Collecting  Photons

Full resolution 1974x1266

Objects:             IC1396 (sparse open cluster and associated nebulosity). VdB 142 (reflection nebula) at the end of a dust protusion.

Constellation:     Cepheus

Coordinates of field center: 21h 40m +57° 31'

Notes: IC 1396 is a fantastic object way too big to fit entirely in the field of the 10". This detail is centered around the "Elephant Trunk" nebula a very interesting dust cloud that include the tiny reflection nebula VdB142.
 

Telescope and camera: ASA 10', f 3.6; SBIG STL 11000.

Exposure: Hα 22x16'; R, 18x10'; B 18x10'; G 18x8'. About 14.2 hrs total.

Date: only 3 nights on 30, 31-08-10 and 1-09-10.

Software used: acquisition, CCDsoft, FocusMax, CCDcommander, The Sky VI. Calibration; registration and stacking: CCDstack, Registar; processing: PixInsight, Photoshop CS. 

Processing notes: This nebula presents a major processing challenge: since it is very bright, its dynamic range is vast, and the application of non linear stretching tends to overly compress the brightest range of luminance. If one is interested in preserving all the micro contrasts present in the nebula, and that are especially rich nearby the Trunk, some action has to be taken to reduce the overall luminosity of the nebula. Here, by using the DBE processor of PixInsight, I modeled the low frequency components of the nebula with a spline surface that has been then subtracted from the Hα and from the RGB composition. This procedure "freed" some space to expand the dynamic of the image. As result of that, a complete, and unusual, set of colors appeared in the nebula, reflecting the differential distribution of the OIII and HII signals. Furthermore, a conspicuous reddening caused by dust is now visible in several areas, most notably near the base of the Trunk.

The effects of this process are visible in the roll-on animation, where the original Hα data is presented together with the same image after the high pass filtering.

Copyright © 2010 by Gimmi Ratto. (September 26, 2010)