Perspective Lesson-Are Drones Better Than Telephoto Lenses for Spying?
What a difference PR/public awareness makes.
A lens extender, also called a teleconverter, does exactly what the name implies: it extends the focal length of your lens. So for example if you are shooting with a 200mm lens and use the Canon 2x extender, you are essentially shooting with a 400mm lens. The primary disadvantage is that you lose a few stops; with an f/2.8 lens, you’re reduced to f/5.6 - but that’s still more than enough if you’re shooting in daylight.
And it definitely has the reach to be creepy. I had my friend sit at a local park while I went to my roof, lens in hand. For perspective, here is where my friend was sitting: