Examples of Shutterless Guiding
Following are some examples of the trailing effects of shutterless and
eraseless guiding. They are images of the NIRSPEC PXL guider taken by Gary
Puniwai.
In the first example, note that the full frame readout does not show any
tails on the image of the bright star at top, but does show a streak through
the guidebox at bottom. In this case the camera was used in a mode in
which full-frame images were shuttered and erased, but guide box images
used neither an erase nor a shutter. The streak through the guide box is
from the bright star at top.
In the next two examples the full frame images also did not use an erase
or a shutter. Hence all of the images have two-sided tails. Note two
things:
- The tails above the stars are weaker than the tails below. The tails
below are caused during readout of the image you are seeing. The tails
above are left over from the previous image when there is no erase.
The latter are weaker because the previous image was one in which
only the guide box was read out, which means that the upward
parallel shifting of the rows went very rapidly over most of the
readout time.
- The tails extend both above and below the stars. This tells us
immediately that this was not caused by an inoperative shutter, because
any erase cycle would have made the tails one-sided (smearing downward).
