Why cleaner blackshade at higher FPS?

[Thomas Koba]

First I blackshade at 25 FPS with 180 shutter (1/50)

Then I blackshade at 75 FPS with 180 shutter (1/150)


Then when I go back to recording at 25 FPS 1/50 shutter BUT with the 1/150 blackshade I get a much cleaner picture, when ramping the ISO up to 12000 or when looking at the GIO scope. Cleaner than using the "correct" 1/50 blackshade.

Why is the wrong blackshade giving me a cleaner black? I think it's darker too, so maybe because noise is crushed or something? I don't understand.

I've only been sitting here in the office in the dark, fiddling with the blackshade. Haven't been out shooting and checking the difference.

 

[David Kuhn]

Hmm... counterintuitive. I would expect the 20ms images (1/50) to have more noise if using the 6.6666ms (1/150) calibration data. Noise will increase with exposure duration. Unless you accidentally got them backwards I'd guess that RED is doing some math to try to make a blackshade more flexible... adjusting them to work at more than the exact exposure setting they're captured at - and in this case the adjustment isn't perfect and is crushing the blacks a bit.

Always best to blackshade at the exposure you're going to be shooting at obviously, but it's an interesting data point.

You might try also capturing at the same frame rate but adjust the exposure from 180 degrees to 60 degrees to see if you get the same result.

 

[Thomas Koba]

Wow! There's definently a difference when looking at the R3D too. What do you guys think? I thought it was only the GIO scope.

I've tried blackshading at both settings 3 - 4 times. And I get the same results. (Totally dark room too).

Download link.
https://www.yousendit.com/download/UlRSSmI5R0ZtMElPd3NUQw

As I said. Both of these shot at 25 FPS 180 degrees.

 

[bevan goldswain]

This topic has been covered already: http://www.reduser.net/forum/showthread.php?119602-Black-Shading-Tests

 

[Thomas Koba]

Thanx Bevan, I knew there had to be something wrong with my observation