How to Fish :: Misc Guides :: Photography :: Introduction Selecting a Digital Camera How to take a Photograph Using Manual Controls Digital Photo Touchup

Using manual Controls

Aperture, Shutter speed, ISO and exposure

To understand how an image is formed in a camera, we need to think of light as particles; light that is reflected off an object and captured by the camera. Think of it as drawing a picture by trickling coloured sand over a piece of paper to form an image(as shown before). Too little sand will cause the image not fully formed and too much will overlap the intended image. We need just the right amount of sand particles to form a well exposed image. A camera uses shutter speed and aperture to control the exposure of an image. In auto mode, a digital camera determines the aperture and shutter speed for you.

The camera first determines(metering) the exact amount of particles needed to get a well formed picture(proper exposure)
how much particles(light) entering the camera depends on size of hole(aperture) and time(shutter time/speed) the hole remains open. Sensitivity(ISO) effectively reduces the amount of particles(light) needed. Therefore by controlling the size of the hole, opening time and sensitivity, we can control the exact amount of particles into a camera to form a nice picture!

The relationship of each of these parameters can be summarized with the following table

note 1: table value works vice versa, ie. decreasing shutter speed will increase aperture rating, ISO or exposure.
note 2: increasing aperture rating decreases the size of the aperture.

The effects of exposure

The term 'well exposed' image can differ between a camera's 'eye' and a human eye. Like computers, cameras uses a set of rules or criteria to determine whether an image is well exposed. However, there is no one set of structured rules in a camera that will that will correctly determine a well exposed image(like human eye) for every scene encountered.

That is why most cameras have a few sets of metering mode, each with its own set of rules to determine the right exposure for a specific scene. The details will not be covered here but it should be noted that 'evaluative metering mode' is the most common form of mode which correctly determines the right exposure for most scenes.

Below shows a butterfly under different exposure times. The first one is considered under exposed because details are lost in shadows (ie. the false eye cannot be seen). The image on the right is considered over exposed because the texture on the body of the fish is lost to highlight. With the image in the middle, you can see that the fish contains the most details being able to see the false eye and the texture on its body - that makes the picture will exposed, or rather the subject well exposed.

An example of how an image is exposed to light.

Effects of Shutter and Shutter Speed

Shutter is a mechanism in the camera that controls the amount of light entering the camera by limiting the amount of time the shutter remains open. Shutter speed of consumer digital cameras typically range from 3 secs(slow) - 1/1000 sec(fast). Fast shutter speed has the nature of freezing movement so the image becomes sharp and clear when taken while slow shutter speed tend to produce blur pictures when shooting moving objects.

One must take note of the shutter speed before releasing the shutter because it gives you a good idea whether the image to be taken will likely turn out blurred or not. Assuming we are shooting a stationary object (camera handheld), we typically need at least 1/40 sec shutter speed to get a sharp image.

Use of fast shutter speed freezes the image

Slow shutter speed causes water motion to overlap

Effects of Aperture

Focus and Depth of Field

When a camera attempts to take a picture, the Auto Focus (AF) has to 'guess' which subject(s) in frame you are actually trying to take. How smart the camera is in the guessing depends on how the camera is programmed and the AF mode used, and also the complexity of the scene.

The camera then focuses on the subject at an imaginary plane (Plane of Focus) which is parallel to the camera's lens. When an subject is in focus, it means that the subject is clear and sharp. Depth of Field refers to the area infront and behind Plane of Focus which any subject falls into will still appear to be clear and sharp.

The blue bands in the diagram below represents depth of field as the camera focuses on an apple. The tones of the blue bands denotes the amount of sharpness with dark bands closer to the plane of focus with maximum sharpness and lighter bands denotes less sharpness as it gets further away from the plane of focus.

The depth of field can be controlled using the camera's Aperture. Opening up the aperture bigger decrease the depth of field while a smaller aperture has a high depth of field.

In the example below, three AA batteries are lined one behind the other in a diagonal manner such that the left battery is furthest away and the right one is nearest and the centre one is in the middle. The camera is set to focus on the middle battery; that is to say that the plane of focus is in between leftmost and rightmost battery.

At wide Aperture(ie. F2.8), the leftmost and the rightmost batteries appear out of focus. But as the F-stops increases(decrease aperture size, all the batteries appear to be in focus. This is because depth of field increases with the decrease in aperture size.

Why is there a need to control the depth of field? It is useful to isolate the subject of interest from the surrounding which may cause distraction to the viewer. It also let the photographer have more control over the image to express their creativity.

Effects of ISO

ISO can be understood by the camera's sensitivity to light. That means if the camera is set to higher sensitivity(ISO value), it can take shorter shorter exposure time to take a photo. This translates to the ability to use higher shutter speed which results in less likelyhood of a blurred photo taken.

For most cases, we want fastest shutter speed, so why are different ISO available to us? The reason is although increasing ISO helps us to gain shutter speed, it also increased the amount of noise/grains onto the picture. Noise, or grains can be seen as speckles in an image when high ISO is used. All digital cameras have noise suppression techniques to reduce this visible noise but they often cause loss of details to the image.

The below demonstrates the effect of ISO by taking a subject using different values of ISO:

This is a resized full frame of the subject.

As you can see, noise/grain becomes quite noticeable with ISO 400 and beyond and significant loss of details at ISO 800 and ISO 1600. Do note that different cameras have different range of ISO value and they often produce different amount of noise at a given ISO value.

So the ISO should be used wisely when taking a photograph, taking into account to the shutter speed gain and the loss of image quality. Use the lowest ISO value to shoot whenever possible to get the best quality picture.

Conclusion

The manual controls of the camera may seem rather complex at first, but with time, it will become a second nature. Full manual controls are good for unique/difficult scenes but not always necessary for normal use. Semi auto controls are often enough to handle most situations with spending less time fiddling with the controls.

Mastering the these control will allow photographers to extend their creativity in shooting as well as making the best out of the camera in any given scenario. Capture the golden moments in fishing.

- End-

created 20th june 07