Sorry for the late entry to this thread, but I just found it. I use a Nikon D80, and for tank photography an 80 mm macro Nikkor lens. Using a longer lens like the 80 mm (105 would be even better) allows me to do close up photos without getting too close to the subject, which is important for fish photography unless you have an underwater camera
. I don't know why anyone would say that the Nikon D80 has an "internal motor". There are two motors involved in photography. One would be for automatically advancing the film - but in digital there is no film, so it can't be that. A motor is also involved in the auto-focus mechanism. In some brands the motor for this is, indeed, in the camera. However, in all Nikons the motor comes in each lens, not in the body. This increases the cost of the lenses, but makes the camera body somewhat lighter and produces (IMHO) better auto-focus. All of my lenses are Nikkor with the exception of my long 200-500 mm, which is a Tamron. I'm very happy with it since it features auto-focus and vibration reduction, and gives me pretty good images (sharp, good contrast). Whatever you choose, don't obsess over it. You have narrowed your choices to two "can't lose" brands, Nikon and Canon, and whatever you buy will be fine. Don't rush into lens purchases until take lots of pictures and begin to understand what focal lengths you need for the type of work you are doing. I do lots of nature photography, so long lenses are my thing, although I did just add a 12-24 mm zoom which is giving me some interesting flower pictures. Good luck! Here are a few D80 shots:
