Tips to a Great Photo, Part 6 | ISO, Aperture, & Shutter Speed

May 17, 2011

And so here we are at the end of my Tips to a Great Photo series.  I hope the information that I’ve provided has been helpful as you’ve practiced on your kids, siblings, or pets.  As a quick reminder, first you learned what’s important when it comes to buying the right camera for you.  Next I discussed the importance of studying your camera by actually reading and learning from its manual.  Then we really started getting into it and I gave you some pointers about lighting.  I quickly discussed posing your subjects vs. taking candid photos.  Then most recently I explained some aspects of composition and where to place your subjects for a more compelling photo.  This final tip has to do with the triad of confusion: ISO, Aperture, & Shutter Speed.  I’m still learning about these three aspects myself and I so implored my sweet husband, Tim, to write this post for you.  Sometimes he gets very technical, but he didn’t really have a choice, as this topic is naturally technical. I hope this final tip rounds out any questions you may have had about photography.

These three aspects of photography are extremely difficult to understand, harder to put into practice, yet equally imperative for great photography.  That being said, I really hope I am able to explain some of the basics of ISO, aperture, and shutter speed.


First, I am going to be kinda technical so just bear with me and it will get really practical.  Back in the day, with old school film cameras, ISO referred to the film’s sensitivity to light.  The ISO is determined by the number given to the film because of the film speed.  Such as, ISO 100 (being the least sensitive to light), ISO 200 (twice as sensitive as 100), and several intervals all the way up to ISO 102,400 (which can now only be found on EXTREMELY high dollar digital cameras).

Still talking about old school film: film speed (ISO) is related to the grain of the film.  Stick with me.  The smaller the ISO number, the smaller the grain, and therefore the less sensitive to light.  The larger the number, the larger the grain, and therefore the more sensitive it is to light.  I am really simplifying things, but that is the general gist of how it works.

Great, so what does this all mean???  Well, in short, it means that if you use a smaller number ISO (100, 200, etc.) your photos will be more crisp, less grainy, but will also be exposed darker because the film is less sensitive to light, and if you use a high numbered ISO (800, 1600, 3200, 4000, etc.) your photos will expose brighter but will be more grainy.  Old school photographers would use this higher grain to produce cool effects for black and white photos sometimes.

“Tim, seriously, none of us are using film.  Can you please drop the film garbage and tell me what this means for me?”  Okay, Okay, calm down.  All of that pretty much transfers from film to digital.  The only difference is that the “grain” in photos is actually called “noise,” and is generally viewed as a bad thing among professional photographers.  This is because it doesn’t really make a desirable or “cool” effect in digital photos.  In fact, it usually looks bad.  With your digital camera, using a low ISO will generally take a crisp, clean, darker photo (just like with film), and photos taken with a high ISO will take photos that are generally pretty crumby looking and very noisy.

In the last sentence there, I said “generally” because the noisiness of a photo at high ISOs really depends on the size of the image sensor in your camera.  The image sensor is the “film” of your digital camera.  It is what captures your picture.  Cheaper cameras will have smaller image sensors that will not respond well to high ISO photos while the more expensive professional cameras will have larger image sensors that are capable of taking higher ISO photos with less noise.

“BLAH BLAH BLAH, what does it all mean?”  Ok, here it is practically:  In low light situations you are going to have to use a higher ISO to achieve a bright enough picture.  The risk here is that you may end up with noisy photos.  This is really where you have to know your camera and what ISO you can safely use before your photos are just too noisy.  For example, with our Canon T2i, I know that ISO 400 is about as far as I am comfortable going before the photos get too noisy.  However, with our Canon 5d Mark II I can use an ISO 4000 if I need to and the photo won’t be too noisy, but that is because the 5d Mark II has a much larger image sensor.

In brighter situations, you can use a low ISO for great photos and you don’t have to worry about noise.  When I am outside on a sunny or slightly over cast day, I ALWAYS shoot with my ISO at 100 because I know that I will be able to get bright enough photos and they will be crisp and clean.

The lighting is the key.  If you don’t have enough light, sometimes the best thing to do is not take a photo or move somewhere that there is enough light.

So, in general, low light situations require high ISOs and in high light situations you can use low ISOs.

As you will soon find out, this is not a hard and fast rule.  In addition to the light governing your ISO, how you set your aperture and shutter speed will also determine what ISO you need to use.

Again, I am simplifying things to a ridiculous degree.  If you want to learn more, just go online and read some stuff on the measurements and calculations regarding digital ISO.  Warning: Your brain will hurt if you go read about it.


To put it simply, the aperture on your camera is a series of flaps arranged in a circle that control the amount of light that is allowed to reach the image sensor.

You can think of it like the pupil in your eye.  Your pupils dilate in the dark to let more light in to reach the rods & cones (or image sensor, if you will) so that you can see well in the dark.  When it is bright your pupils get really tiny to keep light out so everything isn’t too bright.  That’s why it seems SO bright outside when you walk out of a movie theater.  Your eyes have to adjust to having a very wide aperture . . . I mean dilated pupils ;) and then when you walk outside it takes a second for them to adjust to the harsh brightness.

Okay, when you are controlling the aperture on your camera, the smaller the number, the wider the aperture, the larger the number the smaller the aperture.  Look at this diagram to help understand.

When you are deciding how you want to set your aperture, you HAVE to consider a few things.  First, obviously, the smaller the aperture the less light, the wider the aperture the more light is let in.

Second, and one might argue, more importantly, your aperture controls your depth of field or your focal length.  These terms describe the amount of your photo (on the Z axis, with X being horizontal and Y being vertical) that is in focus.  This is crucial for your shots because your depth of field has a lot to do with how artistic you can be and how crisp your shots will come out.  In controlling your depth of field, a wide aperture (smaller number) will give you a very narrow depth of field and a small aperture (large number) will give you a very deep depth of field.  See the example below.

Third, if you have a digital SLR camera, the aperture isn’t in the camera, it’s in the lens.  And lenses are expensive, well, the good ones are!  If you are looking to buy an SLR, then don’t buy the kit that comes with the lens.  Buy just the camera body and spend the extra money (and then some) on a good lens.  That means get one that suits your needs and that has a good range on the aperture.  Lenses are usually more expensive when they have wider apertures.

Shutter Speed

The shutter speed controls the amount of time the light is allowed to reach the image sensor.  The number you will be working with on your camera is typically going to be a fraction unless you are trying to be super artistic with some long shutter speeds, but I will explain that in a second.

The fractions refer to the fraction of a second the shutter will open and allow light to reach the image sensor before it closes again.  Obviously, with this the higher the denominator the less light will be let in and the lower the denominator the more light will be allowed in.

Keep in mind that while the shutter is open the image sensor is consistently capturing light.  This means that if you are trying to get a picture of something that is moving, the longer your shutter is open the blurrier those moving parts will be.  This is why those pictures you took of your kids running around with your point and shoot camera set on auto are always blurry.  It’s because your camera (set on auto) goes for good exposure regardless of what is happening in the photo.  Having the shutter open for a long time can have a very cool effect on some photos.  Most pictures you have seen of waterfalls or rivers flowing are taken with the camera on a tripod with a long shutter speed to give the appearance that the water is moving.  Also, have you ever wondered how photographers get killer shots of lightening?  You guessed it!  Long shutter speeds.  Since it is dark outside they just leave the shutter open for a long time until lightening strikes and BOOM (literally) they have their shot of lightening.  They don’t just have really fast reflexes.  ;)

In conclusion, these are probably the three most important aspects of photography.  And they are all very difficult to learn and use together.  Each of them is very dependent on the others.  If your aperture is very wide so you have a shallow depth of field, but it is bright outside you are going to need a really fast shutter speed and a low ISO.  If you want to get a good group picture in low light you will need a small aperture (for a deep depth of field) and decent shutter speed, which would give you an underexposed photo unless you turn up your ISO.  I could give you tons of examples, but I have already written a lot and left a lot out.  This is by NO means an extensive explanation of all of these topics but merely the basics.

Hopefully this helps . . . if you have any questions about a specific situation or need further explanation please feel free to ask.  I would love to help out. Also, if Katie or I missed ANY question you have regarding ANY aspect of photography, now is the time to ask!

Capturing Memories,




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