NGC 3718

NGC 3718
All Images Copyright Steve Cannistra

Please click here for a larger image (60%).

Magnitude:  11.6
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 diffuse "S" 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 galaxies 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.

Photographic Details:
Date:  April 24, 2008
Scope:  Vixen VC200L at f9 (FL = 1800 mm) on the Takahashi NJP Mount.
Autoguider:  SBIG ST-402 with Sky90 at f4.5.
Camera:  Apogee U32 -20C.

Astronomik 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.
Post-processing:  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 bit format).

Please note:  Graphics on this website may not be reproduced without author permission.

Back to Galaxies