ASTR 597: 3D Optical Raytracing Topics
Following are suggested activities for investigating astronomical
instrumentation topics using the 3D
raytracing apparatus. Many of them relate to the APO 3.5 meter optical
design, which has the prescription:
2
1.0
-1.0 0.0 -12279.7 -1.01927
1.0 -4833.421 -3164.172 -2.18427
- What is the on-axis performance of the APO 3.5 m telescope. Put in
context by relating the RMS and total extent of the spot pattern to
arcseconds, pixels, typical seeing, etc.
- Use an off-axis bundle (comes in at an angle) of modest proportions
(typical field angle for this telescope) to deduce the plate scale in
microns per arcsecond. For a reasonable maximum field angle, what is the
fractional blur in arcseconds, and compared to the offset (fractional blur
vs. displacement)?
- Investigate the field curvature of the 3.5 m focal plane. What radius
do you deduce for the focal plane?
- Investigate distortion of the focal plane. Is it pincushion or barrel
distortion? How large is the effect (in % of the field) for SPICAM, which
has a 2000-pixel CCD sitting at the focal plane of the telescope?
- Using the skew measure to indicate asymmetry arising from coma, at what
point (what field angle) does astigmatism take over from coma as the
primary aberration (when does the skew peak and start to roll over?).
- If we want to maintain 0.5 arcsec imaging capability (say 0.25 arcsec
RMS), how large can our field be if we require that it is physically flat?
You can pick a compromise focus (screen) position that allows the largest
possible field.
- If we want to maintain 0.5 arcsec imaging capability (say 0.25 arcsec
RMS), how large can our field be if we allow it to curve with the focal
plane (hard to do, in practice)?
- If I put a 1 cm-thick flat glass plate 5 cm in front of the image plane
so I can put the detector in vacuum, I will create some negative spherical
aberration. We want to know how serious this is. Evaluate the impact (in
arcseconds, pixels, etc.) for a field point on-axis and off at 3 arcminutes
(in the sky).
- Compare the above design of the 3.5 m to the ideal RC telescope as
developed on page 2-15 of the class handouts (following the Wikipedia
prescription). Evaluate at field center, and at an angle where coma
asymmetry is apparent.
- Other investigations may involve other telescopes, field-flatteners, etc.
Go nuts!
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