Exposure Triangle pt. 2 - Aperture

This post contains some pretty deep ramblings for DSLR shooters:

What is Aperture?  What does it do?  Why should you care?

 Fast glass, and shallow depth of field.

   

     If you missed part 1, you can go back and read Exposure Triangle pt. 1 - ISO.

     In that post, I rambled on somewhat about how each of the three points on the triangle will affect the other two, and all three combined will determine the final exposure.  Each of these settings is adjustable, and each adjustment comes with it's own "secondary results", sometimes positive, and sometimes negative.  As we mentioned in part 1, ISO can be increased to improve exposure (brighten the scene).  But the secondary result of increasing ISO is greater noise, or "grain" in the photo.  In this post we'll look at Aperture, and we will see how adjusting our aperture affects our exposure, while also causing some secondary results.

     So what in tarnation is it anyway??  Aperture is actually not a camera setting at all... I mean, you can control it from the camera, but the aperture is inside the lens.  It's the opening inside the lens that lets the light pass through, and it's adjustable from little to big.  Obviously a small aperture lets in only a little bit of light, while a big aperture lets a bunch of light pass through.  And so it's easy to see how our Exposure  is very directly affected by our aperture setting.  

     Okay, well, so that's pretty straight-forward.  But here is the goofy part- the way in which the aperture setting is measured can be a little tough to grasp at first.  See.. Aperture settings are read in f-stops.  An f-stop is a measurement of light.  So, the aperture setting (the f-number) indicates how much light is required to make a proper exposure, using the given aperture size.  Therefore, (are you following this?) a bunch of light, which would measure something like f22, only needs a very small aperture.  A dim, poorly lit scene, measuring say.. f2, would require a much larger aperture in order to properly expose the sensor.  

     If you're still reading this.. it's really starting to sound like a bunch of gobbledygook, but I'm coming to a point, I think.  Here it is...  This explains why the settings on your camera's aperture adjustment are read in f-numbers, and it also sort of explains why those f-numbers seem to be backwards.  What I mean is, f2 is a very large aperture, and f32 is a very small aperture.  Get it?  f2= large opening=not much light required.  f32= small opening= lots of light required.  

     Now let's just assume that you've chosen to completely skip over the previous two paragraphs....  Here is what you really need to know about your camera's Aperture setting.  When you are shooting in a dimly lit environment, like a gymnasium, you will want to set your aperture to a low f-number.  Typical lenses have a maximum aperture value of around f4.  Some lenses get all the way down to f1.2, this is a very large aperture.  If you are shooting outside on a sunny day, you may use a much smaller aperture, like f16 or f22.  

     If you are shooting in Auto mode or Program mode, your camera will automatically select an appropriate aperture setting, as well as shutter speed, for you.  But sometimes the camera may not give you what you really want.  A while ago I said that your aperture setting yields some secondary results.  Besides affecting exposure, your aperture setting directly controls the depth of field in your photos.  Shoot with a high f-number, (small aperture opening) like f22, and your photo will have very deep depth of field, meaning everything in the scene will appear in sharp focus.  Select an aperture setting of f2.8 or f4, and your photo will have a very shallow depth of field, meaning only a thin slice of the image will be in focus while the background appears soft and blurry.  This soft, dreamy background look is the popular style for portraits.  

 f2.8

     So how to get that look...  Set your camera mode to Aperture Priority (AV on Canons), and use the finger dial to roll the aperture setting down to the lowest available number. Aperture Priority mode lets you set the aperture, and your camera automatically adjusts the shutter speed to compensate.  You can amplify the effect by stepping back a little and zooming in tight on your subject.  

     Want even more soft, blurry, dreaminess to your backgrounds? - Get some faster glass.  A "fast" lens is one with a very wide aperture, like f1.8 or f1.2.  It's called "fast" because the wide aperture allows for faster shutter speeds.  A really fast lens can get you that super shallow depth of field look, where your subject's eyes are in sharp focus while the ears are very soft.  It can get a little crazy.

f2.0

     If landscape photos are more your thing, set your aperture to around f16 or f22, and focus about 1/3 of the distance into the scene.  This will ensure that everything in the photo will be nice and sharp.  But be careful... very small apertures like f22 can drive your shutter speed down too slow, causing motion blur.  If this is the case, increase your ISO............  see the triangle at work.

Tim

     #digital photography #aperture priority

#depth of field

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Exposure Triangle pt.1 - ISO

   Recently I was at a high school basketball game to take pictures of my daughters who were part of a pre-game dance routine.  It was Homecoming night and several members of the Homecoming court were seated in the stands, dressed in their gowns, awaiting the big half-time ceremony.  The father of one of the girls in front of us, toting a Canon Rebel asked if I could give him some advice.  Seemed in the dimly lit gymnasium all of his photos were looking very blurry.  I explained that this is a very common problem.  Gymnasiums usually appear pretty bright to our eyes, but actually even the nicer newer gyms are typically very poorly lit.  Using his cameras default settings, the dim lighting was driving his shutter speed down so slow that all of his shots were blurred.
     This is where the Exposure triangle comes in......  at least one corner of it - ISO.  Photography is all about recording light.  When you press the shutter button, light travels into the lens, through the Aperture opening, bounces around in the top of the camera a bit, passes through the open Shutter and finally strikes the cameras sensor.  Three main elements here comprise what is commonly referred to as the Exposure Triangle - 1. Aperture (the size of the lens opening), 2. Shutter speed (how long the shutter remains open), and finally 3. ISO.  I S Who?? What?   ISO is simply the sensitivity level of the cameras sensor.  (remember the ASA number on the film boxes?  Same thing)   The higher the ISO number, the more sensitive the sensor becomes, and therefore less light is required to make a good exposure.  A very low ISO number such as 100, will typically be used outdoors on a sunny day.  In the very bright sunlight the sensor need not be very sensitive to record ample light.  Inside a high school gymnasium however, is a very different scene.
     So getting back the Homecoming ceremony, how do we fix Dad's burry photo issue?  First, I had him do the unthinkable - take the mode dial out of the green Auto mode!!  It has to happen sometime!  "P" mode is a good place to start.  "P" stands for Program Mode.  With the mode dial selected to Program mode, the camera will still automatically set your Aperture and Shutter speed for you, but you have the freedom to change other settings such as White Balance, Focus Points, and of course ISO.  So next we accessed the ISO selection, (on Canon DSLR's look for an ISO button on the top of the camera) and we cranked the ISO number way up.  In this case the maximum ISO for his camera was 1600, so that's what we selected.  some cameras today will go much higher, but 1600 - 3200 is usually sufficient for gym light.  So that's it!  With his ISO set to 1600 the sensor is much more light sensitive.  The camera will still set the shutter speed automatically, but it can now use a much faster shutter speed due to the increased sensitivity.  The faster shutter speed means less blur caused by camera shake and moving subjects. We can see a little bit of how each point on the Exposure Triangle affects the other points.  In other words- ISO affects Shutter Speed affects Aperture affects ISO affects Aperture affects Shutter Speed..............  and so on.
     Easy enough right?  Just select "P" on your mode selector, then adjust your ISO up to around 1600.  Your shutter speed will get faster and your blurry photos will get sharper.  BUT.... there is a catch :(  Everything in photography is a compromise.  Here it is - The higher your ISO, the more grainy (or noisy) the image will be.  The amount of noise in the photo varies with different camera models.  Some of the newest and greatest DSLR's produce amazingly clean images even at incredibly high ISO's.  Generally speaking, a noisy image is better than a blurry image.  This is especially true considering most images will only be viewed on a computer screen or in small prints, and will likely never be blown up to large size.  When viewing at typical size, even moderate noise is barely noticeable to most folks.  So don't get too overly concerned with noise.  Good exposure is priority one.

Tim

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