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Obstruction Calculator

Obstruction Calculator allows you to compute the percentage of light obstructed from the primary by the secondary in an instrument's optical system. Obstruction is used by the visibility model for double stars.

Instrument Type allows you to select one of:

▪Reflector - a typical Newtonian design with a primary mirror and a secondary mirror.

▪Refractor/Binoculars - a typical refractor or binocular design has an unobstructed primary lens or lens group. Secondary Aperture is disabled for this selection.

▪Catadioptric - a typical Maksutov or Schmidt-Cassegrain design has a primary mirror, a secondary mirror and a front corrector plate.

The calculator supports the computation of obstruction for only the above instrument designs. If your intrument is of a different design, you can calculate the system obstruction by calculating the following:

system obstruction = (total linear diameter of obstruction elements / linear diameter of primary). Note that the unit of measure of the primary and obstructing elements should be the same.

Primary Aperture displays the diameter of the primary element of the instrument. It is set by the Instrument Browser and is specified in the units (either millimeters or inches) selected in the Instrument Browser.

Secondary Aperture allows you to enter the linear diameter of the secondary element of the instrument. It should be entered in the same unit of measure as the primary element (either millimeters or inches)

The total system obstruction is calculated and shown as both a fraction and a percentage on the dialog box. If Secondary Aperture is enabled for Reflector or Catadioptric types and set to zero, total system obstruction is not displayed.

Press OK to accept the changes and return the system obstruction value to Obstruction in the Instrument Browser, or Cancel to leave Obstruction in the Instrument Browser unchanged.