At long last, an update to my fabled IR Filter Cheat Sheet. Not every camera responds the same way to IR; make sure you have the right filter for the right job.
Here it is, version 2 of the Art Adams IR Filter Cheat Sheet:
There are two crucial additions here:
The newly-released Arri Alexa responds to far red in a similar fashion to the Sony F35 and the Sony EX1 and EX3 cameras.
Tiffen has released a Hot Mirror IR ND filter that combines the T1 far red filter with a Hot Mirror. This combination does a great job on the RED ONE (both M and MX) and is just a little bit of overkill compared to the other hot mirror filters on the market, because the other hot mirror filters don’t have the additional T1 far red dye.
These filters, in theory, should work equally well on both the RED ONE and the far red sensitive cameras (Alexa/F35/EX) even though they have different requirements: hot mirrors don’t do any good on the Alexa/F35/EX cameras, and the T1 and IR ND filters without hot mirrors do nothing for the RED ONE on their own. It shouldn’t hurt to use these combination filters on either camera–just be aware that although they combine hot mirror and T1 dye technologies, only one technology works on any given camera.
The IR ND filters are designed so that the green dye that removes far red is proportionate to the amount of ND. That means you can’t use them with regular ND filters as the amount of far red passed will overwhelm the level of dye in the IR ND. For example, an IR ND .90 blocks ND .90 worth of far red, so if you add a regular ND .60 filter you’re going to see far red contamination: ND .90 plus ND .60 equals ND 1.5 worth of far red, but an IR ND .90 only blocks ND .90 worth of far red.
The Tiffen T1 filter on its own, which is basically an IR ND without any ND, will reduce far red through quite a number of regular ND filters, even though that is not its intended purpose. On the Arri Alexa, for example, the T1 worked quite well even when combined with a regular ND 1.2 filter.
When in doubt, TEST.