I need to reduce the light when shooting outdoors with a 1DC & 24mm T1.5 LF Cine Lens.

At the moment it's on 100 ISO with the aperture as fully closed as it will go.

Whereas I would prefer to have more flexibility with the aperture as indoors opening it up gives me very nice bokeh.

I'm considering introducing a ND filter into the equation, but I need to be sure it's the right measurement to fit on top of the lens, the right density to free up all of my aperture like indoors and finally of sufficient quality that it won't mitigate the 5k piece of glass...

Anybody have any suggestions?

114mm diameter.... but I'm just not sure about what the good nd filters are... you can buy them for really any price it seems...

You can use this: Schneider 68-041745 1.5 Neutral Density Filter 68-041745 B&H

Thanks Sabyasachi!

By the way, do you think I could use the 1DC's exposure compensation to deal with this issue, or is the only way to open the aperture up at 100 ISO without it being overexposed in sunlight to use NDs?

Hi Pierre,
The exposure compensation (+ or -) will help you in fine tuning the exposure. If you have set the metering mode as Av, Tv the camera suggests an exposure. If you dial in an exposure compensation, you will be overriding the exposure decision of the camera.

For example, if the light is bright and you are in Tv mode at ISO 100 you get 1/50, f7.1 and you want 1/50 at f5.6, and if you dial -2/3 stop, the camera will set exposure which is -2/3rd stop than the normal exposure decided by the camera. That means you are under exposing by 2/3rd stops and you get 1/50 at f5.6. You now get your desired bokeh. However, your image is underexposed by 2/3rd stops. You can pull up the exposure in your editing suite. However, you are likely to get a little bit more noise and you have to be careful about the black areas in your scene. Depending on your scene you can do it for sometime but not much.

If you are in Manual mode, it will show you a suggested exposure as well when you look through the viewfinder. When you dial a negative exposure compensation, the bar will come down the middle and keep on showing that according to the camera you are underexposing. You will be able to freely change the shutter speed and the aperture and decide on your exposure. The principle remains the same. In this mode also you can set the same exposure like the earlier example.

I would strongly suggest you to shoot in manual mode while filming with the 1D C. The reason is, if you are shooting in Av or Tv mode, then during the scene the exposure can change slightly.

I hope I am able to clear your doubt.
Cheers,
Sabyasachi

Thanks - I really appreciate your response!

I managed to crack this today. I shot at 400 ISO, aperture fully open in the woods - image initially so washed out it was pure white.

Got a bit confused about how to get the exposure compensation going and ended up having to set it in STILL mode and then switch to MOVIE where it still seemed to be activated.... and I simply dialed down exposure.

The result was astonishing. I did more later in the car with my son. Again, looked beautiful.

I'm starting to realise this camera's best feature is not even the 4K (which I adore) but it's low light integrity.

In fact, it's those two factors combined...