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The Sun on Your Face

Blog Entry: Basic Photography for Beginners.

Basic Photography for Beginners.

Photography

3rd August 2011

An Introduction to the Very Basics of Photograph

Hovis Hill in Shaftesbury

I am a very basic very amateur photographer and so I am always forgetting the simple things.

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Aperture Size

A smaller value on the camera indicates a larger the aperture size. F-stops are a measurement of aperture size. The diameter of the aperture is expressed as fraction of the focal length of the lens.

The aperture diameter of a lens with a focal length of 40mm at a setting of f 8 will be 5mm.

  	Aperture size 	=	focal length ÷ f stop

			=	40 ÷ 8

			=	5
   

For then same lens with an f stop setting of 16, the aperture diameter will be 40 ÷ 16 or 2.5mm.

On a camera the aperture setting is often referred to by the f stop number e.g. f8 or f16. As the calculations above show:

Thus the larger the f stop number, the smaller the aperture. The largest aperture on my camera is often f3.5 whereas the smallest is f32, depending on the focal length being used.

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Changing the Focal Length

The focal length of a lens is a measurement from the optical centre of the lens to the image censor.

Effect of Changing Focal Length on Field of View

Basically, the longer the lens, the longer the focal length.

Altering the focal length will either widen or narrow the field of view

This is why telephoto lenses have narrower field of view.

Focal Length: 20.0mm

A photograph of hot air balloons with a focal length of 20mm showing a wide field of view

Focal Length: 135.0mm

A close up of a hot air balloon taken with a telephoto lens with a focal length of
  		135mm showing a narrow field of view

Focal Length: 180.0mm

A close up of a hot air balloon taken with a telephoto lens with a focal length of
  		180mm showing a very narrow field of view

In the above photos of balloons, the closer we get to the balloon by using a telephoto lens, the narrower our field of view becomes.

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Factors Determining What ISO Setting to Use

The ISO setting determines the sensitivity of the camera sensor and therefore, in conjunction with shutter speeds and aperture sizes determines how much light is captured by the camera.

To increase the amount of light captured ( e.g. if an image is underexposed )

To decrease the amount of light captured ( e.g. if an image is overexposed )

For general photography, or where a tripod can be used, the standard ISO setting (50-100) should be used.

Reasons When You Might Change the ISO
  1. Take photographs indoors without using the flash.
  2. Freeze action with faster shutter speeds in lower light conditions.
  3. Increase the shutter speed to avoid camera shake in lower light conditions.
  4. Increase the effective range of the flash, or in low light conditions where a flash is prohibited e.g. Museums.

Cost:

Increasing the ISO increases the noise on the photograph leading to a graininess that is more noticeable the higher the ISO is set. It should only be used as a last resort.

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Altering The Depth of Field

A lens focuses precisely on only one plane at a time, but there is a also a certain distance before and after this point that also appears sharp. This is the depth of field and it varies predominantly depending on

To achieve a narrower depth of field:

Focal Length: 55.0mm Aperture: F/5.6

Photograph of grass seeds to demonstrate a narrow depth of field
To achieve a wider depth of field:

Focal Length: 100.0mm Aperture: F/14

Photograph of the Alps to demonstrate a wide depth of field
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Using Preset Focus Modes

Most DSLRs have a number of preset focus modes that can be used quickly depending different circumstances. When using these modes the camera will automatically choose what it thinks are the most appropriate settings to achieve the best results depending on what the context is.

Most DSLRs offer the similar preset modes. On my Canon EOS 450D, the following settings are available.

  1. Full Automatic

    Canon Full Automatic camera icon - black square on a white background

    A half press of the shutter button will set the focus and the camera automatically takes care of all other settings.

    If you are focusing on a moving subject, the Al Servo AF will lock focus on the subject automatically as long as you keep the AF point on the subject and the shutter button pressed halfway.

  2. Portrait

    Canon Portrait camera icon - black side profile of a face on a white background

    This sets the aperture as large as possible under the conditions to narrow the depth of focus so that the face stands out from a blurred background.

    Focal Length: 34.0mm Aperture: F/5.6

    Portrait of a cats face
  3. Landscape

    Canon Landscape camera icon - black profile of a mountain on a white background

    This sets the aperture as small as possible given the conditions to increase the depth of field to sharpen as much of the scene as possible.

    Focal Length: 31.0mm Aperture: F/9.0

    Landscape view across wheat fields in Hampshire
  4. Sports

    Canon Sports camera icon - black sporting figure on a white background

    This sets the highest shutter speed to freeze the action. Focus is set to continuous while the shutter is pressed halfway.

    Shutter Speed: 1/320 sec Aperture: F/3.5

    A dog running, well ambling, in a garden
  5. Close Up

    Canon Close Up camera icon - black flower profile on a white background

    This sets a medium aperture so that there is some depth of field while the background is slightly out of focus.

    Focal Length: 31.0mm Aperture: F/4.5

    A close up of some chicken wire
  6. Night Portrait

    Canon Night portrait camera icon - white figure and a white star on a black background

    This balances the flash on the subject with the existing light in the background.

    Focal Length: 18.0mm Aperture: F/3.5

    A side portrait of a dogs face at night in a garden
  7. Disable Flash

    Canon Disable Flash camera icon - black lighting strike arrow
  						with a diagonal slash through it on a white background

    This disables the flash.

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Manipulating Manual Focus Modes

There are a number of exposure modes that you can set that allow you to set certain properties while the camera will automatically adjust the others. My Canon 400D has the following: