Celestron CR-150 HD - Manual (Page 37)

Celestial Observing • 37
Although overlooked by many amateur astronomers, solar observation is both
rewarding and fun. However, because the Sun is so bright, special precautions must
be taken when observing our star so as not to damage your eyes or your telescope.
WARNING: WARNING: WARNING: WARNING: WARNING: Never project an image of the Sun through the telescope. Because of Never project an image of the Sun through the telescope. Because of Never project an image of the Sun through the telescope. Because of Never project an image of the Sun through the telescope. Because of Never project an image of the Sun through the telescope. Because of
the folded optical design, tremendous heat build-up will result inside
the folded optical design, tremendous heat build-up will result inside the folded optical design, tremendous heat build-up will result inside the folded optical design, tremendous heat build-up will result inside the folded optical design, tremendous heat build-up will result inside
the optical tube. This can damage the telescope and/or any accesso-
the optical tube. This can damage the telescope and/or any accesso- the optical tube. This can damage the telescope and/or any accesso- the optical tube. This can damage the telescope and/or any accesso- the optical tube. This can damage the telescope and/or any accesso-
ries attached to the telescope.
ries attached to the telescope. ries attached to the telescope. ries attached to the telescope. ries attached to the telescope.
For safe solar viewing, use a Celestron solar filter. This filter reduces the intensity
of the Sun’s light, making it safe to view. With this filter you can see sunspots as
they move across the solar disk and faculae, which are bright patches seen near the
Sun’s edge. Be sure to cover the objective lens of the finder or com-
Be sure to cover the objective lens of the finder or com- Be sure to cover the objective lens of the finder or com- Be sure to cover the objective lens of the finder or com- Be sure to cover the objective lens of the finder or com-
pletely remove the finder when observing the Sun. This will ensure pletely remove the finder when observing the Sun. This will ensure pletely remove the finder when observing the Sun. This will ensure pletely remove the finder when observing the Sun. This will ensure pletely remove the finder when observing the Sun. This will ensure
that the finder itself is not damaged and that no one looks through it
that the finder itself is not damaged and that no one looks through it that the finder itself is not damaged and that no one looks through it that the finder itself is not damaged and that no one looks through it that the finder itself is not damaged and that no one looks through it
inadvertently.
inadvertently. inadvertently. inadvertently. inadvertently.
SOLAR OBSERVING HINTS SOLAR OBSERVING HINTS SOLAR OBSERVING HINTS SOLAR OBSERVING HINTS SOLAR OBSERVING HINTS
• The best time to observe the Sun is in the early morning or late afternoon
when the air is cooler.
• To locate the Sun without a finder, watch the shadow of the telescope tube
until it forms a circular shadow.
Observing the Sun Observing the Sun Observing the Sun Observing the Sun Observing the Sun
Using the Lens Cap Aperture Stop
As mentioned in the introduction, all refractive optics will exhibit some amount of
chromatic aberration due to the prism effect of lenses. Chromatic aberration will
become more pronounced the farther the incoming light rays are off-axis (i.e.
passing through the edge of the objective lens) and virtually unnoticeable on-axis
(passing through the center of the objective lens). This type of aberration is only
evident when observing very bright sources of light, such as bright planets and very
luminous stars (like Sirius). There are several techniques that the observer can
employ to suppress visible signs of chromatic aberration, these include; reducing
the aperture and using filters.
The objective lens cap covering the objective lens of the telescope has a built-in
112mm aperture stop in the center. By leaving the lens cap on the telescope with the
aperture stop removed, you will allow all the incoming light to pass closer to the
center of the optical axis. Since, most planets are extremely bright objects (visible to
the unaided eye) any loss of light from reducing the aperture will be unnoticeable.
The lens cap should always be completely removed when observing deep-sky
objects such as galaxies and nebulae, where aperture (light gathering power) is
essential and chromatic aberration is not an issue.
Another useful technique for reducing aberrations and improving planetary detail is
the use of colored eyepiece filters. Filters are commonly used to bring out particular
planetary detail, such as the polar caps on Mars or the bands and zones around
Jupiter. The use of colored filters (especially red and green filters) reduces the
effect of chromatic aberration as well as improves contrast and resolution.
NOTE: NOTE: NOTE: NOTE: NOTE: