The Design File Examples The following design files are included with this release of the program TRACE. A description of each of the example optical systems is given below. NEWT.DES This design file models a simple Newtonian telescope with a paraboloidal primary mirror having a focal length of 60" and a diameter of 10". The secondary has a diameter of 1.8". The design file is given below. Object 0 10 Obstruction 54 1.8 Mirror 0 120.0 -1 10 Aperture 54 1.8 Aperture 58 2 FocalPlane 60 The units are inches. The first element, Object, creates parallel rays at the surface of the primary over a circular aperture 10" in diameter, the rays being started in the negative z-direction. The next element, Obstruction, models the obstruction caused by the secondary mirror by extrapolating the rays back to the secondary location and determining if these rays are blocked by the secondary. The next element is the primary mirror which has axial location z=0, paraxial radius of curvature equal to 120 inches, deformation constant of a parabola (SC=-1), and a 10" diameter. The next element, Aperture, is the circular aperture caused by the secondary mirror located at z=54", having a diameter of 1.8". Rays that do not fall within this diameter do not make it to the image plane. The final element is the focal plane located at z=60". In practice, the secondary mirror would reflect the light towards the side of the tube. Since this program only supports axially symmetric optical systems, no mirror is used for the secondary in the design file, instead the rays are allowed to continue along the axis of the system to the focal plane. Since the secondary is flat, this causes no inaccuracy in the spot diagram calculations. However, this method does induce a small inaccuracy in the calculation of the light transmitted by the system. NEWTP.DES This design file shows the use of a point source and also exemplifies the spherical aberration induced by a paraboloidal mirror when the source is not at infinity. The design file follows: PointSource 0 10 1000 Obstruction 54 1.8 Mirror 0 120 -1 10 Aperture 54 1.8 FocalPlane 63.8393 The units are inches. This design is the same as the previous except that the element Object has been replaced by the element PointSource. The origin of the light is a point source located 1000 inches from the entrance pupil. The rays are constructed so as to fill the entrance pupil, which is located in this example at z=0, having a diameter of 10". The PointSource element is discussed in more detail in the element descriptions. Notice that the focal plane has moved from it's previous location, exemplifying the formula 1/i = 1/f - 1/o, where i is the image distance, f is the focal length and o is the object distance. GREG.DES This design file models a visual Gregorian telescope with a focal length of 3600 mm. It uses two concave mirrors, and a flat tertiary mirror to bring the focal surface to the side of the telescope. Sam Michael supplied this design. The design file is given in the following: Object 0 317.5 Obstruction 1577 88 Mirror 0 2540 -1 317.5 Obstruction 945 25.4 Mirror 1577 -454 -0.23 88 Aperture 945 25.4 SphericalFocus 705.884 -381.018 The units are millimeters. The Object element creates parallel rays at location z=0 over a circular aperture of diameter 317.5 mm (12.5 inches). This defines the entrance pupil of the optical system as the surface of the primary mirror. The next element, Obstruction, models the obstruction caused by the secondary mirror which has a diameter of 88 mm and is located at z=1577 mm. The program extrapolates the rays backward from the entrance pupil to determine if a ray is blocked by this obstruction. If so, the blocked ray does not make it to the focal surface. The next element is the primary mirror which is located at z=0 and has a radius of curvature of 2540 mm. It has a diameter of 317.5 mm and a conic deformation constant of SC=-1 (paraboloidal). The next element models the obstruction caused by the tertiary mirror located at z=945 mm with diameter 25.4mm. Once again, if the ray hits this obstruction, then it does not make it to the focal surface. The next element is the secondary mirror located at z=1577,having a radius of curvature of -454 mm and a deformation constant of SC=-0.23 (prolate ellipsoid). Notice that the radius of curvature of this element is negative, denoting that the surface opens downward, therefore it is a concave mirror. The next element, Aperture, is the aperture caused by the tertiary mirror. Rays that are outside of this aperture do not make it to the focal surface. The final element is the focal surface. It has an axial location of z=705.884 mm and a radius of curvature of -381.018 mm. Notice that in the real telescope light would be reflected by the flat tertiary to the side of the tube. Since this program only supports axially symmetric optical systems, no mirror is used for the tertiary in the design file, instead the rays are allowed to continue down the axis of the system to the focal surface. Since the tertiary is flat, this causes no inaccuracy in the spot diagram calculations. Also notice that the focal surface is spherical. The negative radius of curvature of the focal surface implies that this surface opens downwards. CSCT.DES This is the design file for a concentric Schmidt Cassegrain telescope. This optical system is intended to be used as a wide field camera, and as such has good off-axis performance over a 4" diameter field of view and a flat focal surface. It uses a Schmidt corrector plate, a spherical primary, a spherical secondary and a lens that is just in front of the focal plane to flatten the focal surface. This design makes a nice example showing most of the features of the program. Since apertures and obstructions have been discussed extensively in the above, no further discussion of these elements will be presented. The design file follows: Object 36 11 Corrector BK7 36 0.25 -0.000122 2.43486e-06 11 Obstruction 11.6 5.5 Obstruction 0 5 Mirror 0 38 0 12.5 Mirror 11.6 24 0 5.5 Aperture 0 5 Refraction BK7 -6.9 11.5 Refraction Air -7.1 10000 FocalPlane -7.16582 The units are inches. As usual, an Object element creates the rays at the entrance pupil of the system. In this particular system the entrance pupil is located at, and defined by, the corrector plate. The first optical element is the corrector plate itself, which is made from BK7 glass, having a thickness of 0.25" and a clear diameter of 11". Two obstructions model the effects of the secondary mirror and the hole in the primary. The next two optical elements are the spherical primary and secondary mirrors, and then an Aperture element is used to model the vignetting caused by the hole in the primary. The next element is the front surface of the focal flattener lens, the lens itself being made from BK7 glass. This surface is located at z=-6.9" (which is in back of the primary) and has a radius of curvature of 11.5 inches (concave upward). The next element is the rear surface of the flattener lens, having a large radius of curvature to approximate a flat surface. It is located at z=-7.1", i.e., the lens hasa center thickness of 0.2". Finally, the focal plane is located at approx. -7.166", i.e., 0.066" from the back surface of the flattener lens. FRAUN.DES This design file models the classical Fraunhofer doublet objective and serves as a good example of chromatic aberration. The design file is given below: Object 0 200 Refraction BK7 0 -2009.75 Refraction Air -31.336 976.245 Refraction F3 -34.651 985.291 Refraction Air -59.76 3636.84 FocalPlane -3028.01 WAVELENGTH 0.643 0.54 0.486 The units are millimeters. The entrance pupil, defined by the Object element, is located at z=0. The lenses are then place at negative z-locations. The lens surfaces are given by the four Refraction elements. The first element refracts the light into BK7 glass with a radius of curvature of approx. 2000 mm. This surface opens downward (convex). The next element refracts the light back to Air with the surface opening upward. This is also a convex surface since it is the backside of the first lens. The third element refracts the light to F3 (a flint glass) having a concave surface, and the fourth element refracts the light back to Air and has a convex surface. When simulating this design, try changing the wavelength, Lambda3, to 0.42 microns to see the so-called violet bloom. The short wavelength performance of this lens is quite bad. RC.DES This is a Ritchey-Chretien (RC) Cassegrain telescope. The design was taken out of "Telescope Optics". An RC design simultaneously minimizes the off-axis coma and astigmatism, but in doing so forces both the primary and secondary mirrors to be hyperbolic. The units are millimeters. CLASCASS.DES This is the classical Cassegrain design taken from "Telescope Optics". It uses a paraboloidal primary and a hyperbolic secondary. The units are millimeters. SIGLER.DES This is a Maksutov-Cassegrain telescope known as a Sigler that uses a meniscus lens as a corrector. The design is out of "Telescope Optics". The units are millimeters. ROWE.DES This is a design of my own. It uses a paraboloidal mirror and a two-lens coma corrector / focal reducer to reduce comatic aberration, thus making the system useful for astrophotography. Notice that the spot size stays quite small out to an off-axis distance of 1.5" which is sufficient for medium format photography. The units are inches. Return to the program description.