Lens abberations

Building a camera lens with a single convex element is no big deal, but producing satisfactory results with such a construction is not really possible.

imageAn image that could be created using just a single lens element. Those defects can be minimised by combining lenses skillfully.

This is due to the innate imperfections of the lens, also known as aberrations. The final image may then contain partial unsharpness, distortion from the centre of the image to its edges (field curvature) and variations of image illumination as well as small colour shifts when reproducing small detail. Reducing the aberrations of a single lens is very difficult.

However, to correct such aberrations, it is often necessary to skilfully combine several lens elements (single lenses), some of which may be convex and some concave. The lens elements may be cemented together or arranged at accurately calculated distances to correct the aberrations of the individual lenses. Progress in optical engineering, i.e. lens design and materials (glass or plastic) has also led to noticeable improvements in image quality.

Minolta has been a leading manufacturer of high-quality lenses for many years and its G-Lens series has made a name for itself among professionals due to its outstanding image quality and craftsmanship. These lenses offer superior colour rendition with unsurpassed contrast, promising extraordinary imaging performance in the entire image.

G-Lens

A cross-section of the very complex construction of a Minolta GT lens; in this case the lens of the DiMAGE 7.

The area of a digital camera’s sensor, the CCD, is usually smaller than the frame of a 35mm film. Therefore, a CCD is prone to react more sensitively to lens aberrations than 35mm film. This explains the need for high-quality standards when manufacturing lenses for digital cameras. In order to attain the best possible image quality the G-Lens technology is applied to all DiMAGE cameras. These GT-Lenses are specially designed to maximise the image quality of the CCD.

 

Focal lengths and their effect on the image

In the beginning, lenses only had one focal length; hence the phrase fixed focal length. If different focal lengths were required the photographer had to carry all kinds of interchangeable lenses with different focal lengths. Modern zoom lenses, which have become increasingly popular in recent years, are those whose effective focal length can be varied within a specific range.

 

The importance of focal length

The choice of a lens’s focal length can be an important criterion when composing an image. But what exactly is the focal length of a lens?

In technical terms, this refers to the distance between the rear nodal point of the lens and the focal plane, meaning the plane where subjects at infinity come into focus. In practical terms, and using the example with the magnifying glass mentioned above, the focal length of the magnifying glass would be the distance between the magnifying glass itself and the piece of paper when the image of the sun (the little patch of light) is smallest.

The importance of focal length

When burning paper with a magnifying glass, the distance between the magnifying glass and the paper equals the focal length of the magnifying glass's lens.

If you try the same experiment with a different magnifying glass where its distance to the piece of paper is smaller, you may state without doubt, that the second magnifying glass has a shorter focal length.

Photoworld Articles

* This content is taken from the konicaminoltaphotoworld.com website that was unfortunately taken offline. I take full responsibility for offering this here on dyxum but I honestly believe that this contests SHOULD be available to all Konica Minolta customers; this is the least they can do !

mladen sever

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