Author Topic: Real world light gathering experiences or comparing a 80mm refractor to a 6 inch  (Read 31 times)

Bilal Luck

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Sorry for the long title but I wondered if anyone can confirm that this is true:
Comparing  a 6 inch F5 with a 80mm f7.5, the 80mm would require 8x more time to gather the same amount of light assuming they're both being used for astrophotography.
This is from dividing this ((6x24.5)^2/80^2) by this 5^2/7.5^2