If you have never used CineEI before it can be difficult to get your head around it. So for my first post here I thought I would share some things that may make it easier to understand this mode. It certainly took me a little while to figure it out the very first time I came across it. If you are someone that has shot with conventional video cameras all your life, then using CineEI is going to be very alien and you do need to think very differently. You need to discard most of what you have learnt about video cameras and instead think "film camera". For me the lightbulb moment came when someone told me to pretend the camera is a film camera that only has one film stock.
CineEI stands for Cine Exposure Index. EI or exposure index is used by just about every digital cinema camera. It is used because a video sensor will only perform at its very best when operated at or very close to its native sensitivity and when the full output range of the sensor is precicesly matched to the recording range. Adding gain to the sensors output will reduce the dynamic range that can be recorded. So, when shooting S-Log3 or raw, to really get the best from the camera you must record at the cameras native (or "base") sensitivity.
When shooting using Exposure Index you will come across two very similar sounding things, but they are very different from each other. One is ISO and the other is EI. Both have a numerical value and sometimes that value will be the same for both. But each has a different meaning and they should not be muddled, each has a specific meaning and I find it helps me to understand the CineEI mode if I think of each as the different things they are.
ISO = The sensitivity of the sensor - often called the "base" ISO.
EI = The sensitivity of the LUT that you are using.
When the two match, when the LUT is correctly exposed then the sensor will be exposed at a normal level.
When the EI is higher than the ISO the LUT becomes brighter than normal. If, looking at the LUT image, when you see a brighter image the normal response is to close the aperture until the LUT looks correct again. This will then result in less light falling on the sensor and a darker recording. A darker recording will be more noisy, have fewer shadow textures but also have a larger highlight range and this might help with a scene with a lot of very bright highlights.
An EI that is lower than the ISO will make the LUT darker. When you see that darker LUT image in the viewfinder you will open the aperture to make the image look correct. This puts more light on to the sensor and this will increase the amount of shadow information but decrease the highlight range. More light going on to the sensor also means the final image will have less noise.
If you were to use a light meter you would set the light meter to the EI to achieve the same result. A lower EI will result in a brighter and generally less noisy exposure with increased shadow range but reduced highlight range and a higher EI will result in a darker and generally more noisy image with increased highlight range but reduced shadow range.
So... something to think about - when shooting under low light don't raise the EI. It won't make the camera more sensitive and the brighter image might make you think that your exposure is fine, when in fact it might be excessivly noisy. Instead keep the EI at the same value as the base ISO. This way you will be better able to deteremine how under exposed you might be. If you can, use an EI a bit lower than the ISO as this will encourage you to find more light or put more light on the sensor which will help overcome any noise.
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