shot. If you shoot hand-held it’s a guessing game and you end up making a lot of exposures before you get one that is framed right, aligned with the horizon, and sharp.
Shoot at a relatively small aperture. IR light focuses on a different plane than visible light (with most lenses). (See the cocam link for a visual illustration.) In the old days lenses had IR marks on the focusing ring to tell you how much to offset your focus. Few do today. Since I’m shooting blind anyway I let the AF focus with the filter on and shoot at a smaller aperture to get greater depth of field, in case the AF accuracy is lower in IR. I haven’t tested it, but logically it seems like the AF should work fine with the filter in place. Until you test yours, stop down.
Get plenty of exposure. On the D70 with the R72 filter, most of the exposure is on the red channel (as evidenced by Plate 3). Since I usually get most of my data from the green channel for the B&W image, I want to get enough exposure in that channel for a usable image. You may need to overexpose by a stop or two.
Block the light coming in the viewfinder. I usually have the camera set on auto exposure, aperture priority. Unless you set the exposure manually, you will definitely need to cover your eyepiece for the exposure. Otherwise the relatively bright unfiltered light coming in through the viewfinder will make the meter underexpose the heavily filtered light coming through the lens. (It can make a three stop difference or more on my camera.) Better cameras have an eyepiece blind for this situation. I use my thumb on the D70. If you are using manual exposure, this won’t be an issue.
Consider using a faster ISO setting. I usually set the D70 to ISO 800 for IR. One of the characteristics of the old HIE film was its very noticeable grain. On my D70 the noise caused by the higher ISO, longer exposure, and frequent underexposure of the green and blue channels looks a lot like the grain of the film. Alternatively, this can be simulated in post-processing.
Try white balancing with the filter on. After returning from Cambodia, I read about someone who does a custom white balance with the IR filter on the lens. I’m eager to try that, as it would make the initial images much more neutral in color. It would probably also make any overexposure bias unnecessary to get adequate exposure on the green channel.
Choosing a Subject:
You never know what will be a good subject. Certainly most scenes with foliage are potential subjects. Blue skies with some puffy or wispy clouds can really add drama. The haze-cutting ability of IR will often add depth to landscapes with distant vistas. And don’t shy away from portraits either. The best advice is just to shoot a lot of pictures and learn what catches your eye and produces the look you want.
1. The first step for post-processing an IR shot is to balance out the three channels with an auto-level in Aperture or Photoshop (Image > Adjustments > Auto Levels). In our example, Plate 4 is the result. (Compare Plates 2 and 4 to see the dramatic reduction in the haze.) (Note also that this step would probably be unnecessary if you do an auto white balance before taking the picture.)
I do the remaining steps in PS. I’m using PS CS2 in this example.
2. Convert the image to B&W. I use the Image > Adjustments > Channel Mixer to both convert to monochrome and strip out the channels I don’t want. First I select the monochrome check box. Then I use the sliders to obtain the desired effect.
On the D70 with R72, usually the red channel is the softest and has the least noise. The blue channel has by far the most noise, but can offer darker skies and water. The green channel is usually the sharpest with moderate noise.
Each image varies, but a starting point is 100% Green, maybe 25-30% Red, 0% Blue, and a “Constant” adjustment of -20 or so to get the brightness right.
Make sure that you keep any highlight tones where you wish to keep detail in the final image a little darker than usual since the last step will blow out the brightest highlights.
3. Take care of spots, tonal range, and any other retouching if needed. Often I’ll use Image > Adjustments > Shadow/Highlight to bring up detail in the shadows and get detail back in the highlights at this point.
4. Sharpen the image. I use Filter > Sharpen > Unsharp Mask to sharpen the image at this step of the process.
Depending on your preferences, you might want to stop here. I like the look of HIE, so I continue with one last effect to mimic its glow.
5. Convert down the image from RGB/16 to Gray/8. Image > Mode > Grayscale, then Image > Mode > 8 bits/channel. Necessary because the final filter step only supports 8 bit depth.
6. Use the Diffuse Glow filter. Filter > Distort > Diffuse Glow. You don’t need much. I already have the grain, so I leave Graininess at 0. As a starting point I try Glow Amount 2 and Clear Amount at 17. I can’t describe exactly what each one does, but you’ll see it as you play with the sliders.
The result is Plate 1 at the top of the post. It’s fun to play with and sometimes the results are very nice. And it is definitely much easier than the old film method using HIE.
For those who do not have a suitable camera or filter, or just don’t want to shoot blind, there are options. Of course, one option is to buy an older camera like the Nikon Coolpix 9xx and a filter for it. Since point and shoot cameras typically have a live LCD viewfinder, you can see the scene just like with visible light.
Check out http://www.nickgallery.com/web_pages/technical%2020.htm for a simulated IR effect PS process that doesn’t require any filters or special camera techniques. I don’t expect that you would get the same haze-cutting ability as true IR, but otherwise it might produce similar results.
If you get really excited about IR photography, then there’s really only one thing you can do. Convert your DSLR to an IR-only camera! A number of sites on the web discuss how to remove the hot filter from your sensor and replace it with an IR-pass filter. Or there are others who will do it for you or sell you a camera with it already done. That gives you a dedicated-use IR camera that needs no filter, is sensitive enough to IR to allow normal exposure settings, and retains the use of the viewfinder for composition.
You can find many web sites discussing digital IR photography. Here are a few good ones I’ve found:
http://www.naturfotograf.com/UV_IR_rev00.html#top_page – Bjorn Rorslett’s excellent site
http://www.wrotniak.net/photo/infrared/- just about every aspect of IR photography
http://www.cocam.co.uk/CoCamWS/Infrared/INFRARED.HTM – another good IR site