Black shading - questions and thoughts

[Petri Teittinen]

Mr. Marchant's fantastic graphs made me think about black shading and the implications of heat.

Setting aside for a moment the fact that I don't quite understand why RED's cameras need black shading when competition does not (or do they?), I got to worrying about the temperature range where black shading applies.

The shooting temperature range appears to be from 40 to 75 degrees Celsius. That's quite a wide range and it feels to me that a black shading done at 40 degrees can not be valid all the way up to 75C (although I could just as easily be wrong about that).

This thinking lead to questions.

- If I perform black shading at 40 degrees and begin a long take, how high can the temperature rise before I might see problems in the image?
- Should I run the temp to 60-65 degrees before black shading if I knew in advance the takes will be long?
- Alternatively, would a black shading closer to 40-45 degrees make sense if I knew in advance the takes will be short (and far apart, with enough idle time to allow for cooling)?

I'd love to see RED introduce a sensor certification feature and some sort of dynamic black shading which would rid us of the need for black shading. Here's how I imagine it might work: (Warning! Non-engineer rambling ahead!)

1) Connect EPIC/SCARLET to a power source with enough juice to run the camera for a couple of hours non-stop.
2) Make sure no light gets to the sensor.
3) Boot camera up, insert REDMAG, enter Maintenance Menu and select "Sensor Certification"
4) The camera begins running a series of automated black shadings at different frame rates, resolutions, shutter speeds and temperatures. This will take quite a while.
5) As a result, a large-ish data file is saved on the REDMAG.
6) Copy the file from REDMAG to your PC/Mac. Download & install a "Black Shading Calculator" software application from RED and load the data file into the app.
7) Based on the data file's contents, the application creates a black shading file which is then copied to a REDMAG and loaded into the camera.
8) The camera now "knows" how its sensor behaves in various different scenarios and operator-performed black shading is no longer needed.

One can dream, right?

[Jaakko Rinne]

AFAIK most cameras do a blackshade on startup. For some reason RED's way of doing a black shade takes a bit longer.

On Marchant's graphs the sensor temp never goes much higher than 40. The core temp goes up to 75, but that doesn't have an effect on blackshading, only the sensor temp matters.

[Petri Teittinen]

On Marchant's graphs the sensor temp never goes much higher than 40.

Ah, indeed. The sensor temp variance is 31-42 degrees, according to the graph. But that does not change my question any: how sensitive is the sensor to temperature changes? Should black shading be done at 40 degrees when doing long takes and at 32 degrees when doing short takes with plenty of time for cooling down between takes?

[Jaakko Rinne]

I think in an earlier thread there was talk about a difference of 5 degrees and up being where blackshade might start to make a difference, but even then it depends on what ISO you intend to use, if you'll be crushing blacks and also if you're shooting tungsten or daylight. I've done the blackshade on my Scarlet-X at 40 degrees, since after the camera has been on for more than a few minutes the temperature won't be too far from that and won't rise much higher even when recording a longer take. For a shoot outside in colder weather I'd probably test where the temperature settles and do a blackshade at that temp if possible.

Haven't had problems shooting in the studio with the camera running for hours or run and gunning with the camera recording as soon as it boots up, but I've also never had to go above ISO 1600 and have always tried to stay at 5600K. It might be useful if someone had the time to do some blackshade vs. temperature tests.

EDIT to add: I'd personally like to see an option to set the fans to automatically try to keep the sensor/core at a set temperature. If the temp stayed the same, this would be a pretty moot discussion.

[Erich Ocean]

AFAIK most cameras do a blackshade on startup.

As I understand it, the Canon C300 is blackshading continuously, using the look around area. This is why it's so killer in low light.

[Petri Teittinen]

even then it depends on what ISO you intend to use

How come? As I understand it, ISO on RED cameras does not work like it does on, for example, DSLR cameras. ISO setting on Epic and Scarlet does not alter sensor sensitivity or gain. ISO setting is just metadata, in other words.

[Petri Teittinen]

As I understand it, the Canon C300 is blackshading continuously, using the look around area.

That sounds pretty wild! :)

[Patrick Tresch]

EDIT to add: I'd personally like to see an option to set the fans to automatically try to keep the sensor/core at a set temperature. If the temp stayed the same, this would be a pretty moot discussion.

+1

How does ISO affect blackshading? :

You can see good or bad blackshading when pushing iso and digging info in the noise area, and there fore it does depend if you entend to use 3200 iso or 320 iso as the base, and this will change how critical it is to have the right blackshading.

Pat

[Enrique Blein]

How do you check the internal temperature? Is it in the menu? Maybe it should be on screen...

[Bob Gundu]

How do you check the internal temperature? Is it in the menu? Maybe it should be on screen...

In the main menu next to the histogram.