Photography forum: Photography 050: Light – ISO, Aperture, and Shutter Speed

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Name: Asa

Bee Lover Garden Photography Region: Utah Garden Ideas: Master Level Photo Contest Winner: 2016
Sep 21, 2014 8:24 PM CST
I’ve been lurking on ATP for a good while (and maybe you’ve seen a photo or two of mine in the database or in a thread :lol:). But after learning about this photography section, I figured I’d create a login and chime in here. What follows is a not-so-technical discussion of really basic stuff about cameras and light. I don't think it's quite at a 101 level.

I’ll contribute plant/flower/garden shots going forward. There’s a wealth of magnificent subject matter around me ;) !!

Here goes: --Photography 050: Light – ISO, Aperture, and Shutter Speed--

In the simplest terms, photography is writing with light. In fact, that’s what the word means:
from Greek graphe "writing," and photo-, (comb. form of phos (genitive photos)) "light".

No matter which camera you use (film, DSLR, digital point-and-shoot, or even your iPhone), light goes through the lens and hits a photo-sensitive medium—either film or the digital photosensor. Assuming good focus (which is another discussion completely), the key to lightwriting is exposing the film or photo senor to the right amount of light (to avoid a washed-out or too-dark picture).

There are three variables that determine how much light gets written:
1) How sensitive the medium is to light
2) The quantity of light allowed through the lens
3) How long the medium is exposed to light

In photography terms, these translate to:
1) ISO (film speed)
2) Aperture (f-stop)
3) Shutter Speed

Digital cameras, your phone, and even modern film cameras can (and do) control these variables automatically to ensure proper exposure. But even if you never use your camera’s manual (or semi-manual) settings, it’s helpful to know that these are the variables in play that account for the exposure of a photograph. It’s also key to understand here that if you change (or the camera automatically changes) one of these variables, at least one of the other two will also need to change in order to produce a photograph with proper exposure.

The ISO value (number) describes how sensitive the film is to light. ISO 100 film is less sensitive to light than ISO 800 film is…and therefore requires more light to produce a properly exposed image. In photographyspeak, ISO 100 is called a “slow film” whereas ISO 800 is a relatively fast film. Slower films produce richer images whereas the faster the film, the grainier or noisier the photos will be.

Digital cameras mimic the ISO settings of film cameras (electronically) and the same quality concerns hold true – the higher the ISO setting on the digital camera, the noisier the photograph will be.

Fast films (and higher digital ISO settings) are commonly used to photograph in low-light situations or for shooting quickly-moving targets (sports, etc.), whereas slower films (lower digital ISO settings) are used for portraiture, landscapes, etc. – stuff that generally holds still.

Aperture (f-stop)
To understand the aperture of a lens, think about the pupil of your eye. When it’s dark, your pupil dilates (gets bigger) to let in more light. When it’s bright out, your pupil it contracts to allow less light to hit the optic nerve (your own photosensor).
The dilation of the camera’s pupil (aperture) is measured in f-stops—the lower the f-stop, the more light hits the photo-sensitive medium.

(Notice here that the higher the f-stop, the less of the lens’ surface area is used to pass light through. That’s a really important concept to understand when thinking about “depth of field” (think focus depth) – but to keep it simple here: the higher the f-stop, the deeper the focus will be.)

Shutter Speed
Shutter Speed is a number, measured in fractions of a second (or even whole seconds), that describes how long the photo-sensitive medium is exposed to light. This variable is pretty intuitive, but it’s important to note that the slower the shutter speed, the longer you have to hold the camera still (and a that’s a very good reason to get a tripod).

So what? How do these variables affect my pictures and picture taking?
Ah, I’m glad you asked. Here are some examples of the same subject taken with absurdly different variables. See if you can get a sense of how each of the three variables affects the final product.

ISO – here are several photographs of a gargoyle shot using increasing ISO values. If you look closely at the flower on his ear, you can see that it gets grainier and nosier (and ultimately becomes unusable). The camera is holding the aperture fairly steady (wide open) but it increases the shutter speed somewhat as the ISO values increase.
Takeaway: for richer shots, shoot using the lowest ISO value that is reasonable (given other constraints/considerations).
Thumb of 2014-09-22/evermorelawnless/d9c67a Thumb of 2014-09-22/evermorelawnless/6b9c30 Thumb of 2014-09-22/evermorelawnless/53d2b7 Thumb of 2014-09-22/evermorelawnless/5694b4 Thumb of 2014-09-22/evermorelawnless/a332c0 Thumb of 2014-09-22/evermorelawnless/97e37f Thumb of 2014-09-22/evermorelawnless/5f8ffa Thumb of 2014-09-22/evermorelawnless/2fbe08

Aperture – here are a few more photographs of the same guy. Because I was shooting in pretty low light (ambient window light and room lighting – no flash), the camera popped the ISO value to the maximum that I had bracketed (ISO 1600) and changed the shutter speed to account for the shrinking aperture through the progression.
Although we’re supposed to be talking mostly about light here, notice how only his nose is in sharp focus in the first shot (wide open for this lens – f-4.5) and even the background is in pretty good focus in the last shot (tiny pupil at f-29). Key stuff in discussions about focus.
Thumb of 2014-09-22/evermorelawnless/f11316 Thumb of 2014-09-22/evermorelawnless/2864a4 Thumb of 2014-09-22/evermorelawnless/f73db0 Thumb of 2014-09-22/evermorelawnless/f5f692 Thumb of 2014-09-22/evermorelawnless/fd6e4e Thumb of 2014-09-22/evermorelawnless/908de8

Shutter Speed – in this series, I started with a VERY slow shutter speed of 1/2 second. The camera accounted for that by decreasing the aperture to f-8 and used the slowest ISO value that it could (ISO 100). As I increased the shutter speed, the camera responded by increasing the ISO value and opening the aperture (to f-5.6 in the next and then to f-4.5 in the remaining shots). The camera complained when I tried to shoot the last shot at 1/1000th of a second because even with the fastest ISO value available (ISO 12800) and the aperture wide open (f-4.5), there just wasn’t enough light coming in for that shutter speed.
Thumb of 2014-09-22/evermorelawnless/e372e3 Thumb of 2014-09-22/evermorelawnless/8d199b Thumb of 2014-09-22/evermorelawnless/d796f9 Thumb of 2014-09-22/evermorelawnless/b39fa0 Thumb of 2014-09-22/evermorelawnless/ca0235 Thumb of 2014-09-22/evermorelawnless/a748f7 Thumb of 2014-09-22/evermorelawnless/b2d909 Thumb of 2014-09-22/evermorelawnless/ac7a14 Thumb of 2014-09-22/evermorelawnless/e6e457 Thumb of 2014-09-22/evermorelawnless/d41c3c

How your digital camera thinks about this stuff
Your camera probably has a dial that you can use to select from a few icons – automatic, a tulip, a guy running, a mountain, an icon of a person, moon and a dude, etc., (and then maybe some strange letters like SV, AV, M, and other junk), right? This isn’t the right place to go into detail about these settings, but it’s instructive to have an idea about how the camera is deciding to write the light on each. I’ll use my Pentax K-X as the example here, but your camera will have similar (if not more or fewer) settings (check your manual if it’s interesting to you).
What follows are broad, sweeping generalizations, but should give you some idea of the decisions that your camera is making for you about light in each mode (I've left other nuances about the modes alone here). Keep in mind that the camera’s first priority is to get the exposure right – so the emphases described below are only that – emphases. Your camera reserves the right to go entirely rogue in order to get the exposure right. That’s what it cares about most.

Automatic – automatically selects the most appropriate of the modes below:

Portrait (person icon)
Emphasis: shallow depth of field (focused face, blurry foreground/background)
Outcomes: smaller f-stop number (more open aperture), lower ISO value (see note), and slower shutter speed
Note: Some will not allow an ISO value that exceeds a certain threshold in this mode.
Here’s the same gargoyle shot in Portrait Mode:
Thumb of 2014-09-22/evermorelawnless/86444b

Landscape (mountain icon)
Emphasis: getting as much in focus as possible
Outcomes: larger f-stop number, higher ISO value, slower shutter speed

Macro (flower icon)
Emphasis: deeper depth of field
Outcomes: larger f-stop number, higher ISO value, slower shutter speed
Note: Some cameras will not allow focus to infinity in macro mode (which makes focusing quicker). Some cameras also allow you to get closer to the object than in other modes – sometimes even closer than the lens should physically (physics) allow (lots of math and maybe some fudging here, depending on the camera/brand).
Other note: This concept is a bit beyond the scope of this discussion…but it’s important to nod at, at least. Although the camera is trying to increase the depth of field in this mode (and actually is), the chunk or slice of what can potentially be in focus decreases the closer the lens is to the subject.
Here’s the same gargoyle shot in Macro Mode. Notice how different it is from the one shot in portrait mode (and how the settings differ, too). (Also, I forgot to bracket down the ISO range...I usually have it set at'll be disappointed shooting portraits at ISO 3200.)
Thumb of 2014-09-22/evermorelawnless/1b1c2c

Moving Object/Sport Mode (runner icon)
Emphasis: freezing the in-motion subject (blur reduction/elimination)
Outcomes: fast shutter speed, higher ISO value, smaller f-stop number
Note: in order to achieve a fast shutter speed, the camera will often necessarily bump up the ISO value to the maximum that you allow. Expect your photos to be less rich (grainier or noisier) than those shot in other modes.

Night Scene (guy with moon and stars icon)
Emphasis: the first emphasis is to get enough light on the subject (person) in the foreground and the second is to get enough light on the background
Outcomes: the flash will fire to illuminate the person in the foreground, and then the shutter will stay open for a while afterward in order to expose the background properly – smart stuff!

How can I control these values?
Your camera probably has a few semi-automatic modes that are similar to mine. Look your manual if your settings are not somewhat parallel (or intuitive).

SV (sensitivity priority) – Use this one to set the ISO value manually. The camera will then adjust the aperture (f-stop) and shutter speed for proper exposure.

TV (shutter priority) – Use this one to set shutter speed manually. The camera will then adjust the aperture (f-stop) and ISO value for proper exposure.

AV (aperture priority) – Use this one to set the aperture (f-stop) manually. The camera will then adjust the ISO value and shutter speed for proper exposure.

M (manual) – you’re on your own and in deep water with this one. As you fool around with the other values, though, you’ll get a sense of where to start…and can look results in near-real time on your LCD screen to dial things in. Sometimes, manual is the only way to achieve the results you’re after. Sometimes you just have to outthink the camera.

So that’s that. Stuff that maybe isn’t at the forefront of your mind when you’re point-and-shooting, but your camera is sure thinking about it and trying to make good decisions for you using those three variables as it writes your light.

[Last edited by evermorelawnless - Sep 21, 2014 8:26 PM (+)]
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Name: Dirt
(Zone 5b)
Plant Lover: Loves 'em all! Garden Photography Bee Lover Region: Utah Photo Contest Winner: 2014 Celebrating Gardening: 2015
Photo Contest Winner: 2015 Photo Contest Winner: 2016 Million Pollinator Garden Challenge
Sep 21, 2014 8:48 PM CST
Oh wow!
That's a great explanation and a cute gargoyle Welcome! to ATP
Name: Anne
Summerville, SC (Zone 8a)
Only dead fish go with the flow!
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Sep 21, 2014 8:48 PM CST
Well done! This isn't Photography 050, this should be 201. Very detailed and informative.
"The Universe speaks in many languages, but only one voice. It speaks in the language of hope; It speaks in the language of trust; It speaks in the language of strength, and the language of compassion. It is the language of the heart and the language of the soul. But always, it is the same voice. It is the voice of our ancestors, speaking through us, And the voice of our inheritors, waiting to be born. It is the small, still voice that says: We are one. No matter the blood; No matter the skin; No matter the world; No matter the star; We are one. No matter the pain; No matter the darkness; No matter the loss; No matter the fear; We are one. Here, gathered together in common cause. we agree to recognize this singular truth, and this singular rule: That we must be kind to one another, because each voice enriches us and ennobles us, and each voice lost diminishes us. We are the voice of the Universe, the soul of creation, the fire that will light the way to a better future. We are one."

Name: Marilyn
Greenwood Village, CO (Zone 5b)
Garden today. Clean next week.
Bookworm Region: Colorado Garden Procrastinator Heucheras Region: Southwest Gardening Container Gardener
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Sep 22, 2014 9:05 AM CST
Thanks, I got some of it and will be re-reading it several times to get more! Once I get my new eyes (cataracts) I may be able to see the differences better. Rolling my eyes.
Name: Asa

Bee Lover Garden Photography Region: Utah Garden Ideas: Master Level Photo Contest Winner: 2016
Sep 22, 2014 9:32 AM CST
CDsSister said:Thanks, I got some of it and will be re-reading it several times to get more! Once I get my new eyes (cataracts) I may be able to see the differences better. Rolling my eyes.

If any of it doesn't make sense, that's my fault. Please ask about what's unclear and I'll try to explain...and then clean up the first post.

I'm also not very happy with some of the examples - I didn't take very long to set up the gargoyle shoot and the contrast among/between settings could have been shot in a clearer way. Also, some of the distinctions between the shots are lots easier to see in the original resolutions.

For example, the difference between ISO 100 (crop preserving original resolution from picture labeled IMGP9076 above) and ISO 12800 (IMGP9083) isn't all that clear in the two photos that I posted - but if I crop the photos to just the flowers, you can really see the decrementation of the quality.
Thumb of 2014-09-22/evermorelawnless/72b4c9 Thumb of 2014-09-22/evermorelawnless/278125

Similarly, with cropping, it's easier to see the difference in focus depth at f-4.5 (IMGP9060) and f-29 (IMGP9065).
Thumb of 2014-09-22/evermorelawnless/3bd302 Thumb of 2014-09-22/evermorelawnless/1eaa26

Anyway...please don't hesitate to ask for clarification - if it doesn't make sense, it's on me...not you. Worst that can happen is I will say, "I don't know the answer".

Name: Marilyn
Greenwood Village, CO (Zone 5b)
Garden today. Clean next week.
Bookworm Region: Colorado Garden Procrastinator Heucheras Region: Southwest Gardening Container Gardener
Enjoys or suffers cold winters Sempervivums Annuals Foliage Fan Herbs Garden Ideas: Level 2
Sep 22, 2014 11:09 AM CST

I see. The one thing I failed to do is click on the picture Which of course allows me to see the differences a bit more clearly. DUHHHHHH!
Thanks for your patience.
Name: Mother Raphaela
Holy Myrrhbearers Monastery NY (Zone 4b)
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Sep 23, 2014 6:48 PM CST
Thank You! Some of this is starting to make sense. I'm truly grateful for those of you who have managed to understand all of this -- and are helping some of the rest of us get there! I tip my hat to you.

Mother Raphaela
Name: Catmint/Robin
Maryland (Zone 7a)
Region: Mid-Atlantic Butterflies Forum moderator Native Plants and Wildflowers Bee Lover Echinacea
Region: Maryland Garden Photography Cottage Gardener Garden Ideas: Master Level Celebrating Gardening: 2015 The WITWIT Badge
Sep 26, 2014 6:58 AM CST
wow, this is really enlightening, Lawnless! I just got a brand new android upgrade (moto X), and the photo options are more basic and it's taking less good photos than my previous android did. Sad E.g., my older android had all the icons you're talking about above (my fault I was clueless about what they meant), whereas the newer model does not have these. I consider this to be the opposite of what should be happening, but there it is. I do still have a point and shoot camera. Maybe I should take it out again.
"One of the pleasures of being a gardener comes from the enjoyment you get looking at other people's yards”
― Thalassa Cruso

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