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Sigma 19mm f2.8 EX DN A Art for infrared


altitude50 15 16.1k United Kingdom
5 Jul 2018 3:39PM
I am thinking of buying a (used) Sigma 19mm f2.8 EX DN A Art lens for my Panasonic GX-7. This camera is permanently converted for infrared photography.
I need to know if anyone has actually used one of these lenses for infrared and if it is liable to the dreaded IR 'hotspot'.
I have checked every internet source that I can find including Kolari and found nothing on this actual lens.

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Dave_Canon 13 1.6k United Kingdom
5 Jul 2018 8:38PM
You are right to check. I have a Canon DSLR converted to IR and found the performance for my lenses varied. Two of my Canon lenses are excellent for IR (my 10-20mm and my 24-105mm) but my Canon 70-200 is not in the good list but I have never had reason to use it for IR. However, I have a Sigma 12-24mm which is excellent for visible light but appalling for IR (unusable).

Would it be an option to borrow the lens and try it? Hot spots are no the only problem as you can also get flare which results in very poor contrast.

Dave
altitude50 15 16.1k United Kingdom
6 Jul 2018 6:44AM
Thanks for that. I can't borrow that lens as it is a long way away! Also I have read that results can vary in different lenses of the same model.

Up to a few months ago I was using a Sigma SD 15 dslr for infrared and had three different lenses, the zoom that I used most (about 80% of the time or more) was rated as bad for hot spot by Kolari but I never detected anything at all.
altitude50 15 16.1k United Kingdom
9 Jul 2018 4:40PM
I gave up on the Sigma and did some more research. It appears that one of the best prime lenses for IR on MFT is the Panasonic Lumix 14mm f2.5 so I have ordered one.

As an aside, I have a 3 element Olympus 15mm f 8 'bodycap' lens which has quite poor ratings for flare and I tried it out at the seaside in bright sun, for IR, pointing in various directions and it was fine for hotspots and flare, just a bit lacking in fine detail IQ (Unsurprisingly!).

With zoom lenses there are more surfaces and surface coatings to aggravate hotspots and some expensive zoom lenses are quite poor in this respect for infrared use.
altitude50 15 16.1k United Kingdom
11 Jul 2018 4:32PM
The Lumix 14mm has arrived, used but in excellent condition. Tried it out from my window on the garden, hedges, trees and the Yucca spikes in the garden next door. (They came out sharp! Grin)
Towards and across the sun. All looks good so far.

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