The Abicana webstore
Mail: aquila_grande@yahoo.no
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The Abicana webstore
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Mail: aquila_grande@yahoo.no
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Scientific products for hobby and professional use - also other hobby items
If you have science as your hobby, you can find a lot of articles for your speartime activities here for an affordable prize: Kits and components for hobby electronics, microscope for the hobby biologist, telescopes for hobby astronomers, binoculars you can use in field investiqations, and a lot more. Many of the most advanced products are of professional standard, and can also be used in professional environments. You can also find other hobby equipment like remote controle models of helicopters, aircrafts, cars and boats. Further down on this page there is also an article about telescope design.
The products exhibited on this page are only examples of a huge collections. By clicking on the links, you can learn more about the exhibited products or find a lot of other products of the same type.
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Imaginova - hobby science and learning materials: This is a great store of hobby science and scientific learning materials.
Dino Direct - a general store with many advanced objects for reduced prizes,
among those also microscopes, telescopes and other scientific instruments. In this store you can find all kind of optical and audiovisual equipment for
hobby, education and proffessional use.
MEDEXSUPPLY - a medical equipment store with a great inventory of microscopes and optical instruments for general scientific, medical and biological use - You can also find any kind of medical equipment here.
MICROSCOPES By clicking at any of the
following links, you will also find other microscopes of all prize
cathegories that those exhibited
at this page. TELESCOPES By clicking at any of the
following links, you will also find many other telescopes that those
exhibited at this page. BINOCULARS AND BINOCULAR CAMERAS By clicking at any of the
following links, you will also find a huge collection of other binoculars
with a variety of spedific characteristics: Lens width, magification,
nighttime vision capabilities, infrared spotlight, waterproofness, physical
sizes and shapes, combination with camera, and more. <
NIGHT VISION SCOPES, BINOCULARS AND CAMERAS Finding the right night vision
device, depends heavily upon your purpose. Through these links you can buy
the exhibited products of finde many others that comform to special demands.
METAL DETECTORS
ELECTRONIC SETS AND COMPONENTS Here are examples of the electronic building sets available. By clicking at the link you can find many more electronic sets and a huge collection of electronic components of any kind.
CHEMISTRY AND PHYSICS SETS Here are example of the chemistry sets available. Please click on the links to browse for even more chemistry kits.
CAMERAS AND CAMCORDERS Quality digital cameras and equipment for good prizes: This is a great shop of cameras an all other types of optical equipment. Products Digital Concepts, Hewlett-Packard, Nikon, Olympus, Panasonic, Pentax, Samsung, Sony, Casio, Digital Blue, Disney, FujiFilm, Girl Gear, Hallo Kitty, Rollei, Sakar, Sealife, Sigma, Spy Chix, VuPointsAll types of camera accessories: Digital SLR, Compact Cameras, Digital Picture Frames, Camera & Printer Kits, Lenses, Memory, Batteries, Bags & Cases, Filters, Tripods, Flashes, Tutorials, Studio Lighting, Docking Stations, Software. Free shipping and no sales tax. Please click at this banner to exactly the camera or equipment you want. Please click at this product link either to get this camera or to browse for all the others.
ALL KINDS OF ELECTRONIC EQUIPMENT AND INTERNET PRODUCTS Consumer electronics: Computers, Televisions, DVD Players / Recorders, Home Audio / Video, MP3 Players / iPod Accessories, Satellite Radio, Headphones, Mobile Audio / Video, GPS / Navigation, Home Electronics, Telephones & Fax, Personal Electronics, Electronic Accessories Please click here for electronic equipment of all kind
PhoneSale.com - Affordable unlocked cellphones and cellphones with plans: Cellphones and phone accessories from many producents for good prizes. The shop specializes in unlocked cellphones but you can also find cellphones bound to a carrier's plan, which of cource will gie you an even lower entrance prize. PhoneSale.com - please click here to enter the shop
GOOD GENERAL HOBBY ITEM SHOPS AND SHOPS OF SCIENTIFIC HOBBY ITEMS In these shops you can find many hoppy science items and all other types of hobby products. A general hobby store
Another general hobby store
GOOD ONLINE STORES OF MODELS OF AIRCRAFTS, CARS AND BOATS Xenonproject.com - All types of RC gear -This comprehensive shop of RC models and RC equipment is organized in a logical fashion so that you can browse through the cathegories and find exactly those products that adhere to your won requirements or that fit the purson you buy something for as a gift.
Special collection of nitro driven modelsThis is a very great collection of nitro diven airplane models with various motor technologies.
Nitro and electric driven redcats: Examples: Hurricane XP PRO, Monsoon XP, Avalamche XP, Tornado BP, Tsunami, Tsunami ultrawide, Volcano SV SV Pro, Tremor ATV XTB XtG XTK XTR. Electric redcats: Lightning XTK, Tornado EPX, Tsunami EPX, Volcano EPXr.
A special store for helicopter models
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GENERAL TECHNICAL INFORMATION
Here is some information about telescopes. To find other information resources, please go to this page
OPTICAL TELESCOPES
Generally
about optical telescopes
An optical telescope gathers and focuses light mainly from the visible part
of the Electromagnetic spectrum (although some work in the infrared and
ultraviolet). Thereby also pictures of the objects that the light originates
from will be focused. Optical telescopes increase the apparent angular size
of distant objects, as well as their apparent brightness. Telescopes work by
employing one or more curved optical elements - lenses or mirrors - to
gather light or other electromagnetic radiation and bring that light or
radiation to a focus where the image can be observed, photographed or
studied.
Practical telescopes have at least two main lenses or lens collections. The objective resceives the light and focuses it. The oculular or eyepiece enlarges the image of the object further. The objective will make the image up- to down and right to left. To counteract this effect, many telescopes have a third element between to convert back.
The focusing can be done with convexe lenses, that is lenses that are thickest in the mid. They can also be done by concave mirrors, that is mirrors that bulge inwards at the side that collects the light. A combination of lenses and mirrors can also be used.
It is also possible to use mirrors to let the light go forth and back through the same tube. In this way the telescope can be made a lot shorter. There are three main types of telescopes.
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The refracting telescope in which the light goes only through a collection
of lenses to be focused after having passed.
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The reflecting telescope which uses only an arrangement of mirrors that
eventually reflects the light onto a plane.
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The catadioptric telescope which uses a combination of mirrors and lenses.
Optical telescopes are used for astronomy and in many non-astronomical instruments including theodolites, transits, spotting scopes, monoculars, binoculars, camera lenses, and spyglasses.
Refractor telescopes
A typical refractor has two basic
elements, a convex objective lens and an eyepiece lens. The objective in a
refracting telescope refracts or bends light at each end using lenses. This
refraction causes parallel light rays to converge at a focal point; while
those which were not parallel converge upon a focal plane. This can enable a
user to view the image of a distant object as if it were brighter, clearer,
and/or larger. Refracting telescopes can come in many different
configurations to correct for image orientation and types of aberration.
Galilean telescope -
The original design Galileo came up
with is commonly called a Galilean telescope. It uses a convex objective
lens and a concave eyepiece lens.
The first telescope used the same principles that all telescopes would rely
upon. The combination of the two lenses gathered more light than the human
eye could collect on its own, focused it, and formed an image. Because the
image was formed by the bending of light, or refraction, these telescopes
came to be known as refracting telescopes or, simply, refractors.
Galileo’s best telescope magnified objects about 30 times. Because of flaws
in its design, such as the shape of the lens, the images were blurry and
distorted. But it was good enough for Galileo to explore the sky.
Keplerian Telescope -
The Keplerian Telescope, invented by Johannes Kepler in 1611, is an
improvement on Galileo's design. It uses a convex lens as the eyepiece
instead of Galileo's concave one. The advantage of this arrangement is the
rays of light emerging from the eyepiece are converging. This allows for a
much wider field of view and greater eye relief but the image for the viewer
is inverted. Considerably higher magnifications can be reached with this
design but to overcome aberrations the simple objective lens needs to have a
very high f-ratio (Johannes Hevelius built one with a 45 m (150 ft.) focal
length). The design also allows for use of a micrometer at the focal plane
(used to determining the angular size and/or distance between objects
observed).
Achromatic
telescope - The Achromatic
refracting lens was invented in 1733 by an English barrister named Chester
Moore Hall although it was independently invented and patented by John
Dollond. The design limits the effects of chromatic and spherical aberration
by using an objective made of two pieces of glass (with different dispersion),
"crown" and "flint glass". Each side of each piece is ground and polished,
and then the two pieces are assembled together. Achromatic lenses are
corrected to bring two wavelengths (typically red and blue) into focus in
the same plane.
Apochromatic refractors
- Apochromatic refractors have
objectives built with special, extra-low dispersion materials. They are
designed to bring three wavelengths (typically red, green, and blue) into
focus in the same plane. The residual color error (secondary spectrum) can
be up to an order of magnitude less than that of an achromatic lens. Such
telescopes contain elements of fluorite or special, extra-low dispersion
(ED) glass in the objective and produce a very crisp image that is virtually
free of chromatic aberration. Such telescopes are sold in the high-end
amateur telescope market. Apochromatic refractors are available with
objectives of up to 553mm in diameter, but most are between 80 and 152mm.
Reflector telescopes
A curved primary mirror is the reflector
telescope's basic optical element and creates an image at the focal plane.
The distance from the mirror to the focal plane is called the focal length.
Film or a digital sensor may be located here to record the image, or an
eyepiece for visual observation.
Mirrors eliminate chromatic aberration but still produce other types of
aberrations: In general, on axis they produce spherical aberration - the
outer and inner zones of the telescope do not share a common focus. This was
the construction flaw in the Hubble Space Telescope mirrors. Spherical
aberration can be eliminated with aspheric (non-spherical) mirrors. Off axis,
additional aberrations will become apparent:
Coma -
a variation of telescope magnification with radial zone on the mirror
typically appears as a radial smudging of the images which gets worse at the
edges of the field. Spherical aberration and coma are eliminated in two
mirror Ritchey Chretien designs. The best image plane is in general curved,
which may not correspond to the detector's shape and leads to a focus error
across the field.
Astigmatism - is an azimuthal variation of focus around the aperture. Near the center of the field astigmatism is not usually a problem, but it gets rapidly worse once it becomes apparent - it varies quadratically with field angle.
Distortion over the field of view - Distortion does not affect image quality (sharpness) but does affect object shapes. It can be corrected by image processing.
There are reflector designs and
modifications such as catadioptrics that correct some of these aberrations.
Nearly all large research-grade astronomical telescopes are reflectors.
There are several reasons for this:
In a lens the entire volume of material has to be free of imperfection and
inhomogeneities, whereas in a mirror, only one surface has to be perfectly
polished.
Light of different wavelengths travels through a medium other than vacuum at different speeds. This causes chromatic aberration in uncorrected lenses and creating an aberration-free large lens is a costly process. A mirror can eliminate this problem entirely.
Reflectors work in a wider spectrum of light since certain wavelengths are absorbed when passing through glass elements like those found in a refractor or catadioptric.
There are structural problems involved in manufacturing and manipulating large-aperture lenses. A lens can only be held in place by its edge, which means that the sag due to gravity can be sufficient to distort the image. In contrast, a mirror can be supported by the whole side opposite its reflecting face.
While the Newtonian focus design is still used in amateur astronomy, professionals now tend to use prime focus, Cassegrain focus, and coudé focus designs. By 2001, there were at least 49 reflectors with primary mirrors having diameters of 2 meters or more.
Catadiopteric telescopes
Catadioptric telescopes are designs that
combine specifically shaped mirrors and lenses to allow very fast focal
ratios (when used at the prime focus), while controlling coma and
astigmatism.
Telescope makers also use catadioptric designs for any or all of the
following reasons:
They employ spherical surfaces that are easier to manufacture.
When used in a cassegrain configuration it results in a long focal length
instrument that is "folded" into a much smaller package.
Catadioptric designs are low maintenance and rugged since some or all of
their elements are fixed in alignment (collimation).
Combining a moving primary mirror with a cassegrain configuration allow for
large movements in the focal plane to accommodate cameras and CCDS.
The corrector plates seal the tube assembly from dust and dirt. They also
block air currents from the interior of the tube, thereby increasing image
stability.
A disadvantage to this design is that the secondary mirror blocks a portion
of the light entering the tube.
Schmidt-Cassegrain -
The Schmidt-Cassegrain is a classic wide-field telescope. The first optical
element is a Schmidt corrector plate. The plate is figured by placing a
vacuum on one side, and grinding the exact correction required to correct
the spherical aberration caused by the primary mirror.
Thousands of amateur astronomers have purchased and used Schmidt-Cassegrain
telescopes, with diameters from 20 cm (8 in.) to 48 cm (16 in.), since this
type of telescope was introduced by Celestron in the 1960s. Now many
companies mass-produce this type of telescope, at prices that make them
quite affordable for many amateurs. One of the major advantages of the
Schmidt-Cassegrain is that its folded light path makes the optical tube very
short and squat, thus increasing its portability. It also has optics that
are good for both planetary and deep sky observing.
Maksutov-Cassegrain -
Light path in a Maksutov-CassegrainMain
article: Maksutov telescope
The Maksutov-Cassegrain is a variation of the Maksutov telescope, invented
by Dmitri Maksutov. It starts with an optically transparent corrector lens
that is a section of a hollow sphere. It has a spherical primary mirror, and
a spherical secondary that is often just a mirrored section of the corrector
lens. Maksutovs are mechanically simpler than small Cassegrains, have a
closed tube and all-spherical optics. The key difference from the similar
Schmidt telescope design is the meniscus-shaped corrector plate, that has
easy-to-make spherical surfaces, and not the complex aspherical form of the
Schmidt design. Maksutovs tend to have a narrower field of view than
Schmidt-Cassegrains due to their longer focal length and are generally
heavier as well. However, their small secondary mirror gives them better
resolution than a Schmidt-Cassegrain.
Picture of a Schmidt-Cassegrain telescope
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
RADIO TELESCOPES
Radio telescopes are directional radio
antennae that often have a parabolic shape. The dishes are sometimes
constructed of a conductive wire mesh whose openings are smaller than the
wavelength being observed. Multi-element Radio telescopes are constructed
from pairs or larger groups of these dishes to synthesize large "virtual"
apertures that are similar in size to the separation between the telescopes:
see aperture synthesis. As of 2005, the current record array size is many
times the width of the Earth, utilizing space-based Very Long Baseline
Interferometry (VLBI) telescopes such as the Japanese HALCA (Highly Advanced
Laboratory for Communications and Astronomy) VSOP (VLBI Space Observatory
Program) satellite. Aperture synthesis is now also being applied to optical
telescopes using optical interferometers (arrays of optical telescopes) and
Aperture Masking Interferometry at single reflecting telescopes.
X-ray and gamma-ray telescopes
X-ray and gamma-ray telescopes have a
problem because these rays go through most metals and glasses. Some x-ray
telescopes use ring-shaped "glancing" mirrors, made of heavy metals, that
reflect the rays just a few degrees. The mirrors are usually a section of a
rotated parabola. Gamma-ray telescopes give up on focusing entirely, and use
coded aperture masks; the pattern of shadows the mask creates can be
reconstructed to form an image.
These types of telescopes are usually on Earth-orbiting satellites or
high-flying balloons, since the Earth's atmosphere is opaque to this part of
the electromagnetic spectrum.
(The information above mostly originates from wikipedia.org and it is therefore free to copy and reuse)
