What are the benefits of infrared conversion?

Question

I just picked up a Hoya R72 infrared filter, and I'm having a lot of fun experimenting with it. I'm in love with the false color style that can be added. So now I'm contemplating converting my DSLR to a dedicated infrared camera. I own a Nikon D40, which apparently has a reputation for being a decent unmodified infrared camera (when using a IR filter).

I've put my own list of conclusions and considerations in the answers section. Please post an alternative answer if any of my assumptions are wrong. I'm also interested in what other differences (if any) I would see in my photos if I did the IR conversion. What else am I missing/overlooking?

Answer 1

I've had a camera converted, and some experience using IR filters with an unmodified camera.

• A converted camera is a real joy to use compared to using filters. The ability to see through the viewfinder and snap away handheld is worth it compared to 30s exposures with a tripod.

• Live view is really good with IR converted cameras, not only for dead on autofocus but also just to be able to see the world in infrared, as infrared can be unpredictable.

• As well as autofocus metering will be out as it's designed for visible light. It's just a matter of setting +1.5 stops exposure compensation and occasionally reshooting.

• Hot spots are still a problem with IR conversions, you just have to try a lot of lenses to find ones that work well in IR.

Answer 2

After doing some reading about infrared, and what it would take to convert, and playing with the R72 filter, I've come to a few conclusions on my own. Here is a mixed list of some pros and cons about whether to convert:

• A IR filter only allows infrared light to pass, and blocks the visible spectrum. So if you use an IR filter over the lens, your viewfinder will be worthless. This makes taking pictures..."more challenging". (oh, why didn't I think about that before I bought the R72 filter!)

• Modifying the camera should resolve that problem, as the IR filter would be installed over the camera sensor, and behind the lens, which will let you see normal light through the viewfinder again.

• Long exposure time is needed using an unmodified camera. Most DSLRs have an IR blocking filter installed. The D40 just has a poor one. I guess the strategy to get around the IR blocking filter is to leave the shutter open longer, which will (slowly) let more IR pass through. But now you have to work around a long shutter requirement. My shots today needed over 1 second to get a proper exposure, even in direct sunlight. That means you need a tripod in most cases :(

• Again, modifying the camera should resolve the shutter speed problem, as IR light will enter the sensor much more quickly, now that the blocking filter is removed.

• I tried bumping up the ISO to get around the shutter speed problem, but noise seemed to creep in much sooner than a normal picture would. Not sure if that is expected when shooting IR photos, or just a one time occurrence.

• When pointing the camera near the sun, I was much more prone to lens flare (even with a lens hood), or maybe it was this IR hot spot thing I read about. Would this problem go away if I did the conversion?

• Modifying a camera for IR is risky (you literally have to take your camera apart!), and can be expensive if you pay someone else to do it.

Answer 3

Infrared light focuses on a slightly different plane than visible light (unless using a specially designed or mirror lens), so your auto-focus will be always missing unless you convert AF sensors also (it's going to be more complicated). If your lens has infrared focusing marks, you could use those to correct focus.

Considering ease of focusing, a camera with Live View capability might be better suitable for converting.