Lensmonkey

Does this monitoring/level mismatch occur in the screen/evf or only when externally monitored? Thank you for your informative posts regarding this phenomenon, and the sharing of knowledge!

Hi all,
I have invested much time to investigate on the monitoring and ISO behavior of the fp. Finally in combination with the Ninja V I have found a working solution for me which gets both the monitoring picture and the metering right.
Basically after reading through your posts I understood that the fp is ISO invariant and has only two native ISO values available for metering and recording. (ISO 100 & ISO 3200) Others are digitally amplified. 
False color screen with the Ninja V is working on both of these ISO values to meter the correct exposure. However as a lot of you have mentioned the Rec709 monitor view is only showing the correct picture in ISO 100. The 3200 setting will be overexposed and useless.
After several tests I have figured out that if you set the Ninja V to PQ the ISO 3200 screen will look correct. Different story for ISO 100, but this can be tricked if you select ISO 400 in camera. Screen will look exactly the same now for both ISO values. Metering for ISO 100 is unaffected, since the false color mode is only showing the values for ISO 100.
Since the recorded ISO values of the Ninja V are pushed into Final Cut Pro X you will get an overblown picture in Rec709, BUT and this is really nice, if you select ISO 100 instead of ISO 400 and ISO 640 instead of ISO 3200 everything will look as expected. Correctly metered and captured. Remember, in the additional manual of the fp in regards to the ISO behavior, Sigma is mentioning ISO 100 and ISO 640 for photos...
If you need to work with Zebras the correct settings are for ISO 400 => 55% and for ISO 3200 => 60% if you want to avoid anything in the 100% range. You could go slightly higher as the fp has some more headroom over 100 IRE.
Quite a lot of hassle if you ask me, but once you have got used to this you will get a nice picture on both. 
 
Hoping this will help some of you 🙂
 

In the interest of clarification I'd like to see if a few observations are correct. I am talking about DNG forward. It has been my understanding that "base ISO" is determined  by the least noise vs the highest dynamic range. Sigma has proscribed that the base ISO is 100.  I think we have established that the FP uses a linear curve. There are +/_ 12.5 stops of range.  If shot at base ISO then neutral grey should be at the middle of this. The camera's waveform and zebras are correct with this. In my understanding, changing the ISO on camera or in post results in changing the amount of information available  above or below that grey exposing properly-AKA grey is grey. If we choose, or "pretend" that the ISO is 800, we say "I choose grey will be here", whites will still clip at the same amount of light with this much light reaching the lens. We will have less information to convert the above grey-to-blown-out to the +/_ 6 stops of rec 709, but more in the below-grey-to black, which will still go black with the same lack of light amount reaching the sensor.  When changing ISO on camera The FP changes the waveform and clipping point zebras when you change the ISO! As if it is looking at an initial transform at 100, and then you are boosting that image thus indicating clipping where there is none. This makes on the fly protection of highlights and checking of black levels problematic! 
I thought maybe, use 100 ISO to check clipping, set exposure, then switch to what ISO you might choose to monitor and eventually use as the working ISO to expose grey properly. When shooting, then remember, (or make a sticker for the camera!) how many stops above or below your chosen ISO there is to that blown point or black. A spot meter is a pretty good tool to have at this point. Not great for moving fast. Or start to develop your eye. faster, but more accurate than you might think! 
This business of 3200 is a real conundrum though. If I read Rawshooter's generous contributions right, the very metering is wrong, and math with a base ISO check or a spot-meter is the only way through. And all monitoring in camera is going to be off by two stops at proper exposure. Damn. So to move quickly, dial in 3200 + look at recommended exposure, then open up two stops, deal with a blown out monitor image use it as a framing reference. Spot meter the highlights (or gage with your eye haha) to know where the image will blow out.
There is a fundamental question that is kind of pivotal to this and my understanding as a question though.  If I have a camera that has a base ISO of 100, and it has a 5 stop dynamic range (for ease of math), If I choose (shooting raw) to set the ISO at 1600 (one stop of information before blow out), when choosing a rec 709 transform, will the remaining stop of information above middle grey be parsed into the  3 stops rec 709 sees as above grey to white? Here is where I am sure I sound stupid because a stop is a stop, double the light. 
Here's a bit for thought... or telling me to shut up and that's your last glass of wine Mr. I have gotten used to looking at a good monitor and knowing what I see is what will be delivered. It is a pretty seductive thing. I shot film though for 20+ years and I see a lot of parallel with shooting RAW. When shooting film you used a meter and knew the filmstock, what it could handle, how and when it would blow out, how it would handle underexposure (black pixels matter yo! haha) You did not see the printed image for a couple of days (quicker if you were shooting for the studio!)I used a meter and knew the sensitometry of any given film stock, knew what it would matriculate to when graded. Raw seems like this. We look at a proxy image awaiting development. That sounds like knowing the sensor. I got to work with some greats, they could tell an exposure without a meter by eye. We used to play a game when I was a camera assistant on big pictures, and try to guess the shooting stop.  After a while, we nearly always got it. Practical experience of the sensor, no matter whether it's film or digital is key. Knowing the tools is the mark of a cinematographer. I'd like us to have a clear idea of how this camera deals with light, put it in in the back of our minds and then go shoot wicked cool stuff with it.