Help Me Understand "Stops"

[karenmorelandphotography]

<p>I've done quite a bit of reading about stops and I still feel confused. Please help!<br>

My understanding is that there are 3 times the word "stop" is used in photography. An "f-stop" which relates to aperture, meaning how wide or narrow the aperture is, and also a "stop" in shutter speed (which, I'm not entirely sure how these are calculated or whatever), and also a "stop" in ISO, meaning, it starts at ISO 100, then doubles to 200, then 400, then 800, etc. I understand each time the ISO doubles it's called a "stop".<br>

I think I understand the basic concept which is that stops are used to increase or decrease the exposure. When ISO, aperture, and shutter speed are all working together to produce the correct exposure, each has to be adjusted, therefore, if one is increased, the other may need to be decreased, etc. I understand that all three have to have the perfect combination to expose the picture to the desired level. <br>

I'm confused because on these modern DSLRs there are full stops and increments of stops, so for me, I've just worked the numbers by trial and error. If I decide aperture is my strongest interest in the photo, I set it accordingly, then set my ISO and my shutter speed until I get the desired outcome. And it seems to work just fine for me. Why do I need to know or use the term "stop" when I can just pick numbers for each value and the pictures come out great? What is the relevance? Is it just the proper terminology that I need to use? <br>

Sorry if this sounds ridiculous, but I feel like this is a foundation of photography and after 7 months, I still feel lost. TIA. :)</p>

[devon_mccarroll]

I've never heard the term "stop" used in reference to shutter speed or ISO. The term "stop down my lens" means choosing a smaller

aperture. Aperture is a more widely used term than f-stop, but they are the same thing. Modern DSLRs do have more aperture

increments than older cameras did way back when.

You are understanding correctly that the three things work together to create the perfect (or artistically desired) photo. If you're checking

your meter and your histogram, you shouldn't need to guess at exposure. And if you're aiming for shallow depth of field, for instance, you

can always set your camera to aperture priority and let the camera choose the rest.

If you open up your aperture a full stop but don't want to change your exposure, then reduce your shutter speed the equivalent amount.

As for proper terminology, it's always good to know and use, so that when you need to ask a question here or elsewhere, the people

you're asking understand what you're talking about.

[William Kahn]

<p>Karen, there are a couple of good Wikipedia articles you might want to take a look at, one for shutter speed:</p>

<p>http://en.wikipedia.org/wiki/Shutter_speed</p>

<p>and another for aperture:</p>

<p>http://en.wikipedia.org/wiki/F-number</p>

<p>Don't worry about the math equations, just scroll down to where the purpose and effect of aperture and shutter speeds are explained. Then, come back here and ask more questions...</p>

[michael_darnton2]

<p>"stop" is essentially photo slang for a unit of exposure change, based on doubling or halving.</p>

<p>Though the concept belongs to lens openings, which originally used plates with individual holes in them, called "stops" to change exposure up and down, instead of the continuous diaphragm cameras use now, it's conventionally extended to the idea of doubling or halving exposure anywhere on the camera.</p>

<p>On lenses it's moving up and down the scale of 1, 1.4, 2, 2.8, etc., which numbers have the effect of 2X or 1/2X on the exposure, depending on which direction you're going. On shutter speeds it's doubling or halving the shutter speed, and on film speed or Exposure Index, it's doubling or halving those numbers, too. On exposure compensation dials, + or - 1 is a one stop change, + or - 2 is a two stop change, etc. When light doubles of halves in brightness, it's said to have changed one stop.</p>

<p>Essentially the "stop" is the standard unit of measurement for exposure, and the word applies with regard to the doubling or halving of any exposure change, regardless of through which particular mechanism.</p>

<p>The particular place all this comes in handy is when changing exposure, whether by Exposure Index, compensation, shutter speed or lens opening, all these methods use the same unit: one stop. So if you want to double your shutter speed to freeze action better (moving one stop towards underexposure by halving the time), you know that to compensate for this and bring the exposure back to normal you can open the lens one stop, OR you can double the Exposure Index, changing it one stop. Or, you can turn on two light bulbs, doubling the exposure (one stop) to compensate for the halved shutter speed. Any one of these will result in a one unit change in exposure--one stop--to compensate for changing the shutter speed.</p>

[karenmorelandphotography]

<p>Thank you for the responses so far! I really appreciate them.</p>

<p>Devon M--I honestly don't know about a meter or histogram. I've heard of these as external separate devices but I'm assuming these are built into my camera? And is there a place I should be checking it before I set up my shot? </p>

<p>William K--thank you for the links. I read over them and they do help. So let me ask this now: would it be better for me to start referring to values as stops rather than continuing to just use trial and error on my numbers? It seems like there are so many figures!! How many figures would you say the average photographer knows off hand and refers to regularly (or is this just good to know <em>of</em>)?</p>

<p>Michael D--thank you for your explanation as well! So would a person ever need to discuss stops with another person only if they were viewing the same image together or would this come up otherwise? I'm trying to figure out how far my knowledge of stops would be used in an everyday situation. Is this something photographers are just knowledgeable about or are stops discussed regularly in other ways? I don't know why this is so baffling to me. lol. Just trying to wrap my head around its use in photography beyond learning. </p>

<p>Thank you everyone!!</p>

 

[Alan Marcus]

<p>Camera makers and photographers concluded years ago that the increment of exposure adjustment should be a doubling or halving of the light energy playing on film. Now exposure consists of two comingled dynamics: First is the ability of the lens to gather light. A camera lens acts like a funnel, the larger its working diameter, the more light it can gather. Consider that the camera aperture is a circular entrance and modern cameras sports a mechanism that allows the working diameter to be changed. This mechanism mimics the human eye iris. Our iris changes its working diameter in response to scene brightness. The hole that allows light to enter is called the pupil, another word for aperture. The human iris is the colored portion of the human eye, named for the Greek god of the rainbow. <br /> <br /> When we mechanically change the working diameter of our camera lens, to achieve a doubling or halving of the light energy, we must change the surface area of the working diameter of the aperture. This is a key fact. Since we are dealing with a circular orifice, we must use the geometry of circles to do this deed. Factoid: Multiply the diameter of any circle by the square root of 2 and the product will be the revised diameter needed to construct a circle with twice the surface area. The square root of 2 = 1.414, and for our purposes we can round this value to 1.4. <br /> <br /> Consider the following number set.<br /> 1 – 1.4 – 2 – 2.8 – 4 – 5.6 – 8 – 11 – 16 – 22 – 32 -45 -64<br /> Note each number going right is its neighbor on the left multiplied by 1.4. Additionally, going left, each number is its neighbor on the right divided by 1.4. This number set is the f/number set.<br /> <br /> One of the first to devise a method to adjust the working diameter of lenses was Waterhouse. He devised metal slides that inserted into the barrel of a lens. The slides came in a series of holes or apertures. The year was 1868, and his invention was called Waterhouse Stops.<br /> <br /> Next, consider that exposure has two components -- the amount of light playing on the film, and the time the light is allowed to play. Now we are talking about shutter speed. The same doubling or halving of the exposure time is the unit of change. To accomplish this we need a number set that allows exposure time changes using a unit of doubling or halving. These changes are often labeled using the word “stop”.<br /> The exposure time number set is:<br /> 1 – 1/2 - 1/4 – 1/8 – 1/15 – 1/30 – 1/60 – 1/125 – 1/250 – 1/500 – 1/1000 – 1/2000 etc.<br /> The slight rounding error at 1/15 and 1/125 keeps the number set elegant and is of no consequence as to its influence on the doubling or halving result . <br /> Technically the equation for exposure is E= IxT. States as Exposure = the Intensity of the light multiplied by the Time light is allowed to play on film. This is called the Law Of Photographic Blackening. The fancy name used in textbooks is the Law Of Reciprocity.</p>

[michael_darnton2]

<p>About the only way you'd use "stop" in polite company would be something along the line of<br>

"My picture seems a little dark."<br>

"Yeah, it's about a stop and a half underexposed, that's why."</p>

<p>The main use is in your mind as you're changing exposure: "The shot looks a little light--maybe I should give it a half-stop less."</p>

[karenmorelandphotography]

<p>Thanks for the detailed response Alan. And thank you for clarifying, Michael. That makes a lot more sense now. </p>

<p>All these responses are great--just what I was hoping for. The more I hear it in different ways from different people, the more it sinks in. It's much easier to understand in layman's terms versus reading countless texts and articles without discussion and explanation. </p>

[User_6502147]

<p>As to "stops" (or "f-stops" - same)...usually they are referred to the aperture of a particular lens. These can be 2.8, 4.0, 5.6, 8, 16, 22 and so on. Most DSLR's permits you to divide those stops (of aperture) into 1/3 or 1/2s for more finely tuned exposure.</p>

<p>Lets say you are taking a portrait of someone and you like the way F4.0 (bokeh...as background blur) 'stop' renders from experience or you like the amount of DOF (depth of field). You dial-in the F4.0, and you also need to consider the other two factors of the overall exposure, the shutter speed and the ISO. Also, drawing on experience, you're handholding the camera (lets presume it's not on the tripod) and you'd likely need shutter speed that's minimum of 1/250sec shutter or higher on a portrait lens/es such as 85/90/105mm (in FF)....or a zoom. If you have a sturdier hands you might be able to get away with 1/160sec. OK, you need to adjust the ISO's to fit the rest of this set up. However, the lower the ISO's, the less noise you'll have to deal with. Let's assume that you don't want to go beyond ISO 1600 (since it still renders clean photos for you), but you notice that you are still on the darker side of the exposure. You can lower the shutter speed to 1/160th and you see (on the meter) that this will give you a perfect exposure. You can brace your elbow (the hand that holds the camera) against a fence post, tree, telephone pole, etc....holding breath helps too... and with little practice the results will be sharp. Anyway, I was just following up on your desire where the 'aperture is [your] strongest interest in the photo'.</p>

<p>It's much easier to dial in F4.0, 1/250+ and ISO 200 (assuming the correct amount of light is there) and be done with it vs wrestling w/lower level lighting as in the above example. In any case, since exposure operates on (3) axis, as I like to say, you can use those variations to your liking....you might even want to decide to go with the 2.8 or the 3.5 (between the 2.8-4.0 'stop') as a starting point...and follow that up with an appropriate shutter speed or ISO's.</p>

<p>Please consider one more variable. If you shoot RAW files, the camera records enough information where you can adjust minor discrepancies (over/under exposure) in the edit. I'm not suggesting that you lean on this, but to use this more as a "rescue" technique.</p>

<p>So long you adjust all the 3 values (since they are related) within the exposure to a desired end....the actual terminology of the 'stops' is little more flexible. Some peeps will say "I clicked it to 4.0" or "I used F16" ('f-stops' implied).</p>

<p>Hope this helps.</p>

<p>Les<br>

</p>

[paddler4]

<p>To answer your question about how many of these numbers photographers know: the key is knowing the sequence Alan mentioned -- the multiples of roughly 1.4 (the square root of 2). You need to know these numbers to be able to translate aperture values-- for example, to know that going from halving the light requires going from f/4.0 to f/5.6, not to f/8.0. There are no special numbers you need to memorize for shutter speeds or ISO, because in both of those cases, the relationship is obvious: halving the exposure requires halving the time the shutter is open or halving the ISO value.</p>

[karenmorelandphotography]

Thanks Les and Dan! Les, I also learned something about the suggested shutter speed for handheld portraiture! :) And

Dan, that really simplifies the numbers for me. Thanks!!

[SCL]

<p>Karen - I think you got it! I try to explain it to novices I'm teaching as the energy (quantity of light) hitting the sensor or film. You can control the duration of time light hits the sensor via the shutter; the quantity of light at a given shutter speed by the aperture (f stop), or the sensitivity of the light receptor (the ISO, also called the ASA or DIN - all slightly different but in this context meaning the same thing). All 3 are components of proper exposure. Modern cameras are programmed so that you can change as many of the 3 variables as you desire, or let the camera computer do everything.</p>

[NetR]

<p>There is just one number it might be helpful to remember. With full sunlight, the correct exposure is 1 divided by the ISO at f/16. That is, if the camera is set at 100 ISO(ASA), the speed should be 1/100 at f/16. If you want to let more light in and open one stop to f/11, the correct exposure will halve to 1/200. Etc.</p>

[James G. Dainis]

In the old days lens aperture rings were marked with the aperture openings in whole stops:

 

1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, ...

 

Photographers soon got used to that and knew the stops. It was easy to understand and you just had to look at the lens to see the whole stop numbers. You will see in the posts above that the responders use those numbers:

 

"...halving the light requires going from f/4.0 to f/5.6..."

 

"...at f/16. If you want to let more light in and open one stop to f/11..."

 

The trouble with digital cameras is they don't always give whole stops for the meter exposure values. You most often have 1/2 and 1/3 stops given. Ask a photographer how to open up one stop from f/5.6 and he will immediately say, "Go to f/4". Ask him how to open up one stop from f/7.1 and he will most likely say "er...". ( f/5.0 is the answer and I had to look it up).

 

Practice using your camera in Aperture priority with whole stops (2, 2.8, 4, 5.6, 8 etc.) selected until you get used to that. Change from f/5.6 to f/4 and see how your shutter speed changes from, let us say, 1/125 sec to 1/250 sec. Play around with the whole stops like that until you understand them and they become second nature.

 

You do have to know the relevance of stops. Meters try to average out a scene. If there is too much lights or darks in a scene the meter will be "fooled" and give the wrong exposure. To get the correct exposure of a person's face you will be told to take a direct meter reading off the person's face and open up one stop. That is just one example of knowing the relevance of stops.

[AlanKlein]

<p>A stop is called a stop because on original lenses and cameras, the apertures and shutter selection dials "stopped" at each full exposure difference. There are indents built into the aperture ring and shutter ring or dial. Each "click" or "stop" as you turn the mechanical dial is another full exposure change such as f/8 to f/11 on the aperture or 1/60 to 1/120 on the shutter dial. Some aperture rings "click" at 1/2 or 1/3 stops to give you more adjustment capability. These are called 1/2 stops or 1/3 stops.</p>

<p> Indents were manufactured into the lenses and cameras so it would be easy to "stop" at a setting. Otherwise, you'd have to look and guess whether you are at a full stop. Also, with mechcanial clicking "stops", it was easy to change one full stop without having to look at the rings on the camera or lens. You can feel the change from one stop to the next. You could keep your eye on the subject.</p>

<p>Today, many digital camera have continued to use the mechanical indent "stop" for ease of use and for the same reasons older film cameras had them. </p>

[AlanKlein]

<p>Now that you know where the word "stop" comes from, the term as others described is to represent a difference in light of either 1/2 or 2x when going from one stop to the next depending which way you go. Since both aperture stops and shutter stops both equal 1/2 or 2x from one stop to the next, it is easy to adjust aperture and speed. (Let's leave auto-ISO out of the discussion for the moment. That didn't exist with older film cameras).</p>

<p>Let's say your intial setting for a scene to get proper exposure is 1/60 of a second at f/11. Since you were shooting a basketball game, you know from experience that you need a faster shutter speed to catch the action. So you turn the shutter manually 3 clicks or stops going from 1/60 to 1/120 to 1/250 to 1/500 of a second. Since you reduced the amount of light 3 stops, you have to compensate by opening the aperture 3 stops as well. So you mechanically turn the aperture ring: f/11 to f/8 to f/5.6 to f/4. You'll get the same amount of light to enter the camera as the original setting 1/60 at f/11 equals 1/500 at f/4. You're good to go! (Note that changing aperture changes depth of field of what is in focus. But that's another discussion.)</p>

<p>ISO is just another way of varying the amount of light captured. So if you were using ISO of 100 with the original 1/60 and f/11, you could have increased the shutter to 1/500 and left the aperture at f/11. However, you would have to increase the ISO 3 stops to keep the light the same 100 to 200 to 400 to 800.</p>

<p>Working in fixed amounts of light called stops, make changing adjustments easy and quick with little thinking. If you had dials that did not click at stops, it would have become extremely difficult to get proper exposure. With digital, you still have stops. But the LED display shows the stops rather than "clicking" although some digital cameras still have mechanical click stops built in.</p>

<p>Edit: the change in the example is 3 stops not 4.</p>

[devon_mccarroll]

<p>Karen, in answer to your question to me earlier, all modern DSLRs have a built in meter that you should see through the viewfinder, which shows if you're overexposed (toward the "+" sign) or underexposed (toward the "-" sign), and the histogram will be accessed via one of the dials, which is different for every camera model, but will be in your camera manual. The histogram, which you can get tons of info about online, shows if you're clipping your highlights or are too dark in some areas.<br>

This might be helpful to read:<br>

http://www.canvas-of-light.com/2013/07/what-is-histogram-how-to-use-it/</p>

[karenmorelandphotography]

<p>Thank you for all the GREAT responses!!! I really appreciate the time and thoughtfulness everyone has contributed. I am starting to understand stops much much better now! :)</p>

[goldbergbarry]

<p>You may also consider a really amazing book called Understanding Exposure from Bryan Peterson. He does an excellent job in teaching these basics.</p>

[dan_south]

<p>A 'stop' is a measurement like a foot or a pound. You can add a foot to the length of something. Or you can trim the length by a foot.</p>

<p>Similarly, you can change the amount of light that goes into your camera. You can add to it, or your can cut it back.</p>

<p>Leaving all other controls untouched, imagine that you took a shot at 1/60th of a second. If you look at it an feel that it's too dark, and you decide that you want to DOUBLE the amount of light that enters the camera, you could shoot again at 1/30th of a second, which is twice as much time as 1/60th. This is known as "adding a stop" or "opening up a full stop."</p>

<p>If you think that your original photo is too light (over exposed) and you want to cut down the amount of light that the camera uses, you could shoot again at 1/125th of a second, or about half of 1/60th. (I realized that it's not exactly half, but we use slight approximations to make the numbers easier to calculate.) This is known as "closing down a full stop."</p>

<p>You can make similar adjustments to the diameter of the aperture, which works like the iris in the eye. The trick here is that in order to double the size of the AREA covered by the opening of the aperture, you don't exactly double the numbers. That's why f-stops come in this strange series of numbers (1.4, 2, 2.8, 4, 5.6, 8, 11, etc.).</p>

<p>Moving from one of the f-numbers to the next larger number closes down one stop (cuts the amount of light entering the camera in half).</p>

<p>Moving from one of the f-numbers to the next smaller number open up one stop (doubles the amount of light).</p>

<p>The reason for the strange numbers is that the area of the circle (aperture) changes by the SQUARE of the change to the diameter or the radius. The f-number describes the change in the diameter, not the area.</p>

<p>If you DOUBLE the DIAMETER, the area QUADRUPLES, because your changing the value by 2-squared which equals 4.</p>

<p>In order to double the area of the aperture opening, you need to change the diameter by a special number. You have heard of this special number before. It has a special job in mathematics. It's jobs that if you square it, that is if you multiply it by itself, it becomes 2. (2 for doubling and halving values).</p>

<p>That special number is called the Square Root of 2, and it has a value of approximately 1.4</p>

<p>This is were our f-numbers come from. They are multiples of 1.4</p>

<p>1 times 1.4 = 1.4<br>

1.4 times 1.4 = 2<br>

2 times 1.4 = 2.8<br>

2.8 times 1.4 = 4<br>

4 times 1.4 = 5.6<br>

... and so on ...</p>

<p>So if you change your f-stop from 5.6 to 4, you are increasing the diameter of the aperture by a factor of 1.4. But you are changing the AREA of the opening, which lets in the light, by a factor of 2. In other words, you double the amount of light reaching the sensor, or you are "opening up by 1 stop."</p>

<p>Anecdotally, I find that we notice changes in light that are about one stop. If the lights are dimmed in a room less than one stop, we don't always notice it. If they are dimmed one stop or more, we think, "hey, it just got darker in here."</p>

[paul_noble]

<p>I suggest that the OP get a copy of Bryan Peterson's book "Understanding Exposure". It does an excellent job of explaining "stops" and the relationship between aperture, shutter speed and ISO speed.</p>

<p>It also spends a lot of time on the concepts of "correct exposure", which is any combination of aperture, shutter speed and ISO that gives what is generally considered to be the correct exposure, as well as the "artistic exposure", which is that perticular combination that gives the desired artistic effect, such as shallow depth of field or action-stopping speed.</p>

<p>Its available on Amazon, or, if you have a decent public libary near by, you might find it there.</p>

<p>I've been doing photography since the sixties, and I still learned things from the book.</p>

<p> </p>

[James G. Dainis]

Things used to be easier before they made things easier with today's cameras. The photographer would look at the lens on the front of his camera and this is what he would see:<P>

<center><img src="http://jdainis.com/f_stops.jpg"></center><p>

 

The diamond pointer is pointing at 5.6 indicating the lens aperture is set at f/5.6. If he wanted to open up one or two stops he would turn the aperture ring to 4 or 2.8. If he wanted to close down one or two stops he would turn the aperture ring to 8 or 11. A 1/2 stop would have the pointer between the numbers. Easy. Photographers saw those numbers all the time and that is why they know the sequence of f/stops. <P>

 

Your modernistical digital camera lens most likely doesn't have an aperture ring on it. The aperture has to be set with a dial on the camera. You don't see that range of aperture openings like one saw on an old lens. You just see on the LCD panel, or in the viewfinder, the one aperture opening that the lens is set for. Since that is graded in 1/3rd stops you are more likely to see f/4.5, 5.0, 6.3, 7.1, etc. rather than f/4, 5.6, 8, etc. That makes it a lot harder to learn. As I said, "Things used to be easier before they made things easier." Persevere! <P>

[James G. Dainis]

And, while I am at it, Take a look at the other numbers on that lens photo above. The photographer can tell that the lens is focused at 15 feet. At f/16 everything would be in acceptable focus from 7 feet to infinity. At f/8 everything would be in acceptable focus from 3 meters to 10 meters. The red "R" shows the focus point shift if using infrared film. There used to be a lot of great stuff on lenses. {{Sigh}}

[robbi_cooler]

<p>I read some really good insights into "Stops" in this thread- thanks all.<br>

Another interesting fact about the scale of 1-stop increments 2-2.8-4-5.6-8-11-16- is very useful for studio photographers.<br>

A studio light- bare bulb (no soft-box)- can be moved a distance from the lit subject to halve or double its exposure by simply referring to the 1-stop scale. eg. Move the one bulb from 4ft to 5.6ft will halve the exposure. Moving one bulb from 11ft to 8ft will Double its exposure. And two equal bulbs-one at 4ft, and one at 5.6ft, will be 1-stop difference in exposure (for Main light/ Fill light situations). Two equal bulbs at 4ft & 11ft is a 3-stop difference. etc.<br>

The 1-stop scale numbers can be applied as feet or metres. Knowing the 1-stop increment scale comes in very useful in many situations. Of course it is all about the Inverse Square Law- but that is getting deeper in.</p>