Why does a teleconverter cut light 2 stops for 2x?

4 years 1 month ago #679093 by Kyle O
I've never understood this.  Teleconverter that is 2X brings you two times closer.  Why would it drop your set up 2 stops of light if it's increasing things 2X?  Would there be twice as much light coming into the sensor?


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4 years 1 month ago #679094 by Nikon Shooter
There is a first part of the fall off due to the length of the
tube and explained by the inverse square law.

The second part is that to get the double size, you ignore
A certain quantity of light that will not be recorded.

Together, they add up to +/- 2 ƒ stops

Light is free… capturing it is not!
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4 years 1 month ago #679100 by the four vignettes
Short answer: physics.

Log answer: it's effectively a light/image crop.  That means you're taking the light per unit area of a smaller area  and increasing the area of it covers, reducing light per unit area.  Basically "stretching" light over a larger area.


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4 years 1 month ago #679101 by effron
"...it's effectively a light/image crop."

Yes.

Why so serious?
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4 years 1 month ago #679125 by Kyle O
You all are great, thank you.  Your help was appreciated.  


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