A fundamental aspect of electronic cameras is that the bulk of the noise comes from the sensor. So the amount of noise in the final image is mostly a function of the amount of light you put on to the sensor v the noise the sensor produces (which is more or less constant). This is known as the signal to noise ratio, often abbreviated to SNR.

Whether you use S-Log3 or S-Cinetone, even though the base ISO number the camera displays changes the sensitivity of the camera is actually the same, after all we are not changing the sensor when we change modes. In fact if you set the camera to dB you will see that in custom mode the base for both S-Cinetone and S-log3 (and every other gamma curve) is always 0dB.

All we are changing when we switch between S-Cinetone and S-Log3 is the gamma curve – which is a form of gain curve. The base ISO number changes between S-Log3 and S-Cinetone because if you were using an external light meter this would be the number to put into the meter to get the “correct” exposure, but the actual sensitivity of the camera remains the same.

First let’s think about what is happening at the base ISO of each if we were to use an external light meter to set the exposure…..

If we shoot at S-Cinetone and use the 320 ISO value in the light meter the aperture will be a little over a stop more open than if you shoot with S-Log3 and use 800 ISO for the light meter. So when using S-Cinetone at the base ISO there is a little over twice as much light going on to the sensor compared to S-Log3 at the base ISO and as a result the S-Cinetone will be much less noisy than the S-Log3. Not because of a sensitivity or noise performance difference but simply because you are exposing the sensor more brightly.

And if we use the SAME ISO value for S-Cinetone and S-Log3?

So now think about what might happen if you were to put 400 ISO into your light meter and use the values for shutter and aperture the meter gives and shoot with either S-Cinetone or S-Log3 using the very same aperture and shutter settings so that the same amount of light is hitting the sensor for both. The result will be that the amount of noise in the resulting image will be broadly similar for both and the same would happen if you were to use, let’s say, 4000 ISO (assuming you switch to high base for both).

There will tend to be a bit more noise in the S-Log and CineEI at the default settings, because by default NR is turned off in CineEI. But with the same in camera NR settings, again both the S-Log3 and S-Cinetone will have very, very similar noise levels when the sensor receives the same amount of light.

What about when there isn’t enough light?

So – when you are struggling for light, both will perform similarly from a noise point of view. BUT where there may be a difference is that with S-Cinetone all your image processing is done before it is compressed by the codec and what you see in the viewfinder is what you get. With S-Log3 the “underexposed” image gets compressed and then you will need to process that in post and when you add your post corrections this will be to the recorded image + compression artefacts so there will always be a lot of uncertainty as to how the final image will come out.

Personally I tend to favour S-Cinetone for under exposed situations. Generally if it’s under exposed dynamic range isn’t going to be an issue. S-Cinetone also spreads what image information you do have over a greater range of code values than S-Log3 and this may also help a little. But there is no right or wrong way and any differences will be small.