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.
2b.What does this diffraction chart mean for your infrared pictures?
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There are 10 comments on “Why You Should – and How to – Avoid Diffraction in Infrared Photography”:
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Robert I just read this article with great interest and ran the numbers for the EOS 5D Mk IV and was wondering what I have to do to get a comparison with my converted EOS 5D Mk II?
Martin, you will need to enter the required data (sensor size, total megapixels) manually. Your camera manual should provide you with all the details.
Great stuff Robert and thanks. Your DNG Editor solution for a B&W profile for my 850nm images works a treat. Maybe I can move on from here. Thanks again.
Thank you for the feedback Martin, I am glad you found it useful!
Robert, you raise some interesting issues. I note that in the table you offer only quite new Panasonic cameras. I use older models with larger pixels and wonder if this gives me more flexibility. I rarely experience diffraction, and am about to invest in an f2.8 zoom with IR very much in mind. I hope I am not wasting my money!
Maggie, you are definitely not wasting your money. The combination of a low-megapixel sensor with wide-aperture lenses will give you a lot of flexibility, without running into diffraction issues. I am sure you have already calculated the results for your combination.
I had to restrict the number of models for the calculator, otherwise the list becomes unmanageable. This is why you see only the newer models.
Thank you, Robert! I’ve just placed my order and I’m really looking forward to using it with either of my converted cameras. Best wishes.
Thanks for letting me know Maggie! Have fun with your converted camera!
Robert, thanks for aggregating this info! I had not considered the impact of diffraction in IR. I tend to shoot at f/8 on my Fuji X-T20 (same sensor as X-H1), but I will try lower f-stops to improve sharpness. This could certainly explain the softness of some of my early IR shoots at f/8 with a Canon SL1 (similar sensor as 80D), which appears to be more sensitive to diffraction.
Thank you Rob, I certainly appreciate your feedback! Glad you found this page useful. Now you can in advance determine the optimal aperture setting for a given camera / IR filter combination. It definitely helped my IR photography a lot :-)
You have some very nice IR shots on your website – I would guess some are taken with the Kolari IR Chrome filter?