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174 - The "Why" Behind Your Aperture – Beyond the Bokeh · The Nerdy Photographer Podcast

• 0:04
  Casey Fatchett: Hello, and welcome back to The Nerdy
• 0:07
  Photographer. I'm your host, Casey Fatchett, and I'm glad
• 0:11
  you're here. Because today we're talking about one of the most
• 0:15
  fundamental controls on your camera, aperture, and going
• 0:19
  several layers deeper than the usual, hey, f 1.8 really blurs
• 0:24
  the background. F 16 keeps everything sharp. Explanation
• 0:28
  that you've probably heard several 100 times. Because
• 0:31
  here's the thing, if that's all you know about aperture, you're
• 0:36
  only using it as a creative tool, and it is a creative tool,
• 0:40
  but it's also a physics problem, and if you don't understand
• 0:44
  physics, you're leaving sharpness, clarity, and image
• 0:48
  quality on the table, sometimes literally paying 1000s of
• 0:52
  dollars for performance you're actively throwing away. So today
• 0:57
  we're talking about diffraction, the aperture sweet spot, depth
• 1:01
  of field mechanics, and we're going to bust one of the most
• 1:05
  persistent myths in photography, lens compression, let's get into
• 1:10
  it first. Diffraction, this is the concept that trips people up
• 1:14
  the most. When you stop your lens all the way down, say F 16,
• 1:19
  F 22 you might expect the sharpest possible image, because
• 1:23
  everything is quote unquote in focus. But what is actually
• 1:27
  happening is the opposite. You're losing some sharpness,
• 1:31
  and the reason is because of physics, not technique. Here's
• 1:35
  the way to visualize it. Imagine light as a group of people
• 1:39
  walking through a doorway. Yes, I'm going to use the Three
• 1:43
  Stooges syndrome as a way of describing this to you. When the
• 1:48
  doorway is wide, they move through easily. They stay
• 1:51
  organized and land exactly where they intended on the other side.
• 1:56
  That's your lens at like f 5.6 Everyone gets through cleanly.
• 2:00
  Now shrink that doorway down to a tiny crack. The people at the
• 2:05
  edges have to squeeze, they bump into the frame, and they fan out
• 2:09
  in unpredictable directions on the other side. That spreading,
• 2:14
  that loss of organization, is what happens to light waves when
• 2:18
  you force them through a tiny aperture opening. It's called
• 2:22
  diffraction, and the technical term for what happens when those
• 2:27
  waves interfere with one another after passing through the
• 2:31
  opening is called diffraction limited resolution. In practice,
• 2:35
  what you see on your sensor is that the light from a single
• 2:39
  point in your scene doesn't land on a single pixel, it spreads
• 2:44
  onto neighboring pixels. The result is what photographers
• 2:48
  call diffraction softness, a kind of mushy low contrast look
• 2:52
  that no amount of sharpening in post is going to fully fix for
• 2:56
  you, because the data simply wasn't captured cleanly to begin
• 3:01
  with. On a modern high resolution sensor, say, like 40
• 3:04
  plus megapixels, diffraction become can become visible as
• 3:09
  early as f 11. On a lower res body, you might have a bit more
• 3:13
  headroom pushing F 16 before it gets noticeable, but F 22 on
• 3:17
  almost any modern camera is certainly costing you a little
• 3:21
  bit of sharpness. So, where should you shoot? For most
• 3:25
  lenses, the sharpest aperture, the sweet spot, if you will,
• 3:29
  sits roughly two to three stops from wide open. If your lens
• 3:33
  opens to F 1.8 you're usually looking at peak sharpness
• 3:37
  somewhere around f4 or f5 six. For a lens that opens to F 2.8
• 3:42
  the sweet spot tends to land between F 5.6 and f8 This is not
• 3:46
  random. Wide open, most lenses suffer from a different set of
• 3:50
  optical imperfections, spherical aberration, coma, the corner
• 3:55
  softness. As you stop down, those aberrations are reduced,
• 3:59
  but pushed too far, and diffraction starts to take over.
• 4:03
  The sweet spot is the aperture, where those two competing
• 4:07
  forces, aberrations on one end, diffraction on the other, are
• 4:11
  both minimized. Now this varies by lens. A premium prime at f
• 4:15
  1.4 might be impressively sharp, wide open. A budget zoom might
• 4:20
  need to be stopped down to f8 before it really delivers. The
• 4:24
  homework at the end of this episode will help you find your
• 4:28
  specific lens sweet spot, because no YouTube video can
• 4:32
  tell you what your glass does better than your own testing
• 4:36
  can. So, depth of field, the quick version. While we're here,
• 4:40
  let's quickly revisit depth of field, not just as a stylistic
• 4:45
  choice, but as a mechanical one. Depth of field is the range of
• 4:49
  distance in your scene that appears acceptably sharp. Wide
• 4:53
  apertures, like f 1.4 give you a very shallow depth of field, a
• 4:58
  thin slice of focus with everything else falling off into
• 5:02
  blur. A narrow apertures like F 11 extend that range, so more of
• 5:06
  the scene appears sharp. What most tutorials skip is why this
• 5:11
  happens. The answer comes down to the size of what's called the
• 5:15
  circle of confusion, and believe me, I've been there many times.
• 5:20
  When a point of light is perfectly in focus, it lands as
• 5:24
  a perfect point on your sensor. When it's out of focus, it lands
• 5:28
  as a small circle, and the larger that circle, the more
• 5:32
  blurry that area looks. Wider apertures produce larger out of
• 5:36
  focus circles, which is why background blur is more
• 5:40
  pronounced. Narrower apertures keep those circles small, which
• 5:44
  is why more of the scene looks sharp. That's Boca, not magic
• 5:49
  geometry. Now the compression myth, the myth that we have
• 5:53
  all.. and now, and now the myth we need to address lens
• 5:57
  compression, you've heard it, an 85 millimeter lens compresses
• 6:01
  the face, a 35 millimeter lens distorts it, and there's a
• 6:05
  kernel of truth here, but the explanation most people give is
• 6:09
  wrong, and getting it wrong leads to bad decisions, we don't
• 6:14
  want to make bad decisions as photographers, here's what's
• 6:18
  actually happening, compression, the way the background elements
• 6:22
  appear to stack up behind your subject, or the way a nose
• 6:26
  appears smaller relative to the ears, is entirely a function of
• 6:31
  distance, not focal length. If you stand in the same spot and
• 6:35
  take a photo with a 35 millimeter and an 85 millimeter
• 6:39
  and crop the 35 millimeter shot to match the framing of the 85
• 6:43
  millimeter, the facial proportions will be nearly
• 6:47
  identical. The compression will be the same. The facial
• 6:51
  compression, where the confusion comes from, this is a longer
• 6:55
  focal length forces you to stand farther away from your subject,
• 6:59
  and the distance is what flattens the perspective. So,
• 7:03
  yes, in practice, shooting a portrait at 85 millimeters tends
• 7:08
  to produce more flattering compression than shooting at 35
• 7:12
  millimeters, but only because you're standing farther away
• 7:16
  from your subject. The lens itself isn't doing anything to
• 7:20
  the geometry, it's just changing how much of the room you can
• 7:24
  see. This matters because if you think the lens is creating the
• 7:29
  compression, you might buy an 85 millimeter and shoot it at the
• 7:33
  same distance as your 35 you'll get a tighter frame, but you
• 7:37
  won't get the flattened perspective you were after.
• 7:41
  Distance is the variable, focal length just determines how far
• 7:45
  back you need to stand. So let's recap, recap, recap def
• 7:49
  diffraction is real. F 22 is probably hurting you somewhat,
• 7:54
  and the sweet spot for most lenses is somewhere in the
• 7:57
  middle. Depth of field is geometry, not magic, and
• 8:01
  compression is about where you stand, not which lens is on your
• 8:05
  camera. Understanding why these things work the way that they do
• 8:10
  changes how you make decisions in the field. Instead of
• 8:14
  defaulting to settings, you're working with the physics. Now
• 8:18
  that is being a nerdy photographer. Today's homework
• 8:22
  is what I'm calling the sharpness audit. Mount your
• 8:25
  camera on a tripod, find a subject with fine details - a
• 8:29
  printed map, a piece of currency, or textured fabric
• 8:33
  works really well. Shoot a series from your widest aperture
• 8:37
  all the way to the top to F 22 in one stop increments. Bring
• 8:41
  them into your editing software, zoom to 100% or 200% and compare
• 8:46
  both the center sharpness and the corner sharpness at each
• 8:50
  stop. Find the exact aperture where diffraction softness kicks
• 8:55
  in for your lens on your sensor. Write it down, that's your
• 8:59
  ceiling. And until next time, stay safe and stay nerdy. Hey
• 9:03
  folks, it's Casey. I'm back. There's a couple things I forgot
• 9:07
  to mention. One, please be sure to subscribe to the show. Two,
• 9:12
  please leave a review for the show. Reviews help us with
• 9:16
  discoverability, new people finding the show. So, leave a
• 9:20
  review on Apple Podcasts, Spotify, wherever you can leave
• 9:24
  a review for the podcast. It is greatly, greatly appreciated.
• 9:28
  And finally, I would love to hear what you think of these
• 9:32
  short little nerd lit episodes that we're doing. Do you like
• 9:36
  them? Find me on social media at the Nerdy Photo on pretty much
• 9:41
  everything, Instagram threads, Reddit, Tick Tock, Blue Sky.
• 9:45
  Find me there, mention it. Let me know what you think of these
• 9:49
  episodes, whether I should continue doing them, whether you
• 9:53
  are enjoying them, and if there's a different topic you'd
• 9:57
  like for me to cover in a short episode. I would love to hear
• 10:02
  about it. And now, without further ado, stay safe, stay
• 10:06
  nerdy, see you next time. Bye.