Files in this directory:

SE_970430.gif:
    Comparison of a very good near-zenith image from 1996 July 03 with
    one taken at 2.2 airmasses in the southeast, 1997 April 30. Notice
    the pixel scales. The lookup table is mapped to the cube root
    of the brightness, which accentuates the psf wings.

air_970509.gif:
    Comparison of two image at K', at -55 dec, with primary support
    air pressure normal, then reduced by a factor of four.
    The lookup table is mapped to the cube root
    of the brightness, which accentuates the psf wings.

TT_improv.gif:
    Image improvement from tip-tilt compensation. The upper images
    are K' 20-sec exposures without, and with, the tip-tilt secondary
    in operation. These data are from 1997 May 9. The lower image
    pair is from a NSFCAM K' movieburst sequence, without the tip-tilt
    system. The left image is simply the sum of 2048 10-msec exposures;
    the right image is the sum of the same frames after coalignment
    using cross-correlation. The Strehl improvement is quite similar
    for the pre-acquisition and post-acquisition alignment techniques,
    but the movie frames show more of the structure in the telescope PSF.

Wavefr.gif:
    A wavefront derived from an extrafocal image pair obtained on
    1997 April 23. A coma term of 0.2 micron RMS has been subtracted
    from the Zernicke representation of the wavefront, on the basis that
    the coma can be removed by careful collimation. The remaining
    aberration is primarily in a trefoil term, presumably due to a
    misadjustment of the mirror supports. The lower image is a synthesized
    focal-plane image from the above wavefront; the Strehl ratio is
    about 0.3 in this image.

IRTF_1096_Zern.gif:
    Zernickes from extrafocal images taken 1996 October 1. These are
    with the old secondary. The old top end was installed after the
    tip-tilt top end was removed a week earlier, but no collimation was
    done.

IRTF_1096_??img.gif:
    Comparison of ShiftAdd images at K' with simulated K' images derived
    from the wavefront analysis, at nine sky positions. In each file,
    the left image is the NSFCAM image, resampled to 0.037 arcsec pixels.
    This pixel size is lambda/4D, i.e. it 2x oversamples the Nyquist
    frequency. The right image is the simulated image at K' from the EF
    analysis of the extrafocal images taken with the tip-tilt CCD. The
    pixel size is the same. Both are magnified 2x; the full width of
    the frame (both images together) is 2 x 120 x 0.037 = 8.80 arcsec.

NSFCAM_cvf1-227.gif and friends:
    Effective transmission profiles of the NSFCAM circular variable filter #1
    with the 0.15 arcsecond plate scale optics. The pupil diameter at
    the CVF is 2.0 mm, which broadens the filter slightly. The narrow curves
    represent the small-aperture transmission; the thick curves are the
    aperture-broadened profiles.