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General Stuff, Theory n Technique

Shutter speed, Aperture, ISO: Understanding Basic Exposure


Once you’ve got your new digital camera, the topic of my previous post, you really should pick up that manual and read it cover to cover. Twice. Then read the important parts once more. Run through the index and check out any part you’re not yet too familiar with. Read ’em again. That’s what I did at least. Not that I just enjoy reading…I do…but I do this as I just find that being familiar with everything your camera does, and every feature it has, always comes in handy, especially when you’re taking a quick shot and don’t want to miss it while fiddling with all the menus and buttons. Anyway, for those of you (and that’s probably many of you) who didn’t read the manual even once over, there’s not much use in learning anything from here if you do not know how to apply it to your particular camera – so just take my advice, and read at least the basic controls and menus, and know how everything works in your camera. Then come back here

Once you’ve done that, I think this post is a good place to start. Understanding exposure, and how it works, and what affects it, is THE most important part of photography, if you ask me. Composition, and other techniques used in photography are important, of course…that’s why I’ll be covering those topics very soon as well…but is there any use having a nicely composed image if you get it horribly underexposed, or completely blown out and overexposed? No, I don’t think so. You want it just right. Not too bright, not too dark. Get your exposure right first. Start here

I shall be assuming that you have a camera with manual controls, because if not, this article would be of not much use. Likewise, I’m going to assume that you’re not the type who buys a DSLR and then sticks to the idiot-proof automatic settings. Auto exposure gets it right quite often…like a computer, but…but that’s the problem. You see, the human eye can see and imagine things that your camera (and its light metering system) cannot. Your eye sees a scene, and you imagine how you want it to be…you can see how this can be captured into something different by doing something else…your camera will not. It’ll take a fairly well exposed shot that’s good enough by most standards, but by modifying the exposure yourself, you can artistically vary that image in many ways, one or two of which could really be special, using the basic exposure triangle. That’s what I’ll be trying to explain today…

Exposure in Photography

Ok, to start – in photography, exposure is how much light is allowed to enter the camera and fall on its image sensor (or in a film camera, the film frame). Exposure is controlled by three main factors in your camera: shutter speed, aperture, and ISO sensitivity. The exposure triangle. By setting appropriate values on all three of these, you will end up with a correct exposure. Changing these settings with some knowledge will give you a still correct exposure, but it will create an image that could look very different…better or worse, that depends…but still, different. An automatic camera, or any camera set to an automatic mode, will set all three of these for you, with no prior objective on how the image should look, as long as it is correctly exposed. The only factor that it takes into consideration is keeping the shutter speed to within a range that’s fast enough so you can handhold your camera without getting blurry images. And if you’re an automatic shooter, you might be pretty satisfied with any shots that are not blurred by camera shake at slow shutter speeds – but a photographer will want so much more from their camera

Alright, so…shutter speed, aperture, ISO…you really should know what they do (I sound like a teacher), but here you go anyway:

  • Shutter speed: Your shutter is what stands between your image sensor (or film) and the light entering the lens. The shutter opens when you click the shutter button, allowing the light to fall on the sensor (or film), and expose the image onto it. And yes, it shuts afterwards too. This shutter is usually open for almost always a fraction of a second, and the length of time the shutter is kept open is your shutter speed. A speed of 1/500 means the shutter is open for 1/500th of a second. The longer it is open, the more it exposes the sensor to light,  and obviously the more light is received by the sensor. Shorter speeds means less light, of course
  • Aperture: This is the opening in your lens, which controls how much light passes through it and enters the camera. It is controlled in “f-stops”. A small f-stop number means a larger opening, and vice versa. A wider opening (the smaller f-stop value) means (you guessed it), more light entering the lens
  • ISO sensitivity: This is the sensitivity, or “speed”, of the image sensor (or film) to light. It is given values by numbers i.e. ISO 50, 100, 200, 400, 800 and so on. What this does is it basically controls how much light is necessary to properly expose the image. For example, a slow speed (low sensitivity) ISO of 100 will require more light to enter through the aperture and a slower shutter speed (hence the term, a slow ISO speed) to produce a well exposed image, but if  higher sensitivity ISO is set (faster speed), maybe ISO 400, this tells the camera that it needs less light, so  smaller aperture/faster shutter speed can be used to get the right exposure

NOTE: All three of these settings are increased (or decreased) in ‘stops’. A full stop increase basically doubles the amount of light that the sensor/film is exposed to. A full stop increase from ISO 100 would be ISO 200. A full stop increase in shutter speed from 1/500 second would be 1/250 second. A full stop decrease from 1/500 will be 1/1000. It doesn’t look quite so simple in aperture, as the f-stop values are a bit weird…but aperture in full stops go something like: f2.8, f4.0, f5.6, f8, f11, f16 – so opening the aperture one full stop from f4.0 would be f2.8

So assuming shutter speed and ISO remain the same, a shot taken at f4.0 will expose exactly half the amount of light that a shot taken at f2.8 is exposed to. Or an image taken at f 5.6 will expose exactly double the amount of light that an image taken at f8.0 is exposed to. Why? Because it’s a ‘one stop’ increase (or decrease) in aperture. Same thing for shutter speeds: assuming ISO and aperture remain the same, take one shot at a shutter speed of 1/50 sec, another at 1/25 sec – the second shot will expose twice as much light as the first one. Because it’s a one stop increase again. And if you really need the ISO example also, here we go: assuming aperture and shutter speed remain the same, take a shot at ISO 100 and another at ISO 200 – the ISO 200 shot will expose double the amount of light that the ISO 100 shot exposed. That’s how exposure stops work. Of course, you don’t always increase in full stops – you often make small adjustments in 1/2 or 1/3 stops – but to keep things simple here, I explained it all in full stops. I hope you got it

Alright, those are the basics. There’s a lot more to know about using these three settings to get just the right exposure for your photograph. A whole lot, in fact. I’ll try to stick to the necessary stuff, but I sometimes get carried away. Bear with me

To understand how to use these exposure settings, and how to vary them to suit your image…your vision…you need to know how these settings affect the image, and what can be done by varying them. So, let’s check out shutter speed first…

Shutter speed – I already explained what shutter speed is. But how does it affect the way your photo looks? Let’s break it down to two ranges of speeds, for simplicity: fast and slow. A fast shutter speed can range from 1/8000 of a second (extremely fast) to maybe 1/100 of a second (still fairly fast) – a slow speed  can range from 1/15 of a second to speeds as slow as 1 full second to even 30 seconds or more. Shutter speed becomes most important when you are shooting a fast moving object, and you want to either ‘freeze’ the action, by making the object look stationary, or show movement by introducing a bit of blur (motion blur) in the subject. Using a very fast shutter speed will freeze your moving subject – think about it, even an object moving at a great speed (a fast car for example) will hardly move that much in 1/4000 of a second – so setting your camera to capture the image for just this 1/4000 of a second will result in an image of the moving object that appears to be still. For example, in sports photography, when you see a photo of a football player for instance…the player is often running or jumping, but he often appears frozen in motion: this is achieved by using a fast shutter speed. But you also need to realize that using this fast shutter speed also means that less light is entering the camera; therefore, to compensate for this lack of light due to the fast shutter speed, you need to  either allow more light to enter through the aperture, and/or increase the ISO sensitivity. Keep reading for more on those two. And I hope you’re with me so far

On the other hand, a slow shutter speed can be desirable too. Often, in low light, you are forced to use a slow shutter speed, to gather as much light as possible to expose the shot. However, I am now referring to setting a slow shutter speed to get a particular style/feel or look to your photos, an intentional slow speed used for effect. For example, if you are shooting a fast sports car…and you do not want it to appear to be stationary…you want it to have a hint of motion, to portray the speed of the car – in this case, you can try lowering your shutter speed to show a slight bit of motion blur to create the effect. Of course, there is no one ‘slow speed’ to get it right. It depends on many factors, so to get this effect, you will have to experiment a lot. Possibly, a slow-ish speed of around 1/30 or 1/15 of a second will give this effect. Anything slower and you will want a tripod to ensure the entire shot doesn’t get the horrible blur that comes with camera shake – because, as you should know, slow shutter speeds require you to hold the camera very steady or else every bit of camera shake and wobble will show in your image – and as human hands are not very steady at all, using a tripod is the best solution when shooting slow speeds!

Another more extreme instance where you could use the shutter speed to get the perfect shot is when taking shots of flowing water. A slow shutter speed gives this beautiful smooth look to water that looks great – a fast shutter speed often freezes the water, giving a rather harsh look – but a long exposure (slow shutter) of maybe 10 full seconds gives a glorious misty look to water. Slow speeds for this purpose can range from a reasonably slow speed (1/8 etc) to a very slow speed of 5 to 10 seconds or even more. Experiment! But remember that shooting at very slow speeds requires a tripod or you can be sure your shots will end up a complete blurry disaster. Even at fairly slow speeds of around 1/8 seconds or so, you will have to be very careful to hold your camera steady or you might shake your shot

For night shots, you are forced to use a slow shutter speed, or you will never get enough light. When taking a city skyline at night, your shutter speed will often have to be in the range of 5-15 seconds (need that tripod again!)

For each of these cases, you need to compensate your aperture and ISO to get the shutter speed you want for the perfect image. Using shutter priority mode on your camera, set the shutter speed you want, and it will automatically set the correct aperture to get the right exposure. I recommend setting the ISO yourself. Read on for more details

Here’s a quick and rather lame example shot to show how shutter speeds change the look of a moving subject in your shot…I think it’s good enough for you to get the idea, no? The shot on the left, taken with a rather slow speed of 1/50 clearly shows the motion blur of the CD spinning in the CD drive…while the shot on the right was taken at a much faster speed of 1/800 makes the CD appear still, even though it’s moving at the same speed as the previous shot – also, notice that I’ve had to modify aperture and ISO to get this fast speed


Ok next up…

Aperture – You already know what the aperture does…but how does it change how your image looks? Quite simple, really. First, remember that a small f-stop value i.e. f3.5=wide aperture, and large f-stop value i.e. f22= narrow aperture. So when you shoot at f3.5, more light enters the camera. Ok. If you’re shooting handheld, at night, and you want to maintain a fast shutter speed to avoid camera shake and blurry photos, you will be forced to set the widest aperture your lens offers. And a high ISO. To get the fast shutter speed to get steady shots. However, assuming you are shooting in more favorable circumstances, or you have a tripod to shoot in low light, here’s how you can set your aperture to get the exact look you want from your shot, regardless of everything else

To understand how aperture values change your photos, you first need to understand depth of field (from here on called DOF because I’m lazy to type). Let me try to define DOF without quoting Wikipedia or something: the DOF refers to the range of distance in an image that appears to be in sharp focus. For example, when you see a portrait sharply focused on a person’s face, and the immediate and not very distant background is blurry (out of focus), this is known as shallow depth of field. But a landscape shot, where everything from the mountains in the far distance to the fence in the foreground appears to be in focus, this is a photo with a deep depth of field. Got it? Read my detailed post on Depth Of Field for more on this topic

There are 3 main factors which control DOF, one of which is aperture – and since I’m writing about aperture in this article, I’ll skip the other two for now. Aperture controls DOF very directly: to put it simply, wide aperture results in shallow DOF, and narrow aperture results in a deep DOF. That’s quite easy to remember, isn’t it? Shooting a portrait, or any object you want to appear to ‘pop’ out of the background, and draw immediate attention to it, by blurring the background, use a wide aperture…shallow DOF. And for the shot where you want everything, from the person in the foreground, to the person in the background, and the stuff in between them to be as sharp as can be, set a small narrow aperture, and get that DOF deep. Have a look at this series of quick samples I took of my laptop while writing. I focused (in all the images) on the SONY tag. Notice on the wide apertures, the keyboard is completely out of focus, but while I reduce the aperture the keys slowing start becoming clearer

Read my DOF post where I talk of this theory in much greater detail, but until then I hope you got the basics of the theory and how it is affected by aperture right here

Using the aperture priority mode on your camera, you set the aperture according to what you require from the shot, and the camera sets the correct shutter speed. Again, set ISO yourself according to the situation (set the next part)

And I thought there would be more to explain on aperture…but yeah, that should get you through the basics and get you experimenting with wide apertures on stuff in your bedroom

And the last one…

ISO sensitivity – ISO is generally what I select last when setting my exposure. I like to set it to a low sensitivity, which gives the finest quality, and only change it when I find that the sensitivity is not sufficient to get the results I want with my shutter speed and aperture. Click here for a detailed post on all things ISO

ISO set high means your sensor is very sensitive to light, and you need less of the stuff to expose the shot. However, this comes at a price. Back in the film days, high ISO film meant (and still means) more grain on the film. This could be desirable, or not. But that’s what it means. In digital, high ISO results in ‘noise’ on your images. Most digital cameras offer a degree of noise reduction, and allows shooting at very high ISO levels without noticeable noise or image deterioration, but that doesn’t always work as great as it is supposed to. So, as a general rule, keep your ISO as low as possible

In film photography, you might like to shoot at a higher ISO for the grain, which looks good on some shots. In digital photography, the negative about high ISO (noise) is never really desirable. Keep the ISO as low as possible, but only low enough to allow a shutter speed that won’t cause camera shake. Normally, a shutter speed of 1/(your focal length) is regarded as the slowest speed you can safely go without getting a blurry shot – so if you shoot with your lens at a focal length of 50mm, you can generally shoot steady at 1/50sec shutter speed. But if you set your ISO to a low 100, and you find that your shutter speed is too slow to take the shot handheld, say 1/30sec, you should increase the ISO to 200, which will allow you to get that handhold-able shutter speed. Always remember that a sharp shot with digital noise is far better than getting a blurry shaken up shot that has no noise – so, based on the available light, set your aperture and/or shutter speed – if the available light is not sufficient to handhold your camera on the settings you want, bump up the ISO. Or get a tripod

Note that in some cases, you might want to lower the ISO, if your camera allows it. For example, you want a really slow shutter speed to achieve a certain effect…in daylight…and even at your lens’ smallest aperture, the shot is still overexposed (too bright) – you will then want to lower the sensitivity even more, to try to achieve the shot without being too bright. Look at the bottom of this post for examples of high and low ISO, and noise problems


Yeah, so that’s pretty much it…shutter speed, aperture, ISO…the basics of exposure right there. The triangle. Read it again if you didn’t get some parts. It’s pretty simple when you think about it….and once you get shooting, and gain some experience, it’ll all come naturally. I’m gonna wrap this up by going through some shots that show how aperture/shutter speed/ISO were used to achieve the desired effect:

In this photo, I have used an aperture of f8.0, shutter of 1/200sec, and ISO 800. The point I want to show here is the depth of field. Notice how the wooden frame from very close to the camera is in focus. Then look at the wooden frames at the far end of the shot, furthest from the camera: also in focus. That’s using a small aperture (f8.0) to get a deep DOF

Another shot taken with a small aperture. Notice how the bottom of the tower is in focus, as is the very top? That’s quite a vast distance, this building is HUGE (once the tallest building in the world!) Taken at f8.0, 1/800sec shutter, ISO 200

I have used a very wide aperture of f1.8 in this shot, a shutter speed of 1/4000sec and ISO 200. See how my subject’s face is nicely in focus, but the rest of the photo, the background of the water and plants etc are all nicely out of focus…an almost dreamy blur…making the subject pop out more from this image. This is an example of using a wide aperture purely for the purpose of getting this shallow depth of field. There was plenty of light that afternoon, I could have even used an f8.0 and still had enough light to expose the shot…but I used the wide aperture to get the shallow DOF and point the viewer’s attention to my subject

A couple of examples of using a fast shutter speed to freeze the subject in motion – not the best examples in the world, but I had these shots at hand, and I think you can get the idea from them. First shot of the statue and fountain – notice how the drops of water seem to be frozen in mid-air? You can see it clearer on the crop of the same image on the right. I used a shutter of 1/640sec and aperture f2.0 at ISO 200

Another example below is the shot of the motorbikes on the street – sure, they’re not blazing along at 100mph but they were moving rather fast, and I needed to use a fast 1/1000sec shutter speed (aperture 7.1, ISO 200) to make them appear stationary…or at least more stationary than they were!

However, do not limit yourself to fast shutter speeds when shooting fast moving subjects. This shot was taken at a very slow 1/5sec (for a handheld shot, that’s super slow), ISO 200, aperture f3.5. Notice how the edges of the bike are blurred, showing motion? The background motion adds to the overall feel too (using a technique called panning, more on that later) – the slow shutter speed really works for this shot

f9.0, ISO 100, shutter speed of 8 seconds. A long exposure. Very necessary to expose a night shot like this. A tripod was used, obviously. I guess I could’ve bumped up the ISO to around 1600 or more, shot at a wide aperture, simply so I could’ve handheld the shot. But that’s letting lack of equipment get in the way of the shot. I didn’t want a noisy shot, so I kept the ISO at 100. I wanted everything in focus, from near to far… so I kept the aperture small (f9.0) – and I also wanted to smoothen the water, so the long exposure really worked. In addition, a long exposure also helps the reflections show clearer on the water. So for what I envisioned I wanted from this shot, these settings were ideal

In the above shot, in bright sunlight, it was a bit of a struggle to get the slow shutter speed that I did. Even then, I was not able to get it too slow – the shutter was open for a full second, no more – I had to use an aperture of f29 and ISO 100, and while that’s pretty slow, I would’ve loved to have got something closer to 10 seconds. Anyway, you can get the idea of what I’m talking about with the flowing water/slow shutter effect, right? See how the water looks? Much better than a frozen, harsh look, if you ask me. The monk standing near the top of the frame got a nice ghostly look too. Worked great for this shot!

NOTE: For shots like the above, to achieve long exposures in daylight, a neutral density filter (ND filter) is often used. This filter attaches in front of your lens, and does to your lens what sunglasses do to your eyes: cuts out the light. As the idea of this type of shot is to get a long exposure, this is a good thing. If I had one for the above shot, I might have been able to achieve a shutter speed of maybe 20 seconds! Oh well


To show how ISO affects photographs, I’ll show crops of four different shots…cropped in close to show the detail that you might miss if you view the full image. The first was taken at a low ISO (ISO 100), the other taken at 1600 (a fairly high ISO setting)…the third one is also taken at 1600, but this is a RAW shot, with no noise reduction (NR) applied. The last one is taken at a very high ISO 3200. Notice the rather fine quality of the first one, and the higher amount of noise as the images progress to higher and higher ISO speeds? Yeah, that’s the compromise when you use a faster ISO. Noise. Noise on high ISO shots can be reduced, but this often results in a slight loss in image detail. It always depends on what you value more. It’s always a compromise. Oh, and also notice how I was able to handhold the last shot, due to high sensitivity, as the shutter speed at ISO 3200 was handhold-able…while the others required a tripod to avoid camera shake

However, remember that if a slow ISO speed is used in a low light situation, the result would be a terribly blurry shot that would look far worse than the amount of digital noise visible. You should always aim for a steady, blur-free shot, all the time – even if this means the shot will be ‘noisy’. Keep that in mind

And that’s about it. I hope this helps you understand photography and how photography works. Try to keep this stuff in your mind – always think before you shoot – and keep shooting. More and more. And hopefully you’ll soon be nailing exposures with ease. Now I’m done. Thanks for reading. Please comment if this post helped you, or you’d like to add anything that I missed. Or contact me. Alright then…until next time

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By Heshan Jayakody
All content in this post is my own

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Discussion

22 Responses to “Shutter speed, Aperture, ISO: Understanding Basic Exposure”

  1. Another well structured introduction to photography, nice!

    Posted by timothyyylo | April 10, 2012, 17:37
  2. another superb entry-level post for noobs like myself 🙂 i love your blog. thanks for thinking of us when you write, i can see that you do. that’s why it is kept simple and helpful. cheers!

    Posted by Dominic | February 10, 2013, 15:33
    • Cheers, Dominic 🙂 I always try to keep things simple, thanks for noticing! Haha 😀 I have a lot of similar ‘theory’ type posts that you might find useful, so browse around…and maybe subscribe, coz I keep adding this type of post whenever I think of something to write about!

      Posted by pixelogist | February 10, 2013, 18:22
  3. some of ur posts for newbies are so useful! even for me, i’ve been shooting for over a year, and i know the basics, but understanding it a bit more always helps, and ur post helps me understand exposure better. hope to hear more of ur work soon

    Posted by Jenkin | February 11, 2013, 20:11
    • Glad to hear it! Keep a look out for more new posts coming soon (or subscribe) – you can always ask away in the comments section if you have any questions, too!

      Posted by pixelogist | February 12, 2013, 07:45
  4. i learned a lot from this post. thanks for sharing such good information…in a way that i can understand! kudos man

    Posted by Horatio | March 5, 2013, 21:15
    • You’re most welcome! Glad it helped. If you have any questions, please leave a comment, so we can all read it and discuss – or just email me!

      Posted by pixelogist | March 6, 2013, 12:42
  5. Fantastic post. Really breaks down the basic of exposure, and exposure stops, very well. I easily understand the theory now!

    Posted by Coolio | June 29, 2013, 17:48
  6. So just to be clear, ISO doesn’t affect the picture at all, except for noise? I thought it might do more than that! 😐

    Posted by KP | June 29, 2013, 18:08
    • Well, noise is a major part of it, isn’t it? It is for me! But yeah, apart from that, there’s not much else of an effect that it adds to your shot. But in addition to this, it DOES a lot more! Most importantly, ISO better allows you to get the shutter speed/aperture settings you want. For example, if you’re going for a slow shutter speed for a long exposure, setting the ISO to 100 will give you a much longer exposure than if you set your ISO to 400 or 800. And if you’re shooting at night, bumping up your ISO can get you sharper handheld results than if you shot with a low ISO – and as modern digital cameras can often shoot at ISO 3200 (or possibly even higher) without producing much noise at all, this is hugely beneficial. So yeah, there’s not much EFFECT that ISO sensitivity adds to your shot, other than noise, but that’s not to say it doesn’t do much 🙂

      Posted by pixelogist | June 30, 2013, 07:15
  7. u start ur post here exactly right, read the manual!!! is so important to do this. also ur info on exposure and aperture/iso/shutter is very good and helpful. thanks pixelogist!

    Posted by Kevin | June 30, 2013, 06:59
    • Absolutely. Like I said elsewhere, the camera manual doesn’t just explain the workings of your camera (although that is a very important part of it – you should always know how your camera works exactly) but it also explains basic photo theory that you can work with until you learn more!

      Cheers Kevin 🙂

      Posted by pixelogist | June 30, 2013, 07:16

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