Reducers & Barlow Lenses: How to Change Focal Length Without Changing Focal Length

Описание: NASA defines focal length as the distance light travels from the center of aperture to where it comes into focus, a fixed and physical property. But reducers cut back focal length and make images brighter while Barlow lenses increase focal length and make images dimmer, yet they don't make telescopes longer nor give them more aperture. What dark magic is this!

To watch: What Happens to Light When It Comes Into Focus:    • What Happens to Light When It Comes Into F...  

To watch: Understanding Focal Length: Trading Speed for Detail:    • Understanding Focal Length: Trading Speed ...  

To see high res versions of the images used in this video, check out the Sky Story Astrobin: https://www.astrobin.com/users/SkyStory/

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