How can be with GST?Sure...
There is no sales tax in HK but if you bring back the cameras through local customs, you might be liable to pay 7% GST if SG customs ask for proof of purchase. Basically if just shop warranty only, you can be pretty certain the HK price is a "water goods" price. Good luck getting service if you have a major problem. To my understanding, once you walk out of the shop with the goods, you're pretty much on your own.