[July 2021] - I have recently become aware that some of the latest Tamron lenses for Sony Mirrorless cameras are excellent in Infrared, with little or no hot spots. I contacted Tamron's UK Distributor [transcontinenta.co.uk] and they have kindly agreed to loan me a few lenses to test specifically in IR. This page will expand in the coming weeks and months as I work through their range, they will not be detailed reviews, but general impressions with real world examples.
Having been searching for a good standard zoom lens for a while, so I was thrilled when I first got my hands on the Tamron 28-75mm f/2.8 Di III RXD Lens. The images are almost completely free from hot spots at any aperture, certainly from f/2.8 to f/11. The above shot at f/5.6 is the full width of the frame, cropped slightly at top and bottom, but very little other work other than just levels and BW conversion. No sign of any hot spot and not too much darkening towards the corners. As of July 2021 this is my new favourite lens for IR work, I have tried Sony's GM 16-35 f/2.8 and although not bad is not a patch on the Tamron in IR, the Sony G 24-105 f/4.0 and the Sony 28-70 Kit lens are not great either, both have significant hot spot issues at all apertures. I haven't tried Sony GM 24-70mm F/2.8 lens, but there are some good shots in the Full Frame Gallery from that lens, so that's one to look at as well.
Here's a few more shots with the Tamron 28-75mm f/2.8 Lens, Click on the images for a larger view;
Tamron 28-75mm f/2.8 Di III RXD [Model A036] Lens in 720nm Infrared
The Tamron 17-28mm f/2.8 has just arrived and it throws the cat amongst the pigeons, the lens is quite a bit smaller and lighter than the Tamron 28-75mm and the focal length range is more to my liking for IR work as with the wider angle you can get more sky and clouds in the shot. First impressions are very good indeed, very little sign of any hot spots at apertures up to f/11 at any focal length, perhaps a smidge worse than the excellent Tamron 28-75mm above, but I think my favourite lens may be changing to this one as of August 2021!! Both Tamrons tested so far are condsiderably better in IR than any other zoom lens in this range I have tried.
Here are a few shots with the Tamron 17-28mm f/2.8 Lens, Click on the images for a larger view;
As you can see from the above/below shots the lens is excellent in IR, it focuses very quickly and completely silently and also the minimum focus distance is very short, only an few inches from the front element. I would probably say the Tamron 28-75 may be a tad sharper across the frame and into the corners, but the 17-28mm is still excellent and generally wide enough, 17-35mm would be better, but you can always crop the frame a bit to get a 35mm equivalent. Using the 28-75 I found I was mostly at 28mm and wanting a bit wider, but the 17-28mm feels just right for most work, but the pair combined cover most eventualities. The lens is very light [420g] and compact in comparison to the Sony GM 16-35mm [680g] which is at least double the price and weighs 50% more, it takes 67mm as against 82mm for the Sony GM although they both have a f/2.8 maximum aperture. Tamron have standardised on 67mm filter sizes on all their mirrorless lens designs, with the exception of the new 150-500mm lens. This may partly account for the slightly less generous zoom ranges, the 17-28mm and 28-75mm [550g] lenses would certainly be bigger, heavier and more expensive if they were like the more common Sony GM 16-35mm and 24-70mm f/2.8 [886g] lens ranges. The Tamron pair combined cover the same range [ish] as the Sony GM pair, but weigh about the same as just the GM 24-70mm and cost a lot less than just one of the Sony's.
I found that the image quality of both the 28-75mm and the 17-28mm were much improved by turning off all "Lens Corrections" in the camera's Menu. The Chromatic Abberation introduced by the "correction" was much worse than the lense's actual abberation. This was with my 720nm Infrared converted Sony A7R4, but I suspect it will be the case with all 720 or 850nm uses, where there is very little colour information in the actual image.