Canon Digital Photography Forums f-stop increments
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 5th of March 2009 (Thu) #1 Sibil Goldmember   Join Date: Jan 2009 Location: SoCal Posts: 2,104 f-stop increments What increments on a lens is considered one f-stop? for example, going from 2.8 to 4.0. is this one f-stop? Or, going from 4.0 to 5.6, is this one f-stop? __________________ 7D, 1DIII, 135/2, 85/1.8, 50/1.4, 28/1.8, 100-400/4.5-5.6, 15-85/3.5-5.6, 24-105/4, Kenko 1.4, 580EX II
 5th of March 2009 (Thu) #2 airfrogusmc I'm a chimper. There I said it...   Join Date: May 2007 Location: Oak Park, Illinois Posts: 31,718 Re: f-stop increments When you go from f 1.4 to f 2 you are stopping down 1 stop. Cutting the light in half. Every time you stop down a full f stop like 1.4 to 2 you are cutting the light in half. So the full stops would be 1/4,2,2.8,4,5.6,8,11,16, 22, 32. Now if you go from say f/4 to 2.8 you are opening up one stop doubling the light. Shutter speeds are also set to either double or half the amount the time is allowed to strike a light sensitive surface. If you go from 1/60 of a second to 1/125 you are cutting the time in half. If you go from 1/60 to 1/30 of a second you are doubling the time. There is a law called the law of reciprocity that is a basic tool to use. Basically it say if you have a correct exposure at 1/125 at f8 the same amount of light will strike the light sensitive surface as 1/250 at 5.6 or 1/60 at f/11. So say that 1/30 at f 16 will give you the same amount of light on the light sensitive surface as 1/60 at f 11 and 1/125 at f 8 and 1/250 at 5.6 and 1/500 at f 4 and 1/1000 at f 2.8 and 1/2000 at f 2. Read this: http://en.wikipedia.org/wiki/Science_of_photography
 5th of March 2009 (Thu) #3 rdompor Member     Join Date: Nov 2008 Location: New Jersey Posts: 668 Re: f-stop increments Actually, Allen, I think that he is asking what constitutes an increment of one stop. Basically, a 'stop' is defined as multiples of sqrt(2) * the diameter of the aperture. So to find the next stop down from f/2, you multiply f/2 * sqrt(2). To find the next stop down from f/5.6, you multiply f/5.6 * sqrt(2) and so on.
5th of March 2009 (Thu)   #4
airfrogusmc
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Re: f-stop increments

Quote:
 Originally Posted by rdompor Actually, Allen, I think that he is asking what constitutes an increment of one stop. Basically, a 'stop' is defined as multiples of sqrt(2) * the diameter of the aperture. So to find the next stop down from f/2, you multiply f/2 * sqrt(2). To find the next stop down from f/5.6, you multiply f/5.6 * sqrt(2) and so on.
Twice the light when you open a stop 2 and the square root of 2 is 1.414 so to simplify just say 1.4....And to open up from 5.6 you divide the sqrt. 5.6 divided by 1.4 = 4

 5th of March 2009 (Thu) #5 NinetyEight "Banned for life"     Join Date: Sep 2008 Location: Bath - England Posts: 3,052 Re: f-stop increments A 'stop' can also refer to the shutter speed allowing in twice/half the amount of light. __________________ Kev
 5th of March 2009 (Thu) #6 justaf IREMAN Senior Member   Join Date: Feb 2009 Location: Henderson, NV Posts: 1,148 Re: f-stop increments 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 __________________ current gear...1DIII, X-E1, X-PRO 1, X100, Lumix LX5, Fujinon 35 1.4, 85LII, 430EXII, 430EX.... past canon gear....XS, 7D, 2 5DII, 2 1DIII, , 18-55IS, 24-70L, 85 F1.8, 85LII, 35F2, 35L, 24L, 200 F2L, 580EXII....
 5th of March 2009 (Thu) #7 Bill Ng Senior Member     Join Date: May 2005 Location: Hartsdale, NY Posts: 1,201 Re: f-stop increments Standard aperture "stops": f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32 Standard shutter "stops" 1/8000, 1/4000, 1/2000, 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1, 2, 4, 8, 15, 30 Standard ISO "stops" 100, 200, 400, 800, 1600, 3200, 6400, 12800, 25600 Each "stop" represents either the doubling or halving of exposure. I use the word exposure because there are 3 aspects of light that dictate exposure - Quantity, Time, and Sensitivity. ISO = Sensitivity to light Shutter = Time light is exposed to sensor Aperture = Amount of light If you change any one of these variables by 1 stop, you are halving/doubling the exposure. Learning to move the 3 of these to attain the desired photographic affect is what you are striving for. Start off with the 101: http://photography-on-the.net/forum/...d.php?t=249006 Billy Ng
 5th of March 2009 (Thu) #8 toxic Goldmember   Join Date: Nov 2008 Location: California Posts: 3,498 Re: f-stop increments In numbers, it's simply multiples of sqrt(2). Half-stops are a little more confusing... F-stops in 1/2 are (full-stops bolded): 1.0 1.2 1.4 1.8 2.0 2.5 2.8 3.5 4.0 4.5 5.6 6.7 8.0... Last edited by toxic : 5th of March 2009 (Thu) at 12:33.
5th of March 2009 (Thu)   #9
NinetyEight
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Re: f-stop increments

Quote:
 Originally Posted by justaf IREMAN 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32
These are considered 'full' stop values, but 'a stop' can be considered to be any actual value as long as it is mathematically correct.
So you could be using 1/3 stop increments and use any value and simply by moving the dial 3 clicks will be a stop difference - or by doing the same with a shutter speed or ISO value
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5th of March 2009 (Thu)   #10
Sean
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Re: f-stop increments

Quote:
 Originally Posted by NinetyEight These are considered 'full' stop values, but 'a stop' can be considered to be any actual value as long as it is mathematically correct. So you could be using 1/3 stop increments and use any value and simply by moving the dial 3 clicks will be a stop difference - or by doing the same with a shutter speed or ISO value
True. However it's not always perfect. Some camera's don't really adjust the ISO by a 1/3rd or 1/2 stop, they mimic it though the processor. Can't remember which do that.
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5th of March 2009 (Thu)   #11
hollis_f
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Re: f-stop increments

Quote:
 Originally Posted by Sibil What increments on a lens is considered one f-stop? for example, going from 2.8 to 4.0. is this one f-stop? Or, going from 4.0 to 5.6, is this one f-stop?
Yes and Yes.

Easy way to remember - doubling the f value means 2 stops.

One stop is multiplying by 1.4
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5th of March 2009 (Thu)   #12
justaf IREMAN
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Re: f-stop increments

Quote:
 Originally Posted by Sibil What increments on a lens is considered one f-stop? for example, going from 2.8 to 4.0. is this one f-stop? Or, going from 4.0 to 5.6, is this one f-stop?
Quote:
 Originally Posted by NinetyEight These are considered 'full' stop values, but 'a stop' can be considered to be any actual value as long as it is mathematically correct. So you could be using 1/3 stop increments and use any value and simply by moving the dial 3 clicks will be a stop difference - or by doing the same with a shutter speed or ISO value
the post stated "one f stop". the op was not asking about iso or shutter speed, i could be wrong but i think sibil was asking aperture specific.
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Last edited by justaf IREMAN : 5th of March 2009 (Thu) at 13:04.

5th of March 2009 (Thu)   #13
NinetyEight
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Re: f-stop increments

Quote:
 Originally Posted by justaf IREMAN the post stated "one f stop". the op was not asking about iso or shutter speed, i could be wrong but i think sibil was asking aperture specific.
I realise that, but thought I'd point out that it does not just apply to the aperture. Just trying to be informative
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5th of March 2009 (Thu)   #14
NinetyEight
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Re: f-stop increments

Quote:
 Originally Posted by Sean True. However it's not always perfect. Some camera's don't really adjust the ISO by a 1/3rd or 1/2 stop, they mimic it though the processor. Can't remember which do that.
I appreciate this and this is the reason I only use full ISO values - I was just pointing it out that ISO can be measured as stops.
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5th of March 2009 (Thu)   #15
justaf IREMAN
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Re: f-stop increments

Quote:
 Originally Posted by NinetyEight I realise that, but thought I'd point out that it does not just apply to the aperture. Just trying to be informative
gotcha
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