Log/Rec.709, Headroom, and Dynamic Range....

[Dj Joofa]

"Rating" the camera higher in order to underexpose (say from 640 instead of 320) has very little to do with setting the ASA on the camera. The important factor is setting your light meter to your desired rating (again, say 640), and then exposing based on the meter. Regardless of the on-camera ASA and preview you are seeing, it's how you use your light meter to set your iris that makes the difference. Changing the ASA on the camera does very little, as we have found out.

That being said, if you do rate at 640, you might as well set the ASA on the camera to 640, but it's the lightmeter and iris, not the setting, that are important.

Sure.

And, Consider this experiment: Suppose you are shooting the same exact scene with two film cameras one with stock rated 320 ASA and the other 640 and you drive the metering options using light meter correspondingly, so that you final image looks more or less the same for both camera.

Now suppose you did the same experiment with Red. However, since Red's sensor is fixed and not changeable like film stock, then any signal values you acquired by metering for 640 ASA has to be changed in software to match the image acquired with metering using 320.

And, that is where I have a small issue if the gain is provided in software and not in-camera using analog gain. Digitization provided by ADC looses some analog detail which could have been useful in gain before digitization. Hence, images brightened by digital gain can have posterization effects more noticeable in the dark/shadows. Though, it is possible to reduce some of this posterization by using several techniques.

 

[Michael Brennan]

Both CMOS and CCD sensors have a particular energy level needed to reach saturation point.

Think about keeping highlight "energy" to a level below the saturation point.
Then consider their is a level of noise that makes shadow detail unusable.
This is more subjective appraisal than seeing highlight detail disappear as the sensor is saturated.


Referring to what happens on the sensor, if you put highlights one stop below the saturation point then you are losing one stop of deepest shadow detail.

However the AD, gamma curves or log recording can disguise what is going on and certainly it gets confusing to the point where some people begin to think that you are actually improving dynamic range of the sensor.


Both CMOS and CCD do not have dynamic range on the sensor to compare with film, improvements are being found by reducing noise in the blacks.

A re-occuring theme on REDuser is underexposing rather than controlling (when possible) dynamic range within the scene.

Shooting a complete project with an underexposing strategy is a shame.


Mike Brennan

 

[donatello b]

TEST your camera ... know what it does if you over/under expose in different scenes (that could have 3 - 20 stop range) ...
then you make CREATIVE choices or it could be choice based on budget/time.
just as long as you know the what the results will look like if you "choose" to under/over expose ...
IMO nothing wrong with shooting at ISO 1000/2000 if that suits the scene/project.