« on: March 27, 2013, 04:33:21 AM »
I agree with Alan F, the question posed has to wide a gambit. An extender on a lens such as the 100-400 will degrade IQ. If the native lens has flaws this will be replicated with the addition of an extender. On my 300f2.8mkii the addition of the new 1.4mkiii extender does not degrade image quality, I am constantly amazed at the images this combo can achieve. I have yet to try the new mkiii 2 x extender.
From a personal point of view I think to much is made of so called bench tests, yes they have their place but real world photography is where it counts. Wherever possible I will always use a sturdy tripod when mounting long lenses and extender, whilst I may loose some control over composition, images in the main tend to be very sharp.
I have recently conducted some tests where I have compared the 300/1.4 combo mounted on a tripod as well as hand held at shutter speeds exceeding 1/2000 of a second. The images taken with the help of the tripod always look sharper.
So many people complain that their images are not sharp and has poor IQ, they blame the equipment, the environment but never themselves. If my images are poor then it is my technique that needs to be looked at and not the equipment used.