f/stops


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May 19, 2007
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#1
Hi everyone,

i have searched on google about what is stop down 2 fstop. But too chim to understand.

for example, my 50mm lens f1.8.

2 stop down from f1.8, what is the fstop ? I seen the formula but very complicated.

anyone have a simple way to calculate ?
 

yc2005

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May 14, 2009
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#2
U can try googling for it

http://en.wikipedia.org/wiki/F-number

1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22

Those are the typical 1 stop difference. Anything in between would be 1/3 or 1/2 stop difference, depending on ur camera.

1 stop difference means half the light of the previous stop. So basically, at f/1.4 you will get half the light of f/1. And at f/2, it will be half the light of f/1.4 and one quarter the light of f/1. ;)

To ans ur qn, 2 stops below f/1.8 would be f/3.5
 

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May 19, 2007
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#3
so simply it means, if my camera is set to 1/2 stop. to get to 1 stop from the fstop, i dial 2 times, for 2 stop i just turn the dial 4 time.

in short,

1/2 + 1/2 = 1
1/2 + 1/2 + 1/2 + 1/2 = 2

am i right ?
 

ZerocoolAstra

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Mar 13, 2008
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#5
i don't suppose you want to know why f/1.4 ---> f/2 (and not f/2.8) is 1-stop (i.e. halving the aperture size)...... hahahaha :)
 

night86mare

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Aug 25, 2006
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#6
anyone have a simple way to calculate ?
it is far easier to just keep working with f-stops

after a while you just get used to it, at least the part that matters to what you shoot.

for example, i am more familiar with small aperture side.. because i shoot landscapes.
 

ziploc

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Jan 17, 2002
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#7
Actually it is very easy to remember the f numbers. Just remember 1 and 1.4. The rest are just x2 of these 2 numbers.

So:
1, 1.4
2, 2.8 (because 1x2=2, 1.4x2=2.8)
4, 5.6
8, 11
16, 22

Each of the above is 1 stop from the next. So f/1 to f/1.4 is one stop, f/1.4 to f/2 is one stop, and so on. The bigger the number, the smaller the aperture (just take f as a constant, e.g. 1. So 1/8 is smaller then 1/11, for example). Stop down means to reduce the aperture. So stop down 2 stops means reducing 2 stops. You can easily find that out from the aperture numbers listed above.
 

May 19, 2007
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#8
Actually it is very easy to remember the f numbers. Just remember 1 and 1.4. The rest are just x2 of these 2 numbers.

So:
1, 1.4
2, 2.8 (because 1x2=2, 1.4x2=2.8)
4, 5.6
8, 11
16, 22

Each of the above is 1 stop from the next. So f/1 to f/1.4 is one stop, f/1.4 to f/2 is one stop, and so on. The bigger the number, the smaller the aperture (just take f as a constant, e.g. 1. So 1/8 is smaller then 1/11, for example). Stop down means to reduce the aperture. So stop down 2 stops means reducing 2 stops. You can easily find that out from the aperture numbers listed above.
cool, this makes it clearer now...
 

ziploc

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#9
Erm mixed up. f/11 is smaller then f/8. Just discovered this mistake. :p
 

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