1) but how far is 18mm in real life distance and how far is 55mm in real life distance?

2) So is it true that the smaller the 1st number, the wider the lens? ie 10mm/50mm is wider than 18mm/50mm?

3) Then how far can 10mm/50mm zoom as compared to 50mm/ 250mm ? do we base on the number of times zoom of do we base on the 2nd number on the lens?

4) if we use prime lens ie 50mm f1.4, does it mean this lens only got 1 fixed clear area at 50mm? meaning we have to walk front and back to get the ideal sharpness? can autofocus if slightly behind or in front of focus area?

would appreciate some foto guru advice? many tks

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