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10/02/2003 09:42:12 PM · #1 |
Greetings...
I am working on a tutorial article on exposure. Here's what I have so far... I would love to hear any feedback on how I can improve this...
Exposure:
(a work in progress)
Exposure is the process of recording light onto film or a digital sensor. When we press the camera button, several elements allow this exposure to happen. The lens opening (aperture) allows light into the lens. The shutter opens long enough to expose the film. The film sensitivity is described in terms of an ISO number.
There are three elements of exposure: Aperture, Shutter Speed, and ISO.
Aperture:
The aperture of your camera lens is like the iris of your eye. It opens wider to allow more light into the lens or it closes down to reduce the amount of light. The aperture also controls your depth of field, or the amount of your scene that is in focus. Wider apertures produce less depth of field and smaller apertures produce more depth of field. When you see a portrait photograph where the subject is in focus and the surroundings are blurry, the photographer has likely chosen a large aperture for the photo. The purpose of this technique is to make the subject the most prominent part of the photograph. When you see a photograph where there is a lot of depth and everything is in sharp focus, the photographer probably used a small aperture setting.
Aperture is referred to as the "F Number". Increases and decreases in aperture settings are referred to as "stops." A one stop change in the size of the aperture either doubles or halves the area of the opening. The following chart describes the aperture settings (in full stop increments) of a standard 50mm lens:
F Number
Aperture Diameter
Aperture Area
f/2.0
25.0 mm
491 sq mm
f/2.8
17.9 mm
250.4 sq mm
f/4.0
12.5 mm
122.7 sq mm
f/5.6
8.9 mm
62.6 sq mm
f/8.0
6.3 mm
30.7 sq mm
f/11.0
4.5 mm
16.2 sq mm
f/16.0
3.1 mm
7.7 sq mm
f/22.0
2.3 mm
4.1 sq mm
As you can see in this chart, each one stop change in the aperture changes the area of the aperture by either twice or half (roughly, but very close). The "F" describes the aperture diameter in terms of focal length divided by aperture number. The numbers in the above chart for diameter are derived from this equation.
Shutter Speed:
The shutter in your camera is a window that opens and allows the light to hit the film or the digital sensor in your camera. The shutter may be opened for various lengths of time based on the aperture and ISO settings you have chosen or that have been automatically chosen for you. Shutter speeds are used to either freeze motion or to create motion in a photograph. Slower shutter speeds allow your moving subjects to be a bit blurred, depending on the speed you choose. The motion blur creates a sense of movement in the photograph. Faster shutter speeds freeze motion.
Changes in shutter speed can also be examined in terms of "stops". Doubling or halving the shutter speed is a one stop change in either direction. The following chart shows the standard one stop changes in shutter speeds:
Shutter Stops
1"
1/2"
1/4"
1/8"
1/16"
1/30"
1/60"
1/125"
1/250"
1/500"
1/1000"
1/2000"
ISO:
The ISO number of the film or digital sensor determines how sensitive the film is to the light coming in through your lens. Lower number ISO settings are less sensitive to light and higher numbers are more sensitive. ISO 200 film is twice as sensitive as ISO 100, which means it will expose twice as fast. ISO 400 film is twice as sensitive as ISO 200, which means it will expose twice as fast as 200 or 4 times as fast as 100.
The purpose of changing the film sensitivity is primarily to allow a photographer to get a faster shutter speed when it is desirable to do so. Sports action photographers often like to freeze the action. In many cases, they are not close enough to the action for a flash to work effectively. Using a higher ISO film will allow a correct exposure at a faster shutter speed. This will be discussed more later.
Metering:
The "meter" inside your camera examines the amount of light in the scene. If you have your camera set in automatic mode, the meter will set your aperture and shutter speed to give you a correct exposure on the given scene. If you are in aperture priority mode, the camera will automatically select a shutter speed to go with the aperture you have chosen. If you are in shutter priority mode, the camera will select an aperture to go with the shutter speed you have chosen.
The meter works several different ways.
Average Metering:
In the normal default "average" metering mode, your camera examines multiple areas of your composition to choose aperture and shutter speed settings. In many cases, this mode will produce a good exposure.
Center Weighted Metering:
In the center weighted metering mode, your camera only examines the area in the center of your composition to determine the correct camera settings.
Spot Metering:
In the spot mode, the camera only samples a very small area in the center of your composition to determine the correct camera settings.
Metering is very important in creating a correct exposure. Certain compositions are difficult to "meter" because there are extreme variations between light and dark in the same area. Other scenes, which are evenly lit are much easier to meter correctly. A scene that is primarily white is difficult to meter. A scene that is primarily black is equally difficult to meter. Our objective with metering is to find the correct aperture and shutter settings to create a "correct" exposure. Learning to use your spot meter effectively will help you get a correct exposure in just about any situation. You must also keep in mind that some situations are simply BAD photo opportunities.
LIGHT is everything. There is good light and bad light. Part of learning exposure and photography in general is learning how to find the good light. There are certain situations where, no matter how hard you try or how much you know, will not produce an excellent exposure.
"Correct" Exposure Combinations:
There is more than one "correct" way to expose a photo. Let's look at an example:
We point our camera at a particular scene. The camera "meters" the scene and decides that it will set your aperture for f/4.0 and your shutter speed to 1/125" with an ISO setting of 100. We could use this as our baseline for making manual exposure adjustments based on our desired outcome of the photograph.
When preparing for a photograph, you need to spend a moment thinking about your desired result. Is depth of field more important or is shutter speed more important? Do you want a very shallow depth of field to blur out a background? Do you want a deep depth of field to have everything in sharp focus? Do you want to freeze the action? Do you want to create some motion blur? Answers to these questions will help you determine what adjustments you want to make to your baseline exposure readings.
If you want a shallow depth of field, you will want to use a wider aperture. We have several ways to accomplish this from our baseline exposure of f/4.0 and 1/125" at ISO 100. If we increase the size of our aperture to f/2.8 (a one stop increase), we must increase our shutter speed by one stop to 1/250". Making this change will render the same exposure levels and give us a more shallow depth of field. By increasing the size of our aperture, we must increase the shutter speed. Increasing the size of the aperture allows more light into the lens. If we don't increase the shutter speed by the same number of "stops" we will end up over exposing the photo by one stop.
If we decide that we want a deep depth of field in this photograph, we would want to reduce the size of the aperture. If we wanted to change our aperture to f/16, we would need to determine how many stops that is and then decrease our shutter speed by the same number of stops. By referring back to the aperture chart above, f/4.0 to f/16 is 4 stops. So if we change our aperture to f/16, we should change the shutter speed from 1/125" to 1/8" to produce the correct level of exposure at the new aperture size.
Maybe we want to freeze the action in our photo. Freezing action requires a fast shutter speed. It's generally a good idea to shoot at 1/250" or faster to freeze action. 1/500" and 1/1000" is even better. From our baseline settings of f/4.0 and 1/125", if we want to change the shutter speed to 1/500", we must increase the aperture by two stops to compensate for that change. A two stop increase in aperture from f/4.0 would be f/2.0, so our new combination would be f/2.0 and 1/500".
If we want to create a little motion blur in our photo, we need to choose a slower shutter speed. If we switch from 1/125" to 1/30", that is a two stop increase in shutter speed. We must decrease the size of our aperture by two stops as well. That would be from f/4.0 to f/8.0 in this case.
These examples should give you an idea of how to adjust manual exposure settings based on a meter reading. There are other types of metering techniques that I will discuss later.
There are also some special situations where the ISO setting comes into play when adjusting exposure. The ISO setting comes into play most frequently when you are unable to get a fast enough shutter speed to meet your needs. If you are working in a poorly lit environment without a tripod, you need to have (in general) a shutter speed of 1/60" or faster to help eliminate camera shake and the blur caused by it. Let's look at another example...
You are at a party... The indoor lighting is not that great. You look at your camera meter readings for the scenario. The camera decides that f/2.8 and 1/15" at ISO 100 is the required setting for a correct exposure. 1/15" is too slow for the average hand held photo. We need 1/60" or faster. 1/125" would be even better. If we want to get to 1/125", we would have to increase the size of our aperture by 3 stops. Chances are, our lens won't allow an aperture larger than f/2.8. If we increase our ISO setting by 3 stops, we should be able to get the 1/125" shutter speed. If our ISO is set at 100, we could increase it to 800. Making this change would allow us to get our correct exposure at f/2.8 and a shutter speed of 1/125". Stops on the ISO scale are also calculated by doubling or halving the ISO number.
Special Metering:
Your spot meter is your friend and you need to learn how to use it effectively to find the best exposure for different lighting situations. Since the spot meter only looks at a very tiny portion of a scene, you can use it to find a "neutral" color area to set your exposure. When you are in manual exposure mode with the spot meter on, you can move your camera around and watch the meter readings. The readings will tell you how far over or under the exposure will be for whatever aperture/shutter/ISO combination you are working with.
Maybe you want to make a portrait photo in an outdoor environment where the sun is behind your subject. Normal average metering would likely create an exposure that would make the face of your subject dark and under exposed. However, if you spot meter on your subject's face that is in the shadows, you can adjust your exposure to bring the exposure to a level where the face will be properly exposed.
In a nutshell, you want to spot meter on whatever part of your scene that needs to be correctly exposed if the entire scene can't be.
The Gray Card:
Photographers often use a tool called a "gray card" to properly meter a scene. A gray card is just that... a gray card. The gray card is going to reflect 18% of the light that falls on it. When you spot meter on the gray card and set your correct exposure based on that reading, you will have proper exposure if the scene is evenly lit.
A gray card is very useful for metering scenes that are primarily dark or primarily white. If our card was black instead of gray, it would reflect approximately 9% of the light that falls on it. If our card was white, it would reflect approximately 36% of the light that falls on it. If we metered on a white card, our resulting photograph would be underexposed by one stop. If we metered on a black card, our result would be over exposed by one stop. Metering on the white card, which reflects twice as much light as the gray card would cause us to expose for twice the amount of light that we actually have to work with. The opposite is true for a black card. We would expose for half the light that we actually had available in the scene.
Metering on white and black is good to think about though. If you are out shooting a snow scene where white is the dominant color in the photograph, and you forgot your gray card, you can work with this knowledge. You simply meter on the snow and adjust that reading to overexpose by one stop. This would mean choosing an aperture one stop larger or cut the shutter speed in half. If our meter tells us that we need an exposure of f/5.6 and 1/500" at ISO 100, we would either adjust the shutter speed to 1/250" or adjust the aperture to f/4.
[sample photo of white dominant scene with evaluative metering]
[sample photo of white dominant scene spot metered on the white]
[sample photo of white dominant scene spot metered on white and adjusted +1]
If we were photographing a scene that was primarily dark, we could meter on a dark area and then adjust the exposure in the other direction by one stop. We would decrease the aperture size by one stop or double the shutter speed. If our meter tells us that we would need a an exposure of f/4 and 1/60" at ISO 100, we would either adjust the aperture to f/5.6 or adjust the shutter to 1/30" to get the correct exposure for the scene.
[sample photo of dark dominant scene with evaluative metering]
[sample photo of dark dominant scene spot metered on the dark]
[sample photo of dark dominant scene spot metered on white and adjusted -1]
(to be continued)
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10/02/2003 10:37:30 PM · #2 |
I'm not sure of your target audience, but I am assuming that you are going after people new to photography. I think you have done a good job getting all the details in here, but to a newbie, it may be like drinking from a firehose. You may risk overwhelming or intimidating them with too much too soon. When I was learning the basics of exposure, I always liked the metaphor of the film being like a glass of water that you are trying to fill to the top. The shutter speed is like the time it takes to fill the glass. The aperture is like how far the faucet is turned on.
Very basic, but it's enough to get concept across. Then you can fill in the details.
Also, you discuss DOF through the portrait example right away. I think that will confuse people. You might consider discussing how different aperture/shutter speed combinations provide equivalent exposure levels and then discuss why you would choose different combinations i.e. stopping motion and controlling DOF. Then finally bring in the concept of ISO. In the glass example, it would be equivalent to having differnet size glasses.
This is just my $0.02.
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10/02/2003 11:47:47 PM · #3 |
John, for whom is this article intended? Since you indicated it's a tutorial, do you expect a range of photographic expertise from your audience? If you expect new photographers to read this article, might I suggest having links to additional articles, footnotes, or an appendix/glossary in which new terms and ideas are given more attention. Some terms which might deserve such attention are: aperture, shutter, stop/f-stop, f-number, focal length, ISO, et cetera. The critical term in your article is "stop" or f-stop and you might consider indicating that this is effectively your exposure "unit".
You provide a sample table for a 50mm lens, demonstrating the relationship between f-number and the diameter and area of the aperture. These numbers are distracting to new photgraphers and the f-number is really the thing that needs their attention. I would suggest that a simple example comparing two apertures might get condense the message into a more digestible size.
You sometimes refer to "film or a digital sensor" and sometimes only refer to "film"/"film sensitivity". I recommend introducing the idea early on that where you use "film" you mean either chemical film or digital film/sensor. You can then use just "film" consistently throughout your article. A footnote might be appropriate for this.
Another term that is not consistently used is "stop", which is sometimes quoted and other times not. In order to avoid confusion, you might consider using f-stop when you are referring to the unit and use stop as a verb (e.g., stopping down). Similarly, you might consider using f-number when you are referring to the unitless value (like f/22) and aperture when you are referring to the lens iris opening.
I provide additional annotations below:
Originally posted by jmsetzler:
There are three elements of exposure: Aperture, Shutter Speed, and ISO. |
I would add that "available light" is the 4th variable here, but that it is exceptional in that it is not always under one's control. Recall that (delta)EV 1 is equivalent to a full stop and can/should be taken into account. Your article details the first three variables and how one can change/control them to suit exposure needs. Near the end there is a discussing of metering and this is where the "available variable" comes into play. I would suggest being more explicit about this 4th variable.
Originally posted by jmsetzler:
The "F" describes the aperture diameter in terms of focal length divided by aperture number. |
The "f" in "f-number" refers to the focal length, so I assume you mean f-number where you have written "F". The phrasing here seems a little awkward particularly where the f-number (the 22 in f/22 for example) is (approximately) the inverse of focal length divided by aperture diameter. In any case "divided by aperture number" should read "divided by aperture diameter". The first "aperture diameter" can probably be replaced with just "aperture".
Originally posted by jmsetzler:
Changes in shutter speed can also be examined in terms of "stops". Doubling or halving the shutter speed is a one stop change in either direction.
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And I think it is here that you have hit upon an important element, that f-stop is the "unit" by which exposure is measured/adjusted. All the exposure variables (aperture, shutter speed, ISO, and [available] light) are best viewed in relation to the f-stop "unit". I feel the article would be improved if this kind of information was added as a preamble of sorts.
Originally posted by jmsetzler:
Metering: |
This is the section which brushes upon the idea of the 4th exposure variable, but only in terms of how it is measured and what other variables to change when available light doesn't correspond to your desired shooting conditions. Perhaps this section could be improved by exploring this relationship (metering/measuring available light and f-stop).
Originally posted by jmsetzler:
The "meter" inside your camera examines the amount of light in the scene. |
I would not quote "meter" here. There really is a meter in the camera and it's making those measurements of available light to arrive at reasonable values for your two primary (and volatile) variables, aperture and shutter speed.
Originally posted by jmsetzler:
LIGHT is everything. There is good light and bad light. |
I think this touches on the idea that good & bad light are correlated with (not) fitting into the range of reasonable f-stop limits. Sometimes (or often), our desired vision is restricted by lens or camera limitations. Some lenses just can't go wider than f/4 for example. Below, you might want to touch on lens/camera limitations, especially in the example you gave of going two f-stops from f/4 to f/2. Many lenses can't get there.
Finally, based on reading over a luminous-landscape.com, metering for digital cameras, especially when shooting in raw mode, seems to be different than for (chemical) film. The article, Expose Right contains some information that might be useful as a digital addendum to your article, especially as it related to exposure.
Message edited by author 2003-10-02 23:49:48. |
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10/03/2003 12:20:43 AM · #4 |
Originally posted by jmsetzler:
Exposure:
There are three elements of exposure: Aperture, Shutter Speed, and ISO.
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You might think about the relationship of light into this equation. Also, you've chosen elements which the user can control on the camera.
You might consider a user-friendly rewrite. I fully agree with Spazmo's point about your target audience. You seem to be aiming for beginners, but you treat a lot of the actual concepts rather dryly and introduce them quickly without much glossing. His idea of using metaphors is valuable.
You need to consider your audience more carefully. Your text contains a lot of information, some of which not entirely connected to exposure and more at home in a general 'how to photograph' tutorial. For example, for an intended audience of consumer-class digital owners wanting to move up to the prosumer class, you can take less for granted than for an audience of prosumers having problems with exposure and needing a quick fix.
Originally posted by jmsetzler:
Aperture:
The following chart describes the aperture settings (in full stop increments) of a standard 50mm lens:
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Again, the issue of readership arises. If you're writing a tutorial for a digital beginner audience, the early introduction of this chart will be meaningless. The numbers, themselves, are dry, with no application suggested.
Originally posted by jmsetzler:
ISO:
The ISO number of the film or digital sensor determines how sensitive the film is to the light coming in through your lens. Lower number ISO settings are less sensitive to light and higher numbers are more sensitive. ISO 200 film is twice as sensitive as ISO 100, which means it will expose twice as fast. ISO 400 film is twice as sensitive as ISO 200, which means it will expose twice as fast as 200 or 4 times as fast as 100.
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For a beginner (which I'm assuming is the target audience), the terms 'sensitive' and 'fast' are not easy ones to conceptualise. You seem to be assuming that the common English word provides enough information about the precise photographic meaning, a mistake, I believe. Metaphors might help here.
Originally posted by jmsetzler:
Metering:
The "meter" inside your camera examines the amount of light in the scene. If you have your camera set in automatic mode, the meter will set your aperture and shutter speed to give you a correct exposure on the given scene. If you are in aperture priority mode, the camera will automatically select a shutter speed to go with the aperture you have chosen. If you are in shutter priority mode, the camera will select an aperture to go with the shutter speed you have chosen.
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Beyond the points mentioned above, you have a lot of redundancy in your expression. If you'd like my opinion about actual writing techniques, I'd be happy to oblige. Here, I'll give just one example.
"If you have your camera set in automatic mode" can be reset simply as 'In automatic mode' without any loss of meaning.
Originally posted by jmsetzler:
Average Metering:
In the normal default "average" metering mode, your camera examines multiple areas of your composition to choose aperture and shutter speed settings.
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... only if the camera is in programme mode. In aperture priority mode, the meter selects an appropriate shutter speed, and in shutter priority mode, an appropriate aperture width.
Originally posted by jmsetzler:
In many cases, this mode will produce a good exposure.
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This might confuse readers. You might consider expanding this to indicate when the average metering mode works best and when it fails.
Originally posted by jmsetzler:
Spot Metering:
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Without mentioning the mid-point or 18% (13%) grey (already a difficult area), the concept of spot metering becomes unpractical. For example, photographing a black sheet will confuse a meter because the meter tries to balance the entire scene (or the area of the spot) to the 18% grey level. In zone system terminology, black is zone 0 or 1, but 18% is zone 5. When you point your spot meter at a black sheet, it reads the black as midpoint grey. Exposing correctly requires an adjustment of 4 stops down to zone 1. With your present explanation, beginners will think that by simply using the spot meter, they can achieve accurate exposure for that luminosity. They can't unless that luminosity just happens to be at the mid-point.
Originally posted by jmsetzler:
"Correct" Exposure Combinations:
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This discussion is accurate, but relies on beginners having proceduralised the information set out above. It might be an idea to discuss each choice separately and include links to example photographs throughout.
Originally posted by jmsetzler:
The Gray Card:
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There are a number of items missing from this section. For example, there is no mention of external, hand-held meters, nor light sources (light falling onto the subject or into the camera), nor the camera's base calibration. While these elements are not that important for a rank beginner, they do play a part in the exposure equation and are relevant to the isssues you do bring up. I do like the examples, however.
All told, I think that there's a number of problems here: a confusion about audience; a lack of concrete examples; a skipping over of base concepts very quickly, just because they're obvious to you doesn't mean that everyone will pick them up easily; the sheer amount of particular information in a short space; and, finally, a writing style which is, at times, a touch long-winded.
That said, you've presented a very difficult topic well. I'm sure that the final product will make a very valuable addition to (our?) tutorials. |
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10/03/2003 06:55:02 AM · #5 |
John - I can now relate to why my editor always say the same thing to all my first drafts :D
To quote - "Great article, now please expand it to double the length"
You are a photographer and you know what you are talking about and a photographer as experienced as you will know it too - BUT - for a person like me, am being presumtive that I am targeted, -
"you treat a lot of the actual concepts rather dryly and introduce them quickly without much glossing." as Koriyama has put it.
Instead of dissecting the entire article I will just give a quick illustration. At the end of discussion on aperture you say
"As you can see in this chart, each one stop change in the aperture changes the area of the aperture by either twice or half (roughly, but very close). The "F" describes the aperture diameter in terms of focal length divided by aperture number. The numbers in the above chart for diameter are derived from this equation"
Makes me, as a reader, want to say "I am sorry but I cannot see what you are trying to explain :(" Once I am in that frame of mind things go very rapidly downhill for me.
Apologies if I sound blunt and thanks for a self realization, I will hence forth treat my fellow coders more kindly :)
Message edited by author 2003-10-03 06:56:01. |
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10/03/2003 07:34:27 AM · #6 |
As a journalist and editor:
- Way too long-winded. I am not sure what your target length is, but you are wasting space
- This is not an article. It is an introduction written in a variety of styles. You seem to write for photographers at one point, aimed at children at other times, and writing in-between most of the time
- Work on your language. General rules: Dont use ellipses (...). Remember it isn't a crime to split up your sentences into shorter ones
- DOn't belittle your audience. People reading it are likely to want to learn about photography. The sentence "Photographers often use a tool called a "gray card"", for example, implies that people reading it are not photographers. Either use "professional photographers", "seasoned photographers" or something like that.
Also, you are going to have to choose:Either you write an article that is an introduction (drop all the tables and use textual examples instead, making sure to use far fewer entries than in your listings, it breaks up the article, unless your subeditor is willing to include them is extra infoboxes), or write something that is the all-and-everything about exposure (save your time and have people read Ansel Adam's book instead)
You have made a good start, but if I were your editor, I'd send you back to your drawing table.
As a photographer:
A clear, if not concise, introduction to the theme. Good work.
Also see Exposure Value, an E2 entry where you can find two fairly good writeups on EV - closely related to your article.
hj
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10/03/2003 07:59:52 AM · #7 |
Thanks for all the input. I will use your suggestions as I continue...
Thanks :)
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10/03/2003 09:27:27 AM · #8 |
A few more things you may want to work in:
Digital noise increases with larger ISO values.
Exposure compensation is something you do mention. But most cameras have this capability, even many that don't have aperture/shutter priority modes. I think it needs a bit more emphasis.
Bracketing when you are unsure of the best exposure. (It fits right in with exposure compensation.) |
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10/03/2003 09:31:50 AM · #9 |
Thank you for the great tutorial. I am new to this site and also to photography of any kind. I have been lurking for about a month and am constantly amazed at what I have learned :)
Help me out a little with some setting for night as this is when I get to use my camera the most!
Suzanne |
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10/03/2003 01:33:02 PM · #10 |
Originally posted by Spazmo99:
I always liked the metaphor of the film being like a glass of water that you are trying to fill to the top. The shutter speed is like the time it takes to fill the glass. The aperture is like how far the faucet is turned on.
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I like this analogy and i think I'll use it in my re-write. I'm trying to figure out how to work ISO in to the same analogy.
Shutter speed: time it takes to fill the glass
Aperture: size of the hose (diameter)
ISO: ??
Maybe the ISO should be related to the 'pressure' behind the water in the hose? A large diameter hose (large aperture) can deliver water at a slow rate or a fast rate... the 'rate' would somewhat represent the sensitivity of the film? I higher amount of pressure would be like increasing the sensitivity of the film.
Thoughts?
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10/03/2003 01:43:13 PM · #11 |
Originally posted by jmsetzler:
Originally posted by Spazmo99:
I always liked the metaphor of the film being like a glass of water that you are trying to fill to the top. The shutter speed is like the time it takes to fill the glass. The aperture is like how far the faucet is turned on.
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I like this analogy and i think I'll use it in my re-write. I'm trying to figure out how to work ISO in to the same analogy.
Shutter speed: time it takes to fill the glass
Aperture: size of the hose (diameter)
ISO: ??
Maybe the ISO should be related to the 'pressure' behind the water in the hose? A large diameter hose (large aperture) can deliver water at a slow rate or a fast rate... the 'rate' would somewhat represent the sensitivity of the film? I higher amount of pressure would be like increasing the sensitivity of the film.
Thoughts? |
Think of ISO as the size of glass that is being filled. The goal is to fill the glass, regardless of size. Slower ISO=bigger glass and Faster ISO=smaller glass.
Message edited by author 2003-10-03 13:43:59.
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10/03/2003 01:59:31 PM · #12 |
How about changing 'water' to 'ball-bearings' or something like that? The larger ball-bearings are a higher ISO, so it will fill up quicker. A wider aperture would let more through the wider hose.
Or how about ISO = number of ice cubes already in the glass?
Actually I think i've totally missed the point. :P
Message edited by author 2003-10-03 14:03:32.
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10/03/2003 02:07:55 PM · #13 |
I found what you've written right on target with where I'm at in my learning curve... I came into it knowing what the various things were, but with just a general understanding of how they work together so I appreciate what you have written! By chance, I read a similar forum posting just yesterday by Ed Halley that did a good job (I thought) of being fairly simplistic about all of the concepts yet letting me come out of it know more than when I started reading it.
His post was here:
//forums.dpreview.com/forums/read.asp?forum=1019&message=6257244
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10/03/2003 02:42:40 PM · #14 |
Here is a draft of the re-write for the introduction to this article/tutorial:
Exposure, in photographic terms, is the process of capturing light with your camera to produce an image on film or a digital sensor (film and digital sensor will be referred to as film throughout this document). Your camera mechanically controls the incoming light and directs it to the film. The film is sensitive to the light and is 'exposed'.
We can create a simple analogy of exposure in terms of filling a glass of water. We can fill the glass slowly with a small stream of water, or we can fill it quickly with a large stream. In either situation, it will take a combination of time and water flow to fill the glass. The size of the glass is also a consideration. A small glass will fill more quickly than a large one.
Based on this brief analogy, we have three items to consider. We have water flow, the amount of time it takes to fill the glass, and the size of the glass. We can approach our fill the glass project from any angle. We can choose to use a larger or smaller hose. We can choose to fill the glass quickly or slowly. We can choose the size of glass we want to fill. Which ever approach or combination of approaches we take, the result will be the same. We will fill our glass.
How do we relate this analogy to our camera?
Our camera's aperture is the hose. The camera's aperture is the device that controls the amount of light that is allowed into the lens. This aperture is adjustable. You can make it larger or smaller.
Our camera's shutter speed is the amount of time it takes to fill the glass. The camera's shutter is the device that opens to allow the incoming light to expose the film.
The film's sensitivity (ISO Number) is the size of the glass. The sensitivity of the film determines how long it takes to expose it. Some films expose faster than others.
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Does this sound simple enough and to the point?
Message edited by author 2003-10-03 14:45:04.
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10/03/2003 03:21:28 PM · #15 |
John -
I'd like to disagree and propose an alternative.
Analogy: We're filling a bucket of water. (or a glass from the sink)
(do you really fill a glass with a hose? :) )
Aperature - size of the spicket.
Shutter Speed - the amout of time the spicket is open.
ISO - the rate at which the water flows (or pressure).
Exposure - the volume of water.
I'd be ok with ISO determining the glass size, but I think metering should be used to determine the amount of water needed (aka, glass size). That way you can use different glass for different situations. It may lend itself to a better scenario for exposure compensation, too.
Obviously we have control of 3 independant variables, the fourth is the dependant. (that was for math geeks)
If we open the aperature wider and keep the shutter speed and ISO constant, we'll get more water. If we double the aperature, we can cut the speed in half (reduce blur) or use a lower ISO (redure noise) to get teh same amount of water.
[insert numerous other variations here]
I hope this helps make a better analogy.
- Dave |
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10/03/2003 03:31:27 PM · #16 |
There are a lot of ways to write this analogy for sure. I don't want to use the analogy to completely describe all aspects of exposure. I just want to use it to allow someone who knows nothing about exposure some tangible comparison to what is going on inside the camera.
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10/03/2003 06:42:05 PM · #17 |
I fear the analogy works for those who already have some understanding of this topic, but may be inappropriate for new photographers.
I recommend testing out any such analogy on anyone currently unfamiliar with the topic. |
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10/03/2003 06:51:16 PM · #18 |
| I think of ISO as how clean the water is : ) |
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10/03/2003 08:30:03 PM · #19 |
Originally posted by ellamay:
I think of ISO as how clean the water is : ) |
:)
i suppose that is in reference to grain. The purpose of ISO is not the noise though. The noise is just a by product of the real function of various film sensitivities :)
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10/06/2003 10:05:03 AM · #20 |
This project has progressed. I have decided to make an attempt to appeal to the novice. From the way things are going, it's gonna turn out to look like a textbook of sorts...
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10/07/2003 03:11:25 AM · #21 |
| I would also suggest that anyone with a digicam use the lcd display as a learning tool . The changes in exposure are immediatley evident. This is also a great tool for white balance which plays a part in exposure as well . |
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10/18/2003 05:13:03 PM · #22 |
I need a couple proof readers to go over what I have done with this... Please let me know if you are interested.
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10/18/2003 05:41:20 PM · #23 |
John
I would be happy to proofread what you have done
Let me know
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10/18/2003 06:31:02 PM · #24 |
I am a good proofreader and slightly below novice as far as the camera...I would be happy to help out if you think I could be of assistance. Anne
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10/19/2003 11:08:21 AM · #25 |
I can proofread too -- I'll try to avoid any more editing!
You proofreading types might also be interested in volunteering for Project Gutenberg. |
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