Size: about 10'
Distance: 42 million light years
RA (J2000): 11h 32m 35s
Dec (J2000): +53 degrees 04' 02"
Position Angle (Pinpoint): 89 degrees
NGC 3718 is characterized by the
shape of its arms, as well as the tan brown dust lane that runs through
the center (reminiscent of Centaurus A).
To the right of NGC 3718 in this image can be found a cluster of 5
known as Uppsala General Catalog (UGC) 06527 (aka Arp 322 or Hickson
56). This is the third light image of my new modified
Cassegrain scope (VC200L), which I have now collimated to my
satisfaction. I performed the collimation indoors in the
basement, with the heat off so that thermal currents would be
minimized, using an artificial star made by poking a tiny pinhole into
a shoebox cover and placing it in front of a light bulb (yes, I am high
tech, guilty as charged). The key to collimation was to use a
reticle eyepiece from my manual guiding days (I'm glad that I didn't
sell it), so that I could bring the star exactly back to center after
each adjustment. The reticle also permits an accurate assessment
of the symmetry of the donut (initially) or diffraction rings (last
step). The other trick to accurate collimation is to use as small
a donut as possible in the initial phases of adjustment- a large donut
will make the procedure insensitive. Although this image is taken
at an image scale of 0.78 "/pixel, the seeing in my area is typically
no better than 3" (as it was this night), and the aperture of the scope
is only 203mm (8 inches). Both of these constraints will limit my
resolution, compared to a larger aperture and better seeing (as shown
in this terrific
image from Johannes Schedler). Nevertheless, for a scope that
only cost me $1,799, produces a respectably flat field, has a fixed
primary mirror (i.e., no mirror flop, which means that I can use an
external guidescope without worries), and is very lightweight
(important since my setup is portable), I am going to have some fun
this galaxy season. In addition to the scope being better
collimated, the other difference between this image and my previous M51 shot
(which I was not happy with, even though my friends were trying to be
supportive <g>) is that I used an unblocked filter this time
(i.e., a clear filter, not blocked in NIR). This made a
noticeable difference in the amount of signal that I captured in a
relatively short period of time (details below). More information
about NGC 3718 may be found here.
Date: April 24, 2008
Scope: Vixen VC200L at f9 (FL = 1800 mm) on the
Autoguider: SBIG ST-402 with
Sky90 at f4.5.
Camera: Apogee U32 -20C.
Clear (unblocked) filter.
Exposures: 14 x 10' Total
exposure 2.3 hours.
Conditions: Transparency good; seeing (FWHM)
approximately 3"; Temperature dropped to approximately 48 degrees
F during the night.
Calibrated, aligned, and Sigma Clip combined
in Maxim, followed
by deconvolution using Bob Vanderbei's Fat
Tail Deconvolution script. DDP
in ImagesPlus (IP). Further processing in Photoshop CS (16
note: Graphics on this website
may not be reproduced without author permission.
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