Caz Photo Blog

Background
You might have heard some lenses described as “wide angle” or “telephoto”. This article should help you get to grips with different types of lenses and what they do.

Theory
With a 35mm film camera, a 50mm lens is called a “standard” lens because it shows the same angle of view and perspective as the human eye. It’s focal length is said to be 50mm. Using one of these lenses, you will see objects in the correct size and relationship to each other. Other lens types are:

• Wide angle - below 50mm, eg 24mm
  Shows a greater angle of view in the viewfinder than 50mm, but things “seem” to be further away.
• Telephoto - lenses above 50mm, eg 300mm
  Shows a smaller fraction of the scene than 50mm, so things “seem” to be nearer.

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Background
Have you ever wondered why the photos you take indoors sometimes come out looking very yellow? It’s a common mistake to make, and this tutorial should help you understand why it happens, and how to get it right!

Theory
The human eye is very good at adjusting to different light sources, and the brain compensates without you noticing, when going from outdoors to inside. If you look at a piece of white paper under both sorts of light, you won’t see any difference - but a camera will.

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Background
I’ve already mentioned Depth of Field briefly, in my tutorial on Apertures and F-Numbers. But it’s not just the aperture you are using which determines how much depth of field your pictures have.

Theory
Three factors influence the depth of field of an image. They are:

• Aperture of lens - the f-number you use at the time of taking the image
• Focal length of lens - eg, 28mm for a wide angle, 300mm for a telephoto.
• Distance to subject - how far you are from the main focus of the image.

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Background
I’ve already explained the basics of ISO speed, apertures and shutter speeds. Now it’s time to put them all together and see how they relate to the overall exposure of an image. The EV or Exposure Value for any given scene and lighting is always a constant.

Theory
The correct exposure for an image is governed by a complicated formula. However, all you really need to know is what effect altering any of the three options has on your pictures. So, for a particular scene and lighting conditions, your camera might suggest this exposure:

ISO 200, 1/250th @ f/5.6

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Background
The shutter speed is the amount of time that the film or CCD sensor is exposed to light, also known as the exposure or exposure time.

Theory
Shutter speeds are normally quoted in fractions of a second, written as eg. 1/30, which would mean one thirtieth of a second. Like apertures and ISO speeds, they normally follow a standard pattern:

1/1000th, 1/500th, 1/250th, 1/125th, 1/60th, 1/30th, 1/15th etc.

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