The $1299 was a one-day DealZone deal. After the DealZone special pricing they placed it on sale for the $300 Instant Savings, hence the $1699 pricing when you hit the link. A very nice lens, I originally purchased the lens from Adorama for $1799 with the Sigma dock ($59 value at the time) to change AF settings etc. I also purchased the Sigma 1.4 extender, which is ok, but the loss of a stop of light can challenge AF on DSLRs. The lens is a beast, and I find that lesser quality ball heads have trouble managing the weight of the lens, which result in lack of sharpness due to motion, as gravity overcomes the weaker ball heads. The Sports line of Sigma means that there is a much more robust weather sealing over the Art and Contemporary lines. It was a steal at $1299.
