BetterPhoto Q&A
Category: New Answers

LENSES

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June 02, 2006

Years ago it was determined that the normal lens for any camera is a lens with a focal length that closely matches the diagonal measure of the film format. In the case of a standard 35mm camera the image size (film format) is 24mm x 36mm and the diagonal measure of this rectangle is 43.3mm. Now 43.3 is an awkward length for a lens plus a little longer than the diagonal measure does no harm, so most 35mm cameras are sold with a normal lens of 50mm. This does two things. 1. The field of view closely replicates the normal angle of view of human beings. 2. All lenses project an image of the outside world onto the film/chip. Actually this image is a large circle and the film/chip frame sits in it’s center. All images so projected are dimmer at the peripheral. This phenomenon is known as a vignette. Now the longer the focal length the less the vignette effect. Thus the 50mm became the standard.

For other film formats and digital, the diagonal rule applies. You need to know your chip (sensor) size so you can calculate the diagonal. In the case of you camera, the chip is 15.6mm x 23.7mm and the diagonal measure is 28.4mm. Thus the normal lens for this camera is about 30mm. Anything shorter would be considered a wide angle and anything longer a telephoto.

Since most people think about lenses based on the 35mm camera experence, you can need to calculate a factor to convert back and forth between the two formats. In this case the factor is 1.5. As an example, your camera fitted with a 35mm focal length will function (have the same prospective) as a 52.5mm lens mounted on a 35mm camera.

To more directly answer your question:
Most lenses made for a 35mm camera, when mounted on your camera will be a little too long, otherwise they function OK. Sometimes long is better! As an example, it is widely thought that a 105mm lens is best for portraiture when using a 35mm camera. This focal length duplicates the prospective familiar to most as it is the prospective they see in their make-up mirror. Using the 1.5 factor, you would mount a 70mm on your camera to duplicate the same perspective. Thus you would use a 70mm (or longer) for portraiture.

Don’t hesitate to mount and use any lens. Just keep in mind the 1.5 conversion factor.

Best of luck,
Alan Marcus
ammarcus@earthlink.net

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June 03, 2006

A digitial lens is designed so that light hits the sensor straight-on, making the most use of the light coming into the lens.

You'll have success with either type of lens, though you'll probably find the digitial lenses are a bit cheaper. They're optimized for the size of the sensor and can be made smaller than their full-frame counterparts.

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June 03, 2006