It Takes mk.iii TC's very well. Here is a shot with a 2x TC mk.iii attached to a Sony a6000 crop body via a Fotodiox adapter I took yesterday for an effective FoV of 1200mm. But given the density of the crop sensor, the reach is closer to 1600mm on a 5d3 type body.
Wonderful shot, great sharpness @ that FoV, though i didn't get the math, does the Fotodiox adapter has a crop to it?
Sony's have a crop of 1.5 not 1.6. so FoV is 800x 1.5 = 1200mm.
The reach was just an estimate, based on the ability to throw more pixels per square inch... I forget how I did the math for that. Let me try again:
Density of 5d3 sensor 2.58 mp per sq cm, Density of a6000 6.65 mp per sq cm. So the a6000 can throw 2.58x more pixels per sq cm than the 5d3. Less the 1.5x crop equals about 1.72x more reach (not FoV) so 1.72 x 800mm = 1372mm in other words, a 1372mm lens mounted on a 5d3, will yield similar magnification/ resolution as a 800mm mounted on a a6000.
People like me sometimes use the FoV (crop factor) interchangeably with reach (ability to crop without losing detail) , but I think they are different... as you can see one yields an equivalent of 1200mm, the other 1372mm (assuming my math was good). In other words, if the a6000 sensor density is scaled to Full frame, it would be a 62.6 mp sensor (interestingly the new Sony A9/ A7rii is rumored to be 59 mp).
So in post you can crop much deeper with a 62mp sensor than 22mp... this is what the a6000 does with out needing to crop more. Ofcourse... it's much more noisier at higher iso's.... quite noisy :-)