Meade ETX-90PE instruction manual Choosing an Eyepiece, Too Much Power?

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Fig. 18: Turn the top (13) or side (14) Smartfinder adjustment screws.

Fig. 19: Meade Super

Plössl eyepieces.

Tip: If you plan on viewing using higher magnification eyepieces, first locate, center and focus the object using a low-power eyepiece (e.g., 26mm eyepiece). Then remove the low- power eyepiece and replace it with a higher- power eyepiece; the object should still be centered in the field of view. Objects are much easier to locate and center at lower powers; higher powers are employed simply by changing eyepieces.

Fig. 20a & 20b: Jupiter: Examples of the right amount of magnification and too much magnification.

possible, in the SP 26mm eyepiece's field of view. Tighten the vertical and horizontal locks (6 and 9, Fig. 1) so that the tube cannot move and the object remains centered.

2.While looking through the SmartFinder, turn the top or side alignment screws (13 and 14, Fig. 18), until the red dot of the SmartFinder points at precisely the same position as the view through the eyepiece of the main telescope.

The SmartFinder is now aligned to the main telescope. Unless the alignment screws are disturbed or the LNT Module is moved out of place, the SmartFinder should remain aligned indefinitely.

Choosing an Eyepiece

The magnification or power, at which a telescope is operating is determined by two factors: the focal length of the telescope and the focal length of the eyepiece.

Telescope Focal Length is the distance that light travels inside the telescope before reaching a focus. In the mirror-lens design of the ETX models, the focal length is compressed by the telescope’s secondary mirror, so that a long focal length is housed in the short ETX optical tube. For example, the ETX-90PE’s focal length is 1250mm or about 49”. This means that if the ETX–90PE were a classical refracting-type of telescope, the optical tube would be more than four feet long instead of the ETX–90PE's compact 11” tube length.

Eyepiece Focal Length is the distance light travels inside the eyepiece before reaching focus. Focal length is usually printed on the side of the eyepiece, for example, 26mm. Low-power eyepieces are typically available in 26mm, 32mm and 40mm sizes (see OPTIONAL ACCESSORIES, page 42). The low-power eyepiece provided with your ETX is designed to provide a wide, comfortable field of view with high image resolution.

Calculating Magnification: On a telescope, such as the ETX, different eyepiece focal lengths are used to achieve different magnifications, from low to high. A 26mm eye- piece yields 48X (“48-power”) on the ETX-90PE, 57X on the ETX-105PE and 73X on the ETX-125PE. A variety of powers may be obtained with the addition of optional eye- pieces as well as the #126 2X Barlow Lens which doubles the power of an eyepiece (see OPTIONAL ACCESSORIES, page 42). To calculate magnification, divide the focal length of the telescope’s optical tube by the focal length of the eyepiece. For example:

Telescope Focal Length divided by Eyepiece Focal

Length

= Power

1250mm divided by

26mm

= 73X

With Barlow: 73 x 2

= 146X

The eyepiece power or magnification is therefore 73X and 146X with the Barlow.

Most observers should have 3 or 4 eyepieces plus the #126 2X Barlow to achieve the full range of reasonable magnifications possible with ETX models.

ETX TIPS

Too Much Power?

Can you ever have too much power? If the type of power you’re referring to is eyepiece magnification, yes, you can! The most common mistake of the beginning observer is to “overpower” a telescope by using high magnifications which the telescope and atmospheric conditions cannot reasonably support. Keep in mind that a smaller, but bright and well-resolved image is far superior to one that is larger, but dim and poorly resolved (see Figs. 20a and 20b). Powers above 300X should be employed only under the steadiest atmospheric conditions.

AutoStar can calculate the best eyepiece for you to use. Try out the “Eyepiece Calc” feature in the Utilities menu.

Most observers should have three or four additional eyepieces to achieve the full range of reasonable magnifications possible with the ETX telescopes. See OPTIONAL ACCESSORIES, page 42.

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Contents ETX Premier Edition Telescope Series Page Contents QUICK-START Guide Enter Key Scroll Scroll Up Down Telescope Features B and FigSmartfinder Ascension and Declination setting circles? SeeTelescope Controls SmartFinder? See AligningAlt/Az, Right Ascension, Computer Control Panel see FigDefinitions Autostar Features Tour the Cosmos with Just the Push of a ButtonAutoStar to the topmost screen Select Item Object ETX Tips About changing slewGetting Started Parts ListingHow to Assemble Your Telescope and Tripod Using SmartFinder Aligning SmartFinderToo Much Power? Choosing an EyepieceObserving by Moving the Telescope Manually Observing Using AutoStar Arrow KeysObserving Terrestrial ObservingObserve the Moon Slew SpeedsAstronomical Observing To Track an Object AutomaticallyAutomatic Alignment How to perform the Automatic Alignment procedureInitializing AutoStar for the First Time Observe a Star using the Automatic Tracking Feature Which One’s the Alignment Star?Using the Guided Tour Go To SaturnAutoStar Navigation Exercise Autostar OperationAutostar To Calculate Sunset timeEntering data into AutoStar Look into the FutureAutostars Menus Select Item ObjectUse the Object menu to select an object from the database Object MenuObject Menu options include Observing Satellites? SeeUse the Event menu Event MenuGlossary Menu Use the Glossary menuUtilities Menu TipsSetup Menu Periodic Error Correction? See Tip Adding and editing sites? See ShiftTo Add a Site to the user-defined site list Advanced Autostar OperationAdding Observing Sites To Edit a SiteTo GO to a user-entered object Using AutoStar to Find Objects Not in the DatabaseObserving Satellites Tour Modes How to Create Your Own Guided TourWhat you will need Writing a Tour Command LineComment Line Moon Landmarks Downloading ToursTo Select a landmark from the database IdentifyTo Add a landmark to the database To perform a Landmark SurveyTwo-Star Alt/Az Alignment and Easy Align Advanced Alt/Az AlignmentDisplayed information Example PEC Train Menu Option Smart Drive Training Periodic Error CorrectionOne-Star Alt/Az Alignment PEC Erase Menu Option PEC Update Menu OptionBrowse Photography Photography with a 35mm CameraFew Tips on Photography Photography with a Digital CameraPhotography with Meade’s AutoStar Suite Deep Sky ImagerOptional Accessories #505 Cable Connector Kit With Meade AstroFinder#932 45 Erecting Prism Maintenance Inspecting the Optics TroubleshootingStorage and Transport Meade Customer Service Telescope does not track a celestial objectSpecifications ETX-105PE Astro Telescope SpecificationsSpecifications ETX-90PE Astro Telescope Telescope dimensions 43cm x 25cm x 20cm 17 x 10 x Specifications ETX-125PE Astro TelescopeAutoStar Specifications AutoStar DimensionsEquatorial Alignment Celestial CoordinatesLoosen control latch Set latitude Locating Polaris City State/Prov./Country Latitude Appendix B Latitude ChartLatitude Chart for Major Cities of the World City Country LatitudeAppendix C Training the Drive Further StudyAppendix Dchanging the LNT Module Battery To replace the batteryMoon Appendix Ebasic AstronomyAutoStar Glossary Planets Deep-Sky ObjectsPage Meade Limited Warranty

ETX-90PE specifications

The Meade ETX-90PE is a well-regarded telescope that combines portability and performance, making it a popular choice among both amateur astronomers and seasoned stargazers. Its compact design and advanced features make it an ideal instrument for those who seek to explore the night sky with ease.

At the heart of the ETX-90PE is its Maksutov-Cassegrain optical design, which utilizes a spherical primary mirror and a corrector lens to deliver exceptional image quality. With a focal length of 1250mm and a 90mm aperture, it strikes a balance between light-gathering ability and magnification, allowing users to observe celestial objects such as planets, star clusters, and distant galaxies in remarkable detail. The telescope's focal ratio of f/13.9 provides crisp and sharp views, making it particularly well-suited for planetary observation.

One of the standout features of the ETX-90PE is its Electronic Control System (ECS), which allows for easy and intuitive operation. The telescope is equipped with a built-in AutoStar Computerized GoTo mount, enabling users to locate and track over 30,000 celestial objects with just a few simple commands. With automatic alignment features, even beginners can get started quickly, making the wonders of the universe accessible to everyone.

Portability is a key characteristic of the Meade ETX-90PE. Weighing in at a mere 12.5 pounds, it can be easily transported to dark sky locations. Its compact design not only translates to ease of transport but also means it can be stored conveniently when not in use. The included sturdy aluminum tripod provides stable support, even during extended observation sessions.

The ETX-90PE further enhances the user experience with its high-quality accessories. It comes with a set of eyepieces, including a 26mm Super Plössl and a 9.7mm Plössl, allowing for various magnifications to suit different observing preferences. The telescope also features a built-in flip mirror, allowing for easier viewing through both the eyepiece and a camera, making astrophotography more accessible.

Additionally, the ETX-90PE is designed with user comfort in mind. The telescope offers adjustable slow-motion controls for fine-tuning views and an optical finder scope to help locate objects before zooming in. With robust construction, excellent optics, and a range of advanced features, the Meade ETX-90PE stands out as a versatile, high-quality telescope for both casual observers and serious astronomers alike. Its combination of technology and user-friendly functions makes it an enduring favorite for anyone looking to embark on a journey through the cosmos.
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