Originally posted by maxloxton I am thinking of buying a longer lens for the mountain closeup shots; so far the only options I have got is 300mm f4 or 400 5.6. Thats why I was asking to choose the one which would go better for that.
A while ago I did some comparisons began the FA150-300, 300 FA* and the FA 400. If you look through this thread you will find the pictures. I found that the 300 FA* has less or shall I say near zero CA, whereas the 400mm is prone to some CA in some situations. Since then I have found that at closer distances the 300* is actually a little bit sharper. But at further distances beyond +/-200m I would say they are equal, except for the CA issue in high contrast parts of the image.
The big benefit of the FA300* is that it pairs very well with the 1.4 TC, whereas the 400 does not, at least in my experience.
The two pictures below are with the FA* 300mm and with the 1.4TC. I have not tested this on objects further away, but at least in this instance at abt 10m there seems to be no loss of quality. Except of course that the TC is manual focus only.
On these jpg pictures the TC picture look a bit sharper, which is because of the jpg loss and resizing. In raw they are equal in sharpness.