C & C my words??

[ericz83]

No pics on this one, but C&C my words??

OK - I know this is kind of silly, but just wanted to throw this out there as I am attempting to teach myself about photography - starting with what I was told to start with, the Exposure Triangle.

I am typing this without looking at anything else. Really just to see if I am starting off on the right foot, don't want to misinterpret something - and have it stuck in my head the wrong way! I am well aware that this will not be a technical description and may even pick the wrong words - but am I at least on the way to understanding?

First, the triangle explains how light can be manipulated to make pictures, basically. ( = exposure )

First is aperture - set in the camera through f-stops. This is basically the size of the "hole" or opening that lets light pass through to the film (or sensor, in digital). The lower the f-stop, the larger the opening. The larger the f-stop, the smaller the opening. This effects depth of field in a picture.

Then, shutter. You adjust the speed of the shutter to determine how long you let the light pass through the lens to the film. A faster shutter speed "freezes time" faster - so you would use that in sporting events, fast motion stuff. A slower shutter speed, then, obviously, lets the light pass through for a longer time. Movement will then become blurred. But you can use slow shutter speeds where there is low light and no movement, to obtain good exposure.

Lastly, ISO. ISO describes how sensitive the film (or sensor) is to light. A lower ISO means that the film is more sensitive to light. As ISO rises the film becomes less sensitive. Problems with higher ISO's is noise in the picture. I am guessing this is due to changes in light?? Higher ISO's are good for low light conditions.


OK am I on the right track? (I tried not to make this too long! )

 

[Kerbouchard]

You have ISO backwards. Higher ISO means the film is more sensitive to light. Lower ISO is less sensitive.

Other than, that's pretty much the gist of it.

 

[ericz83]

You have ISO backwards. Higher ISO means the film is more sensitive to light. Lower ISO is less sensitive.

Other than, that's pretty much the gist of it.

Ooh I did get it backwards. Thanks! Would like to say I knew that - but now I'm not so sure I did. I knew you used high ISO in low light - which make sense, higher ISO = more sensitive. See thats what I was trying to avoid, starting off wrong, haha.

Thanks a lot!

 

[dxqcanada]

With film the physical size of the silver halide grains are larger with higher ISO ... thus it looks "grainier".

 

[KmH]

F-numbers are fractions. F/2.8 is a bigger number, and is a larger lens aperture, than f/5.6 is.

The exposure triad is more easily manipulated if one understands the concept of a 'stop' of exposure.

A stop is an doubleing or a halving. A shutter speed of 1/100 is a double, 2 x longer, than a shutter speed of 1/200, which is 1/2 as long a shutter speed as 1/100 is.

ISO 100 is 2x less sensitive to light as ISO 200 is.

Both shutter speed and ISO double and halve by 2.

Lens aperture is about the area of the lens opening, not the diameter of the opening, so doubleing and halving of aperture is based on the square root of 2 - which is apporximately, 1.4142.

So a stop smaller aperture than f/2, is 2 x 1.4142 = 2.828, or rounded off - f/2.8. F/5.6 x 1.4142 = 7.9195 or - f/8..

As an example - You know you get a correct exposure with 1/1000, f/ 8, and ISO 100. However, you want want to use an aperture of f/4 to get less (shallower) depth-of-field (DoF) so the background will be more out-of-focus.
F/4 (f/8 - f/5.6 - f/4) will let in 2 more stops of light than f/8 will, so you can change the shutter speed to 2 stops quicker, or 1/4000 (1/1000 to 1/2000 is one stop, and 1/2000 to 1/4000 is the second stop).
The new settings of 1/4000, f/4, ISO 100 gives the same exposure that 1/1000, f/8, ISO 100 did, but the photo will have a shallower DoF.

You also have the option of changing the ISO 2 stops, to IS0 400, instead of changeing the shutter speed.

In other words, the following are all the same exposure, but each has a different effect on the look of the image produced:
1/1000, f/8, ISO 100
i/4000, f/4, ISO 100 - shallower DoF from the larger lens aperture, more motion stopping capability from the quicker shutter speed, the same image noise.
I/1000 f/4, ISO 400 - shallower DoF from the larger lens aperture, the same shutter speed motion stopping capability as 1/1000, more image noise from the more sensitive to light ISO setting.

 

[SCraig]

Keep in mind that those three elements describe a TRIANGLE. And like any triangle you cannot change one side without changing another side. For a given exposure, if you change aperture you will have to change shutter speed or ISO to compensate. Same for shutter speed; if you change it you will have to change aperture or ISO to compensate. Each of the three elements has distinct advantages and disadvantages and it is up to the photographer to know the limitations and determine which element to change for a given shot.

 

[ericz83]

With film the physical size of the silver halide grains are larger with higher ISO ... thus it looks "grainier".

Thanks for that explanation - I was trying to guess why it would occur. Makes sense now.

 

[ericz83]

The exposure triad is more easily manipulated if one understands the concept of a 'stop' of exposure.

Thanks, that does help. I do understand it, but I guess in the heat of the moment, at least for me anyways, don't want to figure out all of the math involved - so one can understand the stops by the dial on the camera correct? Let the camera do the math for you. (In terms of watching the meter) One tick represents one 'stop' - right? While we are on that topic - my camera can set stops on aperture by 1/2 or 1/3. The way you described is the 1/2 stop - right?

 

[ericz83]

Keep in mind that those three elements describe a TRIANGLE. And like any triangle you cannot change one side without changing another side. For a given exposure, if you change aperture you will have to change shutter speed or ISO to compensate. Same for shutter speed; if you change it you will have to change aperture or ISO to compensate. Each of the three elements has distinct advantages and disadvantages and it is up to the photographer to know the limitations and determine which element to change for a given shot.

I feel like I know why I'm adjusting shutter speed and aperture to get the picture I want - related to motion and DOF ... I understand ISO but am a bit confused. I wouldn't think you would ever want a picture with more noise, unless it is an artistic reason. But I guess, if I'm right, adjusting ISO simply allows you to get shots you might not be able to get, because of low light? But at the expense of creating more noise. Or would there be another reason to adjust ISO?

 

[WhiskeyTango]

Keep in mind that those three elements describe a TRIANGLE. And like any triangle you cannot change one side without changing another side. For a given exposure, if you change aperture you will have to change shutter speed or ISO to compensate. Same for shutter speed; if you change it you will have to change aperture or ISO to compensate. Each of the three elements has distinct advantages and disadvantages and it is up to the photographer to know the limitations and determine which element to change for a given shot.

I feel like I know why I'm adjusting shutter speed and aperture to get the picture I want - related to motion and DOF ... I understand ISO but am a bit confused. I wouldn't think you would ever want a picture with more noise, unless it is an artistic reason. But I guess, if I'm right, adjusting ISO simply allows you to get shots you might not be able to get, because of low light? But at the expense of creating more noise. Or would there be another reason to adjust ISO?

Nope. That's pretty much it. If you can get what you want at ISO 200 by adjusting shutter speed and aperture, then stay at ISO 200. You increase ISO when shutter speed and aperture won't get you there. It's particularly useful when you need shutter speeds of 1/500 or greater to freeze sports indoors...

 

[TCampbell]

Lens aperture is about the area of the lens opening, not the diameter of the opening, so doubleing and halving of aperture is based on the square root of 2 - which is apporximately, 1.4142.

The f-stop is a ratio. It's related to area, but the area by itself doesn't indicate anything meaningful until it becomes a ratio. It's the diameter of clear aperture divided into the focal length. If you have a 50mm lens with 25mm of clear aperture than you have an f/2.0 lens because 50mm (the focal length) ÷ 25mm (the clear aperture diameter) = 2.

The example I use is this:

Imagine you're in a large tunnel or cave. The cave is 10' in diameter. You are standing at the entrance to the cave. At this point there is nearly as much where you stand in the cave as there is if you take one step outside the cave.

Now imagine that you walk 10' into the cave. There's still a lot of light merely 10' inside a cave with a 10' diameter. Not quite as much light as there was when you were at the entrance. You are now at f/1.

Now walk 50' into the cave. It's starting to get darker.. but there is still enough light to see. You look back at the opening of the cave and see the round opening of light coming in, but the walls around you are dark. You are now at f/5.

Now you walk 100' into the cave. It's very dark. The walls are dark. You can scarcely see your hand in front of your face. As you look back toward the opening, it's just a small dot of light in the blackness. You are now at f/10.

The point is that the diameter or "area" of the opening never changed... it was always a 10' diameter. And yet... as you travel farther and farther in, it continues to get darker. The "ratio" of the diameter of clear aperture divided into the length (or distance from the opening) controls how much light is present. If you increased the diameter of the 100' cave to a 50' diameter then you'd have an f/2 cave. It would be the same amount of light as if you traveled 20' into the 10' diameter cave. Anytime the ratio of the diameter divided into the length is an equivalent value the amount of light delivered will also be equivalent.

The f-stops (focal ratios) are always powers of the square root of 2 (rounded to simply 1.4). This is due to the inverse square law of light (Inverse-square law - Wikipedia, the free encyclopedia) The order of "full" f-stops is f/1.0 (square root of 2 raised to the 0 power), f/1.4 (square root of 2 raised to the 1st power), f/2.0 (square root of 2 raised to the 2nd power... in other words the square root of two squared... which is simply "2"), f/2.8 (square root of 2 raised to the 3rd power), f/4 (square root of 2 raised to the 4th power), etc.

Full "stops" of shutter speed are based on halving the shutter starting at 1 second. 1, 1/2, 1/4, 1/8, 1/15th (a round-off of 1/16th because it's easier to remember), 1/30th, 1/60th, 1/125th (notice that's another "round off" to keep the numbers easier to remember), 1/250th, 1/500th, and 1/1000th. The very fractional round offs which make it easier to memorize the shutter speeds are not enough to have any significant impact on exposure.

 

[KmH]

Thanks, that does help. I do understand it, but I guess in the heat of the moment, at least for me anyways, don't want to figure out all of the math involved - so one can understand the stops by the dial on the camera correct? Let the camera do the math for you. (In terms of watching the meter) One tick represents one 'stop' - right? While we are on that topic - my camera can set stops on aperture by 1/2 or 1/3. The way you described is the 1/2 stop - right?

Most DSLR cameras are shipped with default settings that adjust exposure settings in 1/3 stop increments per click, which allows finer exposure control. many DSLR's also allow setting to full stop steps.

Here is a 1/3 stop scale:

0.7

0.8

0.9

1.0

1.1

1.2

1.4

1.6

1.8

2

2.2

2.5

2.8

3.2

3.5

4

4.5

5.0

5.6

6.3

7.1

8

9

10

11

13

14

16

18

20

22

Here is a 1/2 stop scale:

0.7

0.8

1.0

1.2

1.4

1.7

2

2.4

2.8

3.3

4

4.8

5.6

6.7

8

9.5

11

13

16

19

22

27

32

 

[ericz83]

Thanks, that does help. I do understand it, but I guess in the heat of the moment, at least for me anyways, don't want to figure out all of the math involved - so one can understand the stops by the dial on the camera correct? Let the camera do the math for you. (In terms of watching the meter) One tick represents one 'stop' - right? While we are on that topic - my camera can set stops on aperture by 1/2 or 1/3. The way you described is the 1/2 stop - right?

Most DSLR cameras are shipped with default settings that adjust exposure settings in 1/3 stop increments per click, which allows finer exposure control. many DSLR's also allow setting to full stop steps.

Here is a 1/3 stop scale:

0.7

0.8

0.9

1.0

1.1

1.2

1.4

1.6

1.8

2

2.2

2.5

2.8

3.2

3.5

4

4.5

5.0

5.6

6.3

7.1

8

9

10

11

13

14

16

18

20

22

Here is a 1/2 stop scale:

0.7

0.8

1.0

1.2

1.4

1.7

2

2.4

2.8

3.3

4

4.8

5.6

6.7

8

9.5

11

13

16

19

22

27

32

Thanks - this really helps! By the way, I am reading Understanding Exposure - so I am not just throwing out questions out here without researching. I was just asking to make sure I was understanding what I was reading! Everyone has been a big help on here!