LYCOS RETRIEVER 
Lens: Lenses
built 621 days ago
Lenses do not form perfect images, and there is always some degree of distortion or aberration introduced by the lens which causes the image to be an imperfect replica of the object. Careful design of the lens system for a particular application ensures that the aberration is minimized. There are several different types of aberration which can affect image quality.
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NikonNet’s “Legends Behind the Lens” series aims to educate users and, in turn, breathe excitement into photography. Nikon has assembled a comprehensive and intriguing collection of artists to share their most incredible, challenging, emotional and exciting experiences on NikonNet.
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A klystron-powered proton beam was produced by IUCF’s Low Energy Neutron Source (LENS) accelerator for the first time on December 20, 2006. For the last two years, since December 2004, the LENS source has been producing neutrons using an accelerator employing a vacuum tube RF power system. This system was able to deliver less than 750kW of power to the accelerator. With the original RF system, the LENS source was limited to beams of less than 250W. The successful commissioning of the klyston RF power systems, involving two 1MW klystron amplifiers, is the first step in an upgrade that will raise the power of the source over the next several months to 2kW. Future upgrades to the accelerator and conventional AC power systems of the facility will eventually raise the beam power to 20kW or more.
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-- Settling Time - Participants were allowed to view the examination room freely for 15 minutes, while the lens was settling on the eye. -- Reading - Participants read a newspaper with wide text for 2 minutes. -- Visual Search - Participants gazed centrally, and then were instructed to identify a number embedded within the text of a newspaper, read the specified paragraph, and then return to primary position. The paragraphs were positioned randomly from the center of the field in various directions. -- Large versional tasks - Participants were instructed to blink to the sound of a metronome set at 40 beats per minute. At approximately 20- second intervals, they were instructed to gaze at targets located on a large board positioned approximately two-feet away.
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Solid "ears" (see note) on your lens indicate an Non-AI lens. These lenses can not be mounted on many of the later bodies without causing damage because the "ears" strike the body prism when you mount them. See the charts to determine if they will physically mount on your camera body. If the lens will mount on your camera body, then check if it will allow normal metering or if you are required to "stop down" the lens to meter. If you are required to "stop down" to properly meter, you first focus the lens at it's maximum aperture with a bright screen, then "stop down" to meter for proper exposure, then release the shutter. (Not very handy to do) Small picture at right shows the coupling pin on the body.
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Conventional focusing has normallybeen performed by moving either all lens groups as a fixed unit or onlythe first lens group. AF cameras are now widely used, even for close-upphotography. Consequently, demand has arisen for a focusing system thatwill keep the length of the lens unchanged while showing little fluctuationof aberration. In response to this demand, SIGMA has developed a newinner focus system that moves two lens groups inside the telephoto andtelephoto MACRO lenses. This system has floating elements thatsubstantially improve the close-upcapability of the lens. The superwide angle lens having a large front-lens uses a rear focusing system tomove the rear-lens apparatus andenhance the floating effect, and the18-200mm F3.5-6.3 DC features aninner focusing system to move thesecondary lens group duringfocusing.
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