I'm learning...please be patient. Let's say you have these two lenses to work with and for sake of conversation say they are both of the same "quality". 18-70mm 70-300mm You find that the object you want to photograph looks best at 70mm, so essentially you could use either lens. The object would be moving in less than ideal light. Which lens would be better to use? Why? I'm trying to understand how the lens works. I know the amount of light that reaches the sensor is key, especially when you are limited with the light you have to work with. When a lens is all the way "zoomed in" or "zoomed out" will this change the light that enters the lens if they are both at 70mm?