View Full Version : NSOP Lesson #1: Apertures and how they affect your photography!

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09-15-2010, 03:12 PM
Welcome to NSOP's first "lesson". The goal with this is to help people get into photography starting with limited to no prior experience with cameras. These lessons will become more advanced as they go on, but they're going to start with the basics, and if you follow through with the series in order, you should be able to follow along with any current lesson if you've gone through everything before it.

For our first lesson I figured I’d start with something very basic, apertures. What is it? An aperture is the small hole in your lens that controls the amount of light that reaches the sensor (or film plane). The bigger the hole, the more light that gets through, the smaller the hole, the less light. Size size of the hole also affects the image in terms of what portion is in focus. The aperture used affects the Depth Of Field (DOF for short) of the resulting image. When you use a larger aperture (small number, ie f/2.8) you get much less DOF but this does let in more light. When you use a small aperture (big number, ie f/22) you let in much less light, but in return you get a much larger DOF.

When you set your exposure, you typically adjust either the aperture or the shutter speed and the camera adjusts the other option to make a proper exposure. Imagine that the sensor is a bucket you need to fill with water. You need to fill the bucket with a set amount of water, the bucket is a "proper exposure" and the water is light. The aperture is the size of the hose (fire hose -vs- garden hose) and the shutter speed it the amount of time the hose will be turned on. Using the fire hose (wide aperture, small number, ie f/2.8) you can fill the bucket quickly... but it will be messy right? Messy in this example means having less depth of field. Now with the garden hose you can easily fill the bucket without making a mess (more DOF) but this will obviously take longer.

How does this all tie together? If you need to have a very sharp image with a lot of DOF, then you need to "stop down" or go with a smaller aperture (bigger number ie f/22). This will result in a longer exposure. For instance, if I’m shooting a landscape shot, I take my time and make sure everything is in focus. The only possible issues here are things that move in a landscape like water or trees in the wind, but that can be a great affect… Here is an example shot at f/20:


Notice how the leaves in the very front and the trees waaaaay in the back are in focus? I used the small aperture to achieve this affect. Because I chose a small aperture, the resulting shutter speed for this shot is 1.6 seconds. This meant I was forced to use a tripod (which I do for landscape shots anyway). This also means that the water becomes this nice softer looking stream of water instead of a more static look.

Now let’s say you’re trying to separate something from it’s background like in a portrait or sports shot. This is where shallow DOF is a great thing. When you use a wide aperture (ie f/2.8 or smaller numbers, bigger opening) it will have a very shallow DOF. This will blur whatever is behind the subject which helps separate them from their background. It’s a very useful tool in this situation. Here is an example shot at f/1.4:


In that example, the exposure is f/1.4, and 1/125th. If I'd wanted to stop this lens down more than 1.4 (meaning use a smaller hole/aperture with a larger number like say f/2.8) that would have meant I'd need to slow the shutter speed down to give me more time to fill the bucket. While this is good at times (at 1.4 the DOF can be so thin only an eye is in focus while the ears and nose are soft) you also have to be careful with regards to your shutter speed, you want to keep it high enough to make sure you're shots stay sharp w/o any movement from EITHER the subject or the camera. In later lessons we will go over both shutter speeds and ISOs which both play into this equation.

Whenever you’re out shooting if you are thinking in terms of DOF, you should be using AV mode. If you need a lot of DOF you set the aperture to a small hole, large number (f/11~f/22) and shoot away. If you need shallow DOF to help separate a subject from it’s background, then you just go the other way and set it to a larger aperture (small number, f/1.4~f2.8) and you know it will have thin DOF.

One other tip. If you’re not quite sure how the aperture makes a difference, take a lens with a relatively wide aperture (a 50mm f1.8 is great here if you have one). Put the camera in AV mode. Find the DOF preview button on your camera (on Canons it’s on the side of the lens mount). Now look through the viewfinder and dial the dial that changes the aperture value while holding down the DOF preview button. You will notice the viewfinder gets darker at higher values (this is why you need a longer shutter speed, to let in more light) but you will also notice that the DOF gets bigger…
Hopefully this all makes sense. If not, please post questions below!

Read more about DOF here on Wiki:

Also, if you like numbers, you might want to play with our DOF calculator:

09-15-2010, 05:35 PM
<center><form method="post" name="form"><table class="calc" width="425"><tbody><tr><th colspan="3">Depth of Field Calculator</th></tr><tr><td width="192">Sensor/Film Size</td><td colspan="2"><select name="format"> <option value="0.03200">35mm "Full Frame" DSLR or film </option> <option value="0.02551">1.3x "crop" DSLR</option> <option value="0.02107">1.5x "crop" DSLR </option> <option value="0.02000">1.6x "crop" DSLR</option> <option value="0.01600">DSLR with 4/3" Sensor </option> <option value="0.01600">DSLR with MFT" Sensor </option> <option value="0.00814">digital compact with 2/3" Sensor </option> <option value="0.00663">digital compact with 1/1.8" Sensor </option> <option value="0.00592">digital compact with 1/2" Sensor </option> <option value="0.00444">digital compact with 1/3" Sensor </option> </select></td></tr><tr><td width="192">Selected aperture</td><td colspan="2"><select name="aperture"> <option value="1.0">F 1.0 </option> <option value="1.2">F 1.2 </option> <option value="1.4">F 1.4 </option> <option value="1.8">F 1.8 </option> <option value="2.0">F 2.0 </option> <option value="2.8">F 2.8 </option> <option value="4.0">F 4.0 </option> <option value="5.6">F 5.6 </option> <option value="8.0"> F 8.0 </option> <option value="11">F 11 </option> <option value="16">F 16 </option> <option value="22">F 22 </option> <option value="32">F 32 </option> <option value="64">F 64 </option></select></td></tr><tr><td width="192">Actual lens focal length</td><td colspan="2"><input name="focal" size="4" type="text"> mm</td></tr><tr><td width="192">focus distance</td><td><input name="distance" size="4" type="text"> feet</td><td class="but"><input onclick="doField(this.form)" value="Calculate" type="button"></td></tr><tr><td colspan="3" class="result">
<input name="dofhf" size="12" type="text"> Hyperfocal Distance

<input name="dofNear" size="12" type="text"> Closest in focus

<input name="dofFar" size="12" type="text"> Furthest in Focus

<input name="dofTotal" size="12" type="text"> Total in focus</td></tr></tbody></table>

<script src="http://newschoolofphotography.com/formscripts/DOF.js" type="text/javascript"></script>

09-15-2010, 05:37 PM

10-29-2010, 07:27 PM
Wow, that's a fantastic tutorial. Thank you.

10-30-2010, 04:00 AM
thanks for this, good tut!

10-30-2010, 10:49 AM
Thanks, quick and to the point. Have to let Jonas read it over, he's been shooting a lot lately.

10-30-2010, 01:37 PM
thanks guys.

12-21-2010, 08:42 AM
Thanks Ben. I'm trying to bone up on my knowledge before heading out to Botswana on safari next week. I am armed with a canon 17-210mm lens (?) from a friend, my XSi, and this tutorial! Hopefully I'll capture something!

12-21-2010, 09:03 AM
owww, have fun!

03-31-2011, 12:45 AM
Wow, that's a fantastic tutorial. Thank you.

08-24-2011, 06:32 PM
Thank you for lesson 1. I am unable to find lesson 2, however.

08-25-2011, 10:51 AM
it hasn't been written yet.... :tapsfoot: