Blackmagic Forum

I remember reading somewhere that the sensor does little if nothing to filter out IR: thus the reason ND filters cause so much IR pollution.

Has anyone tried to use the BMCC for IR cinematography? like this:

I haven't seen any examples yet online, and would love to see some. and see if it is at all viable for such a unique application.

I have an IR filter lying around... I'll give it a try but I suspect it'll be difficult because the shutter period can't be increased beyond 1/24th of a second under the current firmware (it's tied to the frame rate, even in time-lapse mode and the largest shutter angle is 360 degrees).

hmmm... I might consider purchasing an IR-cut filter in the near future.

I set the camera to 1600 ISO, 24 fps and 360 degree shutter. I attached a 55mm lens at f/2.8 with a very dark, pretty much IR-only filter attached. I ignited a blowtorch and brought it within view and to my surprise a fair portion of the torch was visible on the BMC's monitor.

I'll give it another try tomorrow in daylight, but so far it seems like it could be usable during the day...

Aaron Scheiner wrote:hmmm... I might consider purchasing an IR-cut filter in the near future.

I set the camera to 1600 ISO, 24 fps and 360 degree shutter. I attached a 55mm lens at f/2.8 with a very dark, pretty much IR-only filter attached. I ignited a blowtorch and brought it within view and to my surprise a fair portion of the torch was visible on the BMC's monitor.

I'll give it another try tomorrow in daylight, but so far it seems like it could be usable during the day...

Hopefully with a 1.4 or 1.2 lens we might be able to get a decent exposure outside?
Whatever the results might be, I hope you attach a sample so those interested know what they're up against.

I'll test it tomorrow in daylight with an f/1.4 lens and I'll post some frames.

Here are some frames from three separate shots. They were all shot at ISO 1600, Shutter angle 180 and 24 fps at f/1.4 on a Sigma 30mm lens. They were shot under morning daylight (reasonably strong).

Filter used was a Tiffen TI8762 62mm #87 Infrared Glass Filter.

I heavily colour/color-corrected them in Photoshop. The DNGs are also included below.






DNGs :
http://www.epicpaintball.co.za/personal/IR01.dng
http://www.epicpaintball.co.za/personal/IR02.dng
http://www.epicpaintball.co.za/personal/IR03.dng
http://www.epicpaintball.co.za/personal/IR04.dng

Don't want to sound blunt, but why not doing it all in post and have a ton more control over it?
Seems to be pretty easy to do.

You could use the same argument against tilt-shift lenses... Why not emulate that in post ? Or one step further, why not aim for deep depth-of-field and emulate shallow DOF in post ? Why not shoot with a much higher shutter speed and emulate motion blur in post ?

All of these things give greater control to post, but they are all emulations of real photographic processes. While emulating these processes may be sufficient to create the desired effect they will usually result in a lot more time used and a poorer quality output... Besides that, raw provides a lot of flexibility even in IR.

I guess it comes down to personal taste... and in my case, wanting to experiment.

P.S. Why spell a word correctly when you can spell it incorrectly and people will still understand what you've written ?

Aaron Scheiner wrote:P.S. Why spell a word correctly when you can spell it incorrectly and people will still understand what you've written ?

Yeah, I do that all the time

I see where are you coming from.
I think it all depends on taste and time/work ratio.

Some things are quick to do in the "real world", but than you often spend hours in post to get them where you want them. Some stuff you can add in post pretty fast and have lots of control, but it may look less organic or sheer fake.

I guess it's always going to be some sort of compromise; cost/time vs quality (in the context of the requirements).

As a side note, the first project I ever worked on involved the phrase "we'll fix it later/in post" (we were all to blame). I learnt my lesson; get it right from the start because by the time post comes along you'll be digging your nails into the desk every time you hear those words. This doesn't really relate to the infrared topic, more to the "you often spend hours in post to get them where you want them" sentence.

This is excellent, I didn't realise that the BMCC was quite so sensitive to IR. Ok now to buy some high powered IR lights ready to go filming wildlife at night in glorious 2.5K.

You'll need some very powerful lights . If an f/1.4 lens and EI1600 exposure barely suffices during the day...

So, I don't know how to denoise in photoshop. but this is one posted above, with about 2 minutes of photoshop work done to it. white balanced to the green leaves, then channel switched the red and blue (with some twiddling as well)
A hue and sat filter, a color balance, and another mild desaturated. I wanted to process it for noise, but I am not that skilled yet.

paulkosmala wrote:So, I don't know how to denoise in photoshop. but this is one posted above, with about 2 minutes of photoshop work done to it. white balanced to the green leaves, then channel switched the red and blue (with some twiddling as well)
A hue and sat filter, a color balance, and another mild desaturated. I wanted to process it for noise, but I am not that skilled yet.

but yeah. if this was mid day, a 1.4 lens might be able to do the trick... might not be the best camera for it.

Can someone from BMD confirm: is there an IR blocking piece of glass in front of the filter? or anything that would inhibit IR capture?

Hi

I have modified cameras before by opening them up and removing the IR-cut filter. The BMC does have an IR-cut filter combined with a UV filter; it'd have to have this because a camera without an IR cut filter will produce images with odd results that would be unacceptable for cinematic use.

Examples include colours biased towards red, black objects (absorb visible light but reflect infrared light) showing as brown or magenta. Even some alcohols appear transparent in infrared. Plant leaves also reflect a lot of infrared and show as brown... I'm describing a camera that has no IR-cut filter and no IR-only filter. If you look at the BMC image you colour corrected, the leaves on the plants may be correctly balanced, but many other objects in frame aren't, like the pool doughnut, it is normally blue.

So The BMC definitely has an IR filter and it's quite strong, the sensor itself is very infrared sensitive as are most CMOS sensors.

And there's a lot of IR light during the day, reproducing that amount of light at night would require several kw of tungsten light. If you're serious I'd suggest, depending on your budget, that you either modify a BMC or an older DSLR for IR-only use by getting the IR-cut filter removed.

If you look at the image below, everything that appears white would appear brownish-magenta in a normal image if the camera had no IR-cut filter. By comparison to the BMC, this old Canon 300D exposed this image for 1/50th, f/11, ISO400 on a cloudy day... because it doesn't have an IR-cut filter. It also doesn't focus to infinity, hence the f/11.