Diffraction impacts infrared photography more than in visible light. Calculate the aperture limits for any IR filter, based on your personal requirements.
1.Diffraction in infrared photography is probably worse than you thought
Recently I have completed testing a few Olympus lenses in infrared light, and I have noticed very strong diffraction effects at smaller apertures, much stronger than in visible light. Actually, this is expected since diffraction depends on both the aperture and wavelength of the light. I just did not believe it would be so visible. The picture at the top of this post is such an example.
If you believe diffraction is not important for your infrared pictures, here is a visual comparison of how diffraction impacts sharpness at various apertures. Please note that the crop is 2× enlarged, so even at f/2.8, the picture will not appear perfectly sharp. This is a totally non-scientific example, but it should get the point across:
- Camera: Olympus OM-D E-M5, converted to 720 nm Infrared
- Lens: Olympus ED 12-40mm F2.8 PRO at 25 mm
- Non-sharpened 256 x 256-pixel crops from the picture center, 2× enlarged for better visibility
You can see that starting with f/8, the picture gets more and more blurry. But how can we calculate the maximum aperture we can use without impacting the sharpness of our pictures?
1a.Calculating infrared diffraction limits
There are a lot of sites out there where it is possible to calculate the diffraction limits for your camera, but – to my knowledge – none of them deals with infrared light. This is where I decided to create my own diffraction calculator, specifically for infrared photography. And since I am a visual person, I also wanted to include a nice chart for a graphical representation of the result. Finally, I wanted to compare the levels of diffraction for your chosen infrared filter and visible light, to give you an idea about the difference.
All you need to do is to enter the required values in the below fields and click Calculate. You will be taken to the resulting diagram and further explanations.
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2b.What does this diffraction chart mean for your infrared pictures?
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