Welcome to our community

Be a part of something great, join today!

Log in
  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Playing Around With Infrared on Red

Clint Johnson

Clint Johnson

Well-known member
Joined
Dec 28, 2006
Messages
559
Reaction score
0
Points
16
Website
clintjohnson.com
So there was this music video where they wanted the talent shot with visible light and then composited onto a background shot in infrared. We did some tests with the Red 18-50 zoom but it wasn't letting a lot of IR through what with it being T3 and all. There were some later tests with Superspeeds that the director was happier with.

Yesterday, out of personal curiosity, I decided to go out and test some more with my T3 lens. This time I was undercranking with the shutter set to 360 degrees so that I got:

1) A single frame per second at one second exposure got the most light of course but there were also some hot pixel and noise issues due to the longer exposure. The director of the video didn't want the band to look all creepified from the IR... but I make creepy work.

2) It looks like, with the Red 18-50, wide open at T3, the optimum exposure for light levels with IR is four frames per second with the resulting 1/4 second exposure. It is fast enough that the sensor noise doesn't effect it too much and slow enough that it doesn't have to be pushed too much in post to bring its brightness up.

3) Here is a shot at 24 fps and 1/24th second exposure. The scene was reflecting and emitting about as much infrared as you're going to see here - 1PM, clear day, >30 degrees celsius. While it would probably be usable at SD it is pretty noisy because it really had to be brought up in post.

If you are using fast lenses in the T1.3 or F1.2 range, on a really bright day, then I think you should get away with the 24fps at 1/24th. The optical optimum, but not the temporal optimum, would probably be at 8 or 12 frames per second.

Here is a link to InfraRED Testing.MOV that has samples of the three setting above. I didn't bring the undercranked footage right up to the project speed, nor did I correct it to actual speed- I adjusted it what I found the most pleasing to my eye.
 
Great stuff Clint!

Thanks for sharing.
 
Full Sized Stills

Full Sized Stills

Here are some stills from the test.

Here is a cropped jpg from the first section (1fps - 1 second exposure) to give you an idea of what the DPX looked like. Right click and save the 32MB DPX 002426.DPX if you want to take a looksee.

002426_RedcineOnelight.jpg


And here is a colour corrected version with the hotpixels circled. Since there were so many, I just circled the ones in the sky over my right shoulder. Gotta love that heroic pose eh?

002426_HotPixels.jpg


Here is a JPG crop of the second section (4fps - 1/4 second exposure) of the DPX. And here is the 002952.DPX to download.

002952_RedcineOnelight.jpg


And the colour corrected version. As you can see, there are a lot fewer hot pixels at this point. I probably should have done a black calibration and then ran the tests again to see if it would correct for the hotpixels when done on the day rather than a couple weeks back.

002952_HotPixels.jpg
 
And here are the two from the third sequence (24fps - 1/24th second). Here is the 007375.DPX. As you can see, it is pretty darn dark, soft and noisy. At least with Build 16 the noise is a lot more like film grain and less of the fixed pattern that earlier builds gave us.

007375_RedcineOnelight.jpg


Colour correcting it helps but there is only so much you can do with that image.

007375_PhotoshopAdjustments.jpg


I do think that, if you had the T1.3 lenses and shot in direct sunlight between about 10AM to 3PM, you could probably get some usable results.

One thing to keep in mind is that infrared light focuses at a slightly different plane than the visible spectrum does so if the subject is 10 feet away you'll want to focus the lens closer to 9 feet. I don't think any cine lenses, and few new still lenses, come with the IR witness mark. About all a person can do is use a tape measure on the subject and then nudge focus a smidgen closer, since focusing through the lens isn't easy due to the paucity of light and the inherently diffuse nature of that wavelength. And of course, that smidgen will vary slightly lens to lens.
 
I was using a cheap Kenko R72 screw in filter on the Red 18-50. The R72 designation is used with other makers and formats- and refers to the light being filtered out below 720 microns.

Allstar, did that Cokin let in a lot of visable light or did you do some false colour in post? It looks like it is allowing light in all the way down to 650... maybe even 600 microns?

And the stuff that wasn't time lapse... was that undercranked a bit? It looked like maybe 20 frames per second re-timed to 120%?

It looked good, just trying to get the technicals of it all. I am a curious man.
 
Does somebody know where to find more info on RED problem with infrared light. Thanx!
 
Thats fantastic, looks amazing, thanks for sharing. I too have been waiting test this out.

How clean is the full rez image at the values you shot. Is there a lot of noise or is it quite clean? Its looks quite clean until the 1/24th sec exp.
 
You must log in or register to reply here.
Back
Top