Aaaaaaaaaaaaaaarrrrgh!
I got some numbers wrong. :-(
See below.
Steve Jolly wrote:
Don Sanderson wrote:
How does one figure partial stop numbers?
For instance what stop is half way between 4 and 5.6?
4.76 :-)
And where does 4.76 fall?
Half way between 4 and 5.6 :-)
Or in other words, f4.76 is 1/4 of a stop slower than f4 and 1/4 of a
stop faster than f5.6
Sorry, 1/2 a stop in both cases, not 1/4
This is a 2.8 lens with the
SMCP-F 1.7x converter.
Therefore the 1.7x converter introduces a 3/4 stop decrease in the
effective aperture size.
And that should read "a 1.5 stop decrease".
The rest is correct.
I'm guessing there is a simple multiplier for this but
with my limited knowledge of math I have no clue
what it is.
It's "easy" - multiply by sqrt(2), or by sqrt(sqrt(2)), etc. Here's an
example:
Halfway between f4 and f8 is f5.6
4 * sqrt(2) = 5.6
5.6 * sqrt(2) = 8
Halfway between f4 and f5.6 is f4.76
4 * sqrt(sqrt(2)) = 4.76
4.76 * sqrt(sqrt(2)) = 5.6
Spot the pattern? :-)
This is more out of curiosity than necessity.
Someone posted a link to this info but I can't find
it again.
Well, I haven't tried to explain it exhaustively, 'cos people complain
when I do that... but I've answered your questions at least. ;-)
S
