If you have a lens that generates that dreaded hotspot in the middle of your photos when you try infrared photography, you may want to try this trick. LightRoom offers the “radial filter”, which you can use to make that hotspot disappear.
Most modern lenses are quite poor at infrared photography, because manufacturers no longer take care to use proper internal anti-reflection coatings that are effective against infrared light. There are of course limits to how bad your lens can be, but for many lenses, you can use the radial filter to darken that hotspot and save the picture.
The dreaded hotspot in the middle of the shot
The shot above was taken with a Nikkor 18-55mm kit lens (Nikkor 18-55 3.5-5.6 GII DX VR) that most websites will report as “good” for infrared photography. I used an 850nm infrared filter and took the shot at f/11. The picture looks ruined to my eye, due to that pesky hotspot.
Let’s take a look at what Lightroom can do to try and rescue the shot next.
Configure a radial filter to fix that hotspot
As shown above, select the radial filter, and click the middle of the hotspot in the picture.
Drag the mouse to get the desired diameter for the filter to surround the spot. Make sure to click on “Invert Mask” so that the filter will affect the interior of that circle. Set the feathering amount, so that the edges of the filter circle will blend into the background.
You might want to temporarily set the following, also:
Tools | Adjustment mask overlay | Show overlay
This command will let you see your mask, and it’s quite helpful while you are adjusting the “Feather” amount. After you’re done, select “Hide overlay”. There's also a "Show Selected Mask Overlay" checkbox below the image to turn the mask on/off. Lightroom also lets you change the mask color, if you find it too difficult to evaluate the effect using the default red color.
Fine-tune the radial filter
Decrease the exposure value, until the hotspot is darkened to match its surroundings. When you’re happy with the mask settings, click “Done”.
Go ahead and perform the usual edits after you’re finished using the radial filter.
With the infrared filter I used, I usually prefer to turn the shot into black and white.
The hotspot is gone
As you can see above, the hotspot is basically gone. I converted the shot into black and white, which I almost always do with this particular IR 850nm filter. The plug-in Silver Efex Pro 2 can be very helpful in manipulating the shot as black and white, by the way.
You have to be careful that you don’t over-expose the shot to the point where the hotspot gets into the “clipping” region in any of the R, G, or B color channels. At that point, you have to admit defeat; the shot’s not recoverable.
I have a few lenses that are so-so when shooting infrared. There’s a mild hotspot in each of them, particularly when I stop the aperture down beyond about f/5.6. This simple trick can save the shots that I’d otherwise send into the trashcan.