Archive for January, 2007

Exposure Part IV : Daylight Table

By now we know how to control exposure by changing f/stops and shutter speeds, and I believe you know about equivalent exposures! However, how do you find a correct exposure in the first place? This guide is intended for operation in the manual mode, so be wary.

First we have to determine the shutter speed, this depends on the action. If we want to freeze a fast moving object we will need to have a higher shutter speed, similarly we can have a blur/ghost effect of a fast moving object with a slower shutter speed. So it is up to you to decide the shutter speed and comes with a day or two’s little practice.

exposure_table.jpg

Now that we have covered shutter speed, we have to determine how bright the subject is. Look at the daylight table above. The object brightness is the vertical column at the left side of the table. Lets talk about various subjects. An average subject is one that reflects about 18% of light striking it and absorb the rest. This category includes people in medium-colored clothing, most buildings, landscapes with trees, and roads or street scenes. The majority of photographic subjects. While dark subjects reflects only about 9% of the light striking it and absorbs the rest. This makes them only half as bright as an average subjects thus requiring twice the exposure. These includes dark-colored vehicles, people in dark-toned clothing, dark colored animals and very dark or black stones. Now to the bright subjects, which reflects about twice as much light compared to average objects. As a bright subject absorbs much less light they require less exposure than average objects, generally one stop. This includes, fair-skinned, dyed and light haired persons, people in light clothing, light colored animals and light colored buildings. The last is brilliant subjects, which reflects about four times as much light as an average subjects and absorbs relatively little light. As you know by now such an subject will require less exposure compared to an average subject, generally two lens stop less. Examples includes people in white cloths on a white sandy beach, a white boat against a blue sky and white painted buildings.

After considering the shutter speed and subject brightness next would be the environment. Just look at the horizontal row at the top of the table. There are five classes of illumination, bright sun on light sand, bright sun, hazy sun, cloudy bright and open shade. Let us elaborate on this. Bright sun in a clear sky, and sun is far too bright to look directly. Shadows are sharply defined with a hard edge. This type I typically excellent for landscapes, architectural subjects, and anything else for which we want hard, clear definition. However, this is not good for portraits, unless a hard effect is what we want. Sometimes the contrast between the sunlight and shadows are so great, the shadows look black and featureless. Next is bright sun on light sand, as sand act as reflectors they increase the amount of light on the subject, about half stops. All conditions for bright sun applies to this except for contrast, which is usually fairly low as the reflections from the sand casts light into the shadow areas, filling them. The Hazy sun, when the sun is practically obscured by haze or thin high clouds, but the sun’s disc is still clearly visible and bright. Shadows are still easy to see but they are slightly diffused and not clearly defined. In a hazy day distant scenes may be obscured which can be used for good effects. This is good for rugged portraits of people. The shadows are mostly clear enough to bring out skin texture and facial lines, but are often soft enough so that the shaded areas show details. A cloudy but bright day where the sun’ disc is barely visible due to clouds. For us this might look bright enough but typically for a good exposure it requires about two stops more than a bright sunny day. It is possible to capture shadows but normally they are weak and have soft edges. This condition is excellent for general portraiture and scenes of short or middle distances. Distance scenes can be a problem, as they tend to be over exposed and comes featureless white. Next is open shade, a cloudy dull day where the sun can’t be located in the sky because it is entirely obscured by clouds. There are no shadows at all, may be very faint one under vehicles or furniture. The lighting is extremely soft and is good for portraits of children, women or any other subject you wish to show soft. Some times the lack of shadows make the subject flat with no feeling of depth. This is much like the cloudy dull day except that it can be found on a clear sunny day too. Open shades are shades which are open to a lot of sky but shades from the direct rays of the sun. Examples includes shady side of a building with overhead skylight. Shades under a low, densely leafed tree is not “open”. This condition typically needs three stops more light than bright sun does.

A final adjustment might be needed for bright or hazy sun. If the sun is to one side shining across the subject so that part of it is lit by the direct rays of the sun and the rest by the light of the sky, we should open our lens one stop from the table’s recommendation, so that the shadows still show some detail. On the other hand, if the sun is behind the subject and shining on your face, then you should give two stops more than the table.

This daylight exposure table will help in finding out which setting to use outdoors. It is as simple as finding out the needed shutter speed, subject brightness and what type of light is in the environment and adjust the aperture size. Some camera manuals comes with these tables which you can carry around or you can memorize it if you want to (it helps). Alternatively use your intuition to get used to the environment and the required setting (it takes time).

As the name suggest, this table only works outdoors daylight, that is two hours after and before sunrise and sunset. Beyond these times it is completely useless but I guess this table gives a picture of what, how and when we need to tweak the settings. That is it, now you will be wanting some examples and practical advices. Come back soon for more…

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Exposure Part III : Time

Today we are gonna talk about exposure time, which is controlled using the shutter. In the stone ages of photography exposure times were very long. So cameras didn’t need a shutter, just uncover the lens for seconds, minutes or even hours and when done cover it up. However, now a days due to high sensitivity exposure time is shorten to thousandths of a second. So now we are dealing with ultra faster shutters in comparison.
Shutters are made up of thin leaves of metal which are connected to a complex mechanism of gears and springs which make them open and close the path of light through the lens.

ShutterJust like intensity, shutter speed are designed to allow the time to be changed by a factor of two. That is each change in the exposure will change the exposure time by either doubling or halving it. Modern shutters timings are controlled electronically, this makes the mechanism smaller and lighter as lot of early timing gears are eliminated in favor of a very small computer chip. The shutter speed includes full second exposure times of 2,4,8, and some times longer. I find it very little need for the digital enthusiast to go in depth on the common sequences of the shutter speeds, So I will skip it.

Electronic shutters can operate at intermediate speeds, but usually only when the camera is operating in an “automatic” mode. They also have less moving parts, hence less vulnerable. On the negative side these shutters use batteries, which can fail at unexpected times. So it is good practice to carry spare batteries always.
Now to put some of what we have learnt together. In the beginning in part I, I did mention about equivalent exposures. Any number of combination of light intensity and time which will result in the same exposure. The scale goes something like below.

Time Scale

Remember the two scale runs in opposite directions, each of the above combination of f/number and shutter speed provides exactly the same amount of exposure. That is, an exposure of 1 second at f/2 will have the same darkening effect as an exposure of 1/250 second at f/2 and so will all the others in between.
All SLR cameras comes with modes of A, S & M. The A mode will allow the change of aperture and the camera will calculate the required shutter speed. Similarly the S mode will allow to change the shutter speed while the camera will change the aperture size automatically for us. While in manual mode we have total control of changing both the aperture and shutter speed. Most of the other modes are programmed modes which I will be deal in a later stage.
So you want to play around in the manual mode to get a correct exposure? Lets say you are in a dim room, 1 second at f/32 probably won’t be enough and the image will be underexposed. But perhaps an exposure of 1 second at f/5.6 would be enough. All you need to do is slide the two scales past each other until the f/5.6 is opposite the 1 second mark. Then all other shutter speed and f/number combinations will give the equivalent exposures. This is called an “equivalent exposure calculator”. Well, this only comes in handy when you want to play around in the manual mode. So here it is, shutter speeds and f/stops coordinating to give us a variety of choices. So what are the best known, more or less proven, exposure values for photography? Come back soon for the daylight exposure table.

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Exposure Part II : Intensity

As we have learned before in order to control exposure we have to control intensity and time. Here I will talk about controlling light intensity!
Think of the lens like a window, the more you open the window the more light will come in. The concept is the same for a lens. The larger the opening of the lens the greater the light intensity on the photo. Similar to a window you can open and close the lens (aperture).
A diaphragm is the mechanism which control the opening and closing of the lens aperture which also provides us a system to measure this change. Modern lenses use a iris diaphragm, build in replica to the iris of our eye. Thin metal plates are assembled to allow the lens to open and close as needed.
In theory the opening of the aperture is easy to measure. However, different lenses have different focal length, the long, short lenses and by using the zoom feature. For example 100mm lens is twice as far away or long as a 50mm lens when both are looking at the same object. It is like when you stand close to a window you will receive more light while when you move far away from the window the light will become distributed to the whole room and you will receive relatively less light while the opening of the window is the same.

f/number calculation
Hence, f/number system is used to measure or express the amount of receiving light regardless of the focal length! An f/number is the ratio of the lens focal length to the diameter of the lens aperture. For example an 1 inch focal length with an aperture size of 1 inch, the f/number is 1/1 hence 1. Similarly a lens of focal length 4 with an aperture size of 1 inch, the f/number is 4/1 hence 4. In order to identify when we are talking about this ratio f/numbers are written as f/1 or f/4. So when we have a camera A attached with a lens of focal length 8 inch with a aperture diameter of 1 inch it will give f/8. Similarly another camera B with focal length of 16 inch will need an aperture diameter of 2 inch to give f/8. With these settings Camera A and camera B will give the same light intensities. Always keep in mind f/number is not the actual aperture size but the light intensity when aperture size is compared to the focal length.
The standard f/number sequence is 32, 22, 16, 11, 8, 5.6, 4, 2.8 and 2. Digital cameras have in between variations. It as a real pain memorizing these number at first but it was worth it… As each number in this sequence represent a change in the intensity of light by a factor of 2. As the number increase the amount of light passing through the lens decreases to half that of the previous f/number. So if the lens is initially set to f/8 and it is changed to f/11 the light passing through has been reduced exactly half and another change from f/11 to f/16 cuts by another half. The reverse is also true, if changed from f/16 to f/11 the light passing increases by double. Just keep in mind as the f/number increases the light passing through the lens decreases as the aperture size is reducing.
Sequence Table
If you look at the above diagram of the sequence you must be able to note that every other number is twice the value of its predecessor. The key numbers are 1 and 1.4 (an approximate of square root of 2, actual number 1.4142135). If you consider this real number then every other number is either very close or exactly double its predecessor. So this must give you can hint on how to calculate the sequence (but subject to a lot of error due to the ignored decimal place). An easier way to remember is a change is always 2 to the power n. So a change of 3 f/number is 2 X 2 X 2 = 8, a factor of 8.
This f/number is called “stop” as they stop light in exact ways. In practice any change of exposure are referred to as stops. For example to change your shutter speed to 2 stops up.
Even though we have a sequence, lens settings can easily be set at any intermediate points between numbers. I am practicing using my EOS 100, an old film model but the true analogue quality is still unbeatable with the digital cameras (close!). This f/number comes in handy as I do not have a live visual image on the display but rather have to depend on the f-stop ring. However, if you have a digital camera you can change the f-stop and at the same time see a visual more or less a live update of the output instantly. Additionally using digital you can check the shot immediately once you’ve taken it but with the film it is a bit of a pain. I am going through this trouble as I want to get things right the first time – to produce a high-quality image in-camera with minimum tweaking, learning to trust my intuition. This is important to get the exposure I want with confidence when the camera’s being fooled.
In modern SLR cameras you can either control the intensity (aperture size) and let the camera adjust the time (shutter speed) automatically. Alternately you can also change the time and let the intensity be set automatically. So how to control the time? Come back soon to find out…

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Exposure Part I : Theory

canon-eos.jpg At moments when work is pretty darned draining with no signs of sleeping it is time to focus on my undeniable obsessions, this time photography. I consider myself an ameture photographer as I have got lot to learn but I love to share all that I have learned. Though I mostly recommend to rely on your intuition for your utopia experiences a little bit of theory always enhance the adventure.

So today I am gonna share what I know about camera exposure, theory. (Note: I am referring to DSLR cameras which allow us to control the lightning, shutter speed and aperture size). So what is exposure? A photograph is all about lights. Hence, the quality and details depend on how the light is captured. If too much light is captured the image is darken considerable, while when relatively little light is captured the image is too dim. Exposure is how much light is captured in order to get the image.

In capturing any photograph our first concentration must be on the image, second on the varying brightnesses. An image with the same brightness everywhere would be dull and uninteresting – just a splotch of black, gray or white. So when we are dealing with exposure the only question is “how much?” Too little exposure, important parts of the image will be lost while too much exposure will result in total darkness. The external factors influencing these remains the brightness and the reflective characteristics of the subject and the environment.

As we are dealing with light when more light enters the camera it will result in an image that is darker. So what we need to find out is how much light will make the image neither too dark or too light. The correct amount of light have to be correctly and accurately measured to get a perfect shot.

There are two ways we can control this. First we can control the intensity (brightness) or the amount of light entering the camera (aperture size). Second we can control the amount of time it takes for light to enter the camera (shutter speed).

Think of this as filling a bucket with water. The amount of water winding up in the bucket depends on how fast the water was running and how long it was allowed to flow. If you want to fill the bucket to a specific depth, we can do so by either running the water rapidly for a short time or by running it slower for a prolong time. Either way, the bucket will have the same amount of water, the right amount that we wanted.

In photography the rate of flow of light is called intensity and hence the formula becomes.

EXPOSURE = INTENSITY X TIME (E = I X T)

So looking at the formula if we have less light then we must allow more time to get the same exposure. Or if we have less time, then we can increase the intensity. However, there are many combinations of time and intensity that can give the same exposure, which are called equivalent exposures. In theory equivalent exposures are of same image quality however there are artistic considerations.

So how does a SLR camera control exposure so we can selectively correct the exposure to our hearts desire. Come back soon to find out!

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It’s same as free beer

I wonder how many people uses Openoffice? OK, you have never heard of OpenOffice?
OpenOffice.org is an open source version of Sun’s Star Office Suite. OpenOffice.org 2.1 is freely available and redistributable, and supports seven platforms: Windows, Linux x86 and PowerPC, Solaris x86 and SPARC, Mac OS X and FreeBSD. It offers a word processor (Writer), spreadsheet manager (Calc), multimedia presenter (Impress), simple to 3D illustrator (Draw), database manipulator (Base) and a tool to create mathematical equations (Math).

OpenOffice.org: Writer
Among the most significant features includes the file format, open office 2.1 used OASIS OpenDocument, a standardized and well documented file format, an initiative to support global exchange of data. It’s design is focused on improving interoperability with MSOffice package. Which means it can read MSOffice files along with similarities in the GUI. The Openoffice PDF feature is a genuine highlight that makes OpenOffice a powerful tool for creating PDF distributions like documents and forms.

OpenOffice.org: Calc
If you are not addicted to the MS Office Package’s Outlook, InfoPath, OneNote, Groove and Publisher then this is a valid alternative. I would suggest for home users, small businesses and educational facilities on super-tight budgets to make the move today.
So if you want more information or download visit OpenOffice.org website

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A cool toolbar on your desktop

Desktop cluttering was an annoyance until I found the RocketDock by Punk Software. A small nifty customizable toolbar with icons of programs, files, and paths that you use frequently. No more desktop icons and quicklaunch. I have a necessity to open multiple programs at the same time and now they are at a simple click away. You can customize the programs on the bar, the size, the zooming, the background style and position (even in which monitor to display in dual monitors setup).
If you are like me with more than 40 installed programs with 20 of them in constant demand you definitely need to give RocketDock a try http://www.punksoftware.com/

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