davide sorasio Posted April 24, 2018 Share Posted April 24, 2018 Hi guys, I was wondering if anybody could give me a scientific exolanation of how focal lenght doublers work and the reason why there is a 2 stops loss. Thanks in advance Link to comment Share on other sites More sharing options...
David Hessel Posted April 24, 2018 Share Posted April 24, 2018 It enlarges the image circle and as a result dims the brightness of the image in the process. As an example to make this concept more clear imagine a movie projection say 10 feet away from a wall and it is projecting an image on a 50" screen. This is similar to the way a lens works, it projects and focuses an image at a certain distance onto a certain size sensor just like a projector. Now take that projector and move it back to 20", now the image is much larger, 100" across, so the screen has much less image on it and the image that falls on the screen is enlarged. Also as you move the projector back the image gets dimmer because it is spreading the same amount of light over a much larger area. This is essentially what a doubler does, it increases the size of the projection on the sensor which magnifies it. What once filled the entire sensor is now spread well beyond it and since a large amount of its light is no longer falling on the sensor the brightness of the image also decreases. 3 Link to comment Share on other sites More sharing options...
James Malamatinas Posted April 27, 2018 Share Posted April 27, 2018 A super clear explaination - thanks! Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now