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 NexStar 4 GT Maksutov (CAS #21)

4″ f/13 Maksutov with go-to and tracking features. Key pad with 4,000+ objects. Includes red LED StarPointer, tripod, power transformer and user manual. Alt-az mount.

Stored by/Loaned to: Ed P.   Available for checkout.

Meade 4.5″ f/8 Dobsonian “Light Bucket” (CAS #15)

Scope includes a 6x30mm finder and one Konig 23mm eyepiece (40X magnification).  Very easy to use.

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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