Random Orbits said:
My family and I are planning on visiting national parks in the Pacific Northwest including Crater Lake National Park this summer, and I've started looking into what focal lengths would be useful. I've seen a few webpages stating that an UWA lens is a must, but how wide of a lens is useful for Crater Lake NP? Is 16mm on FF wide enough or would a 11-24 or fisheye be useful?
It's been some time since I was there, but here's my best advice. For the lake itself, you'll want gear for wide and panorama. Also remember that there's more to the park than just the lake: depending on how much time you have, you may want to explore some of the areas away from the crater. The car-accessible viewpoints can get very crowded in the summer. If your family are avid hikers, plan an early morning hike away from the road (horizontally or vertically) for a less-crowded view.
One more thing, I wish I'd had this book: http://www.oregonhiking.com/navillus-press/oregon-guides/trails-of-crater-lake-national-park