Wednesday, December 11, 2013

IR Macro and Close-Up Photography

This is my fourth post about things you can do with your infrared camera during the “off season.”  You can read my previous posts about infrared light painting, candlelight IR photography, and more fun with candlelight by following the embedded links.

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Cone Flower Macro IR - Ann Arbor Michigan
Macro photography has many advantages. You don’t have to travel to exotic locations to find interesting and unusual subjects, you can shoot at any time of the day (or night), and you can easily shoot indoors when the weather is inclement. Because you are shooting small objects, macro photographers can control the lighting of the object using relatively inexpensive light sources, reflectors and diffusers.

Infrared macro work is a little more challenging than visible light macro. As you get closer to your subject, the depth of focus becomes very shallow and accurate focusing is very important. Most macro photographers use very small apertures to maximize the DOF. If your lens is prone to hotspotting, the hotspots get worse at smaller apertures. I use the Nikon 105mm f/2.8 VR lens for many of my IR macro photographs and I have not had any problems with hotspots.  Other Nikon macro lenses have significant hotspot issues. 

The Nikonians infrared database provides an excellent initial resource for determining if your Nikon lens has hotspot issues. Kolari Vision and Nasim Mansurov have more extensive databases that show IR lens performance. These databases are not perfect but they provide a great starting point when choosing or using lenses for IR work. 

IR Leaf on Deck Rail.  Ann Arbor Michigan
There is another major challenge with IR macro work. IR does not focus on the sensor in the same place as visible light. During the IR conversion process, the autofocus is adjusted so that the visible light images that reach the autofocus sensor (and the viewfinder) accurately predict the IR light focusing on the sensor. This is at the calibration point. As you move farther from the calibration point, the accuracy of the focus sensor is diminished because the focal point on the sensor changes with the focal length of the lens. 

Let’s use a real-world example. If you have a Nikon D90 that was converted to IR by LifePixel using their standard 18-70mm lens, LifePixel will calibrate the camera autofocus at a point near the wide end of that lens’s focal length. As you use longer focal lengths, the resulting image will have increasing amounts of back focus. You can compensate for some of this by choosing smaller apertures and increasing the DOF but that only goes so far. 

Now imagine that you put a 105mm macro lens on this camera. At that focal length, the accumulated back focus cannot be ameliorated even at f/22. Your super sharp macro lens appears to be “soft” in the infrared spectrum. 

There is a solution to this problem – LiveView. By using LiveView and zooming in on the area of interest, you can accurately focus any lens at any focal length. This is because the image you are working with is the infrared image as seen by the sensor. Newer Nikon cameras have LiveView autofocusing where you can zoom in on the area you want to be sharpest, activate the autofocus, and the camera’s phase detect autofocus system will make it sharp. The downside is that LiveView autofocus is a much slower than normal autofocus. This is not a big deal in the macro world because macro photography is normally a slow deliberate process. LiveView can also be a challenge when there is a lot of glare on the back LCD.

Brown-Eyed Susan, IR.  Ann Arbor, Michigan
There is another solution for the serious macro photographer - calibrating a dedicated IR camera with a fixed focal length macro lens. I did this with a Nikon D90 and the 105mm f/2.8G VR macro lens. This gives me a camera with IR macro and (slow-focusing) short telephoto capabilities and no worries about back focus. The autofocus works very well with this combination and I was able to solve about 70% of my IR macro focus problems with this approach. That said, I still have to use LiveView when the DOF gets really shallow. I have similar problems when I take macro photos with a visible light camera. I would caution others taking this approach because most macro lenses hotspot like crazy.  The new 105mm VR AFS f/2.8G lens is a good performer but most of the other macro lenses are on the “Do Not Use For IR” list.

The first image in this series is a macro photograph of a cone flower taken with a D90 calibrated for the 20mm f/2.8 AFD lens. Yes, you can use wide angle lenses for macro and close-up photography. The advantage of a wide angle lens is that you have a lot more DOF for any given aperture. When you take this approach, you will have to crop more, but modern cameras have lots of megapixels to work with. You also have to move around a lot more to frame the shot. I did not need LiveView for this shot. The image was converted to black and white using Nik SilverEfex Pro 2.

Spirit Level -IR Macro.  Ann Arbor, Michigan

The second photo shows a close-up of a leaf on the deck rail. I shot the back of the leaf because the backside has more structure and because the front of the leaf reflects a lot more IR light. When I tried to photograph the front of the leaf, I lost all of the detail and I had the devil of a time taming the reflections. I even tried using a low-angle flash to enhance the detail by creating shadows. Shooting the front of a dark fuzzy leaf like a Geranium or Tomato may work better, but that is just a guess on my part.  

The third photo is a shallow-focus capture of a brown-eyed Susan. This was image was captured during the blue hour between sunset and full dark. I shot this without LiveView using a monopod. Shallow focus IR photography can be especially difficult if the autofocus is not accurate. I could have captured this with LiveView but it was not necessary for this particular shot. There is a lot more IR light during the blue hour than the camera expects so I had to use manual exposure settings.

The final photograph is an IR macro shot of a Stanley spirit level. I used LiveView autofocusing for this and zoomed on in the right middle ring as it crosses the bubble. I used the LifePixel WB preset with no channel swap. This gave me the tone-on-tone image you see here.

Instead of putting your IR camera away for the winter, you might want to try some IR Macro photography. It could be a fun and rewarding way to spend an evening. 

Shooting Information:
Cone Flower:  D90IR (720nm conversion), Nikkor 20mm f2.8D, f/8, -0.67EV,  1/100 sec, ISO 200, tripod and remote release.

IR Leaf:  Nikon D90IR (720nm conversion), Nikkor 20mm f2.8D, f/10, 1/50 sec, ISO 200, tripod and remote release.  

Brown-Eyed Susan:  Nikon D90IR (720nm conversion), Nikkor 105mm f/2.8G  AFS VR, f/2.2, 1/320 sec, ISO 800. Monopod.
Stanley Spirit Level:  D90IR (720nm conversion), Nikkor Nikkor 105mm f/2.8G  AFS VR,, f/5, 1/13 sec, -1.33 EV, ISO 200. Tripod and exposure delay mode.

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