SCORE NOTES

What Are Hotspots

Essentially this issue is infrared light showing up in the frame where is shouldn't. It's not always a bright spot in the centre of the frame and should not be confused with lens flare. It is NOT something that can be helped by using a lens hood. The issue is predominantly caused by the lens element coatings, although the camera's sensor is probably the initial source of the problem, so APS-C cameras can have better performance and the lenses internal materials also contribute.

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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 each lens scores at different apertures click on the the link for the lens. Also see the key above to understand exactly which version of the lens was tested.

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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 wavelengths coming from visible light, which are unaffected by the issue. 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 sky, where it would otherwise not have any yellow. Once you notice this issue it's hard to ignore it and it's even harder to fix than in a b&w image (see above).

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**Anti-Reflective Filter Coatings

Anti-reflective (AR) coatings on infrared filters can help to slightly reduce the hotspot intensity. In my experience this is mostly noticeable when the coatings are applied to internal filters. External filter coatings (in front of the lens) 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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