Q: "50mm "normal" lens, would that be the same as the 50mm setting on my existing lens" Yes Q: "i notice the f/numbers to be different but what exactly does that mean?" The f/# is the maximum aperture. The lower the number the faster the lens is considered to be, and the more expensive they become. If you are looking at zooms you will often see two f/#'s listed, this means that the maximum aperture value changes depending on the focal length you are working with. There are zooms that have fixed maximum apertures, these also make the price go up. Q: "does the f/number really make that much of a difference to drive the price up that high?" It depends on who you talk to.... for the serious amatuer or professional, yes it's important, and yes it's worth the extra money. For myself...... f/2.8 and fixed maximum aperture is all that I will buy. If that means saving for a year, so be it. Q: "what's the advantage/disadvantage of a mirror lens?" Fun lens.... cheap.... I don't have one but would like one, mostly as a toy to play around with. But really not considered to be a good lens for serious photography. Most have a maximum aperture of f/8..... that is a serious detriment when considering how slow your shutter speeds would need to be in most lighting situations. Hand holding is impossible. Also in certain lighting situations you will see the typical ring effect in images. It literally looks like little ring shaped halos... some hate it, some find it charming. Advantages..... hmmm.... other than the extreme focal length.... and price.... can't think of anything.

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