« on: August 07, 2014, 11:13:05 PM »
I speak from direct personal experience in the Kumbi, Mustang and also Eastern Bhutan. I bring my "travel triumvirate" of the 24-105 (used almost all the time), the 17-40 for interiors of temples, and the 70-200 f/4 IS for the occasional reach. Even with that tele, you'll likely do some cropping when you get home. Of the 3, the 24-105 was used for about 80% of my shots. Of course, you need to consider the weight and how much support you will have.
I also cannot emphasize the need for batteries. If you are camping, there will be very few opportunities to recharge the battery. Even if you stay in tea houses or lodges, there might not always be an ample power supply. I trek with 5 batteries and avoid chimping to prolong the battery life. The 5Diii powers up so quickly that I turn it off when not shooting. I don't bring a flash. I don't bring backup drives to save weight but carry a whole lot of memory cards. I delete nothing until I am off the trek. I do not bring a tripod but you might consider one of the combo hiking pole/monopods if you feel you need camera legs. The going can be tough. You will be at altitude. Don't expect to cover huge distances each day. Don't carry anything that is not needed. If support is an option for your trek, the locals who are quite accustomed to the altitude and weather can be hired to help carry your gear. This is not meant to be abusive to these folks but I live at about 1200 feet and they live at 9 or 10 thousand feet altitude. Carrying some of your gear is a great job for them. Do expect dust and do take appropriate precautions to protect your gear.
Obviously, this all depends on your shooting style and where you will be. If I sounded negative in my comments above, I don't mean to. The Himalaya is an amazing place. The regions in Mustang are a very desolate high desert with incredible cave monasteries while the Eastern area in Bhutan is plush and green with isolated villages. The people are stalwart and amazing. The Tibetan Buddhist culture and temples are fascinating. The weather is unpredictable. If I had to sum up my experiences in Nepal and Bhutan in one word it would be, "Magic." Feel free to PM me if you want any specifics.