Fleetie said:
You could do worse than the new-ish EF-M 18-150mm lens; it was released around the same time as the M5.
I'm pleased with this lens on my M5.
+1 the EF-M 18-150 is a terrific one lens solution. That and a travel tripod.
I currently don't own a 18-150, but am planning to buy one to replace my current EF-M 15-45 and 55-200 for use on my M5. I recently borrowed a 18-150 for a weekend from a friend and found it sharper than my 15-45 and the focal range is terrific.
For a backpacking trip, going light is extremely important, so this one lens and a travel tripod should be able to handle most things that come up. I would suggest to add an EF-M 22 f/2 to give her a low light/shallow DOF option. This lens is so tiny it will not add appreciably to her burden.
A third lens option to add to the kit would be the excellent EF-M 11-22 that would provide a nice ultra wide option for landscapes and architecture. If it were me, I would take all 3 since I love UWA landscapes, but she can take excellent landscapes with the 18-150 or 22 and stitch them together in post if these are not wide enough (although not with the same look that an UWA lens will achieve).
Fortunately, none of the EF-M lenses are heavy or very large. I carry my M5 with 22mm and either 11-22mm or 55-200mm in a moderately small Lowepro Adventura SH10 II belt pack along with a spare battery and SD card. For day hikes, I clip the M5 to my backpack strap using a Peak Design Capture Pro so its ready to shoot at all times, and have room in my belt pack for another EF-M lens. I typically mount my 55-200 when hiking to capture wildlife I run across. For landscapes, I have time to change lenses. I certainly appreciate the weight reduction with this M5 kit compared to previous years carrying a 6D or 5D and FF lenses.
