Hi,
Thanks for your reply. I'm not thinking in terms of resell value, I'm thinking in terms of future proofing your lens selection. I don't want to invest lots of money (and lots of money for me might not be lots of money for others) in something that I won't be able to use properly with the next camera that comes along. As far as I understand, you can't adapt a M43 lens to a larger sensor camera for example. And this isn't about what sensor size is better or anything like that, I just don't want to get glued to a particular system if you see what I mean.
For filming purposes, I'd like to invest in some nice prime lenses and a constant aperture zoom lens for documentary-type projects. As it's all manual, I was thinking of getting some old glass that you can get from ebay at a great value/performance ratio.
For example, I've been looking at these lenses: Canon FDn 35-105 f3.5, Carl Zeiss 25mm f2.8 Distagon C/Y, Carl Zeiss T* Distagon 35mm f2,8 C/Y