# What does it mean to stop up or stop down? - Aperture



## NedM (Feb 6, 2014)

I may sound like a complete noob but don't get me wrong I understand the aperture quite well.

It's just sometimes whenever I'm watching videos on photography or when I hear someone say, "For this next scene, we are going to have to adjust our aperture a stop up or down."
The said person then adjusts his f/number, oh lets say from, f/5.6 to f/8. 

That's when I'm caughtoff guard because I have no clue how much a stop up/down is!?

Or... Do I have this all wrong and whenever you're changing the aperture either higher or lower the term for that is just stopping up/down?

Please elaborate!

I do also see this whenever someone is also talking about the shutter speed as well!
Where can I learn more about this?


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## EIngerson (Feb 6, 2014)

Up = more exposure (lighter) Down = less exposure (darker) Stop = stops of aperture. 

So going from F5.6 to F8 would be stopping down. The bigger the number, the smaller the aperture size (the hole is smaller and lets less light in) 

I hope I'm not insulting your intelligence, just explaining in a simple manner.


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## NedM (Feb 6, 2014)

EIngerson said:


> Up = more exposure (lighter) Down = less exposure (darker) Stop = stops of aperture.
> 
> So going from F5.6 to F8 would be stopping down. The bigger the number, the smaller the aperture size (the hole is smaller and lets less light in)
> 
> I hope I'm not insulting your intelligence, just explaining in a simple manner.



No, no, not at all!
I mean, this was the only thing about the aperture that ever confused. 
Just understanding the terminology.

So, going from F5.6 to F8 or F11 would be stopping down?
There's nothing else to it?
It's just a term used for when adjusting the aperture then?


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## EIngerson (Feb 6, 2014)

NedM said:


> EIngerson said:
> 
> 
> > Up = more exposure (lighter) Down = less exposure (darker) Stop = stops of aperture.
> ...



for that conversation yes, but exposure in general is measured in stops. Heres a couple better explanations than I have time to type. lol

Photography 101.4 - Exposure and Stops - Digital Photography School

A Tedious Explanation of the f/stop


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## NedM (Feb 6, 2014)

EIngerson said:


> NedM said:
> 
> 
> > EIngerson said:
> ...




SO HELPFUL, THANK YOU!


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## KmH (Feb 6, 2014)

A 'stop' is a doubling (2x) or a halving (0.5x) of the amount of light and a stop is a fundamental photography concept.
A stop change in exposure can also apply to shutter speed and ISO.

Since exposure is a triad of adjustments (shutter speed, ISO, lens aperture) you can change 1, 2 or all 3 of the triad settings.

If you want 1 more stop of exposure (brighter) you can adjust just one of the 3 by 1 more stop.
Or, you can change 2 of the 3 by 1/2 more stop each for a net gain of 1 stop of exposure.
Or, you can adjust all 3 by 1/3 more stop for a net gain of 1 stop of exposure.

You can also change the triad of settings and have no change in the exposure.
If you change 1 of the 3 settings by 1 stop more exposure and change a 2nd setting by 1 stop less exposure the net change is zero.
Suppose you subtracted a stop of shutter speed to help stop subject motion, you could add a stop of lens aperture to keep the exposure the same. However, adding a stop of aperture will also effect the total DoF by a small amount. So, if you don't want the DoF to change you would add a stop of ISO instead, However, adding a stop of ISO will increase by some amount the image noise in the photo.

*Note: DSLR cameras are set by default to adjust the exposure settings in 1/3 stop increments.*
Most DSLR cameras let you change that to 1/2 stop or 1 stop increments.
However, the advantage of 1/3 stop step increments is more precise control of exposure.


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## bratkinson (Feb 6, 2014)

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
            == WHAT HE SAID ==


I couldn't have said it better, or more thoroughly.


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## TCampbell (Feb 6, 2014)

The term "stop" comes from the days of industrial machines when levers or dials would have teeth or indentations to allow it to lock the lever at a specific positions.  It "stopped" the lever.  Today, everything is electronic, but we still call them "stops".

A full stop represents either a halving or doubling of the amount of light collected.  Most camera apertures adjust by 1/3rd stop increments.

The order of stops is based on powers of the square root of 2.  This is because the "f" in f-stop stands for "focal ratio" and the value is the number of times that the diameter of the clear aperture can be divided into the focal length of the lens.  E.g. if your lens has a 100mm focal length but the clear aperture is 50mm wide then you are using "f/2" because 100 ÷ 50 = 2.    If you decrease the size of the clear aperture so that it's only 25mm wide then you have f/4.  Notice how the diameter of clear aperture got smaller... but the f-value got larger (a smaller opening divides into the total focal length more times.)

The order of "full" f stops is based on the powers of the square root of 2.  This is because the formula for the area of a circle is: area = pi * radius^2.   So if you have a 25mm diameter area, then the radius is 12.5mm.  12.5^2 = 156.25.  156.25 * pi = 490.87.  So the "area" of the circle is 490.87 square millimeters.  

If you increase the diameter of that circle by the square root of 2 (about 1.41) then you get:   12.5 * 1.41 = 17.68.  17.68^2 = 312.5.   312.5 * pi = 981.75.    

NOW... notice how we increase the diameter of the circle by the square root of 2 (1.41) and the AREA of the circle EXACTLY DOUBLED.    490.87 x 2 = 981.75  (really 981.74 but only because I truncated the digits of precision.  It really is exactly double... not merely close to double.)

By doubling the area of the aperture opening, you double amount of light that can flow through.  This means each time you change the f-stop by a factor based on the square root of 2 (whether up or down) you are always exactly halving or doubling the amount of light.

In photography, these values are rounded off to simply 1.4 but it really is intended to be the square root of 2.

The order of "full" f-stops is:  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...

f/1.0 = 1.4 raised to the 0th power
f/1.4 = 1.4 raised to the 1st power
f/2.0 = 1.4 raised to the 2nd power
f/2.8 = 1.4 raised to the 3rd power
f/4.0 = 1.4 raised to the 4th power
f/5.6 = 1.4 raised to the 5th power
f/8.0 = 1.4 raised to the 6th power
and we could keep going with f/11, f/16, f/22, and f/32 (and even higher but most lenses cannot stop down beyond f/32... a few can).  Notice that all we do is raise the power by 1 and this halves the amount of light (as f-stop values get bigger, the aperture gets smaller).


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## Derrel (Feb 6, 2014)

The photographic term stop comes from *Waterhouse stops*, which were small metal plates that were drilled with a hole. Different-sized stops were inserted into a slot on the lens barrel, as a way to control the size of the light-admitting aperture. The adjustable "iris diaphragm" was invented later. The Waterhouse stop system was invented in the late 1850's.

"Stopping the lens down," has always meant using a *small-diameter* aperture. "Opening the lens up," has always meant using a wider-diameter aperture.

Here is a web page that shows an old lens in a brass barrel, and a set of Waterhouse stops for that lens. http://www.skgrimes.com/products/shifting-mounts


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## astroNikon (Feb 6, 2014)

OP - don't worry ... when I first started too that "stop" word drove me nuts


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## BillM (Feb 6, 2014)

Great info, someone should make a sticky out of this :thumbup:


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## runnah (Feb 6, 2014)

Aperture settings really are counterintuitive. Larger numbers mean smaller hole, down means more light and up means less.


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## Derrel (Feb 6, 2014)

runnah said:


> Aperture settings really are counterintuitive. Larger numbers mean smaller hole, down means more light and up means less.



I have taught a few beginners by using the idea that f/strops are FRACTIONAL, so a larger denominator means a smaller light-admitting hole.

Using a lens like an 135mm, I'll show them a 1/2 dollar coin, for "f/2" and then move to "f/4", and call that "1/4" or "one-quarter", and show them a 25 cent coin.

Then introduce a US dime, and call that 1/10th...since the hole is small. They seem to get it. Half, quarter,tenth. Pretty simple.

It's just like *gauges*, in shotguns, or in wire, or whatever...the "Low gauges" are the big stuff, the 28-gauge is the inky-dinky shotgun or the tiny wire...


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## runnah (Feb 6, 2014)

That's is actually a good example.

But what photographer has $.85 laying around?


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## KmH (Feb 6, 2014)

They aren't counter-intuitive when one realizes they are fractions/ratios, and f/2 is a bigger number than f/16 is.

The f/number is a ratio of the lens opening compared to the focal length of the lens. Put another way: f = the lens *f*ocal length.

Lets use some numbers that will keep it easy to understand.
If the lens has a focal length of 100 mm, then when set to f/4 the lens opening is 25 mm wide - 100 mm/4 = 25 mm
If the lens has a focal length of 100 mm, then when set to f/2 the lens opening is 50 mm wide - 100 mm/2  = 50 mm

If the lens has a focal length of 50 mm, then when set to f/4 the lens opening is 12.5 mm wide - 50 mm/ 4 = 12.5 mm
If the lens has a focal length of 50 mm, then when set to f/2 the lens opening is 25 mm wide - 50 mm/2 = 25 mm

The classic full stop steps of aperture, as mentioned, are - 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 . . .
*Notice that f/2 is 2 stops from f/4, not 1 stop*.
To halve or double the amount of light the lens aperture lets in we have to halve or double the lens aperture _*AREA*_, not the lens aperture diameter.
To stop up or stop down the lens aperture a full stop we have to change the area of the lens aperture opening by _the square root of 2_, which is 1.4142........ Square root of 2 - Wikipedia, the free encyclopedia

So 1 x 1.4142 = 1.4142 - and gets rounded to f/1.4
2 times smaller lens aperture area then is - f/1.4 x 1.4142 = 1.9799 - and gets rounded to f/2
f/2 x 1.41412 = 2.828 - or f/2.8
f/2.8 x 1.4142 = 3.96 - or f/4
f/4 x 1.4142 = 5.657 - or f/5.6
f/5.6 x 1.4142 = 7.919 - or f/8
rf/8 x 1.4142 - 11.314 - or f/11
and so forth


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