M13 from the Backyard

M13 June 2014

This image was taken under a deadline to get ready for GSSP 2014.

This is a shot of the globular cluster Messier 13, in Hercules.  Taken over two nights in the backyard for testing prior to GSSP 2014.

Was challenged to fix some problems with camera and mount prior to the star party.  The mount part was easy - I re routed some cables so that they didn't snag.  The camera part was not easy.  During waiting fo rthe skies to clear, I ran the camera to capture a series of dark frames.  Unfortunately, during these sequences a piece of flocking paper fell down into the camera body and blocked the movement of the shutter.  The shutter electronics a dead and now it will not open.  I've had to hot glue the shutter open and now rely on the motion of the mirror plus the electronics of the CCD to time the exposures.  Biggest follow up to the shutter issue has been taking flats.  Because short duration flats allow over exposure as the mirror flaps up and down, long duration flats are better.  I'm now recording flats with a duration of .7 seconds vs 1/60 second.  I may consider building a strobe box to further experiment.

This image is a sum of 18 exposures at 1200 seconds each at 100 ISO. 
Standard setup: Stellarvue SV4, Pentax K10D (modified and cooled - and broken shutter), SSF6 flattener
Mount: Losmandy G11 with Gemini 2
Guiding scope: Stellarvue SV70ED with Orion SSAG
Guiding: Maxim 5.24
Exposure control: Star Labs DSLR Shutter and Pentax tethering software

Calibrated in Maxim with 10 darks, 21 flats, and 260 bias
Stacked in DSS 3.3.3 beta 51
Processed in PixInsight 1.8 with Crop, DBE, Masked Stretch, Histogram Stretch to reset black point, TGVDenoise, masked curves to boost saturation and reduce muddy sky glow, and unsharp mask on bright stars to tighten.
Passed through LR5 for export to web

Here's the platesolve from PI
Referentiation Matrix (Gnomonic projection = Matrix * Coords[x,y]):
          -8.66381e-007        -0.000530417           +0.680789
            +0.00053032       -9.15332e-007             -1.0261
                     +0                  +0                  +1
Projection origin.. [1937.076485 1280.333772]pix -> [RA:+16 41 52.45 Dec:+36 29 51.55]
Resolution ........ 1.909 arcsec/pix
Rotation .......... 89.898 deg
Focal ............. 653.58 mm
Pixel size ........ 6.05 um
Field of view ..... 2d 3' 16.7" x 1d 21' 29.8"
Image center ...... RA: 16 41 52.423  Dec: +36 29 51.40
Image bounds:
   top-left ....... RA: 16 45 13.027  Dec: +35 28 07.62
   top-right ...... RA: 16 45 17.404  Dec: +37 31 22.18
   bottom-left .... RA: 16 38 32.813  Dec: +35 27 59.29
   bottom-right ... RA: 16 38 26.431  Dec: +37 31 13.63