Camera bags are separate to hand baggage pieces. No weight mentioned and I have never seen SQ ground staff weigh anything. My guess is that as long as its not a giant metal box of lenses you'll be fine...

You may carry ONE of these items with you on our flights, free of charge, in addition to your cabin baggage allowance (subject to country restrictions, where applicable):

• Ladies’ handbag*
• Camera / Camera bag*
• Document bag*
• Overcoat
• Umbrella
• Laptop / Notebook in bag*
• Infant’s amenities and food for consumption on board. The total weight of these items should not exceed 6kg
• A walking stick, a pair of crutches and/or other prosthetic devices, if you are dependent on them
• A small amount of duty free goods (where permitted)

* The maximum dimensions for these bags are 40x30x10cm each. If your item exceeds the total dimension of 80cm (the length, width and height combined), it will be counted as part of your standard cabin baggage allowance. You will then be required to check in either your cabin bag or the additional item.