On a trek in the Markha Valley of Ladakh, India, I used a photo vest with a LowePro Orion AW fanny pack/day pack. I could easily unsnap the fanny pack from the day pack, swing it around in front of me and change lenses in a snap. I prefer it over photo backpacks that have to be taken off to reach gear. The photo vest is handy for keeping filters, film and small lenses available.