Normally an f/6.3 Meade
focal reducer is used on the telescope which gives a field of view about 25x25 arcmin.
The CCD camera is an Apogee
AP47p with Marconi 47-10 back
illuminated chip. This is a 1024x1024 pixel format chip with 13 micron pixel
size and the imaging area is 13.3x13.3mm in size. The
AP47p is a parallel interface camera and downloads at full resolution (unbinned)
are rather slow.
The CCD camera is generally operated in two binning
modes and with the focal reducer gives:
- 1.5 arcsec per pixel resolution
and image downloads in about 43 seconds unbinned (1x1)
- 3.0 arcsec per pixel resolution,
image downloads in about 13 seconds binned 2x2.
There is some vignetting at f/6.3, a flat field shows
the effect here
which results in a fully exposed circular area of about 25
The CCD shutter latency
(the time taken between an exposure being requested to start and the actual time
the shutter opens) is important to know when dealing with very fast moving Near
Earth Asteroids. A long delay or worse an unpredictable delay in opening the
shutter would introduce errors into the resulting astrometry.
version 4 introduced a function to measure CCD shutter latency directly and
this has been used at Great Shefford to measure the shutter latency of the
AP47p. The result was an average delay of 0.02 seconds ± 0.02 seconds, allowing
good precision for very fast moving objects.