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Viewing conditions affect what you can see through your telescope during an observing session. Conditions include transparency, sky illumination, and seeing.
Understanding viewing conditions and the effect they have on observing will help you get the most out of your telescope.
Transparency
Transparency is the clarity of the atmosphere which is affected by clouds, moisture, and other airborne particles. Thick cumulus clouds are completely opaque while
cirrus can be thin, allowing the light from the brightest stars through. Hazy skies absorb more light than clear skies making fainter objects harder to see and reducing
contrast on brighter objects. Aerosols ejected into the upper atmosphere from volcanic eruptions also affect transparency. Ideal conditions are when the night sky is
inky black.
Sky Illumination
General sky brightening caused by the Moon, aurorae, natural airglow, and light pollution greatly affect transparency. While not a problem for the brighter stars and
planets, bright skies reduce the contrast of extended nebulae making them difficult, if not impossible to see. To maximize your observing, limit deep sky viewing to
moonless nights far from the light polluted skies found around major urban areas. LPR filters enhance deep sky viewing from light polluted areas by blocking
unwanted light while transmitting light from certain deep sky objects. You can, on the other hand, observe planets and stars from light polluted areas or when the Moon
is out.
Seeing
Seeing conditions refers to the stability of the atmosphere and directly affects the amount of fine detail seen in extended objects. The air in our atmosphere acts as a
lens which bends and distorts incoming light rays. The amount of bending depends on air density. Varying temperature layers have different densities and, therefore,
bend light differently. Light rays from the same object arrive slightly displaced creating an imperfect or smeared image. These atmospheric disturbances vary from
time-to-time and place-to-place. The size of the air parcels compared to your aperture determines the "seeing" quality. Under good seeing conditions, fine detail is
visible on the brighter planets like Jupiter and Mars, and stars are pinpoint images. Under poor seeing conditions, images are blurred and stars appear as blobs.
The conditions described here apply to both visual and photographic observations.
Figure 5-3
Seeing conditions directly affect image quality. These drawings represent a point source (i.e., star) under bad
seeing conditions (left) to excellent conditions (right). Most often, seeing conditions produce images that lie
somewhere between these two extremes.
ASTROPHOTOGRAPHY
The PowerSeeker series of telescopes was designed for visual observing. After looking at the night sky for a while you may want to try your hand at photography of it.
There are a few simple forms of photography possible with your telescope for celestial pursuits although celestial photography is best done using an equatorial mount or
computerized altazimuth mount. Below is just a very brief discussion of some of the methods of photography available and suggest you search out various books for
detailed information on the subject matter.
As a minimum you will need a digital camera or 35mm (D)SLR camera. Attach your camera to the telescope with:
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Digital camera – you will need the Universal Digital Camera Adapter (# 93626). The adapter allows the camera to be mounted rigidly prime focus
astrophotography.
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35mm (D)SLR camera – you will need to remove your lens from the camera and attach a T-Ring for your specific camera brand. Then, you will need a T-Adapter
(# 93625) to attach on one end to the T-Ring and the other end to the telescope focus tube. Your telescope is now the camera lens.
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Short exposure prime focus photography is the best way to begin imaging celestial objects. It is done by attaching your camera to the telescope as described in the
paragraph above. A couple of points to keep in mind:
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You can image the Moon as well as the brighter planets with very short exposures. You will have to experiment with various settings and exposure times. Much
information can be obtained from your camera instruction manual which can supplement what you can find in detailed books on the subject matter.
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Do your photography from a dark sky observing site if possible.
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Remember, this is just very simple photography. For more detailed and serious astrophotography you need an equatorial mount or a computerized altazimuth
mount.
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During the last few years a new technology has evolved which makes taking superb images of the planets and moon relatively easy and the results are truly amazing.
Celestron offers the NexImage (# 93712) which is a special camera and included is software for image processing. You can capture planetary images your first night
out which rivals what professionals were doing with large telescopes just a few short years ago.
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Special cameras have been developed for taking images of deep sky images. These have evolved over the last several years to become much more economical and
amateurs can take fantastic images. Several books have been written on how to get the best images possible. The technology continues to evolve with better and easier
to use products on the market.
