Tuesday, June 1, 2004

June 2004 HelpLine

Resizing Images

    * Disappearing Photos
    * IRIS In Digial Cameras
    * Acronym Acrimony

DPMag Published in HelpLine

3. A lot of cameras that have onboard memory have a way of copying images from it to the memory card and vice versa. Since you can view the images on the camera, see if you can copy some of them to onboard memory. Then remove the faulty card and use another memory card to copy them to.

IRIS In Digital Cameras

Q)  Do digital cameras actually stop down their lenses, or is this just a manipulation of factors to control the chip download speed and interval? For example, does the aperture-preferred exposure mode mean the lens actually stops down to give me greater depth of field?

R.E. Jackson,
Collingswood, New Jersey

A)  For those of you who aren't familiar with the term, depth of field is the distance between the farthest and closest points in your scene that are in focus. It's controlled by the focal length of the lens, the aperture (or iris) of the lens, the distance from your camera to your subject and the size of your final print. The aperture settings are measured in ƒ-stops. The ƒ-stop number actually is derived from a ratio between the focal length of the lens and the diameter of the aperture.

Okay, enough of the definitions. Just remember that the larger the ƒ-stop number, the smaller the opening in the lens. When you "stop down" a lens, you're closing the iris of the lens, which increases your depth of field, which, in turn, increases the range of objects that will be in focus in your scene.

It's easy to assume that digital technology has replaced all the features in film-based photography with electronic wizardry. (Accommodating changes in light color temperature through white-balance settings versus putting a filter on the lens is one example of "doing it with electronics.") However, this can't change the optical path of the lens, which is where the iris is located. While digital cameras can adjust the apparent sensitivity of the chip, "stopping down" the lens is still done where it has always been done—in the lens.



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