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Anti-Reflective Coated Filters
Kolari Vision offer these coating on conversions for an extra $100. While I still had a normal conversion (Full Spectrum) and an 'Anti-Reflective' (AR) one, I decided to put them through my hotspot test scoring system to see how they did. The AR coated filter I have is an internal 720nm wavelength. The Full Spectrum conversion used an external Hoya r72 filter. I also ran the tests on the internal 720mn AR conversion with the external Hoya r72 filter on as well, to see what difference that made.
A reminder of the scores: (0=Terrible - 10=Perfect). Here are the results on the brand new Samyang 24/2.8 (native Sony FE) lens...
Initial Results
The first set of results came out pretty consistent throughout the apertures, confirming the lens characteristics remain intact and suggesting that the tests are meaningful and repeatable. The offset between the main two (green and blue) suggest that the AR coating does have a noticeable effect on this lens, although it did not clean up entirely. Adding an external filter (of the same wavelength) in front of the lens as well reduced the effectiveness of the internal coatings, but not massively. This is not quite what I expected, I had hoped the results would improve further, but this is interesting none the less.
OK, all we need now is to see each lens perform in the same order, so let's run this test on another lens and see what we get...
Repetition
Great! Just as the first test the three results are showing up consistently and in the same order. Again the AR coatings are making an improvement, although not as much this time. Adding the filter in front of the lens again diminished the improvement. I do wonder what would happen if we added AR coated external filters as well. Perhaps then the results would improve further, perhaps not.
So far we have tested one 'Acceptable' lens and one 'Poor' one. For my third test I will try one very good performing lens, to challenge the results. This should be interesting because there will be little room for improvement. If we see the AR coating get any worse then the tests will look to be less conclusive...
Three For Three
Ok, the consistency of the results is pretty impressive here. You can just see the green line showing above the red and the blue one below. With almost no improvement to be made there is still some movement and in the same directions as the other two results.
Conclusion
These coatings can help to reduce hotspots, but they are no substitute for a good performing infrared lens. I would love to do these tests at 850nm (internal vs external filters), with and without coatings. From my limimted experience with external coated filters they do not seem to do very much.