Sony Lens FE 85mm F1.4 GM

AR Coating

What is the AR coating and what does it do? The AR coating option adds an IR centered anti-reflective coating onto the IR filter we install when we perform an infrared conversion. It reduces hotspot artifacts that some lenses are prone to, and can reduce other stray reflections. On our full spectrum conversions we apply a broadband AR coating that covers the UV, visible, and IR ranges. The coating does not reduce optical performance in any way and is highly recommended.

Background:

Uncoated glass has a reflection of around 4-5% at all wavelengths, and we found that this reflection off the sensor filter was bouncing off the glass and reflecting back from the lens housing and aperture blades to cause IR hotspots.  We developed this anti-reflective coating that is centered around the IR wavelengths that cause hotspots, and reduced the 5% reflection down to <0.5%

Conversion AR Coating

When applied to our internal conversion filters, we find that hotspots are significantly reduced during infrared photography. Below is a sample from a Nikon 50mm 1.8 which has a strong hotspot at small apertures. Independent tests also available from Mark Hilliard here and Edd Noble here.