Dob Spread Sheet Introdcution


This dobsonian balance calculator is a modified version of the spreadsheet
by Hughes Larouche.  It also contains a number of other calculations that
come in handy during the construction process of an Obsession design
telescope, as described in the Kriege/Berry book on a large aperture dobs.
See the "Other Results" section.  The individual cells are sprinkled with
comments describing specific calculations.

The center of balance is through the middle of the top edge of the mirror
The mirror box is of uniform density except for such add on items as the alt
bearings, internal bracing, and truss tube connectors.
The alt bearings are semi-circular and of uniform densidy.
The mirror cell has 27 support points and is made of three layers of
hardware - a frame, the large steel triangles, and the smaller triangles -
as in the book.
The canted angle of the truss tubes has been ignored for purposes of
balance, but is calculated for purposes of construction (see Other Results
The numbers shown in the spreadsheet are for the 21" f/6.2 scope I am

The spreadsheet calculates the balance of the telescope for a given mirror
box height, along with the necessary counterweight in case the scope is out
of balance.
Enter the various heights and weights, then view the results.

Send comments, questions, bug reports to me at

Clears skies to all,
- Ken Bertapelle