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Orion 9877 - page 1
Astronomical T elescope User Guide OPTICAL VISION LIMITED www.opticalvision.co.uk ® W ARNING!! Never point the telescope directly at or near the Sun at any time. Observing the Sun, even for a fraction of a second, will result in instant and ir r eversible eye damage. Please ensure minors ar e supervised by an adult conversant with this real danger ...
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Orion 9877 - page 2
O f all the many and varied telescopes av ai lab le for use b y am at eur astronomers and nature watchers, all can be cat egor ised into three typ es: th e r e f r a c t o r , the r e flec t or & the c a t a dioptr ic . Each have their relative strengths and weak- nesses, but they all have a common function: to gather and focus light from dista ...
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Orion 9877 - page 3
Consequently, an objective lens is a piece of optical equipment that is difficult to manufac - ture and explains why refractors are the most expensive form of telescope, aperture for aperture. However, a refractor can deliver exquisite images that are very well cor rected and extremly high in contrast, suitable for observing fine lunar and planetar ...
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Orion 9877 - page 4
O f all the many and varied telescopes a vailable for u se by the a mateur astronomers, the mountings that sup- port them fall into two types - the alt-azimuth and the equa torial. The 'Using your telescope ' section of this booklet that follows will tell you more about these terms and the actual use of your instrument, so we will concent ...
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Orion 9877 - page 5
Balancing the Telescope: T o eliminate stresses on the EQ equatorial mounts and to ensure smooth, judder-free motion of the tel escope th e inst r ument needs to be balanced about both the declination and polar (right ascension) axis. This is especially im- portant if you propose to use a motor drive for astrophotography at a future date. (i) Locat ...
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Orion 9877 - page 6
Attaching the finderscope: An essential prerequisite for the easy location of objects on both land and in the sky is the corr ect location and al ignment of the finder- scop e that attac hes to the tube of the tele- scope. It is, in fact, a smaller version of the main telescope that is designed to have a low magnification and a wide field of view s ...
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Orion 9877 - page 7
The focal length of the telescope is usually given on a label near the eyepiece focuser and is the distance from the main lens or mir ror to the point at which it forms an image of a distant object. The magnification of any given telescope/eyepiece combination is given thus: Magnification = focal length of telescope focal length of eyepiece For exa ...
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Orion 9877 - page 8
D e pendi ng on the type of te lescope mount that you possess, there are two ways in which you can move the instr u- ment in order to locate and track objects in the sky. I stress ‘track’ here since, unlike viewing stationary ter r estrial objects, the rota- tion of the Earth on it’s axis once in 24 hours from west to east causes the sky to m ...
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Orion 9877 - page 9
The further that one moves across the sky from Polaris, the apparent motion of the stars becomes more evident and their Altitudes and Azimuths will be continually changing. Taking the star labelled ‘AA’ in Fig. 1, at the instant of the observation its Altitude was 60° and its Azimuth bearing was also 60°. It can be seen that Azimuths are meas ...
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Orion 9877 - page 10
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Orion 9877 - page 11
T he E art h's ea stw ard r otati on c auses stars to apparently rotate around a point in the sky which is a projection of the Earth's axis, called the celestial pole. A star's p ath t h r o ugh th e sky fr om a n ear t h b o u n d o b s e rv e r ' s viewpoint is therefore an arc of this r ota t io n; it ri se s in th e e as t t ...
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Orion 9877 - page 12
12 Polar axis alignment (precise setting) The follow ing process w ill allow tracking without the need for occasional cor rections, an d i s e ss ent ial i f p hoto gra phy us in g a motorised drive is envisioned. If the approx- imate alignment described above has been carried out cor r ectly, only very minor adjust- ments in azimuth (north-south l ...
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Orion 9877 - page 13
13 Once this line of axial movement has been established, set the star at the edge of the field and allow it to drift across via its own motion. If the star drifts upwards from this line ( figure 5a ), then the north end of the polar axis needs to be raised. If the star drifts below this line ( figure 5b ), the north end of the polar axis needs to ...
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Orion 9877 - page 14
14 Using the setting circles (The following applies to telescopes using a single index on the R.A. circle) The easiest way to use setting circles is to off- set from a known position. Set the telescope on an object whose position is known (i.e. a bright star in a recognisable constellation - such as listed in the appendix). Unclamp and turn the R.A ...
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Orion 9877 - page 15
15 W i th t he t el e sco pe as se mb le d, ba la nc ed a n d po l ar -a l i gn e d a s d e s cr i b ed pr e v i o u s l y , yo u a re re ady t o be g in o bs er v a t i o n s . D e cid e o n an eas y to fi nd ob je ct su ch as th e M oo n, i f v i sib le , or a bri gh t st ar t o b eco me a cc us to me d to th e fun c ti on s an d op er at io ns o ...
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Orion 9877 - page 16
16 S ince the dawn of mankind there have bee n indepe ndent thinkers who hav e sought to understand the nature of the Universe and our relationship to it. It is per- haps the city or suburban observer who feels the call of the cosmos most intensely when he or she experiences the majesty of the night sky from a truly rural location for the very firs ...
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Orion 9877 - page 17
17 to cover the seven principal stars that delin- eate the figure of Orion. If we wish to be a little bolder we can relate the span of our outstretched hand to actual angular measure. It so happens that the span of our hand cor r esponds to just over 20 degrees (the symbol for degree is°), while the length of our thumb is about 7°. This latter fi ...
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Orion 9877 - page 18
18 s peci a l fil ters th at can almost magica lly r emove the orange cast to the sky created by sodium streetlights revealing a dark, star - studded sky beyond. These filters are not cheap – you can spend £100 quite easily for two for a pair of binoculars – but to the tele- scope user they are almost mandatory for any se r ious work c o nc er ...
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Orion 9877 - page 19
19 a simple way to avoid camera shake which ruins many a time exposure. So how long should you leave the lens uncov- ered? Under dark skies with ISO 400 film and a 50mm f/2.8 lens you can expose for up to about 20 seconds before the motion of the stars becomes evident as small trails on the film. However, if the sky is exceptionally dark and the ca ...
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Orion 9877 - page 20
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