The Right Lens Can Make All the Difference in IR Photography (Part 1)

It's a relatively well known fact that some lenses work better with IR photography than others. The most common lens issue – hot spots – are bright, visible circles in the image (sort of like flare) typically caused by various lens and barrel coatings which reflect IR light in undesired ways.

A few Canon and Nikon lenses which are prone to hot spot include (according to Life Pixel):

• Canon EF 50mm f/1.4 USM
• Canon EF 16-35mm f/2.8L USM
• Canon EF 16-35mm f/2.8L II USM
• Canon EF 20-35mm f/2.8 USM
• Canon EF 28-70mm f/2.8 USM
• Canon EF 24-70mm f/2.8 II USM
• Nikon AF-S NIKKOR 24-70mm f/2.8G ED
• Nikon AF-S DX NIKKOR 35mm f/1.8G
• Nikon AF-S NIKKOR 24-85mm f/3.5-4.5G ED VR

But I recently ran across another issue when it came to utilizing two different lenses under identical lighting conditions; the images looked completely different (angle of view differences aside). A white balance target taken with one lens didn't seem to work well with the other lens. And even when I took a second white balance target image with the second lens, I could never get the image to look the same as the first image. Hmm...

Bear in mind, I have the Super Color IR conversion which allows you to captures yellow and blue hues in IR imagery. Obtaining the correct white balance in a Super Color IR image is critical for isolating the various wavelengths for proper post processing. At least, I've found it's critical when shooting landscapes. Typically speaking, I take a picture of a pure (or nearly pure) white target in the same light that is illuminating the landscape. With a custom white balance selected in post processing, foliage becomes yellow and the sky remains blue after switching the red and blue color channels.

I called the helpful people at LifePixel to inquire about white balance variations and other differences between lenses. The technician I spoke to believed that various lens coatings might make a significant difference in the quantity (and possibly quality) of IR light that makes it to the sensor.

Intrigued, I decided to conduct a little experiment. I chose five different lenses (two zooms and three primes) which all feature 24mm focal lengths and shot the exact same scene on a cloud free day. The lenses were:

• Canon EF-S 24mm f/2.8 STM
• Canon EF 17-40mm f/4L USM
• Canon EF 24-105mm f/4L IS USM
• Canon TS-E 24mm f/3.5L Tilt-Shift
• Sigma 24mm f/1.4 DG HSM Art

Here was the test setup:

• The camera was set to manual exposure for each test: f/8, 1/250 sec, ISO 100.
• Zoom lenses were set to 24mm (or reasonably close).
• UV filters were removed from the lenses.
• An X-Rite ColorChecker Passport target image was taken directly after the scene was captured by each lens.

In post processing, I white balanced each lens' scene with an identically sampled color patch (pure white) on its corresponding ColorChecker target image. The red and blue color channels were swapped and an identical Hue/Saturation adjustment layer was added with Yellow Saturation set to -100 and Lightness to +100.

Here were the final results:

In the images above, the Canon EF-S 24mm f/2.8 STM produces the results I want to see when capturing IR photography. In other words, there is a very clear distinction between the color hues that are recorded. Notice how muddy most of the other results look by comparison. The only lens that comes close is the Canon EF 24-105mm f/4L IS USM.

Are lens coatings solely to blame for the varying results? I'm not sure. The lenses vary widely in their design, introduction year and [likely] coatings. But one thing is certain; a couple of them look better than the others, and one stands out above them all.

Now I'm curious to know if more simply designed lenses and lenses with minimal (or no) coatings may provide results similar to the Canon EF-S 24mm f/2.8 STM, even though the 24mm STM is advertised as featuring coatings to reduce ghosting and flare. For my next test, I'll disregard focal length differences and choose lenses which I hope will mimic the 24mm STM's results.

Stay tuned.