Celestron CR-150 HD Using the Lens Cap Aperture Stop, Observing the Sun, Solarobservinghints

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Using the Lens Cap Aperture Stop

Using the Lens Cap Aperture Stop

NOTE:

Observing the Sun

Asmentionedintheintroduction,allrefractiveopticswillexhibitsomeamountof 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.

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:

Never project an image of the Sun through the telescope. Because of the folded optical design, tremendous heat build-up will result inside the optical tube. This can damage the telescope and/or any accesso- 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- 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 inadvertently.

SOLAROBSERVINGHINTS

•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.

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Contents The CR-150HD Model #210176 Refractor ii Table of Contents T A B L E O F C O N T E N T SAssembling the CG-5Equatorial Mount Table of Contents Using the Lens Cap Aperture Stop4 Introduction I N T R O D U C T I O NIntroduction How to Use This Manual AWordofCautionThe Mount The Refractor Optical System6 Introduction Unpacking Your CR-150HD A S S E M B L I N G Y O U R C R - 1 5 0 H DThe CR-150HD Assembling the CG-5Equatorial Mount Setting Up the Tripod Adjusting the Tripod HeightTripod Head 10 The CR-150HD Attaching the Accessory TrayAttaching the Equatorial Mount 12 The CR-150HD Attaching the R.A. Slow Motion KnobAttaching the Declination Slow Motion Knob 14 The CR-150HD 1.Lock the DEC clamp to hold the mount in placeTube Rings Dovetail Bracket Attaching the Telescope to the Mount16 The CR-150HD Balancing the Telescope in R.ACOMPLETELY Balancing the Telescope in DECAdjusting the Mount in Azimuth Adjusting the Mount in Altitude18 The CR-150HD Disassembling and Transporting Your CR 150 HD Technical SpecificationsStoring Your CR- 150 HD OPTICAL TUBET E L E S C O P E B A S I C S Attaching the AccessoriesThe Star Diagonal The EyepieceFocuser Tension 1 1/4 AccessoryAdapter Built-inT-AdapterAttaching the Finder Focusing22 Telescope Basics Aligning the Finder YourFirstLook Image OrientationDaytimeObserving NEVER POINT YOUR TELESCOPE AT THE SUN UNLESSNighttime Observing Determining Field of View Calculating Magnification26 Telescope Basics GeneralPhotographyHints Your Celestron telescope can be used for both terrestrial and astronomical photography. Your telescope has a fixed aperture and, as a result, a fixed f/ratio. To properly expose your subjects photographically, you need to set your shutter speed accordingly. Most 35mm single lens reflex SLR cameras offer through-the-lens metering that lets you know if your picture is under or overexposed. This is important for terrestrial photography where exposure times are measured in fractions of a second. In astrophotography, the exposures are much longer, requiring that you use the “B” setting on your camera. The actual exposure time is determined by how long you keep the shutter open. More on this in the section on “Celestial Photography.” The Celestial Coordi- nate System A S T R O N O M Y B A S I C S28 Astronomy Basics Astronomy Basics Motion of the StarsEquator Polar AlignmentDefinition 30 Astronomy BasicsFinding the Pole 32 Astronomy Basics Latitude ScalesPointingatPolaris 34 Astronomy Basics DeclinationDriftPolar Alignment Finders Aligning the R.A Setting CircleObserving the Observing the MoonPlanets C E L E S T I A L O B S E R V I N GObserving the Sun Using the Lens Cap Aperture StopSOLAROBSERVINGHINTS Celestial ObservingObserving Deep-SkyObjects Using the Setting Circles38 Celestial Observing StarHopping 40 Celestial Observing Transparency Viewing ConditionsSky Illumination Seeing42 Celestial Observing Celestial Photography C E L E S T I A L P H O T O G R A P H YLunar Phase Short Exposure Prime FocusCrescent QuarterThe exposure times listed here should be used as a starting point. Always make exposures that are longer and shorter than the recommended time. Also, try bracketing your exposures, taking a few photos at each shutter speed. This will ensure that you will get a good photo. If using black and white film, try a yellow filter to reduce the light intensity and to increase contrast 46 Celestial Photography PiggybackEktar 1000 color print Konica 3200 color print 48 Celestial Photography Projection PhotographyT E L E S C O P E M A I N T E N A N C E Care and Cleaning of the OpticsTelescope Maintenance O P T I O N A L A C C E S S O R I E S 50 Optional AccessoriesDual Axis Drive System - #93523 Super Modified Achromatic SMA EyepiecesOptional Accessories Motor Drive System - #93518 52 Optional AccessoriesNGC# THEMESSIERCATALOGConst Type54 The Messier Catalog Const Epoch LIST OF BRIGHT STARSStar Name ConstellationAstronomy Texts FOR FURTHER READINGAtlases General Observational AstronomyCELESTRON ONE YEAR WARRANTY Torrance, CA Tel Fax Celestron International 2835 Columbia StreetItem #21017-INST Price $10.00
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