O is for Optics
If you have a bagful of lenses, deciding which ones to take and which to leave behind can take a lot of planning. Nobody wants to miss a great shot through having the wrong lens, so think about what your destination is likely to offer and bias your choices accordingly. If landscapes and architecture are high on the agenda for your trip, you’ll need to ensure that wider focal lengths are covered. Conversely, if people and detail shots are more likely, longer lenses will be better.
Most travel photographers covering the whole gamut of disciplines opt for zoom lenses, as they allow you to cover a wide range of focal lengths in one unit. Zooms spanning 10-20mm, 18-70mm, and 70-300mm will cover all eventualities for APS-C cameras, and a 16-35mm, 28-70mm and 70-300mm will do the same for full-frame users. Alternatively, if you need to travel really light, then an 18-270mm or 16-300mm superzoom will cover everything you’ll need in one lens. The laws of physics determine that optical quality won’t be quite as good on these all-purpose ‘travel’ zooms, but the trade-off is a very compact and lightweight camera kit.