New Tutorial: Camera Exposure - Aperture, ISO & Shutter Speed

[McQ]

A new page has just been added to the tutorials section of this website at:

Camera Exposure - Aperture, ISO & Shutter Speed

It's a really basic overview of the exposure triangle, but is a foundational topic that had not yet been covered in the tutorials. Can't think of anything more important to get down than this

As usual, comments/typos/suggestions/etc are all welcome. I'm still in the process of editing it so there may be some minor changes/fixes over the next few days...

edit: the first section has been completely reworked; a refresh is required to see these changes

[Blazing fire]

"The shutter speed specifically refers to how long this light is permitted to enter the camera"

I'm not sure if this is technically correct... Please refer to this to understand my confusion. http://www.wrotniak.net/photo/tech/fp-shutter.html.

"How it Appears. Shutter speed is a powerful tool for freezing or exaggerating the appearance of motion... With waterfalls and other creative shots, motion blur is sometimes desirable, but for most other shots this is avoided. Therefore all one usually cares about with shutter speed is whether it results in a sharp photo -- either by freezing movement or because the shot can be taken hand-held."

Perhaps colin's photo might be added, with his consent of course. It clearly illustrates how a long exposure can smoothen the water and sky. You might wish to quantify how long is long (15minutes in colin's case).

Eg 1,2,3,4,5,6,7. I would chose "The Lord of Akersten's Bitter/Sweet Revenge!" & "The Mountains and the Mist - Revisited" among the 7.

You might wish to talk about the light transmission in addition to aperature. Since it's not that important, you may include this section in fine print. Also consider adding that the aperture number represents the focal length of the lens divided by the diameter of the aperture. Since it's a ratio, it has no units. Perhaps include what "stop down/up" means. If you want to complicate things, add in the inverse square law.

Great tutorial all in all!

[carregwen]

Looks good, Sean. And very important for all beginners to understand this. One slight point...

You said that "ISO speed: determines your camera's sensitivity to a given amount of light" I think with a film camera that should read "ISO speed: determines your camera film's sensitivity to a given amount of light" and for digital cameras it should be "ISO speed: adjusts the light signal strength to suit the amount of light" Or something like that. Saying the "camera's sensitivity" doesn't seem very clear to me.

[Dave Humphries]

Hi Sean,

I'll apologise in advance for doing my usual over-thorough, pedantic job on your words

Beside the triangle:
"Aperture: determines area over which light can enter your camera", I wonder whether (while perhaps less technically accurate) "diameter" might replace area as it may be better associated to the size of the hole in the lens (iris)

In SHUTTER SPEED section:

"Shutter speed" and "exposure time" refer to the same concept, although a faster shutter speed means a longer exposure time.

Is the word I have bolded correct here?

I think more could be made of the example pictures, some should be specially commissioned, with your mouse over effects
e.g. for Roundabout; two shots entitled Slow: 1/15 and Fast: 1/250
A waterfall example would be better than the plasma I think, with shutter speeds of Slow: 30s, Med 1/15 and Fast: 1/1000 to show the 'milk', 'stretched drip' and 'frozen drip' effects. Trust me to make more work This also makes the point that what's "slow" for one subject isn't necessarily so for another.

At end of section "-- either by freezing movement or because the shot can be taken hand-held" might benefit by adding " avoiding camera shake" perhaps?

In the APERTURE SETTING section:
In my experience, some bridge/compacts struggle for even 2 stops aperture range; f4 to f8 is probably more common (but perhaps I choose bad cameras ).

In How it appears, the text "Smaller f-stop values correlate with a shallower depth of field:" is followed by two pictures in the opposite order and using alternate terminology. How about
"Lower f-stop numbers correlate with a shallower depth of field:"
Then correct/swap the bracketed text in images titles, currently the bird (shot at say, f2) is described as a "(large f-stop number)", compared to the landscape (f16?) me thinks you didn't mean that!
Perhaps "(low f-stop number)" under the bird and "(high f-stop number)" under the rocky landscape? Perhaps even give examples like f2 and f16.

As mentioned by Blazing Fire, I think defining what "stop down" or "open up" means would be useful to people, as a more experienced person might tell a beginner to do that and the beginner not know what it means and be too shy to ask.

In the ISO SPEED section:
Given that (I think) all the CiC tutorials are written for Digital Photography, I think Rob's point on film might be covered in a small grey technical sentence or two below the main section, stating that for a film camera, the same basic principles apply, but you 'set' the ISO speed required for what you're shooting by the choice of film you put in the camera. (we won't go into 'pushing' speed in developing ) maybe mention somewhere that digital noise equates to film grain.

In the CAMERA EXPOSURE MODES section:
In first table, I would suggest the non-Canon equivalents for "Av" and "Tv" are also shown - that's "A" and "S" repectively

The ending of "; you can choose a corresponding ISO speed & exposure compensation" is not mentioned for Av and Tv rows, although relevant, is this deliberate?

Obviously, for manual, EC becomes irrelevant.
Should EC, not previously mentioned, be described or linked to?

The second table's left column is labelled "Exposure Mode", I suspect it should be "Scene Mode"

In all entries on right hand side, I would query the susceptibility of a novice mistaking terms like "small f-stop" for f16* (if they think if the hole size), whereas "low f number" is less ambiguous (and "-stop" is arguably unnecessary).
* or maybe it's just me

Anyway, on the whole a good tutorial (as usual) and with a few fixes, will be a very useful addition to the site.

Thanks for listening,

[JonathanC]

By the Aperture Settings, paragraph 2, it says "Every time the f-stop value doubles, the light-collecting area quadruples. "

Should that be halves, rather than doubles?

[rick55]

Hi, Sean;

This is another great tutorial, and as you said, one that's critical.

I particularly like the first section with the exposure triangle: it's very clean. I can see the points people have made about how things are described.

Since the tutorial describes things in terms of "sensor" throughout, perhaps it would make sense to just put a note early on saying that film behaves essentially the same, but the ISO is fixed when you load the camera (except it can be pushed around some in the darkroom).

If I can be so bold as to pull together some of the comments, and suggest perhaps:

Aperture: determines the size of the opening the light has to reach the sensor; intuitively, the quantity of light
Shutter speed: determines the duration that light is permitted to act on the sensor
ISO speed: determines the sensitivity of the sensor to a given quantity and duration of light

In the shutter speed section, would it be worth explicitly calling out camera shake? You mention hand-held and tripod, so it's basically there. Maybe it would just add to the confusion, because 1/focal length has gotten so complicated with sensor sizes and image stabilization. But even without the rule of thumb, it would explain why the "camera shake" indicator keeps coming on (or they get blur) in "landscape" mode when it's a little dim, but not in "night" or "portrait" mode, which I think would be very helpful to people.

In the ISO section, instead of, or in addition to, the shots of gray, would it be good to have shots of a low-light scene? It might be useful to see that the noise is most noticeable in low-contrast areas.

I'm creating more work, too, I'm afraid.

Cheers,
Rick

[McQ]

"The shutter speed specifically refers to how long this light is permitted to enter the camera"

I often struggle with wording that is technically correct for an advanced reader, but yet is still simple and easy to understand for the beginner. This is a perfect example of that trade-off . I've changed the wording to be technically correct, although it's perhaps slightly less clear for the beginner:

"determines the effective duration of the exposure"

This satisfies the scenarios with really fast shutter speeds (with only a thin region of the sensor being exposed at a given time), but hopefully also doesn't necessitate introducing that concept so early.

Perhaps colin's photo might be added, with his consent of course. It clearly illustrates how a long exposure can smoothen the water and sky. You might wish to quantify how long is long (15minutes in colin's case).

That's a good idea, but the concern is that this is an article for someone who is *very* new to photography. 15 minute exposures such as Colin's are definitely for people who've been around the block a few times . I'm trying to keep the shots within the range of what someone would likely attempt early on. Certainly something to do for a later article though -- perhaps specifically on really long exposures. I could probably do with a better example than the one that's there though...

You might wish to talk about the light transmission in addition to aperature. Since it's not that important, you may include this section in fine print. Also consider adding that the aperture number represents the focal length of the lens divided by the diameter of the aperture. Since it's a ratio, it has no units. Perhaps include what "stop down/up" means. If you want to complicate things, add in the inverse square law.

Yes, I will add fine-print that some lenses let in less light due to inefficient light transmission, even though their aperture setting is otherwise identical.

Thanks for all the thorough and helpful feedback! Now you see how much editing these articles typically undergo...

[McQ]

You said that "ISO speed: determines your camera's sensitivity to a given amount of light" I think with a film camera that should read "ISO speed: determines your camera film's sensitivity to a given amount of light" and for digital cameras it should be "ISO speed: adjusts the light signal strength to suit the amount of light" Or something like that. Saying the "camera's sensitivity" doesn't seem very clear to me.

How about: "determines the sensitivity of your camera sensor to a given amount of light" ?

[carregwen]

How about: "determines the sensitivity of your camera sensor to a given amount of light" ?

I think it's that word 'determine' that's throwing it out. It can mean several things http://www.merriam-webster.com/dictionary/determine It could mean to set something, especially limits, or it could mean to find out by investigation. Perhaps 'set' might be better? After all, you have used the word 'setting' at the top. But don't listen to me, my degrees are in history!

So it could say...

Each setting controls exposure differently:

Aperture: sets area over which light can enter your camera
Shutter speed: sets the duration of the exposure
ISO speed: sets the sensitivity of your camera sensor to a given amount of light

I think you could also say that a given exposure (dependent upon the scene) is 'x' amount of light, and in order to get 'x' you can manipluate the three parameters of the triangle, but 'x' has to add up to the same amount. A good analogy is a 'bucket of light' for an exposure, and ISO, shutter, aperture are three varying taps that need to fill the bucket.

I've said enough!

[McQ]

In the shutter speed section, would it be worth explicitly calling out camera shake? You mention hand-held and tripod, so it's basically there. Maybe it would just add to the confusion, because 1/focal length has gotten so complicated with sensor sizes and image stabilization. But even without the rule of thumb, it would explain why the "camera shake" indicator keeps coming on (or they get blur) in "landscape" mode when it's a little dim, but not in "night" or "portrait" mode, which I think would be very helpful to people.

Yeah, the 1/focal length rule is much more complicated these days, so I am hesitant to go into this for such a fundamental article. In addition, the concepts of focal length and/or sensor size likely haven't yet been introduced for a reader who is needing to start with this article. I've added a paragraph at the end of the shutter speed section that states:

"How do you know which shutter speed will provide a sharp hand-held shot? With digital cameras, the best way to find out is to just experiment and look at the results on your camera's rear LCD screen (at full zoom). If a properly focused photo comes out blurred, then you'll usually need to either increase the shutter speed, keep your hands steadier or use a camera tripod."

In the ISO section, instead of, or in addition to, the shots of gray, would it be good to have shots of a low-light scene? It might be useful to see that the noise is most noticeable in low-contrast areas.

Yes, I need to use a real-world example instead of just patches of gray at different ISO speeds.

Thanks for the feedback!

[McQ]

By the Aperture Settings, paragraph 2, it says "Every time the f-stop value doubles, the light-collecting area quadruples. "

Should that be halves, rather than doubles?

Thanks for catching this -- it's been fixed. Silly typo

[McQ]

Hi Sean,

[INSERT VERY THOROUGH AND CAREFULLY READ FEEDBACK]

Virtually all of this has been incorporated. There's so much that's changed I'll just leave it at that -- otherwise this reply would be too long

Thanks a ton for all the helpful feedback!

[McQ]

I think it's that word 'determine' that's throwing it out. It can mean several things http://www.merriam-webster.com/dictionary/determine It could mean to set something, especially limits, or it could mean to find out by investigation. Perhaps 'set' might be better? After all, you have used the word 'setting' at the top. But don't listen to me, my degrees are in history!

I'm going back and forth between the use of "sets" vs "controls" -- either seem to be an improvement.

I think you could also say that a given exposure (dependent upon the scene) is 'x' amount of light, and in order to get 'x' you can manipluate the three parameters of the triangle, but 'x' has to add up to the same amount. A good analogy is a 'bucket of light' for an exposure, and ISO, shutter, aperture are three varying taps that need to fill the bucket.

The very first version of this article actually had an analogy at the start, but I ended up cutting it because I didn't feel it improved understandability sufficiently to warrant the extra paragraph at the very start. Perhaps this could go at the end instead...still wavering on its inclusion. I should add something about the total amount of light vs exposure though...

[John C]

Another really good tutorial. By the way, it was the tutorials that attracted me to this website in the first place. It looks to me that the comments above have been addressed. I have a couple more, hopefully these are not duplicates. These comments relate to the Camera Exposure Modes section.
1. For Program Mode, my experience is that the camera selects a combination of shutter speed and aperture and the photographer can adjust between a range of equivalent exposures. For instance, if the camera selects 1/125 sec and f/3.2, the photographer can select 1/60 sec and f/5 or 1/30 sec and f/6.3, from the list of equivalent exposures. I'm not sure if this is true of all cameras but in this form, the Program Mode can be very useful as something of a combination of the A and S (Tv) modes.
2. For Landscape Mode, the reference to a "large f-stop" should be "high f-stop value" to be consistent with the descriptions in the other modes.
3. For Bulb Mode, you might want to mention that a lot of cameras do not have this setting. I could be wrong but this might not be available in most digicams. For Sony DSLRs, the bulb setting is found by setting the shutters peed below 30s.

You might also consider a short section on exposure compensation since a lot of cameras have controls for this and it directly relates to exposure. Beginners will probably be interested in how and when to use those controls. There is a short paragraph in the camera metering tutorial that could be referenced.

[McQ]

I think you could also say that a given exposure (dependent upon the scene) is 'x' amount of light, and in order to get 'x' you can manipluate the three parameters of the triangle, but 'x' has to add up to the same amount. A good analogy is a 'bucket of light' for an exposure, and ISO, shutter, aperture are three varying taps that need to fill the bucket.

OK, the tutorial now has an introductory "understanding exposure" section (shown below) which leads into the exposure triangle. You're right, I think something like this was really needed. The earlier analogy I had just wasn't clear enough.

------
Achieving the correct exposure is a lot like collecting rain in a bucket. While the rate of rainfall is uncontrollable, three factors remain under your control: the bucket's width, the duration you leave it in the rain, and the quantity of rain you want to collect. You just need to ensure you don't collect too little ("underexposed"), but that you also don't collect too much ("overexposed"). The key is that there's many different combinations of width, time and quantity that will achieve this. For example, for the same quantity of water, you can get away with less time in the rain if you pick a bucket that's really wide. Alternatively, for the same duration left in the rain, a really narrow bucket can be used as long as you plan on getting by with less water.

In photography, the exposure settings of aperture, shutter speed and ISO speed are analogous to the width, time and quantity discussed above. Furthermore, just as the rate of rainfall was beyond your control above, so too is natural light for a photographer.
------

[McQ]

I have a couple more, hopefully these are not duplicates. These comments relate to the Camera Exposure Modes section.

Hi John - all the points you brought up have now been addressed. Thanks for the feedback!

[Dave Humphries]

OK, the tutorial now has an introductory "understanding exposure" section (shown below) which leads into the exposure triangle. You're right, I think something like this was really needed. The earlier analogy I had just wasn't clear enough.

------
Achieving the correct exposure is a lot like collecting rain in a bucket. While the rate of rainfall is uncontrollable, three factors remain under your control: the bucket's width, the duration you leave it in the rain, and the quantity of rain you want to collect. You just need to ensure you don't collect too little ("underexposed"), but that you also don't collect too much ("overexposed"). The key is that there's many different combinations of width, time and quantity that will achieve this. For example, for the same quantity of water, you can get away with less time in the rain if you pick a bucket that's really wide. Alternatively, for the same duration left in the rain, a really narrow bucket can be used as long as you plan on getting by with less water.

In photography, the exposure settings of aperture, shutter speed and ISO speed are analogous to the width, time and quantity discussed above. Furthermore, just as the rate of rainfall was beyond your control above, so too is natural light for a photographer.
------

Hi Sean,

I think the missing factor in the analogy is the depth of the bucket (aka ISO), then "quantity" becomes directly related to the triangle of duration (ss), width (representing aperture only) and depth (iso). The bucket can still overflow if too shallow, despite having a narrow opening, if left out too long in a downpour.

Good analogy though, preferred to baths and taps as more natural.

Just don't mention three coloured buckets and clipping when one colour overflows

Cheers,

[carregwen]

Sean

The bucket of light/water analogy reads well. I know it's simplistic, but when you are new to photography it's a hard concept to grasp, and having a simple analogy like this helps a lot.

[McQ]

I think the missing factor in the analogy is the depth of the bucket (aka ISO), then "quantity" becomes directly related to the triangle of duration (ss), width (representing aperture only) and depth (iso). The bucket can still overflow if too shallow, despite having a narrow opening, if left out too long in a downpour.

Heh, I originally had "depth/height" as the third parameter, but the only problem is that it's not independent of the other two like quantity/volume. For example, the only thing that could balance an increase/decrease in height (ISO) is to leave it out for more/less time in the rain (exposure time); width (aperture) would have no impact.

However, I do agree that depth/height is probably simpler and easier to follow...

[Dave Humphries]

Heh, I originally had "depth/height" as the third parameter, but the only problem is that it's not independent of the other two like quantity/volume. For example, the only thing that could balance an increase/decrease in height (ISO) is to leave it out for more/less time in the rain (exposure time); width (aperture) would have no impact.

However, I do agree that depth/height is probably simpler and easier to follow...

Hah, yes, I think I see what you mean! More thought later, but I doubt I'll come up with anything more useful
I was considering a straight sided (i.e. tubular) bucket, not that they're very common!

Regarding the final sentence, it all depends how hard they think about it