Bob,
Thank you for your kind advice
As you said, the weight of tripods is important (it is already very heavy for me to carry a spotting scope, eyepiece, adaptor, a DSLR camera and a tripod), and therefore I would like to choose a light weight tripod head.
1. Manfrotto 501 - 1.6kgs - max 6kgs
2. Manfrotto 503 - 1.95kgs - max 8 kgs
3. Gitzo 2180 - 0.6kgs - max 4kgs
4. Gitzo 2380 - 1.4kgs - max 5kgs
I prefer to choose the Gitzo G2180, the weight is only 0.6 kgs with a maximum loading upto 4kgs. (my camera setup should be around 5.5 - 6 kgs), but I want to collect some existing users' opinion before I buy the tripod head.
Mandy