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Astronomy/Refracting Telecopes

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Expert: - 3/17/2010


Question
A very simple refracting telescope (perhaps the first one invented) had a CONVEX lens as an objective and a CONCAVE lens for an "eyepiece"

Can you also make a refractor with two CONVEX lenses if the eyepiece lens is of shorter focal length?

Am I right in saying that the only reason you need a CONCAVE eyepiece lens is to make the image upright?

Sorry - but I'm a bit confused here!

Thanks in advance!

Answer
Hi Teresa,
All good astronomical telescopes invert the image at the eyepiece, irrespective of curvature.
We just learn to live with it... (besides, a stellar pinpoint is still a pinpoint inverted, right?)  As far as the moon, or the planets, we just get used to it.  Unfortunately, I don't build eyepieces and mirrors, but we do have an expert on staff, Paul Wagner, that builds his own,
including refractor scopes.  So he would know all about those "light ray diagrams" that you
mention here.  So please ask this question of Paul Wagner of astronomy of allexperts.

I just know how to use scopes, not build them... I pay people to build them.  (Just like KC-135
tanker aircraft... I flew it, I didn't build it.)
Clear Skies,
Tom Whiting
Erie, PA  

Astronomy

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Tom Whiting

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Astronomy has been my hobby/pasttime for over 50 years.  Currently own 3 telescopes, the largest of which is a 30 inch Newtonian truss Dob that is portable.I taught Astronomy/Meteorology at the University Level for 13 years before retiring in 1995. Being retired and home most of the time, I am able to answer all questions relatively quickly, unless it's a new moon weekend with good observing conditions.  No astrology questions please, or questions about alleged UFO picture identifications.

Experience

Experience: Astronomy has been my hobby and study for over 50 years. We currently now own a 30 inch portable telescope (Updated - Pennsylvania`s largest portable telescope). It can be seen on our website at:http://www.velocity.net/~bwhiting and also attend several regional starparties during the year, and have been on 5 total solar eclipse expeditions.

Organizations: President, Erie County Mobile Observers Group for over 15 years.

Publications: Wrote the "Over Erie Skies" newspaper article in our local newspaper for 11 years (1975-86).

Education: Masters Degree- Taught at the University level for 13 years. Retired 20 years -USAF Pilot - KC-135 with 180 combat missions;  Also Eagle Scout, Philmont staff 2 Yrs, Order of Arrow Lodge Chief, Ham Radio (inactive).

Awards: two discoveries: The mini-coathanger asterism in Ursa Minor (the little dipper) And the mini-ladle- another asterism in the bowl of Ursa Minor. Clients: Currently President of the ECMOG as mentioned above.

Education/Credentials
BS  Metallurgical Engineering Grove City College, PAMaster's Degree, Gannon University, Erie, PA Also retired USAF pilot, 20 years.

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