Advantages & Disadvantages of Dobsonian Telescopes

Dobsonians are very simple to set up and operate.  There is no computer; target locations are all in paper or smart-phone star charts, or in you own brain.  A good star atlas costs about $20 ( )

130 mm (~5-1/8″) aperture is pretty good for sucking in photons.  However, photons gathered are proportional to the square of the aperture diameter.  A 6″ Dob will gather (6/5.11)^2 = 1.378, and so gathers 37.8% more light.  An 8″ Dob will gather (8/5.11)^2 = 2.451, and so gathers 245% the amount of light of 130mm aperture.  A 10″ Dob will gather (10/5.11)^2 = 3.829, and so gathers 383% the light gathered by 130mm. 

Drawbacks of Dobsonians are:

If it is indeed simple (i.e., up-powered and non-tracking), then you will need to nudge the tube along to track the object as the earth rotates.

If you bounce it around while transporting it, you may need to re-collimate it.  Doing this makes sure all the mirrors are all lined up on the optical axis.

Given that for beginner level, these things are made with rigid tubes, they can increase exponentially in bulk and weight as the aperture increases.  How much weight and size can the owner carry, transport and store at home?

Advantages of Dobsonians are:

You get the most aperture for the dollar.  No money need go to computer, electronics or fine machining of metalwork.

You will learn about how to find objects in the sky.  For a well set up, motorized, Go-To scope, you can observe Messier 57 (the Ring Nebula) by keying in “M57”.  For a Push-To Dobsonian you will need to locate the constellation Lyra in the summer sky, to see the two stars of the outer edge of the parallelogram, and to point the scope at a spot 2/3 the way from Sulafat to Sheliak.  The issue with the motorized, Go-To scope is getting it well set up and polar aligned (I guess you already know about this).

CAS has several Dobsonians.  If you are interested, we should arrange an observing session where you can work with one for the evening. 

Ed P.

CAS Mentor and Equipment Manager

Solar Observing

Learn about our closest star at Solar Viewing with a solar telescope at Ivy Creek Natural Area. The Charlottesville Astronomical Society will present and bring their special viewing scope which will allow us to see flares and other signs of the living cauldron that is our sun without fear of blindness. We’ll start at noon in the education building. Weather permitting we’ll go outside at 12:30. It’s like a solar eclipse made to order on the first Friday on the odd months of the year.

Celestron 4.5″ Newtonian with Dobsonian Mount (CAS #17)

Includes finder scope and 20 mm EP.  Quick and easy to set up!

Loaned/Stored by: James Mc.

Tasco 80mm f/11.3 Refractor on Equatorial Mount (#13)

IMG_1370Vintage, but very well maintained classic.  Great for views of the Moon and Planets. (Currently this scope is not available to be checked out.  It is combined in CAS Scope #5, solar scope pair.)    Loaned to/Stored by: Ed P.

Mead 2045 – 4″ (102mm) f/10 SCT (CAS #11)

P1060229Great for the moon and planets! Set is up on a picnic table with the legs, align to north, and you have an equatorial mount that will allow you to track objects as they move across the sky.  It is a 4″ f/10. Sets up on a table, tracks well, has 32mm and 6.7 mm wide angle EPs and a 2X barlow.

Loaned to/Stored by: Robert F.

6″ Long Tube Newtonian Reflector (Criterion RV-6) (CAS #9)

This scope with an alt/az pier mount will fit in the trunk or back seat of a car.  The pier is meant to be set up on a firm flat surface.   The scope is excellent for viewing the moon, the planets and most deep sky objects.

Loaned/Stored by: Bill P. (being repaired)

Odyssey 10″ Dob Reflector (on Avellone base) (CAS #8)

The scope and cradle are a little on the heavy side and will need to be transported in an SUV, van or station wagon. This scope is especially good with deep sky objects.  Comes with a visual finder scope and and Telrad finder scope.

Loaned/Stored by: Mike K.

Meade ETX 90 mm Maksutov GoTo Computerized Telescope (CAS #6)

This scope comes with table legs or tripod and can be used in Altitude/Azimuth or Right Ascension/Declination mode. The scope is very portable but learning how to operate the computer control can take time. The scope is battery powered. The scope has the ability to find hundreds of objects but the size of the mirror limits what you will be able to see well.

Loaned/Stored by: Larry S.

Orion & Tasco Refractors with H-Alpha & White Light Solar Filters (CAS #5)

H-Alpha Solar Image

White Light Filter Image

This double telescope is piggybacked on German Equatorial Mount (GEM) w/ four (4) D-cell battery drive.  This scope needs to be roughly polar aligned to track the sun or objects in the night sky.  The 100mm f/6 Orion refractor is fitted with a SolarMax 60mm hydrogen-alpha solar filter.  The 80mm f/11.3 Tasco refractor is fitted with a white light solar filter.  Both have 20mm eyepieces.

Loaned/Stored by: Ed P.

Coronado 40 mm PST Calcium K Solar Scope (CAS #4)

CaK Scope Image

This telescope can piggy-back on a scope with a ¼-20 adapter or be used on a heavy duty camera tripod. This scope views the sun at the short wavelength violet/blue end of the visible spectrum. Older observers may have difficulty seeing significant detail because the eye becomes less sensitive to this wavelength with age. The scope can be used with a webcam to image the sun.  Loaned/Stored by: Ed P.   Available for check-out.

Orion 6 inch SkyQuest Classic Dobsonian Telescope (CAS #2)

orion_skyquest_xt6_classic_dobsonian_telescope1This brand new 6″ aperture, 1200mm focal length reflector telescope is ultra stable and comes with an easy to use Dobsonian mount.  This is a great telescope to novice observers to quickly, smoothly and easily learn their way around the night sky!

Loaned/Stored by: Ed T.

The Eye of Horus 6 inch Newtonian on Dobsonian Mount (CAS #1)

Eye of HorusThis is a John Avellone refurbished 6″ f/8 Newtonian telescope on a Dobsonian Alt/Az mount.  Has excellent quality old American optics, two nearly parafocal eyepieces for 55X and 140X magnification.  And a cool name!

Loaned/Stored by: Ed P.

Other Scopes and Equipment

 8″ Orange Tube Celestron SCT, no mount.  Stored by Rich D.

    (1) Aluminum hard-sided pluck-foam eyepiece/equipment case

    (1) Plastic Orion eyepiece case

    (1) 26″ Plastic Toolbox with tray and built in storage bins

    (1) 26″ Yellow Plano Toolbox

    (1) Radio Shack 140 Watt DC to AC Inverter

    (1) TrippLite 300 Watt DC to AC Power Inverter

    (1) 12.5″ Aluminum Hartman Mask for Celestron C11

    (1 Set) Astrodon 1.25 True-Balance LRGB Filters

Heidi’s Night

Leander_McCormick_ObservatoryThe Charlottesville Astronomical Society will hold its tenth Heidi’s Night Activity for students grades 4 – 12 and parents interested in Astronomy on Friday, April 29, 2016 from 8:00 to 10:30 pm at the McCormick Observatory on the grounds of the University of Virginia. The event honors the memory CAS member Heidi Winter, former executive secretary to the Director of the National Radio Astronomy Observatory, who passed away in 2012. Attendees will have the opportunity to participate in four activities during the evening. These include:

A laser tour of the night sky

Heidi's NIght 11.29.13c

A classroom activity

Heidi's NIght 11.29.13b

Viewing the night sky though the historic 26” Clark refractor Heidi's NIght 11.29.13d

View the night sky through a home-built 4” scope

Registration is required. For more information or to register, please contact CAS Outreach Director, Steve Layman . In case of inclement weather, the evening may be shortened and activities would be limited to indoors.

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