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Thread started 05 Mar 2009 (Thursday) 11:16

# f-stop increments

Mar 05, 2009 11:16 |  #1

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?

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Mar 05, 2009 11:29 |  #2

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 1/4,2,2.8,4,5.6,8,11,1​6, 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.

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Mar 05, 2009 11:41 |  #3

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.

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Mar 05, 2009 12:01 |  #4

rdompor wrote in post #7460538
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

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Mar 05, 2009 12:14 |  #5

A 'stop' can also refer to the shutter speed allowing in twice/half the amount of light.

Kev

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Mar 05, 2009 12:23 |  #6

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....

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Mar 05, 2009 12:23 as a reply to  @ NinetyEight's post |  #7

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:

Billy Ng

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Mar 05, 2009 12:25 |  #8

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...

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Mar 05, 2009 12:26 |  #9

justaf IREMAN wrote in post #7460820
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

Kev

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Mar 05, 2009 12:39 |  #10

NinetyEight wrote in post #7460846
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.

Canon 50D - 17-55mm F2.8 IS - 300mm F4L IS - 70-200mm F4L IS - 50mm F1.8 - 580EX II & 430EX - Full Gear Listing
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Mar 05, 2009 12:43 |  #11

Sibil wrote in post #7460373
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

Frank Hollis - Retired mass spectroscopist
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Mar 05, 2009 12:49 |  #12

Sibil wrote in post #7460373
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?

NinetyEight wrote in post #7460846
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.

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....

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Mar 05, 2009 13:18 |  #13

justaf IREMAN wrote in post #7461005
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

Kev

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Mar 05, 2009 13:19 |  #14

Sean wrote in post #7460929
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.

Kev

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Mar 05, 2009 13:25 |  #15

NinetyEight wrote in post #7461185
I realise that, but thought I'd point out that it does not just apply to the aperture. Just trying to be informative

gotcha

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....

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f-stop increments
AAA
 x 1600 y 1600

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