simple DR test A7S: what am I doing wrong?

[paulraymaekers]

hello,

can someone tell me what is wrong in the next test with my A7S

I set zebra's to 100

PP0   ISO 800

I start shutter at 1/25 and aperture 2.8, I illuminate a white paper so I just get zebra's, this is my starting point

by increasing shutter and closing aperture, I click down till the white paper is pitch black so I don't see anything anymore..

from just zebra's to pitch black, I just get 8 1/3  stop  when contrast is -3    (contrast 0, I get 7 1/3 stop)

same test for Slog2, gamut, but ISO 3200

10 or 10 1/3 stops from zebra's to pitch black...

 

where is the test wrong?

paul

 

[Jimmy]

There is probably only X amount of stops between the paper being exposed and black.
You could shoot on Dragon and get the same results.

 

Maybe try it with a light bulb and expose the filament

[caseywilsondp]

try rolling past your 100% and black a couple of stops while recording, then pull those into your coloring suite of choice and see what the results are. my guess is %100 is clipping a bit earlier than you're actually losing all detail. from what i've seen you should have no problem getting to at least 12 stops in slog2

[Guest Ebrahim Saadawi]

It's easy to compare the DR of two cameras, just point then at something containing highlights & shadows see how they reach within each, but to test the DR of a single camera and give an actual number, man that's hard, you'd need specific charts, ambient lighting, measuring tools, delicate grading, and calculate at all ISOs, etc and even then it's not 100% as people will blame your noise-floor-acceptance levels and argue about "roll-off"... It's opening a can of worms... 

edit: sorry for not being of help, It's that I've worked a long time trying to measure DR and failed (or put down) every single time

[mojo43]

The a7s goes to 108 IRE or something like that. If you have zebras at 100+ it doesn't always mean that it is clipping yet.

[hmcindie]

The a7s goes to 108 IRE or something like that. If you have zebras at 100+ it doesn't always mean that it is clipping yet.

​Not with Slog. With Slog it clips at 100. With Cine4 it goes up.

[mojo43]

Ahh is that so? So when I set to 100+ everything that is zebra is clipped?

[paulraymaekers]

try rolling past your 100% and black a couple of stops while recording, then pull those into your coloring suite of choice and see what the results are. my guess is %100 is clipping a bit earlier than you're actually losing all detail. from what i've seen you should have no problem getting to at least 12 stops in slog2

​so did the test again, both in PP0 (contrast -3) at 800 iso, and SLOG2 at 3200

starting 2 stops over zebra clipping down to 2 stops after pitch black

put it into resolve to see the waveform

PP0 I got like 9 1/3 stop  from 1024 down to zero noise

sLog2 got like max 11 stops from 1024 down to zero

what I notice in PP0  I go from 1024 to 512 in 3 stops   so very small  'bandwide' in the highlights

 

(not saying I'm not happy with my A7S, but till now I find only very small advantage between PP0 contrast -3  and Slog2: for everything where I don't need the absolute highest DR, I'm using PP0) 

(if AS7 would have possibility of contrast -6 or lower in PP0, probably there would be no reason to use SLOG2)

 

[hmcindie]

Ahh is that so? So when I set to 100+ everything that is zebra is clipped?

​You'll see it on the histogram (the histogram shows full 0-255). On the slog everything clips at 235, earlier on the histogram. With cine4 it goes up completely.