Originally posted by Simen1 Bokeh can be dealt with sometimes. Just choose a nice smooth background without any details to be messed with.
For me a heavy and expensive tele lens just isn’t an option, regardless of qualities. A mirror lens would be the only way for me, and I'm quite sure there is much that can be improved a lot. WR, AF, ND filter wheel coupled to the aperture leaver, hood, baffles and maybe even a doughnut free design. I will also add a back polarizing filter to reduce the effect of air humidity and smog on sunny days.
Yeah a 400mm lens on an FF typically used in studio with a nice background. a 400mm lens never used to shoot, birds, wildlife or sport were the you don't have that much choice for the background.
This is funny how in one thread a large camera can have very small lenses and how in the next thread then you have to severely compromize the quality of picture to get a lens with fixed apperture, no AF, bad bokeh and so-so sharpness to keep something not to big.
Reality is that if you take a DA*300 f/4, on APSC, you get 420mm f/5.6 equiv and you have only 800g and 850$ to spend to get it. It is not 3000-5000$, it has variable apperture, AF, great bokeh and reasonnably compact.
A DA*200, (that still cover FF) is a bit lighter, significantly shorter, give the same light gathering and would still provide 16-20MP on an m4/3. This could be designed, likely a bit smaller than it is no today as the image circle doesn't have to be the same.
But no, sensor size doesn't change anything to size/weight... as long as you stick to no AF, fixed apperture, crap bokeh, low sharpness mirror lenses. Thank you for your insights !