7x magnification, because more makes 'em jittery and hard to aim. You pretty much need a tripod past 10x, and 7-10 is a good compromise with enough field of view to quickly find an object against an empty sky.
Less than 7 doesn't really show you much more than you can see with the naked eye.
50mm objective lens gives you good light-gathering power. Which you don't need for a day launch or birdwatching, but it's important for night stuff. You could get 7x20's (opera glasses) and be just fine, but the 50's aren't that much more expensive and they'll apply to a lot more situations.
Comments
7x magnification, because more makes 'em jittery and hard to aim. You pretty much need a tripod past 10x, and 7-10 is a good compromise with enough field of view to quickly find an object against an empty sky.
Less than 7 doesn't really show you much more than you can see with the naked eye.
50mm objective lens gives you good light-gathering power. Which you don't need for a day launch or birdwatching, but it's important for night stuff. You could get 7x20's (opera glasses) and be just fine, but the 50's aren't that much more expensive and they'll apply to a lot more situations.