This is an often asked question about the Sony PMW-F55, F5 and FS7 cameras.
There are several modes and options where the LUT’s are not available or restricted to either all on or all off. That is to say that you can’t have LUT’s on for just the viewfinder or just the SDI output, you can only have the LUT’s applied everywhere, including the internal recordings which isn’t normally desirable.
The problem appears to stem from a limitation on the number of video processing units within the cameras. Certain functions within the camera require a video processor. Functions such as adding LUT’s, reading the sensor at high speed for S&Q, providing a 4K output on the SDI or HDMI each appear to require dedicated processing and as there are on so many processors available this limits some of the options we have. I don’t know of the exact architecture of the cameras but the diagrams below represent what I think is going on and why we have limited LUT options in certain modes. Please note that there are a lot of other video processes going on in the camera and this is a very simplified overview of what I think is more or less going on.
One way around the problem of not having LUT’s in S&Q is to use the viewfinders high contrast mode (F5/F55 only). To enable this mode you must assign it to one of the assignable buttons. The high contrast mode applies a rec-709 like gamma curve to the viewfinder image so you will have almost exactly the same contrast and brightness as you would using the 709(800) LUT. As it’s only a gamma correction it will be less saturated than the LUT, but it’s still very useful for judging exposure. Remember if you are not using or unable to use the LUT’s, the waveform and zebras will be measuring the S-log signal, even if you have the VF High Contrast mode enabled.
Another way around this issue is to use a 3rd party viewfinder that can add it’s own LUT’s. Then simply leave the LUT’s off in the camera and use the VF to apply a LUT. The Zacuto Gratical is great for this as you can not only add the LUT in the VF but also send the LUT out over the VF’s SDI or HDMI output. If you want EI then you will need to load some exposure compensated LUT’s directly to the VF and use the appropriate LUT for each EI.