FIGURE 63 (continued):
● Turned down
edge
effect on the PSF and MTF. The P-V errors for 95% zone are
2.5 and 5 waves as needed for the initial 0.80 Strehl (the RMS is
similarly out of proportion). Lost energy is more evenly spread out,
and the central disc becomes enlarged. Odd but expected TE property
- due to a limited, relatively small area of the wavefront affected - is
that further increase in the nominal error beyond 0.80 Strehl error level does almost no
additional damage.
● The effect of ~1/14 and ~1/7 wave RMS wavefront
error of
roughness, resulting in the peak intensity and contrast
drop similar to those with other aberrations. Due to the random
nature of the aberration, its nominal P-V wavefront error can vary
significantly for a given RMS error and image quality level. Shown
is the medium-scale roughness ("primary ripple" or "dog biscuit", in
amateur mirror makers' jargon) effect.
● 0.37 and 0.74 wave
P-V of wavefront error caused by pinching
having the typical
3-sided symmetry (trefoil). The aberration is radially asymmetric,
with the degree of pattern deformation varying between the maxima
(red MTF line, for the pupil angle θ=0, 2π/3, 4π/3), and minima
(green line, for θ=π/3, π, 5π/3); (the blue line is for a perfect
aperture). Other forms do occur, with or without some form of
symmetry.
● 0.7 and 1.4 wave P-V wavefront error caused by
tube currents
starting at the upper 30% of the tube radius. The energy spreads
mainly in the orientation of wavefront deformation (red PSF line, to
the left). Similarly to the TE,
further increase in the nominal error beyond a certain level has
relatively small effect Contrast and resolution for the
orthogonal to it pattern orientation are as good as perfect (green
MTF line).
● Near-average PSF/MTF effect of ~1/14
and ~1/7 wave RMS wavefront error of
atmospheric turbulence. The atmosphere caused error
fluctuates constantly, and so do image contrast and resolution
level. Larger seeing errors (1/7 wave RMS is rather common with
medium-to-large apertures) result in a drop of contrast in the mid-
and high-frequency range to near-zero level.
