Originally posted by Lowell Goudge What I don't get in your argument is you are going to nikon plus a sigma 500 as the dual system selection. if you consider absolute resolution, it has about the same as the K5 sensor, if it were scaled up to full frame, so except for the difference in megapixels, with an image that fills the entire frame, and perhaps the ability to print that image twice the size of a K5 image, what do you actually gain.
a 300/4 on a K5 would be roughly equal FOV to a 500/4.5 on a full frame. Since you are already considering sigma, any debate on the 560mm pentax is moot (although I too would live to see pentax with this lens this year). so what is it you really want?
I simply do not see any advantage of going full frame for wild life over APS-C
Consider: You are shooting birds with the D800 and a 500mm. For those closer shots a flick of the switch gives you FF (with the Sigma 500mm that's ca. 335mm equiv on APS-C), a bird appears in the middle distance and a flick of a switch later and you are at x1.2 crop (24mp and ca. 400m APS-C / 600mm 35mm equiv. ) and then you spot a small bird 40 yds away and another flick the switch and you are now at x1.5 (APS-C) for your 750mm (35mm equiv. ) with the famous latest and greatest version of Nikon's AF (which you seem to have disregarded even though I made it a feature of my previous post).
Of course people also use the Sigma 500/4.5 on K5s (to great effect indeed) however the D800 gives far greater flexibility, better FF files and IQ and it loses nothing over the K5 in mm or mp in crop mode whilst still retaining all the advanced features and benefits of the D800 and Nikon's AF and a larger, brighter 100% VF that will make it even easier to obtain critical focus when in MF.
I have recently spent quite a bit of time on bird shoots with Canon/Nikon shooters with FF cameras and 500/600/800 lenses. Let me say that those FF cameras with those lenses absolutely rock ! We all chimp our shots but they can get far more into the shot than I can and the IQ is two steps up with lower noise (I'm using the K5+DA*300+AFAx1.7). That said the Sigma 500mm has an advantage for me here - as I like to wander and not always be rooted to the spot, with the much lighter Sigma you can do that, with those CaNikon monster lenses it's not feasible !
I spend a lot of time on FM now (pop over and have a look at their wildlife forum) - not wonderful but
superb bird shots, the like of which I haven't seen from any APS-C camera (Pentax, Nikon or Canon) on any other forum and the vast majority from FF cameras and long lenses, they blow me away.
So my decision wasn't based on a whim. As you said an image that fills the frame and the amazing files that come out of it can be printed at twice the size (which means added cropping potential). I have researched it, checked the results on the web and in person, Googled all of the FF vs APS-C arguments for birding, and have found that no matter how much I would like to deny it, there is an advantage, that I will have to pay for in $$$, but it is definitely there. If there wasn't then all those shooters would be using 7Ds or D300s'.
And finally when I'm not shooting birds I've now got a superb FF camera for those low DoF and low light shots that I love, with that distinct FF 'look'. The D800 is an all-in-one-camera that the 5DIII can't match.
Last edited by Frogfish; 07-26-2012 at 06:32 AM.