Rating the RED

[bobbystone]

Can anyone help me with this? I've been trying to establish an ASA rating for the camera so that I can use my light meter. I consistently get a much lower rating than the 320 established by RED. Here's my methadology:

Put the camera up shooting a grey card with white and black patches. The card is evenly lit in tungsten. I set the view to RAW, turn on False color and adjust the aperture till the grey card is green and the white card is between orange and red. To get the corresponding stop on my light meter(after reading the grey card with the spot meter) I have to adjust the asa on the meter to 80. This is 2 stops LOWER than the advertised rating. I'm not bitching about the rating, but I'd like to establish what it truly is.

Comments, thoughts, critiques on my method?

[Gunleik Groven]

@ tungsten 200 would be about right

[LEON]

The card is evenly lit in tungsten. I set the view to RAW, turn on False color and adjust the aperture till the grey card is green and the white card is between orange and red.
Comments, thoughts, critiques on my method?

Could you try the same test with DAYLIGHT ?

[Harry Clark]

I have been confounded by this as well, though having only tried it a couple of times.
In daylight, by my 3 incident meters, and various gaffers' meters, I've gotten ISO 125 or 160. That's by trying to make 18% grey green with false color (I had been setting exposure in Rec 709, however)
Lighting a scene with the meter set at 320 looks fine, but then opening a stop (depending on the scene) from there almost always looks a bit better. So I've taken to just using false color, with a RAW check to make sure the highs are not too high.
The false color tool is very good; however, keeping consistency in contrast
(fill light), scouting, and prelighting would all be made more efficient with accurate metering. It's puzzling to me why this seems elusive.
Maybe it's me...
Cheers,
Harry

[bobbystone]

I'll redo the test tomorrow in daylight and post results. But 2 stops is a pretty big discrepancy

[Graeme Nattress]

ISO is totally dependent on what LUT is used to map which code value to mid grey. Also, definition of ISO has an absurdly low % for white at 107% compared to mid grey at 18%, which means it offers very little highlight protection.

That's why the ISO of RED is natively set at 320 so you don't clip the highlights like some video camera, and it's also dependent on the precise curve you use to develop the RAW image with.

Graeme

[Dylan Macleod, CSC]

I have been confounded by this as well, though having only tried it a couple of times.
In daylight, by my 3 incident meters, and various gaffers' meters, I've gotten ISO 125 or 160. That's by trying to make 18% grey green with false color (I had been setting exposure in Rec 709, however)
Lighting a scene with the meter set at 320 looks fine, but then opening a stop (depending on the scene) from there almost always looks a bit better. So I've taken to just using false color, with a RAW check to make sure the highs are not too high.
The false color tool is very good; however, keeping consistency in contrast
(fill light), scouting, and prelighting would all be made more efficient with accurate metering. It's puzzling to me why this seems elusive.
Maybe it's me...
Cheers,
Harry

I concur.

I just did a big greenscreen job and metered at 160 (cause of my 80C filter).

Same thing as Harry, I found inevitably I would open up a stop from what my meter said, based on reviewing the histogram and false color.

[Miguel "Macgregor" De Olaso]

Measuring RAW view with the false color and trying to get the grey card in the green zone will not give you any good measuremente for your lightmeter, since the RAW view is a linear 1.0 gamma curve (well, it´s not actually a curve but a line ;D), and you will mostly finish your works with a 2.2 gamma, so it´s with the redspace LUT (or 709) where you want to do that test.

[bjonsson]

Discrepancy? This is a shift in understanding digital - not video. When the Arri D-20 first came out, it too was rated at 320, but by all my testing indicated that it was really 160. The guys at Arri put me on the phone with one of their techs in Germany ( I think we got him out of bed). He clarified the situation. Yes, by following the waveform it would appear to be 160, but by under exposing the grayscale (to around 35 to 37 IRE), the dynamic range was extended or optimized the grayscale , and the "lifting" the image later. This was confirmed by myself after shooting dozens of commercials with the camera.

Remember that the video output is only an interpretation of the RAW image being recorded. Like Graeme said - "ISO is totally dependent on what LUT is used to map which code value to mid grey".

It's kind of like a restaurant that slightly undercooks their take out menu, because they know that people are going to microwave the meal at home - yeilding the perfectly cooked meal.

We know we will need the over-exposure protection later, so we under expose in camera for an extended range later - with no loss in quality. This undercooking is built in by using the 320 ISO rating.


BTW Arri published a slide wheel or disc that showed the relation of ASA to dynamic range. Does anyone have it? This would be helpful to people trying to understand the charecteristics of the RED. I'll dig around to see if I can find mine.

[Brook Willard]

I've found that in most cases, metering at 160 will get you a pretty solid exposure in REDspace. Stuff I've metered at 320 is usually underexposed unless it's a high-contrast scene with some large-area highlights I'm trying to save.

That said, I don't use a light meter.