(02-25-2022, 10:26 AM)Brightcolours Wrote: Sorry for the confusion, Dave.
The 1st one Klaus links to is the RF 400 f2.8, with 2 fluorite elements in purple. The 2nd Klaus links to is the RF 800mm f5.6, with two fluorite elements in purple.
The Canon one I linked to is the EF 800mm f5.6. With two fluorite elements in blue. You can see the similarity to the Nikkor 800mm f5.6 there. The Nikkor and Canon have a slab of glass in front, to not have the fluorite element exposed to touch (it would scratch).
The newer Canon designs don't have fluorite as front element, which explains why the slab of glass in front is not needed.
Well I'm a little bit less confused ....
......... but this optical formula shows one front element ....... and no protective meniscus!!
Perhaps I have scrambled eggs where my brain should be .......