Base ISO Levels for the FX9

First of all. Unless you are actually using a lightmeter to determine your exposure, in custom mode it is far, far easier to use dB of gain. 0dB is always optimum and each time you go up 6dB the picture gets twice as bright (one stop brighter) and the noise doubles. ISO is in most cases nothing more than a rating to use in conjunction with a lightmeter to get the right picture brightness, it will not tell you how much noise you have or whether the camera is at it’s optimum setting. So don’t use ISO just because “ISO is cool and make me sound like I know what I’m doing, it makes me a cinematographer”. This isn’t a film camera, no matter how much you dress it up it is a video camera and dB tells you exactly what it is doing.

Because different gamma curves produce different brightness images the ISO rating will change depending on the gamma curve being used, this isn’t a sensitivity change, it’s an optimum brightness change. Because of this, even when you are at 0dB gain (the native setting) when you switch between different gammas the ISO rating changes. In addition because you have two different base sensitivity modes on the FX9 there are a lot of different base ISO’s (all of which are 0dB gain). I’ve prepared a table of the different base ISO’s.

Screenshot-2019-12-30-at-11.00.53-1024x295 Base ISO Levels for the FX9

In addition if you are not careful it’s possible to end up using too much gain to achieve a certain ISO as many ISO ratings can be realised at both Hi and Low Base sensitivity. You don’t want to be at 2500 ISO in Low Base for example, you would be better off using High base. The table below should help you understand when to switch up to High base from Low base. If you use dB gain, then it’s easy. More than +11dB – switch up. Don’t forget in dB mode you can also go down to -3dB.

Screenshot-2019-12-30-at-12.26.58-1024x342 Base ISO Levels for the FX9

10 thoughts on “Base ISO Levels for the FX9”

  1. Thanks Alister, very helpful.

    I didn’t realize the base ISO’s were now that much lower which is fantastic. It was always a PITA that HG7 and 8 were a native (and minimum) of 1600 ISO.

    1. Hi Chris!

      Long-time no – just got my first Fx9 and yeah can tell you the 320 is really nice. But grain at higher ISO’s is just so much tighter, you just have to see the difference to the F5 for yourself. And it’s a full stop faster at 800 compared to the F5.

      Quick sell your cameras and get these before everyone realizes how much better this camera is!

  2. Find it hard to believe FX9 will not operate at far lower voltages, i.e. 14.8 V-Lock. If 19.5 is truly required, you would have the same complication trying to run off line power such as from an ordinary V-Lock battery charger.

  3. Hello Alister, it took me weeks now to realize that S-Cinetone’s “Base Hi” is not the same as Cine-EI’s “Base 4000” aka. 4000 ISO, but in fact 1600 ISO.

    I kept wondering why “SDR”/S-Cinetone has MUCH less noise compared to Cine-EI when using the native high Base ISO.

    Regarding that the Base ISOs are not equal, it now would finally make sense.

    Any input/confirmation highly appreciated.

    P.S.: Did you try the trick discovered by some people to actually bake in the “SLog3”-LUT to gain access to the lower ISOs?


    “With the FX9, you have to go about it a little differently than the Fs7. In Cine EI, in order to access the lower ISOs, you have to Internal Record the LUT, except the LUT that you choose is SLOG3.
    Internally recording an Slog3-LUT seems to be the same as shooting Slog3 without Internally Recording a LUT.
    This allows me to drop the ISO to say 500 or 320, thus opening up the iris, and exposing the sensor to more light. With this method, the dark shadows end up much cleaner than if it were exposed at 800, and since the Slog3 LUT is baked in, what you see in your viewfinder is exactly what you get in post, so no correction needed, like when you rate the Fs7 at a lower ISO (because the Fs7 doesn’t offer an Slog3 Lut).”

    1. I really don’t understand why anyone would want to bake in a LUT to achieve a lower ISO. All you are really doing is fooling yourself. What is actually happening is the camera is still working at 800 ISO, then you are darkening the recording and restricting the dynamic range via the LUT. Well you can do exactly the same by shooting at 800 ISO with the Exposure Index set to 320 and then adding an offset LUT in post. The end result will be identical – except – this way you retain the cameras full dynamic range.

      1. Exactly.
        It didn’t make sense to me either, because none of those steps actually changes the camera’s ISO.

        All you are getting is a “preview” on your external monitor, but it’s baked in.

        I have to say though, that the Base Hi setting (1600 ISO) in SDR mode shows a lot less noise than “Base 4000” in Cine EI mode.

        Thank you as always, Alister.

  4. I know if I am shooting at a base ISO of 800, i then would shoot a darker scene at 200 EI to preserve my blacks. Now, comparatively, if I am at a base ISO of 4000, what is my same reduced EI equivalent? Or does the EI values not change with switching base? Thanks for any clarification.

    1. That’s really easy. To achieve the same as 200EI / 800 ISO then you need to make the same 2 stop adjustment at 4000 ISO base.
      4000 ISO -1 stop = 2000, 2000 – 1 stop = 1000. So you would use 1000 EI to get the same 2 stop offset.

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