Infra Red and Full Spectrum Camera Conversions

Converted Cameras and Bespoke Camera Conversions

Lenses Suitable for IR Photography

Lenses that are good for general visible light photography may or may not be lenses that great for IR photography. The main problem is the appearence of Hot Spots which are normally circular areas in the centre of the frame which are lighter or milky. These generally get worse as the lens is stopped down more, so a lens may be fine at f/4.0, but has a hot spot from f/8.0 gradually getting worse towards f/22. The other variable with zoom lenses is the focal length, hot spots tend to be worse at the wide angle end, particularly kit lenses. Other variables that effect the hot spot performance are the filter wavelength used, some lenses are worse with a 850nm filter than a 590nm and some are better.

 

The cause of the Hot Spots is debateable, some say its caused by reflections within the camera and or lens, but the most likely cause is the multi coating on the lens elements. One reason I think its the multi coating, is a lot of older lenses with less sophisticated coating are better in IR than more modern lenses. The modern coatings are better in visible light for which they are optimised, this being one of the main areas modern lenses have improved, unfortunately at the expense of IR photography.

 

Hot spots are not the only problem, some lenses just are not suitable for IR, they may not focus at all or give a milky low contrast effect, sometimes varying with the wavelength of the filter being used.

 

It is often said that the longer the wavelength filters give sharper images because limiting the wavelength range of light being recorded will help the lens focus more accurately as there is less spread. This is true to a certain extent, if you have a Full Spectrum camera and don't use any filtration at all the image is likely to be blurry, its very unlikely a normal lens was ever designed to focus UV, Blue, Green, Red, and Infrared light all to the same spot. More expensive "APO" lenses claim to focus 3 wavelengths to the same point, rather than 2 for normal lens. This does not mean an APO lens will be good in IR, it may well be worse as the lens designer was never trying to correct the lens for IR wavelengths. The special glass types used to focus visible wavelengths, may be completely unsuitable for IR.

 

The only way to find out if your lens is any good for IR is to try it out at all apertures and focal lengths with various filtrations. However I will try and help by listing my experiences with various lenses below, please email me with your experiences and I will add them to my list;

 

 

 

Zeiss Loxia 21mm 2.8 for Sony E Mount Full Frame, Manual Focus.

Brilliant in Visible in every possible respect, the best Ultra Wide Angle lens I have ever used.

Still Very Good at 590nm and 720nm, but quite milky at 850nm, Hot area rather than spot from about f/7.1

The Hot Spot appears to be excessive "Blue" sensitivity, which means the deeper Infrared as the Red, Green and Blue channels are reversed in the Infrared zone. This allows the hot spot to be easily controlled when processing as Black and White, by lowering the Blue levels before or during the Black and White conversion.

The other thing I have noticed is the slight Field Curvature present in Visible Light is exaggerated in infrared, again this can be put to advantage as the bottom corners of landscapes are more in focus than normal. The downside is the edges and top corners at infinity are not as sharp. Click on the Images Below;  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The Loxia 21mm is not that great for False Colour work as there always seems to be a Red zone in the centre, after Channel Swapping, which is not that easy to eliminate.

To conclude I would say the Loxia 21mm is absolutely fantastic for 590-720nm Black and White work, but give False Colour a miss with this lens. Its still my favourite lens for 720nm IR work though, the sharpness is incredible.

 

 

Voigtlander Heliar 15mm f/4.5 III, Leica M Mount Lens, this lens is very much like the Loxia 21mm above, great in Black and White at 590-720nm, not so much in False Colour. This probably due to both lenses being made by Cosina in Japan, they probably share similar coatings despite what Zeiss and Voigtlander may say.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Olympus OM 24mm f/2.8 Zuiko MC lens - This is a great all round lens for IR work, no hot spots at all at any aperture and works equally well at 590, 720 and 850nm in Black and White or False Colour. Not quite as sharp as the much more modern and expensive Loxia 21mm, but still very good. My go to lens for False Colour work with deep red R25a filter.

 

Sony E 18-55 f3.5-5.6 OSS Lens - This kit lens for APS-c Sony Nex and a series cameras is very good in IR, has a mild hotspot at the wide end at f/8.0 and above, but not bad for a kit lens. Well built and takes sensible 49mm filters.

 

Sony E 16-50 f3.5-5.6 PZ OSS Lens - This kit lens for APS-c Sony Nex and a series cameras is pretty good in IR, has a mild hotspot at the wide end at f/8.0 and above, but not bad for a kit lens. Not quite as good as the 18-55 above, both in optical and build quality, seems a little delicate, takes  40.5mm filters.

 

Leica M Summicron 35mm f/2.0 [8 Element, Chrome with Goggles] - This lens from the seventies is a rare classic and surprisingly good in IR, no hot spots at any aperture.  Very sharp in the centre, falls off a bit to the edges, but no corner smearing at all on my Full Frame Full Spectrum Sony A7r, because the filter stack is completely removed.

 

Sony E 16mm f/2.8 Lens - Not a great lens at the best of times, seems to suffer wide variation in quality, OK in the centre, but poor edges and corners in IR, not hot spots though. The Sony 16-50 and 18-55 Kit lenses are much better.

 

Sony FE Zeiss 35mm f/2.8 Sonnar Lens - Great full frame lens in visible and great in IR, very mild hot spot at f/11 and higher, good all round performer, very small and light, AF work very well in IR.

 

Canon EF-M 18-55 f3.5-5.6 IS Lens - This kit lens for APS-c Canon EOS-M cameras is very good in IR, has a mild hotspot at the wide end at f/8.0 and above, but not bad for a kit lens. Well built and takes sensible 52mm filters.

 

 

 

 

 

A7r R72 IR_1 A7r R72 IR Web Sony A7r Loxia 21mm f5.0 R72 Filter Sony A7II Wydcombe_Web 8