Mandy,
Using the Nikon 8400 and 20-60x eyepiece on the Swarovski 80HD scope produce some excellent quality results, as attached. Kowloon Park is an excellent place to practise with your camera. Remember to try and stay around the 30x zoom setting on your eyepiece. Focus distance also has an effect on the ammount of vignetting you get, but you can always crop this out with your software program
Bob
PS: All of these shots were taken with the zoom eyepiece