Sometimes the "focal length" of zooms is not what it says it is, and maybe that is the case here. Maybe less than 300mm. I know the Sigma 150-600 is actually only about 560mm and I think even the Canon 100-400 II is a little short of 400mm. Also, we don't know if the focal length of the 80/600 is exactly 600mm. Some testing with a ruler and some simple math might give the answer.
Going by the samples I also get about 255-260%. At any rate, focal length is calculated at infinity, so maybe the distance to the subject is throwing things off. Wish I knew more about it...
Just did a quick test on the neighbors chimney, about 50 meters away. I have to magnify the image from the 75-300 II 215% to match the image from my 90/600.
Another test about 10 meters away, came out to be 230%
Another test about 200 meters away came out to 210%, so there seems to be a pattern here.
Last edited by DanC.Licks : Monday 1st August 2016 at 18:05.