# Explanation needed for the decrease in size of USA in NASA's picture from space taken in 2012-13

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#### Harish

##### New Member

As you can see, the size of USA has changed from the shots taken in 2 different years. I know one is from suomi npp satellite stationed at 400mile odd and another is from DSCOVR satellite 1 million mile away(or from space x, I'm not sure) . But if the reason for its size decrease is due to the difference in the distance from which it is taken, then why don't the outer perimeter (the circle) size also change?

This is a combination of focal length and distance from subject . Take a basketball, and hold a foot from your face. You're mostly going to see the word SPAULDING or whatever taking up most of your view. But you'll see the entire ball. Now put the ball on the table and walk 100' away and look at it through binoculars. You'll see the entire side of the ball that's facing you, and 'SPAULDING' will take up less of the face of the ball.

There's plenty of examples of doing this on photography websites. Here's a good picture showing the same set of 3 cans photographed with the same camera, using 4 different lenses. Each lens has a different focal length and was shot from a different distance (the 24mm was likely shot from a foot away, the 300mm was probably 15' away)

Credit to https://expertphotography.com/understand-focal-length-4-easy-steps/

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