Know Light Exposures

Basic 1 

Before knowing anything, you should know about Light Exposure which is the very foundation  of any photography or any other media.

Basically,there's 3 main elements for exposure:

1.ISO Speed                                     2.Shutter Speed                                    3.Aperture

They are dependent to each other.You can't neglect the importance of any of them.So,here is the explanation to each

1.ISO Speed:

                        ISO measures the sensitivity of the image sensor.The lower the number the less sensitive your camera is to light and the finer the grain. Higher ISO settings are generally used in darker situations to get faster shutter speeds.You have all noticed ISO text in every camera.If ISO increased manually or automatically, you will notice grainy in shadow or dark areas of the photographs.In simple words,know this that sensor tries to throw lights through pixel to make image brighter and that's when the grains emerge out.

ISO generally starts with 100 and extends upto 64,000.

Advanced/Professional DSLR cameras can handle that huge number of ISO.

Do you remember the green,red,blue grains in the photos taken in night with digital camera?Yes,thats the thing from ISO speed (and may also happen if megapixel is lower and if you crop more)

If you can adjust ISO at minimum of ISO 100 maintaining the optimum exposure then you will have very good image with no noise.

Situations where you might need to push ISO to higher settings include:

• Indoor Sports Events – where your subject is moving fast yet you may have limited light available. 
• Concerts – also low in light and often ‘no-flash’ zones Art Galleries, Churches etc- many galleries have rules against using a flash and of course being indoors are not well lit. 
• Birthday Parties – blowing out the candles in a dark room can give you a nice moody shot which would be ruined by a bright flash. Increasing the ISO can help capture the scene. ISO is an important aspect of digital photography to have an understanding of if you want to gain more control of your digital camera. Experiment with different settings and how they impact your images today.

2.Shutter Speed:

                                 Shutter speed is ‘the amount of time that the shutter is open’.In digital photography shutter speed is the length of time that your image sensor letting in the light from the scene you are capturing.In very simple words, it means if you let shutter speed slow or long exposed shutter speed then you might end up with blown out image with white. Shutter speed is measured in seconds – or in most cases fractions of seconds. The bigger the denominator the faster the speed (ie 1/1000 is much faster than 1/30). In most cases you’ll probably be using shutter speeds of 1/60th of a second or faster. This is because anything slower than this is very difficult to use without getting camera shake. Camera shake is when your camera is moving while the shutter is open and results in blur in your photos.

                                If you’re using a slow shutter speed (anything slower than 1/60) you will need to either use a tripod or some some type of image stabilization (more and more cameras are coming with this built in). Shutter speeds available to you on your camera will usually double (approximately) with each setting. As a result you’ll usually have the options for the following shutter speeds – 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8 etc. This ‘doubling’ is handy to keep in mind as aperture settings also double the amount of light that is let in – as a result increasing shutter speed by one stop and decreasing aperture by one stop should give you similar exposure levels (but we’ll talk more about this in a future post).

                              Some cameras also give you the option for very slow shutter speeds that are not fractions of seconds but are measured in seconds (for example 1 second, 10 seconds, 30 seconds etc). These are used in very low light situations, when you’re going after special effects and/or when you’re trying to capture a lot of movement in a shot).

                             Some cameras also give you the option to shoot in ‘B’ (or ‘Bulb’) mode. Bulb mode lets you keep the shutter open for as long as you hold it down. When considering what shutter speed to use in an image you should always ask yourself whether anything in your scene is moving and how you’d like to capture that movement. If there is movement in your scene you have the choice of either freezing the movement (so it looks still) or letting the moving object intentionally blur (giving it a sense of movement).

                           To freeze movement in an image (like in the surfing shot above) you’ll want to choose a faster shutter speed and to let the movement blur you’ll want to choose a slower shutter speed. The actual speeds you should choose will vary depending upon the speed of the subject in your shot and how much you want it to be blurred.

Motion is not always bad – I spoke to one digital camera owner last week who told me that he always used fast shutter speeds and couldn’t understand why anyone would want motion in their images. There are times when motion is good. For example when you’re taking a photo of a waterfall and want to show how fast the water is flowing, or when you’re taking a shot of a racing car and want to give it a feeling of speed, or when you’re taking a shot of a star scape and want to show how the stars move over a longer period of time etc. In all of these instances choosing a longer shutter speed will be the way to go. However in all of these cases you need to use a tripod or you’ll run the risk of ruining the shots by adding camera movement (a different type of blur than motion blur).

Focal Length and Shutter Speed - another thing to consider when choosing shutter speed is the focal length of the lens you’re using. Longer focal lengths will accentuate the amount of camera shake you have and so you’ll need to choose a faster shutter speed (unless you have image stabilization in your lens or camera). The ‘rule’ of thumb to use with focal length in non image stabilized situations) is to choose a shutter speed with a denominator that is larger than the focal length of the lens. For example if you have a lens that is 50mm 1/60th is probably ok but if you have a 200mm lens you’ll probably want to shoot at around 1/250.

3.Aperture :

                       If you can master aperture you put into your grasp real creative control over your camera. In my opinion – aperture is where a lot of the magic happens in photography and as we’ll see below, changes in it can mean the difference between one dimensional and multi dimensional shots.

Aperture is ‘the size of the opening in the lens when a picture is taken.’ When you hit the shutter release button of your camera a hole opens up that allows your cameras image sensor to catch a glimpse of the scene you’re wanting to capture. The aperture that you set impacts the size of that hole. The larger the hole the more light that gets in – the smaller the hole the less light. Aperture is measured in ‘f-stops’. You’ll often see them referred to here at Digital Photography School as f/number – for example f/2.8, f/4, f/5.6,f/8,f/22 etc. Moving from one f-stop to the next doubles or halves the size of the amount of opening in your lens (and the amount of light getting through). Keep in mind that a change in shutter speed from one stop to the next doubles or halves the amount of light that gets in also – this means if you increase one and decrease the other you let the same amount of light in – very handy to keep in mind).
One thing that causes a lot of new photographers confusion is that large apertures (where lots of light gets through) are given f/stop smaller numbers and smaller apertures (where less light gets through) have larger f-stop numbers. So f/2.8 is in fact a much larger aperture than f/22. It seems the wrong way around when you first hear it but you’ll get the hang of it.

Depth of Field and Aperture Depth of Field (DOF) is that amount of your shot that will be in focus. Large depth of field means that most of your image will be in focus whether it’s close to your camera or far away (like the picture to the left where both the foreground and background are largely in focus – taken with an aperture of f/22). Small (or shallow) depth of field means that only part of the image will be in focus and the rest will be fuzzy (like in the flower above of this paragraph. You’ll see in it that the center of the flower is in focus but even though they are only few cm or so behind them that the next flower behind is out of focus. This is a very shallow depth of field and was taken with an aperture of f/4.5).
                                    Aperture has a big impact upon depth of field. Large aperture (remember it’s a smaller number) will decrease depth of field while small aperture (larger numbers) will give you larger depth of field. It can be a little confusing at first but the way I remember it is that small numbers mean small DOF and large numbers mean large DOF.

Many of us always twisting,laying down,stretching,squating to get that DOF(Depth Of Field) or blur effect at background or foreground but focus on the subject.

In most landscape photography you’ll see small aperture settings (large numbers) selected by photographers. This ensures that from the foreground to the horizon is relatively in focus. On the other hand in portrait photography it can be very handy to have your subject perfectly in focus but to have a nice blurry background in order to ensure that your subject is the main focal point and that other elements in the shot are not distracting. In this case you’d choose a large aperture (small number) to ensure a shallow depth of field. Macro photographers tend to be big users of large apertures to ensure that the element of their subject that they are focusing in on totally captures the attention of the viewer of their images while the rest of the image is completely thrown out of focus. SRC : Digital Photography School