| Photographers Guide to Camera Optics |
1. Introduction
Photography has never been more affordable or accessible with todays excellent range of cameras and mobile phones, both of which can produce excellent results with a little knowledge. Similarly, cheap software is readily available to edit, save and export pictures to family, friends and social media. There are plenty of opprtunities to learn photography through social media tutorials, camera clubs and educational establishments.
Whilst photography is very subjective, it is normally critiqued on composition, impact and technical execution. Composition and impact are generally considered as having an eye for a picture. Watching other photographers pictures being critiqued is an ideal opportunity to pick up and practice some of those skills.
The purpose of this thesis is to provide the photographer with a pictorial appreciation of the theory of camera optics.
Whilst some photographers may consider 'Circle of Confusion' to be rather confusing, it is the basis for correlating visual acuity with image sharpness.
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2. Schematic Layout of Sensor, Lens and Subject |
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3. Description of Schematic Layout of Sensor, Lens and Subject |
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3.1 General Description - The Camera Lens, Focal Length (F) is set to an ISO Rating (I), Aperture Number (f) and Shutter Speed (t). It is focused on a Subject (V) and its image is recorded on to the Camera Sensor (S) at an Image Distance (U). The Circle of Confusion (CoC) of the Camera Sensor (S) produces a Depth of Field (DoF) of objects that are in focus both in front (near) and behind (far) of the Subject. Their respective Depths of Focus (dof) are shown for the limiting Circles of Confusion (CoF) for the Camera Sensor (S).
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3.2 Detailed Description of Schematic Layout of Sensor, Lens and Subject
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3.2.1 Camera Lens, Focal Length of a Lens (F) and The Lens Equation
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3.2.2 ISO Rating (I) – Is a measurement of a photographic films sensitivity to light and was originally known as ASA rating. The exposure value of ASA 100 film is identical to that of ISO 100 for digital camera sensors and is normally used as the base sensitivity. When a higher ISO number rating is selected the camera’s software amplifies the signal from the sensor to the digital file to compensate for the lack of light, but this progressively deteriorates the quality of the image in both graininess and loss of colour as the rating is increased. Most cameras will have an ISO rating between 100 and 25600.
Contrary to popular belief the sensor’s sensitivity doesn’t change as the ISO number increases.
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3.2.3 Aperture Diameter (d), Aperture Number (f) and Shutter Speed (t)
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3.2.4 Visual Acuity, Circle of Confusion (CoC)
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3.2.5 Circle of Confusion (CoC) - Sensor (S)
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3.2.6 Depth of Field (DoF)
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3.2.7 Depth of Focus (dof) - From Section 2, Schematic Layout of Sensor, Lens and Subject, it is the distance between the near and far object light rays that form the limiting Circles of Confusion (CoC), which protracts through the camera lens to produce the Depth of Field (DoF).
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3.3 Putting the Theory into Practice - The following is only to be used as guidelines for logic and the numbers are used for illustration purposes only.
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3.3.1 Landscape Photography - In essence, try setting the ISO Rating (I) to ISO 100, the Aperture Number (f) to f8 / f11 and check that the Shutter Speed (t) is faster than 1/60s for a lens of Focal Length (F) 50mm or 1/125s for a lens of Focal Length 200mm, in order to minimse camera shake. If due to poor lighting the Shutter Speed (t) is lower than this, gradually increase the ISO Rating (I) until a satsifactory combination of Aperture Number (f) and Shutter Speed (t) is achieved. Using a tripod would allow the Shutter Speed (t) to be reduced thereby improving the ISO Rating (i) and Aperture Number (f).
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3.3.2 Action Photography - In essence, try setting the ISO Rating (I) to ISO 100, the Shutter Speed (t) to say 1/640s and check that the Aperture Number (f) is at least f5.6. If due to poor lighting the f5.6 cannot be achieved, gradually increase the ISO Rating (I) until a satisfactory comination of Shutter Speed (t) and Aperture Number (f) is achieved. A too slow Shutter Speed may result in motion blur.
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| Last Updated, 03/11/2024 |
