Originally posted by StigVidar I tested F*250-600/5.6 against DA*300/4 and the zoom was better at f/5.6 than the prime at f/5.6
I tested the FA*250-600mm f/5.6 ED [IF] On full frame against the Pentax FA*300mm f/2.8 ED [IF] and A*400mm f/2.8 - on my testing bench* the Primes held an edge over the zoom, due to their inherently wider initial apertures but at f/8 all three lenses delivered essentially identical performance.
*Testing long 35mm lenses on an optics bench is a
nightmare, the tiniest mis-focus can reduce resolution from a lens by 40%. I had one hell of a time comparing the Nikkor 400mm f/2.8 with a 2X teleconverter against the Nikkor AF-S 800mm f/5.6E FL ED VR.