To all who use Sigma 50/2.8 Macro lens please DO NOT play with the focus limiter knob, as the construction of it is very mediocre and can cause you a headache, so always leave it on "full".
Unfortunately, mine was stuck, and when disassembling the lens I was quite disappointed from the inner construction (probably that is one of the reasons to be cheaper).
Now I have a Sony 50/2.8 Macro and I really like it. I paid more than twice the price, but I think it's a right choice (cross fingers). Besides having a great look and ergonometry, the sharpness and IQ are superb.
A99 + a7rII + Sony, Zeiss, Minolta, Rokinon and M42 lensesFlickr