After spending last week shooting with my IR converted D90 for my 365 challenge, I decided that this week’s post would be a nice complement. Shooting in IR can be done with special film or with most digital cameras, whether SLR, ILC or point and shoot. For the most part I’ll be talking about IR photography using a DSLR, but the theory and general technique is the same. I also talk a little bit about UV light photography as the concept of how it is done is similar, but not the same, to IR photography.
What is infrared (IR) light? While the exact cutoffs vary based on the source, most agree that visible light has a wavelength ranging from just below 400nm (violet) to right around 800nm (red). Light below the visible range (shorter wavelengths) is ultra-violet, or UV for short, and light just above the visible range (wavelengths longer than 800nm) is known as infrared. I purposely kept this short and as I could easily give a science lesson on this, but for the purposes of this post, this is all you need to know.
The human eye can only detect light in the visible light range and cannot see ultra-violet or infrared light. However, the CCD and CMOS sensors of digital cameras can. The range of most CCD and CMOS sensors is from around 200-250nm up to about 1100-1200nm. It should be noted, that many people, when they hear the term “infrared photography,” immediately think of thermal imagery. While this is also technically a form of infrared photography, as it is measuring heat which is infrared radiation, the wavelengths in thermal imaging are in the far infrared around 14,000 nm. These are much longer wavelengths than the sensitivity of the CCD and CMOS sensors can handle, so special cameras (also pronounced "very expensive") are used for this type of imaging which then convert the signal to a color spectrum that humans can interpret. Again this is not what I am talking about in this post. I am talking about your regular everyday DSLR or P/S camera being able to see and photograph the near infrared light in the range of 800-1100nm. With that clarification aside, let me continue.
So, you have a DSLR or a point and shoot camera, you should be ready to go to shoot some IR shots, right? Not quite. Most camera makers insert a filter directly in front of the image sensor, known as a cut filter, which works to block any IR and UV light front hitting the sensor. Why would they limit the capability of the camera this way? Well in short, the lenses and camera systems were designed to focus and capture visible light and not IR or UV. As such UV and IR light focus differently than visible light (something I’ll touch on a little later) and in some shooting situations can be more intense than the visible light. The resulting effect is a potential for a lot of noise, a photo that looks a bit out of focus, a photo that can be over or underexposed, and in general just a bad photograph. As camera makers are primarily focused on what the majority of photographers want to shoot, visible light, it benefits the camera maker and the photographer to have this cut sensor in place. How do you take photos in infrared if the camera is designed to block the infrared light from hitting the sensor? The cut sensor doesn’t block all IR, but only enough to prevent it from hitting the sensor during the use of normal shutter speeds. In addition to that, the filter in some cameras is better than that in others, with newer cameras having better filers than those in older cameras. Through a couple of techniques these facts still a photographer to take IR shots even with the cut sensor in place.
By leaving the cut sensor in place in the camera, it means that you can still use your camera to take regular visible light photos. However, it also means you must use a filter on the end of the lens to block out the visible light. How come? In this situation you need to consider that the light you are trying to capture, infrared, is making it to the sensor with significantly less intensity than visible light due to the cut filter. By still allowing the visible light through, it very quickly overwhelms the small amount of infrared light able to get through with the actuation of the shutter. By attaching an infrared pass filter to the front of the lens, it blocks the visible light and allows the infrared light through to hit the sensor. Some of you may have already picked up on them, but there are two very big considerations to take into account when taking infrared photos this way. First off, because the cut filter is still in place, the camera is working against the light, meaning you need significantly longer exposure times to give enough IR light a chance to make it to the sensor. Depending on your camera and its cut filter, this could range from a little less than a full second (like on my D40) up to or exceeding a full minute long exposure (my non-converted D90). The difference in the exposure time is due to the quality and strength of the cut filter. The only way to know how long you need to expose is to experiment with your specific camera. The second big consideration, and this applies to the DSLRs, is that due to the design of the camera the viewfinder works by using a mirror to look through the actual lens to focus and frame your shots. With a filter on the front that blocks visible light, the only light making it to the viewfinder is infrared, which you cannot see. It should be noted that most digital P/S, and cameras with electronic viewfinders (EVF) will produce can image however it will be faint due to the cut filter.
Many photographers who are experimenting with IR photography use this technique. It just means that you need to focus and frame and then place the filter on the end of the lens. It also means you absolutely must use a tripod for every shot. But, it also means you can still use your camera for normal visible light photography without having to buy a 2nd camera to get converted just for IR work (a hefty expense especially if you are just trying it out). I myself started this way and have a set of infrared filters in my camera bag. As with all of other types of filters there is a range of functions and performance in the world of infrared filters. I will touch on 3 specific types here, but there are some variations. The three types by their commonly used names are the R72, Wratten 87C, and the RM90.
The R72 designation for the first filter comes from Hoya, a very popular and large manufacturer of glass filters. The truth is that each company gives each filter a name based on its own naming scheme, but the numbers I provided above are the most commonly used names to reference each type of filter. The R72, also known as the Wratten 89B, has 50% cutoff at 720nm. This means that at 720 nm, only 50% of the light with wavelength shorter than 720nm is passing through the filter, and the drop off is pretty quick. This filter is the most common deep-red/infrared, also known as “false color” infrared, filter around. By false color, I mean that the filter still allows the wavelengths for the deep red visible range through as well as the infrared. This allows for some subjects to retain a small portion of color that can be played around with in post processing by performing a channel swap. For this reason, this is a very popular type of filter. IR purists believe that false color is not as artful and is more of a gimmick because it gives the photos a certain look that is not completely IR. My view is that anything you can do to make photograph appealing to an observer or the artist themselves cannot be a gimmick. If you don’t prefer false color IR photos, then you can just opt to not look at them or have an opinion that you don’t like them, but it doesn’t remove any of the artfulness behind taking the photographs.
However the purists do have a point as it is not a true IR photograph. For that, you need to use at least a Wratten 87C filter. The Wratten numbering system for filters was developed by Kodak for their square gelatin filters, and many other people still refer to filter types similar to those made by Kodak by the Wratten number (like how the Hoya R72 is equivalent to a Wratten 89B and vice versa due to their similar cutoff, although the Hoya is a round, glass filter and the Kodak is a square gel). The Wratten 87C has a 50% cutoff at 850nm which is out of the visible range. The effect here is that the image produced out of the camera appears black and white. Areas that reflect a lot of infrared light (such as foliage) appear white and subjects that absorb IR light (such as the sky) appear dark or black. There are 3 other types of the Wratten 87x filters. The Wratten 87B has a 50% cutoff around 900nm and the Wratten 87A has a cutoff around 1000nm. Lastly there is also a Wratten 87 (no letter) that has a cutoff around 770nm. Only the 87C and the 87 are still produced by Kodak, and other manufacturers also make equivalent filters. There are also other manufacturers who make filters similar to the 87B and 87A. One of these is the Hoya RM90. The RM90 like the 87B has a cutoff at 900nm. The effect in the IR is that it gives a very deep contrast to the IR shots as only the best reflectors of IR light show up as white or tones of gray. The problem is that you need very bright sunlight to get these photos (and photos taken with the 87A equivalent RM100).
If you want to try out false color, I recommend a R72 or equivalent filter. There are also filters with lower cutoffs at 650 and 600nm which also let in part of the yellow spectrum, but I didn’t get into those here. If you want true IR, I recommend a Wratten 87C or equivalent. Use of the high cutoff filters are really for people who already are used to working IR or have a need for that level of cutoff. A last and additional note on the Wratten filters is because they are gelatin filters made in square sizes. If you want the screw on type of the end of the lens, you either need to find a holder for this type of filter that screws in (or hold it by hand), or purchase a round screw-in type from another manufacturer like Hoya, Tiffen or B+W.
For point and shoot cameras, some cameras do have brackets available to hold a standard screw in filter in front of the built in lens of the camera (very few have filter threads on the lens). You can also make an inexpensive filter by using some dark tape, a small piece of a narrow cardboard tube, and either a gel or polyester filter (Lee filters makes some inexpensive by good quality Wratten 87 equivalent filters). Another option for the filter is to use an exposed and developed piece of 35mm film (easily obtained from the exposed end of a film roll that has been developed…although as film is harder and harder to come by, so will this inexpensive method). This DIY device can then be held over the end of the lens on your P/S camera. Try doing a web search for this as there are few different DIY photo sites out there with instructions.
If, and only if, you have already picked up a relatively inexpensive screw-in, or square gelatin type filter and tried doing some long exposures. And if, and only if, you plan to take a lot more infrared photos, should you consider a camera conversion. If you never plan to shoot visible light again then you could get your main camera converted. However, as this would be the case with only a very small group of photographers, I recommend picking up a second camera to have it converted. I did exactly this and picked up a used D90 off of EBay. Before I get into the actual conversion, what should look for in a camera to get converted? Basically you want the same things you wanted from your main visible light camera, but with one caveat. For most photographers, the live view function on a DSLR (being able to view the image on the back LCD and you frame and shoot) can be a handy feature for visible light photography (although some never use it like me). But for shooting in IR, live view can be an invaluable tool . I’ll touch on this more when talk about shooting in IR, but for now just know that if you are planning on getting a DSLR for your IR work, I highly recommend getting one with the ability to view and shoot with the image live on the LCD (most DSLRs in the last few years have this feature). Also, I recommend getting a used DSLR whether through a reputable camera shop or after doing your research on EBay. Why? If you get a brand new camera, you do get a warranty, but as soon as you get it is converted, the warranty is then void. So if you get a good used camera with a low number of actuations, it is really no different than one that is brand new with a voided warranty and could save you several hundred bucks (I personally saved $500 by going used with my second DSLR rather than getting one new, and would do it again in a heartbeat).
When doing a camera conversion, either you (if you are really bold) or, the more recommended route, by using a company that specializes in infrared conversions, will open up the camera body, take out the infrared cut filter on the sensor, and replace it with a specific infrared pass filter. The type of conversion you want takes into consideration many of the same ideas as when selecting a type of filter to screw into the end of the lens. You can get one with a cutoff at 650, 720, 810, 850, 900nm, etc. However with that being said, one big consideration is that the filter is permanent so if you have a 900nm conversion, you cannot undo it by just popping out the filter and popping in in IR in a 720nm filter to do some false color work. Because of this, if you enjoy doing false color work often and only want to do true IR every once in a while, I recommend getting a 720nm or similar conversion. You can always put a Tiffen 87 or a Hoya RM90 on the front of the IR camera to get deeper IR just like if you had an unmodified camera, but the exposures would not be nearly as long. Also, an image taken with a 720nm camera and then converted to black and white is similar to one taken with a higher cutoff (don’t kill me IR purists! I know you will argue that’s not true, but note that I said similar). If you absolutely love true IR and only want to do that type, or if you only do false color once in a blue moon, then I recommend an 810 or and 850nm conversions. You can always throw a Hoya R72 on your visible light camera for some long exposures for false color. Because 900 nm and up is so rarely used , I hardly ever recommend getting this conversion as it is very restrictive in your options. But, if it is right for you and your work, go for it.
As an aside, you can also do the same type of conversion on the other end of the spectrum for UV only. There are other considerations to take into account when shooting in UV but I’m not going to cover those here except to say that an example of one of these considerations is that optical glass absorbs some UV light so the best lenses uses quartz elements, but these are very rare and expensive (many thousands for a used lens).
You can also get full spectrum conversions. This conversion removes the cut filter and replaces it with clear glass to get UV, visible and IR, and then you just swap out with the types of filters you want on the front of the lens. This is the economical way to get all three types in one camera, but if you are really into it and have the money, I recommend cameras that were converted for a specific use so you don't need to mess around with all of those filters. Most of the conversion companies do all three types of conversions on most DSLRs and some point and shoots and ILCs.
Now that you have a camera and have selected what type of conversion you want, it is now time to pick who does the conversion. Many conversion companies will sell you a pre-cut filter for your sensor, so you can do it yourself. While this is very possible, there are a lot of things that can go wrong ranging from getting dust trapped between the filter and the sensor which shows up in all of your photos, up to accidentally damaging your image sensor and having to pay full price for it to be fixed or having to replace the camera. For me, this risk is not worth it and I gladly used some of the money I saved buying a used DSLR to pay for the actual conversion by a company who is equipped to do this work. Before picking a conversion service company to do this work, I did a ton of research. There are local shops that do some of these conversions and then there services where you send your camera to them. In both instances, I emphasize to do your research, read some reviews, and pick wisely. There are tons of stories out there of people who brought their camera to a local shop or mail-in service without reading up on them and got back a camera that didn’t work properly. Just do some research n the web for the mail-in places, ask for references for local places, check out the shop and talk to the people there. Also check out their service guarantee and warranty if you can before dropping off your camera. You are probably paying several hundred dollars for the conversion so make sure when you get it back it will be what you want and it working order.
I personally opted to do mine through a mail-in service. While there are several out there, my research narrowed it down to two different places: Life Pixel and MaxMax (LDP llc.). Both of these companies offer the same types of services performed on clean benches, and both have very satisfied customer bases. Their websites also have a lot of info on what to look for in a conversion as well as about IR photography in general. Going through either of these services will give you a great product when you get it back. They make sure to use a pass filter that is the same thickness as the cut filter they remove so as to not introduce potential issues that could affect the image quality. Additionally they also perform a standard recalibration of the autofocus system to be able to focus properly in the infrared rather than visible light. Both also guarantee their work. I will also take this moment to say that my recommendations here are solely based on my own research. I have no association or am given any benefit to recommend either of these two companies other than to share what I have found with other aspiring IR photographers.
As a side note, I’ll talk about focusing in IR more when I get to shooting in IR in just a minute, but know that both companies adjust the autofocus using a lens they chose as a standard lens for your brand of camera. Both websites list what this lens is. This recalibration works for focal lengths in the range, and know that if you put on a lens that has a focal length outside of this range (particularly when you get a lot further out in the long to super telephoto range) you may still need to do some focus adjustments manually.
I chose Life Pixel to do my conversion, but probably would have been just as happy with MaxMax. I only picked Life Pixel because I thought their website was more professional and I liked the information on it better (see kids, marketing does work!). On the flip side, one advantage of MaxMax is that if you request your original cut filter back, they will send it to you whereas Life Pixel will not. This to me was not an issue as I really don’t need it back. If I did want to convert this camera back, both places also do a conversion back to stock, and often at a discount if you did the original conversion through them. As a bonus for me, after I had made up my mind about using Life Pixel, they announced their spring sale where they offered conversion for 50% off the normal price which at the time, was a savings of $225 for a standard 720nm conversion (technically a 715nm at Life Pixel and MaxMax, but similar to a Hoya R72 filter so I call it a 720nm conversion). And yes, as I just stated I did a 720nm conversion because I do like to do some false color work. Overall the conversion took about 2-3 weeks from the day I sent it to the day it came back, and I couldn’t be happier with the work of Life Pixel. It should be noted, and this is true no matter where you do the conversion, a couple of minor features may not work like the "sensor dust off" feature on the D90. There is no really way to avoid this, but 99% of the features still work.
Now that you have your IR camera, either from being converted or if you are using filters on the end of your lens, what considerations do you need to take into account in order to get great shots in infrared? To start, there are some considerations around subject matter. Some of the most dramatic effects in IR photography occur because of how plant life, human skin, the sky and water reflect and absorb infrared light differently than visible light. As such without some of those elements in a photograph, a black and white infrared shot looks nearly identical to a visible light black and white photograph. Nature scenes by the fact they have a lot of plant life tend to look more dramatic than urban scenes. However this does not mean you cannot have some great shots in urban environments. It just means you need to experiment. The most important factor is that you have some level of contrast in your scene just as if you were taking a visible black and white. All other aspects of photography and composition still hold true.
The biggest differences with shooting infrared versus shooting using visible light are more technical in nature. One of the biggest differences is the ability to focus on DSLRs. Cameras, and more importantly lenses, are designed around capturing visible light. As such, the lenses are optimized to focus light with wavelengths in the range of the visible spectrum and not outside of that range. Infrared light focuses a little bit differently due to the longer wavelength. Lens manufacturers, back in the days of film realized this and used marking on the lenses to allow the photographer to manually shift the focus ring to account for this difference. On older prime lenses, this would be marked with a red dot on the focus ring, or in the distance scale. On zoom lenses this often appeared as a red line in the distance scale as the shift differs depending on the focal length of the lens. Unfortunately on most newer lenses, these markings no longer appear (although I’m not entirely sure why). When using newer lenses, and manually focusing, you really need to figure out the focus shift is by trial and error. If using autofocus on a converted DSLR, and it has not been recalibrated, it will not focus properly as it uses a phase change detection which works with visible light. It uses the image bounced up through the mirror in the SLR. This light coming through the lens has not been filtered for infrared only, and in addition the system does not work solely on infrared light. Most conversions, as I mentioned above, include recalibrating the autofocus mechanism to account for the focus shift on a range of focal lengths (usually those in the normal, but also in the short telephoto and wide angle range). This recalibration of the AF system does not allow the system to see infrared, but since visible light is still coming through the lens it focuses using the visible light and the recalibration just intentionally skews the adjustment to the focus in the lens. As I mentioned above, this works for most general shooting, but a shift may still be needed in the longer telephoto range. Through the viewfinder, the image looks a little out of focus, but will be in focus in the image captured by the sensor. For P/S cameras with a weak cut filter and for DSLRs equipped with live view, the contrast detect autofocus system, while inferior for visible light, works great for infrared shooting because it uses the image being detected by the sensor to focus.
Another difference to account for when shooting in IR is metering the proper exposure. On a converted camera, for most purposes the metering for visible light performed by the internal light meter will work fine, but in scenes with a lot of infrared reflecting subjects, or in scenes with a lot of infrared absorbing subjects, some exposure compensation is needed. The best way to figure this out is to take a few photos and look at the exposure on the preview image or, even better, using the histograms. Exposure compensation can vary greatly as the day progresses. At high noon, the sun, a great IR source, will greatly increase the amount of available IR light, much how it is strongest for visible light at noon. Because of the strong source of IR, you may need to purposely underexpose the images when shooting at noon, and dial in some overexposure when shooting early or later in the day. Again, try-then-adjust is the way to figure out if your exposures are coming out properly. If using screw-in filters on the end of your lens, or on a P/S camera, the exposure will be off by quite a bit due to the cut filter in the camera, and that will vary on the camera. Because of this, often long exposure times are needed just to obtain an image. This obviously means using a tripod and picking subjects that are stationary to prevent blur.
Also, as lenses and the coating are designed around visible light, often hotspots and lens flare can occur when using them for IR. What is a hotspot? It is caused by the way the lenses focus the IR light, as well as internal reflections of the light in the lens, and can appear in an image as spot on the photo that is much lighter, or more exposed, than the rest of the image. Often this occurs in the center of the image. For flare, because lens coatings again are designed to reduce flare from visible light, it means that the same lens can be just a prone to flare as if it has not coating at all. What does this mean for the photographer? It means that your $1000 lens may be junk for IR, and your inexpensive kit lens could be fantastic. For some of Nikon’s lenses, this is exactly the case. In fact, one of the best lenses for IR work from Nikon is the 18-55mm f/3.5-5.6G lens that comes with their entry level DSLRs. This lens is only about $150 if bought separately, but it has fantastic performance in IR with little flare and no hotspots. Unfortunately the same cannot be said the 18-105mm kit lens with the D90/D300/D7000 range of camera. Also, some of the relatively expensive lenses from Nikon can have unwanted hot spots. And, although not expensive, the great and versatile 50mm f/1.8D (every Nikon DSLR owner should own one for visible light) has a very strong hot spot in infrared. There can also be variation from lens to lens of the same model, but in general most lenses of the same model perform similarly in IR. The best way to know if your lens works well in IR is to try it, and if you are looking to buy a new lens for IR work, do some research online as there are some great forums for IR photographers where they have compiled lists of good and bad IR performing lenses.
Lastly, when shooting in IR, care must be taken when using flash to supplement the image (A note on future posts, I plan to do one on modifying the light from the flash using gelatin or polyester filters. As such you can use an infrared filter on the flash so it is barely, or not at all, visible to the observer). As most flash, both built in and dedicated units, are great emitters of IR, when in low light situations, particularly when at wide angle lenses, the camera itself can actually block some of the IR, and if there is not another strong IR source nearby, this will cause a very distinct, dark shadow, which is more pronounced than when shooting in visible light. I would equate it to shooting a picture in a pitch black room using a flash, except this can happen in low light situations, like being indoors, when shooting in IR.
This has been a long, but hopefully beneficial post on IR for photographers who may want to try it out. I love shooting in IR almost as much as visible. Some of the dramatic effects of IR really can have a significant impact on the image you are capturing. It is also a great way to pass the time in the middle of the day, between golden hours, when the visible light is too harsh for shooting, but is just right for shooting in IR. Go out and try it!
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