I have a few general questions.... I recently purchased a Canon Rebel XT, and I got the kit lens....I am in the process of selling it, but have bought a 1.8 mm f/1.8 and 17-85 mm f/4-5.6.....I am wondering what accessories are important to have.... Filters?? - How do they affect/ change your pictures - what are the advantages of using them? Is the lens hood just to protect the lens?? Does it affect the picture in any way? and....Is an alternate flash a must? What are the advantages over the built-in flash? What is the best one to get, for the price (for a beginner)???? THANKS!