Originally posted by twitch Those Nikon and Canon lenses are 1) a stop faster and 2) FF lenses. That's worth a lot isn't it? 1 stop at these focal lengths means big dollars doesn't it?
Originally posted by gazonk And the new 560 is $1400 less expensive than the Nikkor 500mm/4, and $3500 less expensive than the Canon 500mm/4!
That's a crucial point. I'm not so much in the long range photography, but why would it be any better to use a 35mm sensor if it's about range and resolution?
The FOV of a 560 at APS-C equals 859 in 35mm, the light gathering equals 5,6, the DOF will not play a role at this distances and focal range.
It's about the whole system, and so you can go with a Nikon D800E and a Nikkor 500mm/4 for $3.300 and $8.400 - sum $11.700 - and crop it to APS-C FOV with approx. the same amount of resolution and (assumed) IQ as you get with the Pentax K5IIs for (new now) $1.300 and the Pentax 560mm/5,6 for $7.000 in sum $8.300.
Edit: or you add a TC for additional 400$ and end up with a 700mm/5.6, with 36Mp, but you still have to crop to be at 859mm.../Edit
YMMV, but doesn't seem thaaaat bad to me... if I was in search for long tele.