Canon XL1s and Spectra Light Meter

[VPTurner]

I combined my XL1s setup with a Spectra Cine Pro IV-A meter to get more accurate control over light balance and exposure, but I can't seem to find a comprehensive breakdown of the ISO ratings for the camera at various gain settings.

During experimentation, at 1/60 shutter, zero gain, and the in-camera meter dead center, the Spectra (set at 30fps) showed the same F/stop as the camera while it was set to ISO 400. But I read elsewhere that the XL1s supposedly only has an ISO of 160 at zero gain. Of course, this may just be a difference between measuring at the subject versus the average of all light entering the camera lens. There was sunlight in the background that was blocked by the meter.

Has anyone tried the full range of experiments with the Canon XL series to accurately identify the ISO ratings? My first project was horribly underexposed. That will not happen again. I just need to know what to set on the meter for the ISO.

Thanks!

Edit: I just realized I had the circular polarizer on the lens and may have also had one of the ND filters set. I'll lose some light with those. That could explain the disparity. But I'd still like to find a chart if one exists. If not, I guess I'll just have to make one.