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Is there a rule to remember what a full stop is?
Sorry for posting yet another thread but this is another big question I had..

In the book 'Understanding Exposure", the author talks about light in his last chapter and how to properly make an exposure..

He refers to what he calls Brother Sky, meaning, when shooting in low light (night for example), first measure a correct exposure while metering the sky with a wide open aperture (f/2.8) then depending what you need (if depths of field is needed for landscaping) then set f/22, calculate how many stops I went down and do the same to the shutter speed to make sure the exposure stays correct..

But I'm having a hard time with these stops and half stops. With shutter speed I thought it was always /2 , but it's not, and for aperture, f/2.8 , f/5.6, f/8, f/11 ... it doesn't seem to follow any linearity..

I suppose I could just count the number of times I turned the wheel to get from f/2.8 to f/22 and increase the shutter speed by turning the wheel that many number of times... but aside from learning by heart, is there a rule?..

Comments (23)

You're missing f4 here. Hmm.. interesting question, it was something with logarithms but I'm not sure if there's a rule.Don't wait for the Nikon D-whatever, have fun now!http://www.flickr.com/photos/j_wijnands/..

Comment #1

The aperture is the diameter. The light entering the lens is function of the area of the opening thus function of the square of the diameter..

F/2, f/2.8, f/4, f/5.6 are just simplifications. Real are f/2, f/2.82843..., f/4, f/5.65685..., f/8.It's a geometric progression with the rate sqrt(2).VictorBucuresti, Romaniahttp://s106.photobucket.com/albums/m268/victor_petcu/..

Comment #2

TigerLord wrote:.

But I'm having a hard time with these stops and half stops. Withshutter speed I thought it was always /2 , but it's not, and foraperture, f/2.8 , f/5.6, f/8, f/11 ... it doesn't seem to follow anylinearity..

I suppose I could just count the number of times I turned the wheelto get from f/2.8 to f/22 and increase the shutter speed by turningthe wheel that many number of times... but aside from learning byheart, is there a rule?.

You'll get them by heart eventually, just through using the numbers regularly.However, it's very easy to figure out two-stop intervals..

F/2 to f/4 is two stops. So is f/4 to f/8. Doubling or halving the number means two stops. Same with f/5.6 to f/11 or f/11 to f/22. Sometimes it's not exact because the numbers are fractions, rounded to an approximate value..

The complete series such as f/2, f/2.8, f/4, f/5.6 are numbers related by sqrt(2) or roughly 1.414. Not so easy to work out in your head, it is actually easier to just memorise the sequence...

Comment #3

1 F stop is a doubling or halving of the amount of light hitting the sensor,which is equivalent to making the diameter of the hole 0.7x or 1.4x (because the.

Effect on the amount light through the hole is the sqr of the change of diameter.).

1 stop (in general) is doubling or halving the amount of light, so for time (shutter) or ISO it's doubling or halving too..

The dynamic range of our real world is about 10 stops.The dynamic range of an average sensor is about 5 stops..

Enjoying to try making better images again and again and .....

Comment #4

But I'm having a hard time with these stops and half stops. Withshutter speed I thought it was always /2 , but it's not,.

Yes it is.... 1/60 is one stop more exposure than 1/125, which is one stop mroe than 1/250 etc. OK they are not EXACTLY factors of two because of rounding errors, but the main sequence of 'full stops' in shutter speeds goes 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000 seconds etc..

Most cameras now also do intermediate speeds at one-half or one-third stop intervals which may be confusing. If your camera does half-stop intervals then you will see (for example) 1/90 inbetween 1/60 and 1/125; if it does one-third stop intervals you will see two values in between, something like 1/75 and 1/100..

Best wishesMike..

Comment #5

Just to clarify what others already said:.

For the shutter speeds the full stops are always twice as long as the one before:.

1, 1/2, 1/4, 1/8 after that it isn't alway exactly twice, because of rounding errors, but it is pretty close: 1/15, 1/30, 1/60, 1/125 ....

For the aperture it isn't twice as high as the one before, instead it is multiplied by the square root of 2 which is approximately 1.4:1.0, 1.4, 2.0, 2.8, 4.0, 5.6 ....1.4 = 1.0 * 1.42.0 = 1.4 * 1.42.8 = 2.0 * 1.4.

And so on. The easiest way to remember this probably is to remember them in two sequences of two stop increments starting at 1.0 and 1.4:1.0, 2.0, 4.0, 8.0, 16.0and1.4, 2.8, 5.6, 11.0, 22.0.

In both sequences you just double the previous value. If you now interleave both list, i.e. take one value from each list and put them into a new one, you will get the original sequence of full stops.1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11.0, 16.0, 22.0.

Sidenote for the mathematically inlined:1.0 = 1.4^01.4 = 1.4^12.0 = 1.4^22.8 = 1.4^34.0 = 1.4^4and so on.

Bye,Philip..

Comment #6

Roughly speaking it goes like this:.

1 = 1.

& 14 = 2.

& 2 = 4.

& 28 = 8.

& 4 = 16.

& 56 = 32.

& 8 = 64.

& 11 = 132.

So can you see that the things double when squared (more or less, as the f numbers are rounded a bit to engrave on the lens barrel)? We are really talking about the area of glass letting in the light, which is why squaring it shows the obvious..

Equally the shutter speeds don't run in a true sequence of 2, 1, , etc because they were standardised in the 1950's..

And, of course, there are half and third stops and speeds. Like any ruler you don't just get a plain measurement but you get fine adjustments for exact exposures. (A ruler showing just inches wouldn't be much use; not would one that only went down to "... ).

Hope this helps..

Regards, David..

Comment #7

The diameter of the opening as compared to the Focal length. Expressed by a fraction..

Another post explains way the numberimg of F/stops does not always double. (F/4, F/5.6, F/8, F/11, F/16, F/22)..BUT the light doubles from one to the next higher full F/stop..

Example:.............F/1.0 on a 50mm lens is telling you the opening is 50mm in Diameter..........If you replace the "F" with the number "1", it will make more senseFor a 50mm lensF/1.0 or 1/1 = a 50mm openingF/2 or 1/2 = a 25mm openingF/4 or 1/4 = a 12.5mm openingF/8 or 1/8 = 6.25mm opening.

NOW you SEE a linear progression. 1, 1/2, 1/4, 1/8, ........

..If you CLOSE the F/stop by ONE Stop (not 1/2 click) you are cutting off 1/2 the light. If you OPEN the F/stop by ONE Stop. you are letting in 2x the light..

I have used simple F/stops as an example only....I know there are more F/stops involved...Don't get OT......

You can use this expression of F/stops for any Focal length..

F/4 will be F/4 REGUARDLESS of the size of the opening, BECAUSE it is 1/4 of the FL in diameter. A 200mm lens F/4 is 50mm in diameter for example, (4x 50mm = 200). It will let in the SAME amount of light as F/4 on a 50mm lens at F/4. Even though the Diameter 12.5mm on a 50mm..

'Well, Good Luck With That' (SpongeBob SquarePants).

Peter .

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Enjoy your photography images, even if your wife doesn't ! ;-(http://laurence-photography.com/http://www.pbase.com/peterarbib/Cameras in profile...

Comment #8

The rules have about how f-stop squared is related to the exposure have been pretty well explained so far & there's no really simple rule to remember the sequence except memorizing powers of the square root of 2... 1.4, 2, 2.8, 4, 5.6, 8, 11, .....

But, here's a way to avoid that:.

First remember that f/4 lets in 4 times as much light as f/8 - a factor of 2 squared..

Next, count the number of clicks between f/4 & f/8 for your camera - it might be two (f/4 -> f/5.6 -> f/8) in which case each click is a factor of two change in exposure - one EV change in exposure..

Or it might be 4 (f/4->f/4.8->f/5.6->f/6.8->f/8...) in which case each click is a half-stop change -1/2EV change in exposure..

From now on all you need to remember is whether each click for your camera is 1 stop or 1/2 stop..

All you'll need do to change exposure in a known way is to count the number of clicks...

Comment #9

As others have said, the shutter speeds double (or halve) in order to double (or halve) the amount of light. Twice the amount of time equals twice the amount of light. Its a direct relationship. The actual time values listed were changed from their actual values to values that would be easier for people to remember. For example, 1/60 instead of the true 1/64 value. Or 1/500 instead of 1/512.

Actually, I suspect that internally 1/500 really is 1/512 of a sec..

The aperture values, however, are a ratio between two other numbers. Thats why its not a direct relationship like shutter speed is. The two numbers are focal length (as in the 50mm of a 50mm lens) and aperture diameter. Divide the focal length by the aperture diameter and you have the f/stop values. So if you have a 50mm lens and an aperture diameter of 25mm then 50 / 25 = 2. So your f/stop is 2..

But which diameters? The diameter of the aperture dictates the total area of the aperture opening. The diameters used are diameters that double or halve the area of the opening. Here is the linear relationship you were looking for. So for a 50mm lens we have:F/stop  aperture area for 50mm lens1.0  1963 sq mm1.4  10022.0  4912.8  2504.0  1235.6  638.0  31.

As with shutter speeds, the values arent exact...but close enough..

It would be too difficult to always speak in terms of aperture area because each lens would be different. A 1000 sq mm aperture on one lens might give the same amount of light as a 1500 sq mm aperture on a second lens. Since diameter is directly related to area, using aperture diameter is equally confusing. However, by relating the aperture opening to the size of the lens, manufacturers were able to create a system that allows the setting to describe the same amount of light across different lens. F5.6 is F5.6 no matter which lens you're using..

So even if you dont understand the aperture settings, be happy that we have it otherwise things would really be confusing!.

See this web page for more information on f/stophttp://www.uscoles.com/fstop.htm..

Comment #10

Graystar wrote:.

So even if you dont understand the aperture settings, be happy thatwe have it otherwise things would really be confusing!.

Well, instead of a relative aperture system, they could have created a relative area one. E.g.,.

A/1 == f/1a/2 == f/1.4a/4 == f/2a/8 == f/2.8a/16 == f/4a/32 == f/5.6a/64 == f/8a/128 == f/11a/256 == f/16a/512 == f/22.

You could even reverse the scale and make f/1 == a/1024 (or whatever). Then "bigger numbers" (ignoring the foo/ part) == more light and you wouldn't need to explain about SQRT(2)..

The downside would be figuring out how to print a/1024 on a lens barrel.   (That, and the fact that f-stops are too entrenched now to change.)..

Comment #11

Well I did not post the question myself, but have been wondering about this recently, so I really enjoyed this thread. Thank you all so much for your replies, they are very much appreciated..

As a general statement, I just want to say that I have been very happy and quite impressed with this forum wrt the ratio of people who really want to help give others a hand up, and people who just want to show off what they know!.

Thanks again,Scott..

Comment #12

F/stop is a ratio of aperture diameter to focal length.

So, for a a 50mm aperture (or opening through diaphragm blades that approximates a circle of that diameter) on a 100mm lens has a maximum *relative* opening of f/2 (focal length over 2 or 100mm/2 = 50mm aperture).

50mm aperture on a 200mm focal length is f/4.

In the ratio f/x a bigger number in the denominator (x), indicates a smaller amount aperture *relative to* the focal length..

Calculating f/stops this way allows lenses of different focal lengths to be compared by a common number indicating the light transmitted instead of the absolute size of the aperture..

The progression is non-linear, marked in a series of approximate multiples of the square root of 2 (which is 1.41421356....).

F/1 (square root of two raised to the zero power)f/1.4 (square root of two raised to the first power)f/2 (square of the square root of two, i.e. to the second power)f/2.8 (the cube of the square root of two, i.e. to the third power)f/4 (square root of two to the 4th power)f/5.6 (... to the 5th power)... and so on.

High school algebra does come in handy some times. .

..

Comment #13

Tom_N wrote:.

Graystar wrote:.

So even if you dont understand the aperture settings, be happy thatwe have it otherwise things would really be confusing!.

Well, instead of a relative aperture system, they could have createda relative area one..

Hi,.

They used to use that about 1900's to 1920's on the Kodak folding "pocket" cameras. I've an "Autographic" and the lens apertures are shown as 4, 8, 16, 32, 64 but 4 is f/77 which is somewhat confusing. Later models used proper f stops and another model in the series used 1, 2, 3 & 4..

To add to the confusion the shutter speeds availabl are 1/25th and 1/50th and any one reading the manual would not discover that one lets through half as much light as the other! They talk about shutter speed as stopping motion and not exposure - if my memory is working correctly. BTW, the range 4, 8, 16 etc is described as a US scale..

Regards, David..

Comment #14

TigerLord wrote:.

Sorry for posting yet another thread but this is another big questionI had..

In the book 'Understanding Exposure", the author talks about light inhis last chapter and how to properly make an exposure..

He refers to what he calls Brother Sky, meaning, when shooting in lowlight (night for example), first measure a correct exposure whilemetering the sky with a wide open aperture (f/2.8) then dependingwhat you need (if depths of field is needed for landscaping) then setf/22, calculate how many stops I went down and do the same to theshutter speed to make sure the exposure stays correct..

Most modern cameras meter with the lens wide open automatically and only stop down to the selected lens setting as you press the shutter release button. So you don't actually have to go through the routine you described above..

But I'm having a hard time with these stops and half stops. Withshutter speed I thought it was always /2 , but it's not, and foraperture, f/2.8 , f/5.6, f/8, f/11 ... it doesn't seem to follow anylinearity..

Everyone had that point in their lives, don't worry you will eventually get used to the "crooked" numbers. Here is a very simple way of remembering. You only need to remember two numbers (aperture settings). f/1.4 and f/2. These are one stop apart. The rest you can calculate very easily by doubling the values.

F/2.8 ... f/5.6 ... f/11 ... f/22 (each of these a two stops apart)f/2 ... f/4 ...

F/16 ... f/32 (each of those are two stops apart).

To find out what one stop is you simply alternate between the two..

(on modern cameras you will find that you can often select values in between - those are 1/2 or 1/3 steps in between the stops, but I would not worry about this too much)..

I suppose I could just count the number of times I turned the wheelto get from f/2.8 to f/22 and increase the shutter speed by turningthe wheel that many number of times... but aside from learning byheart, is there a rule?..

Comment #15

Yes thank you all VERY much for that very helpful information!..

Comment #16

This information is very helpful. Thanks for all the great advise.I always wondered when I'd be using my high school algebra.  Melissa.

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Comment #17

I've posted A FREE DOWNLOADABLE Microsoft Excel chart (two charts actually) on my photog website. It is on my page w/ three available desktop image 'wallpapers'... also available for free download for non-commercial use..

Lower left side of page..

Sunny 16. Right click and save. This is in 1/3 stops and covers pretty much a wide range of things..

Http://kaptures.net/desktops01.html.

Infrared is for my Nikon D80... Which is VERY IR CHALLENGED. It takes about 12 1/2 stops MORE light to capture using a Hoya R72 IR filter. So, I made a cheat chart specifically for that..

I mean, metering says 1/2000 ISO 160 f/8... Now try to figure in your head 12 2/3 stops... Or count wheel turns (3 per stop) for shutter, ISO, or aperture... I'd rather have my handy chart! lol..

This site is MY OWN, designed by me, managed by me. No content goes on without my doing. Therefore I can assure you it is NOT a virus. It is exactly what I'm claiming... An excel worksheet for the "Sunny 16 photography rule.".

Hope it helps somebody out there? I use it so often, I have to print them on card stock and reprint every few weeks... I need to laminate one. wheeeeeeeeeeee.Cheers.Davidmy flickr: http://www.flickr.com/photos/prodesma/..

Comment #18

Sorry folks... I've noticed a bit of traffic from this link to my desktops page. I've not put it back up there, but....

It is available as a free downloadable .pdf from my photo blog. Here's the direct post link to my blog:.

Http://kaptures.net/blog/2007/09/ansel-adams-and-sunny-16.html.

Cheers.Davidmy flickr: http://www.flickr.com/photos/prodesma/my website: http://kaptures.net/..

Comment #19

Dodgy info here I believe.jules.

TigerLord wrote:.

F/2 to f/4 is two stops. So is f/4 to f/8. Doubling or halving thenumber means two stops...

Comment #20

Please explain.Regards,Peter.

JulesJ wrote:.

Dodgy info here I believe.jules.

TigerLord wrote:.

F/2 to f/4 is two stops. So is f/4 to f/8. Doubling or halving thenumber means two stops...

Comment #21

JulesJ wrote:.

Dodgy info here I believe.jules.

TigerLord wrote:.

F/2 to f/4 is two stops. So is f/4 to f/8. Doubling or halving thenumber means two stops..

What's the problem, Jules? TigerLord's info looks OK to me.. (shrugs) ):-(.

Regards,Baz..

Comment #22

Oh dear, some people do seem to be making this sound rather complicated with all the talk of sq roots etc..

In reality we're dealing with fractions but the simple way to remember them is that (the number representing) each full stop is double the the last but one in the series. Thus in the series2 2.8 4 5.6 8 11 16 22.

2x 2=42x 2.8=5.62x 4=82x 5.6=11 (almost!).

He refers to what he calls Brother Sky, meaning, when shooting in lowlight (night for example), first measure a correct exposure whilemetering the sky with a wide open aperture (f/2.8) then dependingwhat you need (if depths of field is needed for landscaping) then setf/22, calculate how many stops I went down and do the same to theshutter speed to make sure the exposure stays correct..

That methodology is 'sound' but I suspect this is an older book written in the days of film SLRs. Its unnecessary to go through this procedure with most modern cameras - select your chosen aperture in aperture priority mode (Av) and the camera will meter accordingly without you needing to make an adjustment. If it's too dark for the camera to meter then increase the iso setting to the highest available, take a reading, reset the iso to a lower setting (to reduce noise) and increase the shutter speed accordingly. Each doubling of the iso rating = 1 full stop - so, 1s @1600iso would equate to 16s @100iso.

As to choice of aperture, with a dSLR I wouldn't recommend stopping down as far as f22. You'll get much sharper images by sticking to f11 and with digital that should still give you sufficient depth of field from most purposes..

Confused of Malvern'The greatest fool can ask more than the wisest man can answer'..

Comment #23

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