stefsan said:
Although I've never been to Nepal or Tibet, I have some experience with mountain hiking and carrying photo gear. In general I would agree with the other posters to go light. My standard setup is a 7D with 15-85 and 70-300, polarizers, spare batteries and CF cards. What to bring depends on what else you have to lug around and on how much time you have to take photos (there's not much sense in taking too many lenses if you have not the time to change them). And in my experience it depends also on the quality of your backpack. If you don't have one already, it really pays to invest some time (and money) on a very good pack that lets you carry relatively heavy loads comfortably for several hours and allows you quick access to your photo gear…
Most importantly: have fun and take care!
You've already received lots of good advice, Phil
I've not been to Nepal / Tibet - but I have been to SE Asian (eg Thailand), holidaying and trekking there. I also have a lot of experience travelling in and living in Europe (from the Swiss Alps to Western European cities to remote villages in Romania, etc).
My advice would very closely echo stefsan's above. I have a Canon 7D, and would take that as my primary camera with the 15-85mm and 70-300mm L as my first two 'travel lenses'. For a third lens I might take my Sigma 10-20mm, though the Canon 15-85mm @ 15mm can often be sufficient for many landscapes, etc.
When I went to Thailand some years ago, I took all my lenses and 2 camera bodies. It was way overkill. I only used my Canon 100mm macro a few times, and my bright prime once or twice during the few weeks I was there. I didn't bring a flash, as I used a tripod for low light / night shots. IS on lenses and having a camera with ISO capability certainly helps while travelling!
If I would go to do your trip, particularly as you're doing quite a few different areas, packing light adds to the convenience. A back-up body is of course handy in case body #1 breaks. For this, I'd probably take my small, old (but reliable) Canon 350D. I'd probably not take a tripod, but that's me (I often find other things to use or make do without).
Enjoy your time there, indeed. Best wishes... hoping to see some of your photos.
8)
Paul