I inherited a Nikon D50 but sold it and upgraded to Nikon D5100 but still have a nice lense though older from the other camera. It fits and works on my new one. What is it good for? What types of photos? How is it different than my 18-55mm? I also have a Speedlight SB-600 that works with my camera as well. Is this a good flash? Seems to have alot of features.