What is 1200mm f8 on canon aps c in full frame?

1200mm on APS-C (Canon) gives the view of 1920mm on full frame. For the same depth of field, f/8 there behaves like about f/12.8 on full frame. Exposure doesn't change: f/8 gives the same brightness on any sensor.

The same view on every common format:

• Medium format (44 x 33): 2430mm at about f/16.2 for the same depth of field
• Full frame: 1920mm at about f/12.8 for the same depth of field
• APS-C: 1280mm at about f/8.5 for the same depth of field
• APS-C (Canon) (yours): 1200mm at about f/8 for the same depth of field
• Micro Four Thirds: 960mm at about f/6.4 for the same depth of field
• 1-inch: 711mm at about f/4.7 for the same depth of field
• 1/1.3-inch: 533mm at about f/3.6 for the same depth of field
• 1/1.7-inch: 417mm at about f/2.8 for the same depth of field
• 1/2.3-inch: 343mm at about f/2.3 for the same depth of field

Crop factors are by the sensor diagonal, rounded as they're usually quoted; a format with a different shape (4:3 against 3:2) frames a little differently across the width. More in the focal length converter.

Computed from the sensor sizes, not written by a model.