300mm X 1.4 = 420mm
420mm X 2 + 840mm
- -or-
300mm X (1.4 + 2)= 1020mm?????
Weird, I can't think "outside the box" on this.
- -Tim Clark
Don't add, just multiply that is why they are called respectively times 1.4
and times 2.0 adaptors. The calculation is order independent, just multiply
the three terms together in any order to get the same (and correct) result.
Here is a hint: What if the adaptors were X 0.5 (reduce focal length to
1/2 value) and you put 4 of them together. Each additional adaptor would
cut focal length in half giving successively 100, 50, 25, 12.5, and finally
6.25 mm with all four adaptors in place. If you added up the adaptors you
would get X 2.0 and expect the 100mm lense to be converted to a 200mm
lense, clearly not the right expectation since no amount of reducing
something by a factor of 2 over and over will suddenly caluse enlargement
by a factor of 2.
Patrick
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