Infrared lenses need to be carefully chosen as some lens/camera combinations which work fine for regular photography create a ‘hotspot’ when used for infrared photography.
These hotspots show up a brighter area – usually a circle – in the centre of the frame. The effect can vary from very mild – which just looks like lens vignetting, to severe where a small bright area appears right in the middle of your image. If a particular lens is prone to hotspots, the problem gets worse as you stop down so that at very small apertures (eg f22) the hotspot is at its most obvious. I suspect that different infrared conversion filters also affect the way the problem shows up.
Sometimes you can correct for hotspot effects in Photoshop/Lightroom/ACR etc but I’ve found this process hard to automate, takes extra time and occasionally the problem just plain cannot be fixed. Its a much better strategy to find lenses that perform well in the infrared spectrum.
Ironically, the lenses which perform worst seem to be modern, multi-coated (and expensive) ones, while older, simpler lenses seem to do better. However, there are no hard and fast rules, it’s down to trial and error.
There is an extensive list of lenses on the Kolari Vision website but generally its hard to find reliable and consistent information. At the end of the day there are lots of viariables and what works for one combination of kit may not for another. Lenses seem to perform differently at different IR wavelengths. There is also a major difference between converted cameras and using screw -in filters in fornt of the lens. The only reliable way is to either rent or borrow a lens you are considering and try it on your equipment.
For what its worth – here is my infrared lens “Good hotspot” lens lists. These lists are based on personal experience of making images – rather than any kind of scientific or rigorous testing. Most of the time I shoot infrared images at f8. So, for me, if f8 is clear – then its a good IR lens.
Used either with a modified Sony a6000, 720nm filter with Kolari Vision anti-glare option and/or Sony a7Rii, 665 filter with Kolari Vision anti-glare option:
Sadly – quite a short list at the moment…but I have found one lens that makes this list – at least for me.
Canon 17 tse + Metabones V adaptor – a stunning combination. No hotspots at any aperture right up to f22. The image is sharp as a tack across the centre portion of the frame with only a small decrease in sharpness at the extreme edges. (Pin sharp everywhere in regular light). Best corners I’ve seen on any wide lens in infrared.
Only negative is that this lens is prone to flare.
Manual only – but not a problem on Sony cameras – and with all the added benefits of tilt & shift. Shift is especially useful for me as I shoot a lot of architecture and trees in infrared. Also great for panoranic stitching.
Sony 10-18 f4 – a versatile wide angle zoom for APS sensor cameras. Very small and full autofocus. This one is listed as “Poor” on the Kolari Vision list – but I’ve shot thousands of images with it in infrared – mostly at f8 with no problem.
Canon 24-105 f4 L – Sharp across the zoom range with no hotspots at any f stop. (Please note I have the mark I version which is now superceded by the mark II version and which I have not tested for IR.) Used on both a Fotodiox Pro EF-Sny(E) Smart AF Adaptor and a Metabones V.
Canon 24-105 f4 L UPDATE – I have discovered a major problem using the Canon 24-105/Metabones V combination on my 665nm converted Sony A7rii. There is serious light polution at some focal lengths – especially at the wide end – which I think is caused by an internal infrared focus LED. It is easy to spot – turn the camera on with the lens cap in place and look at the monitor – I see bright areas on the left hand side of the screen. Not a useable comination but fine with converted Sony a6000 which doesnt have the LED.
Sony 16-35 f4 – good for infrared up to f11 or so. At the wide end does flare easily.
Sony 24-70 f4 – widley criticised as being soft in regular light – but one of my favourites for infrared shooting where razor sharp corners just dont matter as much.
Lensbaby Velvet 56mm f1.6 – love this lens both for infrared and regular colour work. Its an old school, heavy, glass manual lens and its party trick is to become progressivley soft-focussed from around f4 until at f1.6 its creates a very soft image with a tiny sharp plane of focus. This effect works really welll in infrared.
Lensbaby Velvet 85mm f1.8 – every bit as good as the 56mm
Sony 16-70 f4 – OK performance – depending on the light intensity I often noticed a mild large lighter area in the frame – more like reverse vignetting than a defined hotspot. Nice range for APS camera (24-105 equivalent) but not my favourite for infrared.
Sony FE 70-300mm f4.5-5.6 G OSS – a great lens for regular light – but has very distinct hotposts from 70mm up to about 150mm. At longer lengths than that it works really well.
Sony 16-50 f3.5-5.6 – the aps kit lens – unusable for infrared – major hotspots throughout.
Sony FE 28-70mm f/3.5-5.6 – the full frame kit lens – significant hotspots from f4.
Canon 24-105/Metabones V on converted Sony A7rii – see notes above.