AC90: Camera makes some blacks burgundy

E

Enerjex

Member
Hi all, I've encountered a strange phenomenon a couple of times using the AC90 and I'm wondering if there's any scientific explaination/way to fix or avoid it. It's basically representing some blacks as burgundy. Some black things come out black, but for some reason some of them are recorded burgundy. ie I have a BBQ cover that's black inside and out, the AC90 films the outside as black but the lower hem and inner lining as burgundy. Yesterday I was filming a mate with black shorts on and they also came out burgundy, whereas black surroundings were recorded correctly as black. I may have missed a setting but it seems to do it with all matrix and gamma settings. I did a test and my 60d and Galaxy S3 cameras record these blacks correctly. What could it be?

Cheers,
Karl
 
Thanks Barry. After a couple of google searches and seeing some examples it looks like that's what I'm encountering. Now to find a way to fix it. Tiffen have a 49mm filter for it that might be worth trying, but it's pricey. What are your thoughts mate?

Cheers, Karl
 
An IR-cut filter is almost certainly what you need. Since you'll need this mostly in daylight, you might want to get one combined with a 2- or 3-stop neutral density filter. It will certainly seem a little pricey, but you shouldn't compromise on the quality of any glass that goes directly in the image path. It's a little disappointing to find out there isn't already an adequate IR filter in the lens/prism/sensor system of the AC90.

- Greg
 
To echo Greg, yes, an IR-cut filter will eliminate the color cast.

You can see it in daylight when under heavy ND filtration, or you can see it when under tungsten lighting.
 
ELN614 said:
So do other manufactures have the same problem?
Click to expand...
Of course. The EX1, the Red 1, lots of cameras have occasional IR contamination issues.

The problem here is probably more of an issue of far red, rather than infrared. When tuning a camera for sensitivity, you have to decide where to cut off the light spectrum of what you're going to allow the camera to see. The further you extend the spectrum, the more sensitive the camera can be. The more you cut off, well, that's light that you're cutting off. So the manufacturers have to walk a fine line down at the lower end of the spectrum. If they go too far, you'll see too much infrared and your blacks may (on certain textures or types of black) shift to a burgundy or red tint. If they cut off too much, you'll have pristine blacks but lose sensitivity.

In daylight every camera can have issues, because if you use a lot of ND filtration you cut out the visible spectrum, but ND filters don't cut infrared at all, so proportionally more and more infrared pollutes the signal the more ND you use. That's why most every filter manufacturer now offers IR cut filters, and ND filters with built-in IR cut.

Just google IR contamination, you'll see thousands of threads on it.
 
You must log in or register to reply here.
Back
Top