TELESCOPE MODELLING for Sinclair ZX-80
by B Spencer
from Your Computer, February 1982

TELESCOPE MODELLING should be of general interest, and of special interest
to those who own, or intend to buy or build an astronomical telescope.

When run the program will display:

            DATA OR CALC

If data is input, the screen will display two rows of figures:

LOWEST MAGNITUDE
      11 15 22  33  38  45
MAGNIFICATION
      60 80 120 180 200 400

These figures are related vertically - that is, a magnification of 60 will
resolve stars down to a magnitude of 11. The table of data is useful as a
means of reference when selecting eyepieces in the calculation section.

Key NEWLINE for the calculation section of the program which allows the
telescope optics to be configured.

          OBJECT LENS DIA

means input the desired value - say, 200 for a 200mm lens.

       FOCAL RATIO OF OBJECT

means input the ratio - 10 for an f/10 lens.

The screen will clear and then display the values input plus the focal
length of a mirror which will have been computed for an eyepiece focal
length from which the magnification of the telescope can be calculated. The
following display then appears:

       OBJECT DIA = 200MM
       FOCAL RATIO = F/10
       FOCAL LENGTH = 2000MM
       FOCAL LENGTH EYEPIECE

Input a value for the eyepiece. For example, 25mm, input 25. The screen
will clear and the display is produced.

       OBJECT DIA = 200MM
       FOCAL RATIO = F/10
       FOCAL LENGTH = 2000MM
       FOCAL LENGTH EYEPIECE 25MM
       MAGNIFICATION IS 80.0
       FOCAL LENGTH EYEPIECE

The display now shows all the data input plus the focal length and
magnifications which have been computed by the program. The magnification
is calculated to the first decimal place. Finally, the user is asked for
another eyepiece value. The program can cope with up to four eyepiece
values and gives the resulting magnification. After this the display will
again ask:

         *****DATA OR CALC*****

Should a value of eyepiece focal length be input which would prove to be
beyond the effective magnification of the system - say, too low a value -
then the program will tell you that it is too small.

[In the printed listing, line 300 incorrectly shows a space between the
variables Z and K1 but should be a full stop. Line 70 is also printed
incorrectly and should include the value 33 in the string.]