Yes, the C70 features a motorized internal ND filter system providing 2, 4, 6, 8, and 10 stops of light reduction, controllable via dedicated buttons.
With the standard BP-A30 battery, you can expect approximately 170 to 200 minutes of continuous recording depending on settings.
Yes, by using an EF-EOS R adapter. The Canon Mount Adapter EF-EOS R 0.71x is specifically recommended to maintain the full-frame field of view on the Super 35mm sensor.
No, the Canon C70 is not waterproof. While it features some weather sealing, it should be protected from rain and heavy moisture.