jacklongdo wrote in post #17394768
Thank you John. I read your answer carefully.
The question now focuses on the lens: Can the the lens set @400mm with the 1.4x extender deliver the required by a high definition sensor or will a FF sensor suffice?
I don't think that high-res sensors require anything. The sensor is there to serve the lens; the finer the resolution of the sensor, the closer it is to making a virtual analog capture, and the better it records the lens. TCs and smaller pixels both work towards recording what the lens is actually projecting, more accurately, with less artifact. It matters not a bit if that means that 100% pixel views on our low-res monitors look soft because of it.
The only drawbacks of TCs are that they can sometimes (but usually don't) cause electrical problems that might compromise the image stabilizer, they may lose contrast (micro and/or global) if they are inferior grade, they might interfere with AF, darken the viewfinder, and they might make your composition too tight, if you're too close (it may take too long to remove a TC if you can't or don't want to step back from the subject).
The only downside of higher pixel density is that sometimes (but not always) the biggest pixels on the biggest sensors have the least read noise at high ISOs, per unit of sensor area. They are universally btter at low ISOs, and often at medium ISOs, noise-wise per unit of sensor area. The 7D2 is only about 1/4 to 1/3 stop worse than the 1Dx and Nikon D4s per unit of sensor area in measured high-ISO noise, and is as good or better than most other big-pixel sensors (the 7D2 has one of the best high ISO noise characters of any camera; easy to clean and it cleans up quickly with reductons in displayed image size).
That said, I can get fairly pixel-sharp results (sharp enough that USM works easily without sharpening noise too much) with the original 100-400 with a 7D2 and a 1.4x, so I'm sure the new 100-400 is even sharper, especially wide open. Often the actual practical limit is due to the stability of the camera and subject, and AF error, not the lens sharpness. Reports I've read here and on DPReview suggest that the new 100-400 + 1.4x works like a good 560mm f/8 lens optically, and AF, while not quite as snappy as at f/5.6, works well in the center point.