see also:

• Canon EF lenses

• a unique diffraction optics (DO) optical design allowing a much more compact lens but characteristic DO aberrations

• 400mm f/4
• image stabiliser allows hand held shots to 1/25th sec with some success
• USM AF
• internal focus
• 52mm rear drop in filters
• 9 blades
• 18 elements in 12 groups
• weathersealed
• close focus 3.3m
• Lens hood: ET-120 (WII)
• 1.4x and 2x teleconverters can both be used with this lens to add more flexibility, although using a 2x converter will result in a slow maximum aperture of f/8 with this lens, which may also cause autofocus issues on some Canon camera bodies
• 233mm long
• 2.1kg
• ~$A7500 for version I and ~$A9000 for version II (the f/2.8 lens is ~$A12000)

• https://www.ephotozine.com/article/canon-ef-400mm-f-4-do-is-ii-usm-lens-review-26785
  • sharper at f/4 and f/5.6 than the Canon EF 100-400mm f/4.5-5.6L IS II USM is at f/8
  • CA well controlled
  • 0.23% pincushion distortion
  • extremely resistant to flare and contrast remains high when shooting into the light