The greatest advantage of aspherical lenses: several types of optical aberrations can be corrected at one time. They are used particularly in highquality lenses allowing for the use of fewer lens elements so that a high luminous intensity is attained. Extra-low dispersion ED lens elements Normal glass lenses tend to divide the incident light into its various colour components, as a prism would do. This happens particularly at the edges, adding unwanted colour fringing to the photo.
The longer the focal length of the lens the more apparent is the fringing effect. ED glass is an exceptionally highquality special glass that prevents this socalled chromatic aberration to a very great extent.
Inner Focusing Each lens is composed of several groups of lens elements. With an Inner Focusing design only one of these groups is moved. Inner Focusing brings a number of advantages compared to a conventional focusing design where all the lens groups are moved: it works faster and the overall length of the lens remains unchanged so the centre of balance remains constant.
They are not compatible with 35mm film SLRs. For this reason, because natural light consists of light of various wavelengths, this light fails to converge to a single focal point when passing through a lens.
When an image is enlarged on a computer screen, you can sometimes see purple blurring around images of red points, for example. This is called chromatic aberration. In typical lenses using optical glass, this is difficult to correct as the focal length becomes longer. The appropriate glass types are used for attaining exceptional imaging performance in both telephoto lenses and wide-angle lenses.
In typical lenses, the aberration correction is balanced based on frequently-used shooting distances, but this can result in aberration at other shooting distances. To resolve this problem, PENTAX uses a floating lens system for changing the space between parts of the lens system based on the shooting distance.
In typical lenses, this improves the imaging performance for closeup photography and also enables shorter minimum shooting distances. For large-aperture, wide-angle lenses in particular, this corrects the field curvature which tends to occur at close ranges for providing sharp delineation from near to far distances. Also, in macro lenses which are primarily intended for closeup photography, this enables improved imaging performance at close distances.
This floating system is also incorporated into the inner focus of the lens. It is a type of floating lens system where the front group only of the lens system is moved without moving the rear group during the focusing operation.
Changes in performance based on the shooting distance, which tends to occur at an open F value, are reduced, and this enables sharp delineation performance from near to far distances. In lenses where the iris has a polygonal shape when opened, refraction can cause streaks of light to occur when shooting point light sources. With round iris diaphragms, on the other hand, the light sources appear to be enveloped in soft, rounded light when they are captured.
Even in regular photography, blurred light particles appear soft and natural without a polygonal shape. This mechanism performs diaphragm control operations by receiving electronic signals from the camera body and shifting the aperture blades with the driving motor built into the lens.
It lets the user change aperture settings more flexibly during movie recording, because it operates very quietly by minimizing the diaphragm control noise that otherwise could be recorded in movie clips. It also controls aperture more accurately to assure stable, high-precision exposure control, especially when an AF rear converter is used for shooting. These lenses perform the AF operation using the motor drive in the lens barrel. This enables a quieter and smoother AF operation than body AF operation driven by the focusing mechanism motor inside the camera body, and enables an easy, comfortable focusing operation.
The SDM supersonic motor includes a brake mechanism for allowing high-accuracy speed control and position control. Lenses that employ a drive mechanism which directly links the PLM and lead screw are not only silent, but offer high-speed, high-precision AF operation.
Typical interchangeable lenses use an all-group shifting system where the entire lens group moves to focus. By contrast, an IF system moves only a portion of the lens system to focus.
In the IF system, the lenses driven by the motor during the AF operation are lighter for faster AF operation and shorter minimum shooting distance, which enables improved imaging performance during closeup shooting. Also, the total lens length does not change due to the focusing operation for preventing weight imbalances, which is particularly advantageous for super telephoto lenses.
In zoom lenses where the focal length is controlled while holding an accurate focus, one lens system moves to change the focal length while at the same time, another lens system must correct the focus.
For this reason, at least two lens groups must be moved in a zoom lens. To enable improved performance over the entire zoom range, higher magnification, and a more compact and easy-to-use design, most PENTAX zoom lenses use three to five moving lens groups instead of only two.
These lenses incorporate PENTAX's advanced technology features such as our inner zoom which moves only the internal lens system without changing the total lens length and nonlinear movement zoom where each lens system performs complex movements. They get wider as they get focused closer. FREE lenses achieve low field curvature and low spherical aberrations not only when focused close to infinity but also at very short distances.
For normal applications the FREE system leads to small physical extensions, and thus allows the design of physically smaller and lighter lenses. For macro applications FREE lenses exhibit non-proportionately long extensions which aid precise focusing.
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