08-02-2013 10:14 AM
08-02-2013 04:37 PM
This is the best info I know of.
Adding a 2X to an f2.8 lens will still allow Af on most bodies because you're now an f5.6 lens. It may degrade the image a bit depending on the specific TC so do your homework before shopping.
08-06-2013 10:32 AM
Anytime you add anything into the light path of any lens, you are going to degrade the image quality. Now, that may be a slight or it can be a significant loss.
I have always subscribed to using the original manufacturers accessories and in this case I still think so.
Sigma makes two tele converters that will work with your lens. Both are designed for your lens and retain all features including AF.
The Sigma 70-200mm f2.8 EX DG OS HSM is of such high quality it has room to give up a small amount of IQ, introduced by the tele converter, and still be better that some 70-200mm without one.
Another consideration is how big do you intend to make the prints? Do you use a tripod?
So you must weigh all the factors of IQ and cost plus slower AF, etc, and decide if it is for you.
I recommend the 1.4x over the 2x, though.
08-07-2013 12:59 AM