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View Full Version : Infra Red Filters - Different Strengths Compared


Zuiko
12th May 2011, 10:29 PM
Following the recent interest in infra red photography, and as the weather is ideal for it at the moment, I decided to pop up the forest today for a comparison shot of two different IR filters. These filters are confusingly named because they actually filter, or block, light in the normal visible spectrum, and allow IR light to pass through to the sensor.

First a "normal" shot to set the scene. ISO 200, 1/400th sec @ f8

http://e-group.uk.net/gallery/data/500/HATFIELD_INFRA_RED_003_e_r_s.jpg


Next, shot with a Kood IR72 (720 nanometres) which is a common strength of IR filter. ISO 200, 4 sec @ f8

http://e-group.uk.net/gallery/data/500/HATFIELD_INFRA_RED_006_e_r_s.jpg


Then with a significantly stronger 950 nanometre filter. ISO 400, 60 sec @ f5.6

http://e-group.uk.net/gallery/data/500/HATFIELD_INFRA_RED_013_e_r_s.jpg

Note exposure for the IR72 was a massive 11 stops greater tan without filter. Another 6 stops were added for the IR950, an incredible total of 17 stops greater than the original exposure in exactly the same lighting conditions.

The E-3 obviously has a very strong IR filter (in this context blocking IR light. From memory, it needs approximately 5 extra stops of exposure compensation compared to the E-500 when using an IR72.

The IR950 and the camera's IR filter between them block so much light that the 950 is almost impractical to use. Looking at these different exposures the advantage of a converted camera, like the E-PL1 recently added to Ian's hire stock, is obvious.

Finally, here's another using the IR72. It was taken with the 9-18mm lens. I couldn't repeat this particular shot with the 950 because it is only a 58mm filter, which fits my old 14-45mm.

http://e-group.uk.net/gallery/data/500/HATFIELD_INFRA_RED_034_e_c_r_s.jpg

Wee man
12th May 2011, 11:25 PM
Yep I got a 960 when I started to try this out and found as you did it is almost no use as not much gets through.

stevednp3
12th May 2011, 11:33 PM
Thanks for this john and explains why i havent been getting good results from my 850 filter, i have ordered a 720 filter so fingers crossed i'll get better results ;)

francois
13th May 2011, 12:00 AM
Thanks.

For pure B&W IR, I wonder whether a 780 filter would give better results.

Zuiko
13th May 2011, 12:16 AM
Thanks.

For pure B&W IR, I wonder whether a 780 filter would give better results.

I think you are right, as that wavelength corresponds more closely to the limit of visible light. Whether excluding all visible light will cause a problem with the E-3 I don't know. Quite apart from ridiculous exposures the 950 results look decidedly flat, even after a tweek in levels and a massive contrast boost. I guess that there was just too little light to work with.

Has anyone got a 780 they can comment on?