ND and IR contamination?

F

firehawk

Veteran
I am concerned about outdoor weddings and black clothing:
I'm just about to start using the following 3 cameras which need add-on ND filters.
Sony A6000, EA50U and Panasonic AG AC90A.

Are certain ND filters more prone to introducing IR contamination and any of those cameras sensors also more or less problematic?
Id like to keep the exposure right without having to up the shutter but I don't want black jackets turning rusty red or weird color shifts /adverse effects that make it harder to match cameras or the image worse :)
 
Yes, different cameras are differently sensitive to IR, and it depends on both the sensor and the OLPF and other filtering in front of it.
If you're worried, you should test with a bunch of different fabrics beforehand, or, use filtration as Greg_E mentioned, they're usually called 'hot mirror' or IRND for dual-purpose filtering.
 
This is a tricky subject and one that I have spent a long time and a lot of money to solve for myself (Using Blackmagic cameras). While I'm not familiar with the cameras you're using, I have learned quite a bit on my journey since BM cameras tend to be more sensitive than others, therefore being a little trickier to get right. Matte box systems and high quality filters are expensive. If image quality is of the utmost importance, then this cost is worth it. IR contamination is caused by neutral density filters blocking more of the visible light spectrum than far red (infrared), causing it to start to contaminate the image. How much this contamination occurs depends on many factors including the strength of the ND, amount of IR (heat), the type of fabrics you're shooting, and the OLPF in your camera. Every camera is different and will react to different brands and strengths of ND filtration differently making this all the more challenging to get right.

I would recommend taking some time trying out different filter combinations of IRND, normal NDs, Hot Mirror NDs, and varying strengths of IR Cuts. Mix and match them under a controlled tungsten lighting setup testing all three cameras against different fabrics until you find a set that works well for each. Shoot without any filtration (Stopped down), then with regular NDs, then regular NDs with IR cuts, then IR and ND or IRNDs. The results will speak for themselves. It is also worth repeating that different brands of regular ND will behave differently, especially at or above strengths of 1.2 (4 stops). This is where IR filtration is almost required, but I recommend it at all levels of ND to maintain image quality.

The only real consideration between the different types of IR filtration is how they work. The only important thing to keep in mind is any 'Hot Mirror' filter should be farthest from the lens and the first optical element in the filter stack the light hits. They work by reflecting IR instead of absorbing it like other filters. Putting them behind other filters can cause unwanted reflections (They have a mirror like side — this side faces away from your camera lens).

For me, personally (Using Blackmagic cameras), I'm happy with the Skier IRND Hot Mirror filters. I mix in regular Schneider NDs behind them when more ND filtration is needed. Maybe they'll work for you. I use them in a 4x5.65 matte box system but I believe they also sell them in 4x4 if I'm not mistaken. They are also probably among the cheapest IRND filters that I've tried and they happen to work for my needs.
 
You list the AC90 - I shoot events with the AC130 and have no issues with the built-in ND, fully engaged. Does the 90 not have ND built in?
 
Michael Carter said:
You list the AC90 - I shoot events with the AC130 and have no issues with the built-in ND, fully engaged. Does the 90 not have ND built in?
Click to expand...
It does have built-in ND, but it is lacking in bright environments. I have read not to iris down more than f/6.8 so my understanding is that people use mild external ND with it.

I've run into this same lacking with my HCK10 (HMC 40) on really bright days. It just can't iris down enough so sometimes I have upped the shutter to bring down the light.

My concern and reason for starting this thread was if I start adding external ND to these different cameras, how many new problems will I cause such as IR contamination and color matching issues. I see I will have to set up tungsten lights and test with a bunch of different fabrics and various settings and filters to figure out how to deal with it.
My friend "borrowed" my tungsten lights long ago and has probably beat the tar out of them so now I get to deal with this too.
 
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