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07-23-2010, 11:22 AM   #1
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Macro

I am curious about the "Macro" distinction on the pentax and sigma lenses. It looks like the pentax lenses that have a macro distinction are different focal lengths then the lenses that aren't are those lenses ONLY for macro photography? Several of the Sigma lenses have copies that don't specify Macro and then a copy with the same focal length and features that IS a macro lens. Can those with the macro option be used for general use photography as well as macro photography?

07-26-2010, 08:53 AM   #2
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QuoteOriginally posted by littledrawe Quote
Can those with the macro option be used for general use photography as well as macro photography?
Hello,

The quick answer is yes, Macro lens can be used for general photography.


Many lens manufacturers use the term ďmacroĒ but a true macro lens can focus to what is called 1:1. This term refers to image size which should not be confused with a computers file size. Letís say for example, you are photographing a postage stamp (23mm x 23mm) with a 35mm film (24x36mm in size) camera at 1:1. If you placed your processed film over the postage stamp, the image on film and the stamp would be the same size.

Another way to describe 1:1 is to double a lens focal length distance. Focal length is defined as the distance between the film or sensor surface (known as the focal plane) and the optical center or nodal point of a lens focused at infinity. So a 50mm lensís optical center would be 50mmís from the film or sensor plane at infinity. A 50mm lensís optical center moved 100mmís away from the focal plane (film or sensor) would be able to achieve 1:1. This is how large format photographers calculate macro focusing.

Iíll use Sigmaís Macro lens as an example. They make 4 fixed focal length macro lenses. The line up includes a normal 50mm lens, a 105mm, a 150 mm and a 180mm. At 1:1, the difference between the 4 lenses will be the Minimum Focus Distance. The 50mm lens will have a minimum focus distance of 7.4" (18.9 cm). The 105 will have a minimum focus distance of 12.2" (31 cm), the 150 would be 15" (38 cm) and the 180 1.5' (46 cm).

The differences of which lens to choose when shooting would be the desired working distance in-between the photographer and the subject. For example, if you were to photograph a flower in natural day light. Using the 50mm lens, you would be 7.4 inches away from the flower. You would more than likely block the natural day light, putting the subject in your shadow. Using a longer focal length lens would move you and your camera back, creating a more conducive working distance, allowing the natural day light to illuminate the flower you were photographing.

A shorter lens would be used when using a ring flash, for example. Keeping the flash as close to your subject as possible, would ensure the greatest amount of light reaching your subject, enabling you to use a small f-stop for the greatest amount of depth of field and sharpness.


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