Monday, September 30, 2013

Heart and Soul Widefield

Heart and Soul Widefield by S Migol
Heart and Soul Widefield, a photo by S Migol on Flickr.
Via Flickr:
Heart (IC 1805) and Soul (IC1848) nebula as seen from the backyard. Taken with the modified Pentax K10D using the smc P-A* 1:4 300mm lens. I had some challenges during the sessions with flexure and so I was finally able to get most of the flexure under control by adding a ring attached to a ball mount. There's still some movement so I'd like to revisit this challenge eventually. May consider making something out of wood.

This image is the result of a collection of 9 subexposures all 1200 second long. Lens was set to F5.6, f6.7, and f8 respectively to try to control fringe and off axis coma. Also used a stack of the IDAS LPS P2 filter with the B+W 486 filter to control out of focus NIR leaking through the filter.

Total integration was a low 3 hours.

Guided atop a Losmandy G11 with ST80 guidescope and SSAG.
Calibrated in Maxim with flats for each Fstop.
Stacked in DSS, processed in PixInsight to stretch and remove some noise.
Referentiation Matrix (Gnomonic projection = Matrix * Coords[x,y]):
-0.00119583 -8.21417e-006 +2.3258
+8.01721e-006 -0.00119611 +1.53944
+0 +0 +1
Projection origin.. [1935.998548 1300.008048]pix -> [RA:+02 45 10.36 Dec:+61 05 20.78]
Resolution ........ 4.306 arcsec/pix
Rotation .......... 0.382 deg
Focal ............. 289.83 mm
Pixel size ........ 6.05 um
Field of view ..... 4d 37' 51.3" x 3d 6' 34.6"
Image center ...... RA: 02 45 10.358 Dec: +61 05 20.82
Image bounds:
top-left ....... RA: 03 05 20.870 Dec: +62 32 14.32
top-right ...... RA: 02 25 09.673 Dec: +62 34 11.54
bottom-left .... RA: 03 03 17.995 Dec: +59 26 25.98
bottom-right ... RA: 02 26 51.662 Dec: +59 28 12.04

Some followup thoughts about this session:

First, the lens aberrations are pretty strong.  Look at the CCDI view at F5.6, F6.7, and F8:
Note how the center of the image is strongly corrected and the outer regions are streaked.  I think that the next time I use the lens, I'll focus on a star slightly out from the center and see what that does.  It may fix the performance of the lens nicely.  If this makes the lens perform better, than I can continue to use it at F5.6 as it will be brighter than the SV70ED with a reducer.

Second, using the camera with lens presents challenges regarding portrait vs landscape mode.  I will attempt to make a bracket that will allow easy swap from one orientation to another.  I think that a couple of 2x4 with a tight hinge should do well, especially if the open angle is fixed via spacer.

Third, if attempts to flatten the image a bit more do not work, then I could rent a modern 300mm lens for a week - long enough to do a few sessions over a new moon.

Lastly, even with poor star images in the subs, the process of stacking and PI work seems to tighten up the edge stars nicely.  This makes the effort less of a challenge except to handle purple fringing.

Note how the star images appear in the original stack (and compare with the processed version).  The screenshots below are from PixInsight showing 1:1 with auto STF from the DSS FIT file.
Upper Left

Upper Right

Lower Left

Lower Right

How I put the camera and guidescope for the portrait orientation: