Low End DSLR: digital photography on a budget

April 04, 2008

Classifying lenses: the telephoto lens

This is part of an ongoing series of short articles about lenses and how they are used on Digital SLR cameras. The series currently contains the following articles:

Telephoto

These lenses have focal lengths that are longer than normal. Wildlife and sports photographers favor the longer versions of these lenses (200mm and up) as they allow you to get in close to the subject while still shooting from a distance.

Many portrait photographers like the shorter telephoto lenses such as 85mm or 135mm. These focal lengths make it easier to create a shallow depth of field, blurring the background and isolating the subject.

portrait taken at 200mm showing the blurred background that helps to isolate the subject

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Posted by Mark in: Equipment | Lenses | Tips-n-Tricks | Tutorials

April 03, 2008

Classifying lenses: the wide angle lens

This is part of an ongoing series of short articles about lenses and how they are used on Digital SLR cameras. The series currently contains the following articles:

Wide angle

Lenses with focal lengths that are less than normal are refered to as wide angle lenses. These lenses are best suited for capturing large areas and are preferred by landscape photographers who desire to capture stunning vistas. As lens manufacturing technology has improved, extremely wide angle lenses have been created, as well as fish-eye lenses that give a nearly 180° field of view. The wider a lens is, the more noticable the barrel distortion that these lenses create becomes. Many photographers use this distortion to artistic effect (whether you appreciate the art is another matter).

Wide angle lenses create images that have a lot of depth to them - they exagerrate the apparent distance between foreground and background. This tends to introduce distortion into images in a couple of ways.

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Posted by Mark in: Equipment | Lenses | Tips-n-Tricks | Tutorials

Classifying lenses: the normal lens

This is part of an ongoing series of short articles about lenses and how they are used on Digital SLR cameras. The series currently contains the following articles:

What is normal?

A normal lens is one that creates an image that is very close to how our eyes perceive the world. In other words, images made with these lenses “look normal.” There are no distortions introduced, or apparent compression of space that you might get with other lenses.

What is normal for a given camera depends on the size of whatever is doing the imaging. The formal definition is a lens whose focal lenght equals the diagonal of the image size. So a view camera with a 4" × 5" back has a diagonal of 154mm (96 × 120mm), and therefore a normal lens would be a 150mm lens. A large format 8 × 10 camera would have a 300mm normal lens.

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Posted by Mark in: Equipment | Lenses | Tips-n-Tricks | Tutorials | Comments (1)

Classifying lenses: the crop factor

This is part of an ongoing series of short articles about lenses and how they are used on Digital SLR cameras. The series currently contains the following articles:

Crop Factor

Most digital SLRs use sensors that are slightly smaller than the size of 35mm film. Film has an image diagonal of 43mm, while these smaller sensors have image diagonals of 27mm. The lenses they use are still designed to create an image on a piece of 35mm film. What happens is that the image that is created is effectively a crop of what the image would have been if it were a full frame or film camera. The ratio of full frame to the smaller sensors comes out to 1.6, and many times these cameras are referred to as having a 1.6 crop factor.

The image above should help make this clearer. This is Tunnel View looking east over the Yosemite Valley toward Half Dome. The circle is the image that is projected on the back of a 35mm camera. The red rectangle represents 35mm film, or the area of a full frame sensor. Note that the circle is a bit larger than that area, and in practice probably has even a bit more overlap.

The yellow rectangle represents the area of a 1.6 crop sensor. Notice that nothing about the projected image has changed. The smaller sensor simply records a smaller area of the image, like a croppped area of the image.

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Posted by Mark in: Equipment | Lenses | Tips-n-Tricks | Tutorials

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