A man took his 12 year old daughter out to take some photographs. They had two cameras, one with what is called a Full-Frame sensor, and the other had what is called a Crop sensor. The stood behind a fence, looking at a house in the distance. The man gave his daughter the Full-Frame camera and had her look through the 300mm lens at the house. "It's still kinda small," she said.
The man put the same lens on the Crop camera. "Here, try this one," he said.
She looked through the camera and said, "Hey. the house looks bigger with this camera! It's like I'm closer; like my arms were reaching farther out in front of me!"
"Yes," said the man, "it's like you have greater reach."
"Oh, I understand," said the 12 year old.
"That's because you are still too young to be stupid," said the man, grinning.