AF on nifty fifty

i love the results with my nifty fifty but have realised that the AF may not be up to keeping up with my ever moving newborn on f1.8. i am getting alot of non-keepers due to the shallow DOF and the little man moving.

would i see an improvement in the AF tracking using servo mode if i upgraded to the 50 1.4?

also is it worth the extra money to get the canon or is the sigma as good?

(body is 5d mark 2 and i will probably only use this lens for portrait shots of family and friends).

The 50 1.8 has ridiculous focusing. The 50 1.4 is a significant upgrade to the 1.8, but I did not enjoy the focusing of that lens as well. I *heard* that the Sigma one misses focus more than the Canon 1.4, but I have not tried the Sigma on my own. I'm sure the Canon 1.4 will suffice in terms of focusing speed for a newborn, as well as portraits.

magwai wrote in post #11637935
i love the results with my nifty fifty but have realised that the AF may not be up to keeping up with my ever moving newborn on f1.8. i am getting alot of non-keepers due to the shallow DOF and the little man moving.

would i see an improvement in the AF tracking using servo mode if i upgraded to the 50 1.4?

also is it worth the extra money to get the canon or is the sigma as good?

(body is 5d mark 2 and i will probably only use this lens for portrait shots of family and friends).

Of the (3) you mentioned the Canon f/1.4 is the best. To be honest with you, after owning two Sigma's... I'd rate the Sigma 50mm below even the Nifty Fifty in AF performance.

Just be sure you're steady when taking these shots, with a DOF that shallow not only does the babies movement mean make a difference but so does yours. Primes take some practice, so the lens may not be your only problem.