Tags and keywords
In addition to the primary
mirror of a ReflectingMirror
being curved, it is assumed that it is always a ConcaveMirror
. The property primary
is also tagged as being {aka = "objective"}
and it {subsets mirror}
and {redefines objective}
.
This previously analysed snippet was not quite right, as a Newtonian reflector (as we'll see in more detail a bit later) has a flat secondary mirror:
So the property mirror[0..*]
of OpticalTelescope
has now been promoted to be of the more general type Mirror
.
It turns out that not every reflector design uses a secondary mirror:
So the multiplicity of property secondary
of type Mirror
in the intermediate abstract base ReflectingTelescope
is [0..1] (it can be redefined to be multiplicity [1] in more specialised reflector versions that are known to always have secondary).
When a reflector does have a secondary mirror, the focal length of the telescope is not just that of the primary mirror (objective), hence the editorial annotations for this snippet:
There a discussion of so-called "two mirror" reflectors on this nice amateur telescope optics site telescope-optics.net, which gives the following formula for the 'final system focal length' of a Gregorian or Cassegrain:
ƒ = (ƒ1 ƒ2)/(ƒ1 - ƒ2 - s)
where ƒ1 and ƒ2 are the focal length of the primary and secondary mirror, respectively, and s is the mirror separation.
One of the longer term goals of this tutorial is to be able to model the Giant Magellan Telescope, which is an aplanatic Gregorian with multi-segment primary (and multi-segment secondary mirror):
The abstract block Mirror
is therefore not assumed to be simple or segmented, and specific reflector designs can "mix-in" the composite abstract block SegmentedMirror
as required.