<span style="font-size: 9pt; color: black; font-family: 'Verdana','sans-serif';"]Any idea of where the f-stop changes based on focal length? If it retains an f/4 anywhere close to 200mm it's really going to give the EF 70-200mm f/4.0 L ISa run for its money based on the MTF charts. Its deficiency being10.3 oz of additional heft and extending zoom but what you gain is a 50% increase in focal length and of course it's also 1.71'' shorter when retracted.<o></o>