Sky and Telescope - November 2016 - 68

Amateur Benchmark

PUSHING
the Limit

Sean
Walker

An intrepid astro-imager goes where no amateur has gone before.

AMATEUR ASTROPHOTOGRAPHERS are an insatiable
group. They continually strive to improve everything they
can with their pursuit, be it constant upgrades to equipment
to get the very best performance or developing new and
improved processing techniques to squeeze every last photon
from their images. Often this leads to some friendly competition, with the ultimate goal of producing the best images
possible within their means. Some strive to take the most
detailed image of a planet, while others search for undiscovered objects that range from asteroids to distant nebulosity
in our Milky Way. Others seek to record the faintest object
possible. So how deep can an amateur go?

Going Deep

BIG GUN
Johannes Schedler
in the Chart32
dome next to
its massive fork
mount and 32-inch
corrected Cassegrain. Note the FLI
ProLine PL16803
CCD camera, which
appears dwarfed at
the instrument end
of the telescope.

68

November 2016 sky & telescope

ALL PHOTOS COURTESY OF JOHANNES SCHEDLER & THE CHART32 TEAM

The question of how deep an exposure you can take dates
back to a challenge issued 18 years ago by professional
astronomer Bradley E. Schaefer (S&T: May 1998, p. 119).
Schaefer encouraged readers to tackle a specific, well-studied
field in Serpens. Less than one year later, Paul Boltwood of
Ontario, Canada, who specializes in faint-object photometry, was pronounced the winner. His 20-hour cumulative
exposure using a home-built 16-inch Newtonian reflector and

CCD camera identifies objects down to magnitude 24.1.
Boltwood's record stood for close to a decade before being
seriously challenged. In 2007, amateurs Johannes Schedler
and Ken Crawford joined forces to capture the 24.6-magnitude quasar CFHQS J1641+3755 using 16- and 20-inch reflectors (S&T: Feb. 2008, p. 88). With a redshift of 6, light from
the quasar left the host galaxy 12.7 billion years into the past.
That's looking back more than 90% of the accepted age of the
universe!
While a remarkable accomplishment, it required imaging
at visible through near-infrared wavelengths, while Boltwood's result was recorded in visible light. So while Schedler
and Crawford had bagged the most distant object, Boltwood's
record still stood.
The next challenger came along in 2013. Auckland,
New Zealand amateur Rolf Wahl Olson accumulated an
unprecedented 120 hours of exposure while imaging the
well-studied galaxy Centaurus A over the course of 43 nights
with a 10-inch f/5 Serrurier-truss Newtonian reflector and
QSI 683wsg CCD camera through Astrodon red, green, blue,
and UV/IR-blocked luminance filters (tinyurl.com/z4o78ca).
His image ultimately resolves objects down to an astounding
magnitude 25.4! This was (and still is) an impressive feat,
recognized as the deepest amateur image at the time and
definitively besting Boltwood's 1998 result.
But, as they say, records are made to be broken.

Even Deeper
Earlier this year, Schedler returned to the challenge armed
with the Chart32 32-inch Cassegrain (described later) and
Finger Lakes ProLine PL16803 CCD camera. He targeted the
compact galaxy group Hickson 91 in Piscis Austrinus that
contains several interacting spiral galaxies, including NGC
7214. Schedler recorded 17.7 hours of images through red,
green, blue, and UV/IR-blocked luminance Astrodon filters.
After combining the data, he noticed a faint, distorted
galaxy in the upper-left corner of the image identified using


http://www.tinyurl.com/z4o78ca

Sky and Telescope - November 2016

Table of Contents for the Digital Edition of Sky and Telescope - November 2016

Contents
Sky and Telescope - November 2016 - Cover1
Sky and Telescope - November 2016 - Cover2
Sky and Telescope - November 2016 - 1
Sky and Telescope - November 2016 - Contents
Sky and Telescope - November 2016 - 3
Sky and Telescope - November 2016 - A
Sky and Telescope - November 2016 - B
Sky and Telescope - November 2016 - 4
Sky and Telescope - November 2016 - 5
Sky and Telescope - November 2016 - 6
Sky and Telescope - November 2016 - 7
Sky and Telescope - November 2016 - 8
Sky and Telescope - November 2016 - 9
Sky and Telescope - November 2016 - 10
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