Trying to get my head around Exposure!!

[nycphotography]

Basically, an exposure is a "bucket filled with light".

It helps to visualize a graduated cylinder filled with water. Imagine targeting the 250cc line on a 500cc graduated cylinder as the correct amount of light / water for an exposure.

When taking the exposure, it's like filling the graduated cylinder with a hose.

There are FOUR variables in the process of filling a glass of water.
1) the size of the glass
2) the size of the hose
3) the pressure of the water
4) how long the hose is on

Same thing for an exposure
1) the iso of the film (equiv to the size of the glass)
2) the aperture (size of the hose)
3) brightness (the pressure of the water)
4) shutter speed (how long the hose is on)

In pseudo math, a proper exposure is BALANCED and is: ISO = (some function of) Aperture, Brightness and Time.

Now, if you are UNDER exposed (ie, only getting 125cc of water instead of 250 in a 250c glass)
You can do four things.
1) You can INCREASE the pressure (brighter light = more pressure)
2) You can increase the size of the hose (lower aperture = bigger hose)
3) you can get a smaller glass (higher ISO = smaller glass)
4) leave the water on less time (faster shutter = less time)

In photography, "stops" for everything is DOUBLE and HALF except for aperture (which is an area so it's squares and halves, but luckily, you can simply memorize the fstop series as 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32)

The advantage of fstops is that they can simply be added and substracted. So ISO = APERTURE + BRIGHTNESS + SPEED. If for ANY exposure where the equation is in balance (ie you are getting 250cc in a 205cc cup) you can make "OFFSETTING" "FULL STOP" adjustments and stay in balance.

For example, you can make any of the following adjustments and stay in balance:

one stop faster on shutter (1/125 -> 1/250) and one stop faster on ISO (400 -> 800) (off setting because opposite sides of equality / balance point)

one stop smaller in aperture (f4 -> f5.6) and one stop slower in shutter (1/250 -> 1/125)

one stop dimmer in light / flash (1/4 power -> 1/8 power) and one stop wider in aperture (f5.6 -> f4)

you can also make multiple adjustments at once as long as they all add up / balance across the = sign. One two stops slower on ISO, 1 stop slower on shutter, one stop wider in aperture.

And if I'm off (say -2EV/stops) on the light meter, I can fix that, AND make other changes all at the same time with one set of adjustments. Lessee... I need to BUY two stops MORE light (water). Let's get half by making the glass one size smaller (ISO 100 -> 200) and let's get the other half by making the aperture one size bigger (f4 -> f2.8). Now I've made two unbalanced adjustments that cumulatively get me the 2 stops of light I need.


The advantage of fStops is that they're "normalized units" so you can simply add and subtract them. I find that thinking of it as stacks of "fstops" on balance scale (which is much simpler than water and cups, thus the advantage of normalized units) can also help. Is the left side two "fstops" off from the right? Start adding stops on one side or taking them away from the other until you get it in balance.


Hope this helps.

 

[nycphotography]

DOF has nothing to do with "exposure", other than giving preference (priority) to one single variable (aperture) over all others.

For shallow DOF, you want wide apertures (low fstops). For deep DOF you want small apertures (high fstops).

Also, somewhere above, focal length was mentioned. Focal length is relevant to DOF, but has nothing to do with exposure (except as a lens designer, which is not us as photographers).

 

[Mike_E]

Did you ever cook a frozen pizza?

The pizza is the subject.

The oven temperature is the aperture and the time is the shutter speed.

The subject is really not going to change as you're shooting it so don't worry about that.

The amount of heat needed to cook the pizza is exactly like amount of light energy needed to cook an image, you need a certain time AT a certain temp. IOW you need a certain amount of light for a certain amount of time.

The strength of the light determines how big a hole (your aperture) you need to let enough in for a set time.

So, you could cook you pizza at 400 degrees for 20 minutes or 375 degrees for 25 minutes. Or, you could take you photo at f2.8 for 1/30th of a second or you could use f5.6 at 1/60th of a second.

Digital cameras are designed to work the same as film cameras and film cameras all worked on chemistry, everything depends on the amount of light energy you have to work with and how long it took to make the chemistry of the film work..

 

[Light Guru]

Did you ever cook a frozen pizza?

The pizza is the subject.

The oven temperature is the aperture and the time is the shutter speed.

The subject is really not going to change as you're shooting it so don't worry about that.

The amount of heat needed to cook the pizza is exactly like amount of light energy needed to cook an image, you need a certain time AT a certain temp. IOW you need a certain amount of light for a certain amount of time.

The strength of the light determines how big a hole (your aperture) you need to let enough in for a set time.

So, you could cook you pizza at 400 degrees for 20 minutes or 375 degrees for 25 minutes. Or, you could take you photo at f2.8 for 1/30th of a second or you could use f5.6 at 1/60th of a second.

Excellent analogy!

 

[480sparky41 40]

Did you ever cook a frozen pizza?

The pizza is the subject.

The oven temperature is the aperture and the time is the shutter speed.

The subject is really not going to change as you're shooting it so don't worry about that.

The amount of heat needed to cook the pizza is exactly like amount of light energy needed to cook an image, you need a certain time AT a certain temp. IOW you need a certain amount of light for a certain amount of time.

The strength of the light determines how big a hole (your aperture) you need to let enough in for a set time.

So, you could cook you pizza at 400 degrees for 20 minutes or 375 degrees for 25 minutes. Or, you could take you photo at f2.8 for 1/30th of a second or you could use f5.6 at 1/60th of a second.

Excellent analogy!

Yeah, but I bet he's not gonna buy me dinner. And I'm hungry now!

 

[TCampbell]

I do understand how to get a basic correct exposure by adjusting my settings and looking at the light meter. And I think I pretty much know how to set my ISO accordingly. What I don't know how to do is automatically know which Aperture or Shutter Speed to use based on the scene. For instance...If I want to take a photo of my daughter outside and I want good DOF behind her, I know that my Aperture will give me the DOF but I don't automatically know which Aperture setting to use to give me that DOF and which Shutter Speed to use to go with it to give me a correct exposure.

If anyone knows of a super simple way to explain this, that would be great! TIA

Brian talks about this in his book. Brian calls what you're looking for the "creatively correct" exposure (rather than simply the "correct" exposure). This is because for any given shooting situation there are LOTS of different possible settings I can use to take the same shot and get the right amount of light, but some combinations of settings will give me a result which is more pleasing to the eye.

If you understand how you can decrease one setting, but compensate by increasing another setting to still get the same total value of light, then you understand the exposure triangle.

If the subject is NOT moving then I am completely unrestricted in my settings. If the subject is moving then I may need to use a shutter speed fast enough to "freeze" the action. Even if I want to show some motion blur (which can sometimes be a nice artistic effect), there will be shutter speed which is just right to show some blur without ruining the shot by being too fast or too slow.

If your girl is not moving, then you've got some factors to consider:

Your photo has a primary subject (your daughter) and then you've got a background that you can see. A lot of people don't give much though to the background, but in photography, everything counts. If you're taking a photo of your daughter in front of a beautiful landscape and you WANT the landscape detail to be part of the shot, then you want a very large depth of field. In that case you'd start by setting an f-stop (aperture) that creates a larger depth of field. The larger the f-stop number, the larger the depth of field (focused area). So perhaps you choose f/16. Having established your f-stop, choose a low ISO to keep the digital noise to a minimum (e.g. ISO 100) and then choose a shutter speed (e.g. 1/100th). BTW, I can tell you that if your daughter is in full sun at mid-day, it will actually be ISO 100, f/16, and 1/100th... that particular combination is called the "Sunny 16" exposure.

You COULD also decrease the aperture to f/2.8 (5 stops higher: 16 -> 11 -> 8 -> 5.6 -> 4 -> 2.8) and you'd compensate by increasing the shutter speed to be 5x faster (1/100th -> 1/200th -> 1/400th -> 1/800th -> 1/1600th -> 1/3200th). HOWEVER, if you do that you'll get a very narrow focused area. Your daughter might be nicely focused but the background will be completely blurred. It turns out you might actually WANT the background to be completely blurred... it'll be an abstract blurry suggestion of a landscape but it'll still show the color and the sharply focused daughter set against the very blurry background helps call attention to the fact that your daughter is the subject.

The bottom line here is that there's no "right" way to shoot this because it's up to you if you want the background to be sharp vs. blurry. If it were JUST a landscape with no daughter in the foreground then you'd want to maximize the focused area and the high f-stop (tiny aperture opening) is the way to go.



Suppose it's not just your daughter... suppose your daughter brings over lots of friends and you want a group shot. If her friends are all neatly lined up so that they are at the SAME focused distance, then the f-stop doesn't matter because even a narrow depth of field will get them all nicely focused. But if they're a bit more randomly distributed or lined up front to back (rather than side to size) NOW you want a longer depth of field. When the shot your taking doesn't require control over the depth of field then picking a middle aperture such as f/8 will tend to give the sharpest results.

Notice that in ALL OF THESE EXAMPLES so far, I'm constantly talking about aperture. If you are truly free to pick any exposure then pick the aperture FIRST. No it's not a rule. It's just a general guideline that tends to give you the most control.



If the subject IS moving, then set the shutter speed first and set it to either freeze action or (and this may take a little practice on your part) allow a suggestion of motion blur into the image. This intentional blur queues the viewer to realize that things were moving. Usually you try to follow the subject so that they are relatively sharp and it's the background which appears to be moving. It takes practice. They call this a "panning shot" because you pan the camera from left to right or right to left while shooting. When you find the shutter speed which works best, adjust the aperture to something which provides an adequate focused area and then set the ISO to the lowest value possible to minimize the digital noise in the image.

 

[km78]

Your photo has a primary subject (your daughter) and then you've got a background that you can see. A lot of people don't give much though to the background, but in photography, everything counts. If you're taking a photo of your daughter in front of a beautiful landscape and you WANT the landscape detail to be part of the shot, then you want a very large depth of field. In that case you'd start by setting an f-stop (aperture) that creates a larger depth of field. The larger the f-stop number, the larger the depth of field (focused area). So perhaps you choose f/16. Having established your f-stop, choose a low ISO to keep the digital noise to a minimum (e.g. ISO 100) and then choose a shutter speed (e.g. 1/100th). BTW, I can tell you that if your daughter is in full sun at mid-day, it will actually be ISO 100, f/16, and 1/100th... that particular combination is called the "Sunny 16" exposure.

The sentence in bold is exactly what I am having the hardest time understanding. It is automatically knowing which Shutter Speed to use after I have determined the Aperture that I want or vice versa. Am I just suppose to adjust the Shutter Speed at this point until the light meter reads a correct exposure, or is there a specific formula that I need to memorize? Lets use the Sunny 16 exposure for instance. Say I want the background in full focus so I know that I need to use a large f stop number and I choose f/16. Now, I know that it is sunny outside so I choose to use an ISO of 100. What I don't know at this point is what my shutter speed will need to be to make the exposure correct. At this point (not knowing about the Sunny 16 rule), would I then just adjust my shutter speed until my camera meter reads a correct exposure (which is what I would normally do), or should I automatically know that at f/16 I will need to use a shutter speed of 1/100?

 

[nycphotography]

Your photo has a primary subject (your daughter) and then you've got a background that you can see. A lot of people don't give much though to the background, but in photography, everything counts. If you're taking a photo of your daughter in front of a beautiful landscape and you WANT the landscape detail to be part of the shot, then you want a very large depth of field. In that case you'd start by setting an f-stop (aperture) that creates a larger depth of field. The larger the f-stop number, the larger the depth of field (focused area). So perhaps you choose f/16. Having established your f-stop, choose a low ISO to keep the digital noise to a minimum (e.g. ISO 100) and then choose a shutter speed (e.g. 1/100th). BTW, I can tell you that if your daughter is in full sun at mid-day, it will actually be ISO 100, f/16, and 1/100th... that particular combination is called the "Sunny 16" exposure.

The sentence in bold is exactly what I am having the hardest time understanding. It is automatically knowing which Shutter Speed to use after I have determined the Aperture that I want or vice versa. Am I just suppose to adjust the Shutter Speed at this point until the light meter reads a correct exposure, or is there a specific formula that I need to memorize? Lets use the Sunny 16 exposure for instance. Say I want the background in full focus so I know that I need to use a large f stop number and I choose f/16. Now, I know that it is sunny outside so I choose to use an ISO of 100. What I don't know at this point is what my shutter speed will need to be to make the exposure correct. At this point (not knowing about the Sunny 16 rule), would I then just adjust my shutter speed until my camera meter reads a correct exposure (which is what I would normally do), or should I automatically know that at f/16 I will need to use a shutter speed of 1/100?

SIMPLE ANSWER: At this point, put your camera in A mode, set the aperture to f16, the ISO to 100. You have now "fixed" three of the four variables in exposure, and your camera can pick the right shutter speed.

MORE ADVANCED ANSWER: You can ALSO put your camera in spot meter mode, and take readings at various points which you may want to be "the exposure point",choose the one you want, and set that in M mode.

For example, if you have back lit (sun behind) subject (face): You can spot meter on the sky, and set that as your shutter speed, then get a rich or moody sky and a silhouette for the subject. OR you can spot meter on the subject and set that as your shutter speed, and get a properly exposed face, and a sky that's blown out to white. OR, you can let the camera pick an "average reading" and get an overexposed sky and underexposed face.

EVEN MORE ADVANCED ANSWER: OR, you can spot meter on the sky, and set that as your shutter speed in M mode, THEN SET YOUR SPEEDLIGHT TO TTL, spot meter on the face (in M mode), and shoot. Now you can get a rich or moody sky, and still get a properly exposed face. While different flashes work different ways, and you may have to manually adjust your flash instead of letting it TTL, this in principle is what people mean by "fill flash".

Except most of the time fill flash will still let the camera pick the middle exposure (over sky, under face) and fix the face, but still leave the sky over. By using M mode, you can force the variable the camera lacks the power to overcome (sky) and let it fix (flash) the one it can.

 

[pgriz]

The camera's meter reads reflected light and has been programmed to show zero when the exposure of the metered area results in a tone of medium grey (about 18%). This works reasonably well for "average" scenes which have a mix of tones. If you're shooting a white cat on snow, the meter will be fooled (it doesn't know your scene is mostly white), and it will show an exposure that renders the image medium grey. So under this situation, you'd need to compensate (the exposure compensation function) by a suitable amount, so that the white areas stay white (but not blown out). An exposure adjustment of 2 stops over will render the scene closer to what it should be. Same situation if you're shooting a black cat on black velvet. Camera will overexpose, rendering the cat and velvet grey. You need to override the meter and dial in the appropriate amount of underexposure to get the black subjects back to black tonality. Getting away from the issues of reflected light metering, you could consider using an incident light meter which measures how much light is falling on the scene, and gives you a reading independent from the tone of any subject.

 

[Mike_E]

Km78, you're trying too hard.

All that's going on here is that you need a certain amount of energy (light) to make the image come out right- in other words if you took a photo of an 18% grey card it would look like 18% grey.

There are 3 basic adjustments that you can use: ISO (this is like putting the other two on a shelf, a higher shelf makes them work faster and a lower shelf makes them work slower), aperture (this is how you control which size hole you let the energy in with, the larger the hole [[the smaller the F#, yeah, I know but it's a math thing and just the way it's called]] the faster it pours in and the smaller the hole the slower it goes and then the shutter speed (this fine tunes how much energy you get).

It's just that simple and it's the first step on a ladder leading to where you want to be. Relax and stand on it, it will not let you down.

The next step is playing around with your shutter speed. You need this so that you can stop the subjects from being blurred- or to blur them if you want it that way. With each click of the shutter speed in one direction you will have to click the aperture the other way- yes you can click the ISO but let's not worry about that right now.

You still need just the right amount of energy to cook the shot, right? So, to get the right amount of energy through your lens in a shorter or longer time you have to adjust the size of the hole- the aperture- to get the same amount through.

That's step 2.

The next step is understanding that these things aren't made to be hard, if you change the shutter speed and then have to adjust the aperture the other way then if you adjust the aperture then you have to adjust the shutter speed the opposite way too. Adjusting the aperture is what you do to tell the camera how much of the photo you want to be in focus. A small hole tightens up the focus so that a lot of the picture is in focus (small hole = bigger F# [that math thing again] and a bigger aperture [lower F#] loosens up the focus so that less of the picture is in focus.

That's step 3.

Now, ISO. ISO is the shelf you put the other two on so that they work in the real world. If you put the ISO on a higher shelf then the energy works faster so that you can use either a faster shutter speed or a smaller aperture depending what you want. If you use a lower ISO then you can slow down the shutter or use a bigger aperture, whichever you like.

And that's step 4 and now you should be able to see over the trees and get a clear shot of the forest.

Finally, it really is a Zen thing, be the camera. If you are so focused (yeah, that's a pun) on you holding the thing and trying to make it work under your rules you are going to have a bothersome time. Be the camera and let it be itself and just except that it will work out for the best.

Good luck!

 

[Byrin]

I recommend watching this video from youtube. Very informative. It has answered all questions my son and I had on exposure triangle. good luck.

 

[Rick50]

This has been an interesting read. I mean no offense to all the posters, you all have made good descriptions but my feeling is enough is enough. It's time to practice.
I don't learn this way very well. I mean just read, read, read. I need hands on practice. Especially when a subject is new to me. What works for me is this.

I take one step at a time. Read a little then go try it. When I can do it instinctively then I will remember it. When I get to much information I get out with my camera I become all thumbs and forget everything I read. Frustrating. The best way I know to learn the exposure triangle is to practice one step at a time. One day just play with the shutter speed and let the camera do the rest. Tv mode on canon. Anyway you get the idea, eventually it all sinks in.

Practice, practice, practice....