I'm looking at Saturn through a modest telescope at 50x. What point in space, expressed as the distance from Saturn, let's say it's 750 million miles from Earth, would I need to view Saturn with the naked eye and see it at the same apparent size as viewed from Earth at 50x. How do I estimate this in general for other objects as well. Thanks!
Just divide the actual distance by the magnification. In your example that would give 750 million /50, which is 15 million miles. (Actually saturn is currently over 800 million miles from earth).
The reason this works is that a magnification of M means the object is M times its apparent linear size, which requires being M times closer. This is a slight approximation, but is fine for distant objects.