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Software Vault: The Gold Collection
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Software Vault - The Gold Collection (American Databankers) (1993).ISO
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cdr21
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lensca.zip
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MANUAL.DOC
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1993-05-31
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Using LENSCAD:
LENSCAD is a stand alone program which will calculate the focal
lengths of a lens system with up to three variable parameters and
three wavelengths of light. The only limit to the number of elements
is the memory capacity of your computer and the stack size, which has
been set at 3000.
To start LENSCAD type lc <enter>. You will be asked if you want to
use your old data. If you enter 'n' you will be asked how many
elements in the system you want to design. If at any time you need to
change the number of elements you must restart the program. Once you
tell the program how many elements in your design you will be asked
how many wavelengths of light you want to test the system for and you
will enter those wavelengths. The red, yellow and blue menu choices
enter hydrogen red, sodium yellow, and hydrogen blue spectral line
wavelengths, respectively. You will then be in the main menu. Select
the parameters to enter for the system. You will be prompted for
element and surface numbers, etc.
CONVENTIONS:
The element the ray goes through first is element #1 and the first
surface the ray passes through is surface #1. The space between
elements is identified by the greatest element number of the elements
adjoining the space. Thus the greatest number of the elements
adjoining the space between elements #1 and #2 is #2. Rays are
considered to be coming from the left. The radius of curvature of an
element is negative if the center of the curve is to the left of the
element. Thus a biconvex lens will have a positive radius of
curvature for surface #1 and a negative radius of curvature for
surface #2.
No space between lenses may be set at zero. For elements in contact
set the space to a very small number such as .000001. Note that mks
units are used for all entries (distances in meters). For a plane
surface where the radius of curvature is effectively infinity, use a
large number such as 1000000000 for the radius of curvature.
Any of the three parameters curvature, distance, and element thickness
may be made a variable. You name which curvature, etc. you want to
vary, and give the range. Depending on the number of variables, the
program will calculate over either 11 or 101 points over each range.
If you have one variable parameter the program will divide the range
into one hundred regions and will calculate the focal distance over
101 points. For two or three variable parameters the program divides
the ranges into ten regions and calcualates the focal distance over 11
points. The focal distance given is the distance from the last
surface.
You may review the parameters you have entered by choosing selection 5
in the menu. It is recommended that you save the data for the system
you design prior to calculating the focal length(s) for the system.
Use the SAVE DESIGN PARAMETERS option. Then if you crash the program
you can restart it and use the old data. This is quite handy with a
very large system!
You may choose from a list of standard glass types to establish the
indices of refraction for the elements in your system or you may enter
the indices of refraction for the different wavelengths you are
testing your system for. You must also enter the index of refraction
for the media between elements.
In order to calculate the focal distance of the system you must set
the input to the system. If you forget to do this the program will
prompt you for the information prior to doing the calculations. The
input information for the system consists of the angle the input ray
subtends with the optical axis of the system (in radians) and the
height above the axis the ray enters the system.
If you want to change the number of variable paramters or the
parameter(s) to vary select CHANGE OPTIONS from the menu. You will
then be asked which parameters to vary and the variable ranges.
The MAKE REPORT option will create an ascii text file with a summary
of the design information on your system. You will be prompted for
the filename under which to save the report.
TIPS FOR USING LENSCAD:
Always review the paramaeters of the system you are designing prior to
calculating the focal distance. This will avoid a system crash should
you forget to enter a value for a parameter. Always save your design
parameters before making the focal distance calculation.
The output of LENSCAD consists of the wavelength and variable values
for each variable parameter, and the associated focal distance for
that set of variable values. This format is repeated for all the
wavelengths the system is being tested for. LENSCAD makes all
calculations for one wavelength before making calculations for the
next wavelength. The output for one variable and two wavelengths
would have all the results for the first wavelength in the first half
of the file and all the results for the second wavelength in the last
half of the file, making it very easy to extract the data.
The output for a three variable paramater system with two or more
wavelengths of light is in excess of 360 kilobytes, therefore the data
must be written to a hard disk or a high capacity floppy disk if you
choose this option. If you have only 360kb drives you might run the
program once for each wavelength.
LENSCAD displays the elements of the system matrix during the
calculation of the focal distances. You may see the system matrix for
a particular system by changing options to make all the parameters
constant. The system matrix contains four elements:
SYSTEM(1,1) is the angular magnification of the system.
SYSTEM(1,2) is the equivalent power of the system. Its
reciprocal is the equivalent focal length.
SYSTEM(2,1) is the negative, reduced thickness of the lens.
SYSTEM(2,2), along with (1,1) and (1,2), give the front vertex
length:
a1= SYSTEM(1,1)*n
SYSTEM(1,2)
and the back vertex focal length:
a2= SYSTEM(2,2)*n
SYSTEM(1,2)
The algorithm used by the program was derived from the matrix method
outlined by Jurgen R. Meyer-Arendt, M.D in the 2nd ed. of Introduction
to Classical and Modern Optics (pp.78-89). It is my understanding he
dropped the technique in the 3rd ed. which is a real shame because it
lends itself well to computer approaches to lens design.
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