SCORE NOTES

Reading The Results

The scores you see above are achieved at f/8 using an 850nm infrared filter (effectively only showing invisible IR light). If you would like to see how the lens scores are different apertures click on the the link. Also see the key above to understand exactly which version of the lens that was tested.

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What Are Hotspots

Essentially this is infrared light showing up in the frame where is shouldn't. A 'Hotspot', specifically, is a spot in the center of the image, but there are other forms of internal reflection that serves no purpose in separating, they're all annoying. This should not be confused with lens flare however.

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These issues are caused by the lens, its construction and coatings. Infrared light contamination is usually not caused by the camera, conversion, adapter, filters, exposure time or light from outside of the frame.

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Specific Lens Versions

While making this page I became aware that the infrared performance of a lens drastically depends on the version. This is typified by the various series of manual Nikkor lenses. You can almost see a pattern emerge that suggests newer coatings are progressively worse. For this reason I try to include as much information about the lenses version as I can. Nikkor series F lenses (earlier pr-AI with black metal focus rings) have been consistently some of the best performing for infrared, although it's worth noting that they don't necessarily give sharp results at lower/mixed wavelengths due to channel offsets (especially the wide angles).

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Lower Wavelengths & Colour IR

Lower wavelengths of infrared show less intensity from the hotspot issue. This is due to some of the light coming from visible light, which is unaffected. This works logically when processing like a b&w image. However, the hotspot can appear worse when processed as a colour image. For example if your foliage is yellow and your sky is blue, the hotspot can show up as yellow in the clouds (where it would otherwise be blue or grey). Once you notice this issue it's hard to ignore it and even harder to fix than a b&w image.

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**Anti-Reflective Filter Coatings

Anti-reflective (AR) coatings on infrared filters can help to reduce the hotspot intensity. In my experience this is only noticeable when the coatings are applied to the internal filters. External filter coatings had no obvious effect on the lenses that I tried. However, it's worth noting that this was tested before I started this more accurate rating system. Click here to see how much effect internal AR coated filters had for me (using this same scoring system).

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Perfection Achieved

Until recently I didn't think that it would be possible to see a 10/10 score with a normal lens, but some of the Konica telephoto lenses have reached this level. This means that the brightness of the background in the center of the image is as it would be if the light was not there. Lenses will almost always produce a hotspot to some degree in IR. This is something that commonly affects newer, wider and faster lenses more, but there are no set rules for this so specific testing must be done to be sure. 

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