different DC can have different result for same settings of apeture size and shutter speed
my advice is to
- set ur mode to Manual
- set apeture from f/2.8 to f/8 (use f/8 if you want STAR effect )
- set shutter speed from 1 sec to 8 sec (make sure there is no noise)
- use a stable tripod
- use remote control or timer mode
you are using a DC and can test with different settings for better effect ...