At this point, solid state image sensors have matched or exceeded film in a lot of ways, including light sensitivity, responsiveness to shadow detail, and overall dynamic range -- but that doesn't mean our chips aren't susceptible to certain problems previously avoided by the nature of emulsion. Indeed, 'sensitivity' nowadays means something different altogether -- and with the virtual necessity of neutral density filters as a result, this often means vulnerability to infrared pollution. Unless you like shooting at f/22 or you're already using the Aaton Penelope Delta, you may also require an IR filter with your ND. AbelCine has recently shared a great rundown of which cameras suffer the most from IR pollution -- and what filters work best to correct each.
Here's the short version of AbelCine's IR filters expo, followed by the full length presentation if you want to check out the whole thing.
Below is a price breakdown listing the filters used in the video -- there are many size variants for each, which I've tried to include because some DSLR-shooting readers may prefer the on-lens options over the rectangular matte box solutions (where applicable).
- Tiffen IR ND 2.1 Filter -- Ranging from $50 circular all the way to $450 6.6x6.6" rectangular
- Schneider Optics Platinum IR ND 2.1 Filter -- Ranging from $250 circular all the way to $520 6.6x6.6" rectangular
- Formatt Hitech ProStop IR ND 2.1 Filter -- $200 (circular only)
- Tiffen Hot Mirror HMIRND 1.2 Filter -- Ranging from $350 4x4" rectangular, all the way to $550 circular options, capping out a little under $950 for 6.6x6.6" rectangular -- used in conjunction with a standard .9 ND, which you can get for under $50
I for one was happy to see how well balanced the BMCC performed even sans-protection -- and even more surprising was how well the Canon C500 shot through straight ND. There's no doubt IR filtration will improve your footage out of the gate, as demonstrated in a post by Crunch Motion Design GMBH with the RED MX sensor -- the left grab uses ND 1.5, the middle uses an ND 1.5 Rosco IR filter combination, and the right: ND 1.5 with Schneider IR filtration added. The top triptych is ungraded RAW, while the second (with the same filter arrangements) is corrected in REDCINE:
On the other hand, the same post asks if IR filtration is truly a necessity with the use of ND, having found unfiltered RAW images could be mostly 'recovered' and adjusted in post -- check out the full post for the rest of the findings.
Whether or not you need IR filtration may be as much about your own preference and tastes as it is about your budget and gear -- some cameras will hold up better to post correction of IR pollution than others, so you'll have to use your own judgment depending on what you're using. Many will surely prefer to save the money and just 'live with it,' while others simply won't allow for that upper-red radiation to seep into their image. There's plenty of other IR-centric test and testimonial material out there, so feel free to share any that may have been eye-opening or useful to you -- plus any of your own experience with IR pollution you may have had.