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®
Astronomical
Telescope
User Guide
WARNING!!
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 reversible eye damage. Please ensure minors ar e
supervised by an adult conversant with this real danger when
using telescopes or binoculars.
OPTICAL VISION LIMITED
www.opticalvision.co.uk
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Types of Telescope... f all the many and varied telescopes < The refractor: available for use by amateur This is the type of Oastronomers and nature watchers, all instrument that the lay- can be categorised into three types: the man thinks of when r e f r a c t o r, the reflector & the catadioptric. conjuring up a mental Each have their relative strengths and weak- picture of a telescope. nesses, but they all have a common function: to gather and focus light from distant objects At the end of t
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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 corrected and extremly high in contrast, suitable for observing fine lunar and planetary detail, or for separating difficult double stars. Refractors are well suit- ed for people on the move since it is e x t remely difficult for the optic
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Telescopes & Mounts... The three legs should be attached to the tripod head one by one by the three bolts and wing nuts provided. They should not be overtight- ened, but just made finger tight. Pay par t i c u l a r attention to the orientation of each leg prior to assembly such that the tripod tray bracket is facing inward. The tripod may now be placed ALT-AZ on the ground with the legs splayed enough for the accessory tray to be attached. Adjust the height of each leg so that the tripod he
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screw firmly - the telescope is now balanced about the polar (right ascension) axis. (ii) With the counterweight bar horizontal, ensure that the right ascension clamp is locked and unlock the declination clamp and turn the telescope tube so that it is also hori- EQ-2 zontal. As before, GENTLY release your grip on the tube and note is there is a tendency for one end to rise in the air. If so, slowly loosen the clamps holding the tube and slowly slide the tube towards the end that rises. Lock th
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(iv) Turn the focuser knobs back or forth until Attaching the finderscope: the image becomes crisp and sharp. Do not An essential prerequisite for the easy location be concerned that the image appears upside of objects on both land and in the sky is the down (reflecting telescope) or reversed in a correct location and alignment of the finder- left to right plane (refractor with zenith prism) scope that attaches to the tube of the tele- - this is perfectly natural for an astronomical scope. It
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The focal length of the telescope is usually example would enable us to display the whole given on a label near the eyepiece focuser and of the Moon's disc within the eyepiece's field is the distance from the main lens or mirror of view. to the point at which it forms an image of a How many eyepieces should you have? Three distant object. The magnification of any given is ideal - one low, one medium and one high telescope/eyepiece combination is given thus: magnification - though two will s
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Using your telescop e ... epending on the type of telescope there is provision for slow motion controls in mount that you possess, there are two both altitude and azimuth — this makes for Dways in which you can move the instru- much finer control when tracking celestial ment in order to locate and track objects in objects at high power. the sky. I stress ‘track’ here since, unlike viewing stationary terrestrial objects, the rota- Alt-azimuth conventions: As has been dis- tion of the Earth on it’
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The further that one moves across the sky stars in their diurnal paths across the sky.The from Polaris, the apparent motion of the stars so-called declination axis can remain locked once the desired object has been located. becomes more evident and their Altitudes and Unlike the Alt-azimuth system, the coordi- Azimuths will be continually changing. Taking the star labelled ‘AA’ in Fig. 1, at the instant of nates of objects remain (relatively) fixed and a slightly different convention has to be u
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The equatorial mounting... Setting up and using an equatorial mount he Earth's eastward rotation causes must be very accurately aligned on the celestial stars to apparently rotate around a point pole. The better this is done, the less re q u i re m e nt Tin the sky which is a projection of the there will be for minor adjustments during Earth's axis, called the celestial pole. A star's observation. path t h rough the sky from an ear t h b o u n d o b s e rv e r ' s viewpoint is therefore an
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North Celestial Pole west on the polar axis only as shown in f i g u re 2a) (near Polaris) so that the star is impelled to move from one Declination Circle side of the eyepiece field to the other. It will help if you arrange this line of motion to bisect the eyepiece field (as in figure 2b). Polar axis This procedure can be made easier if a reticle Right Latitude is placed at the eyepiece focus and aligned to Ascension Circle indicate this motion, rather than having to Movement remember it
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Once this line of axial movement has been Having aligned the telescope mount with the established, set the star at the edge of the E a rth's polar axis it now becomes possible to field and allow it to drift across via its own use the sky's co-ordinate system to find objects motion. If the star drifts upwards from this not visible to the eye or finder scope. line (figure 5a), then the north end of the The setting circles polar axis needs to be raised. If the star drifts below this line (figure
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Using the setting circles Figure 6 (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. circle so that the its pointer indexes the observed object's positional hour and minute. E.g. In figure 6 , the R.A. circle has been set to
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Tips on observing with your telescope... ith the telescope assembled, balanced object in the field of view will begin to slowly and polar-aligned as described pr e v i o u s l y, move across the eyepiece field. This motion is Wyou are ready to begin observ a t i o n s . caused by the rotation of the Earth on its axis, Decide on an easy to find object such as the although the planets and stars are for practical Moon, if visible, or a bright star to become purposes fixed in their positions in the
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Get to know the sky... ince the dawn of mankind there have since many are confusingly covered with been independent thinkers who have lines, labels which frequently fail to give any Ssought to understand the nature of the indication as to how large a constellation (or Universe and our relationship to it. It is per- star group) will appear to the naked eye. haps the city or suburban observer who feels the call of the cosmos most intensely when he Joining the dots... : If you were good at see- or
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to cover the seven principal stars that delin- A further hand span to the upper left brings you to the celestial twins of Gemini, Castor eate the figure of Orion. and Pollux. If we wish to be a little bolder we can relate Another very familiar pattern visible through- the span of our outstretched hand to actual out the year is the constellation of Ursa Major, angular measure. It so happens that the span or the Great Bear. Also known as the 'Plough' of our hand corresponds to just over 20 or the
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special filters that can almost magically (or 'B' setting) setting, a standard 50mm lens, remove the orange cast to the sky created by a fast colour (or B/W, it's up to you) film, tri- sodium streetlights revealing a dark, star- pod and cable release. studded sky beyond. These filters are not The film you will need can be print or trans- cheap – you can spend £100 quite easily for parency (slide), but you need to buy one with two for a pair of binoculars – but to the tele- a speed of about ISO 4
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a simple way to avoid camera shake which make sure that the technician knows that your ruins many a time exposure. subject matter is astronomical since it is very frustrating to return to pick up your hard- So how long should you leave the lens uncov- earned snaps only to be told that the roll was ered? Under dark skies with ISO 400 film and unexposed - they're just not used to seeing a 50mm f/2.8 lens you can expose for up to tiny white dots! Just tell them to print all about 20 seconds before
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