That tc issue is the only thing really holding me back but I do need to get some reach beyond 400. I have a 2x TCiii on my 70-200 and it is normally pretty good, but a bit soft on some days.
Anyway just listen to this on that crop issiue. On my 7D it was like switching on the lights upstairs
I am still a novice on this stuff, but as I understand it crop is not zoom. It's field of view.
That rumorred new firmware for the 7D will probably hold me back on a 5d3 and definately a 7D2
Ya...? I'm not sure if this was intended for me or others, but I'm fully familiar with how this works - this hasn't changed in a decade. I'm planning to get whatever the 7D is replaced with for the pixel density (as I stated earlier). Another thing some people don't often factor in to what becomes an "effective" focal length is just that - pixel density. So, a 7D doesn't give you a 1.6x effective zoom because it's a 1.6x crop, it's only about 1.5x or so compared to the 5DII.
If Canon were to release a full-frame camera with the same pixel density as the 7D, it'd likely make sense to get that one... However, it'd cost a lot more, and as I'm cropping most of the images anyway (those shot at 400mm), those extra pixels on the periphery would usually be wasted.
It would be interesting if Canon & others would recognize that those interested in very long lenses are also interested in high pixel density sensors - which are usually not full-frame. As such, I think there would be a large market for a 500mm "S" series lens. Such a lens could be quite a bit lighter than the full-frame counterparts.
I'm still planning to use my 5DII for landscape & portrait photos, where I use the full sensor. But, the 7D+ will sit on my highest focal-length lens like a permanent attachment.
One other factor I'm not sure that video covered - one does reach the point of diminishing returns as photosites on sensors reach higher and higher densities. This is a matter of the physics & wavelength of light. We're not quite there yet, at least when shooting at ~f4-f5.6 (assuming the lenses are adequately sharp wide open), but it's coming... For more on this google "circle of confusion" and have fun. :-)