I use a pair of Leica 8x42's. They are not the best for magnification but like Southwest's Swarovski's 10x42, the quality of the glass is absolutely exceptional. This means the brightness levels are very high. The greater the magnification doesn't automatically make them better. If the lenses are made from cheap glass all you are doing is magnifying distortion. it's a double edge sword, the larger the size, the heavier they are to hold and more chance of shake, and the view will be darker. It's like trying to use a very large zoom lens on a camera without a tripod. I go to Manchester Airport viewing park quite a lot, and have no trouble reading registrations either on the far runway or on the tarmac. People have asked me the reg of aircraft that they can't see even if their binos are more powerful in magnification. This usually happens if the weather is gloomy. I would think that you would need the Hubble Telescope to read registrations at 30,000ft.