Revisiting the Rho Ophiuchi cloud complex

Several years ago I took a sequence of images of the Rho Ophiuchi cloud complex and posted the result on these pages. As noted at the time I used a Nikon D700 paired with a Nikon 85mm Ć’/1.8 lens all mounted on an iOptron Sky Tracker. Images were stacked using Deep Sky Stacker and post processing was done using Photoshop CS6 and Astronomy Tools v1.6.

Rho Ophiuchi cloud complex
Rho Ophiuchi cloud complex

Since then I have been experimenting with different tools for postprocessing astro photos. Along the way I discovered some interesting software called rnc-color-stretch from Clarkvision.com.

The rnc-color-stretch algorithm does 3 main things. 1) Analyze the image histogram to maintain a black point or use set low level color throughout the stretching process. The histogram is analyzed at multiple stages from beginning to end. 2) A power stretch while maintaining the black point. 3) Recover lost color after the stretching process. How far you can stretch an image depends on the signal-to-noise ratio.

I’ve been testing this software on both recent and older images. I thought it might be interesting to try it on the Rho Ophiuchi images taken in 2015. Once again, I used Deep Sky Stacker to register and align the images. Then I ran rnc-color-stretch. The result is the image shown above. I thnk it did a fine job of pulling out the details and the color.

Comet Lovejoy still visible in constellation Cassiopeia

Comet C/2014 Q2 Lovejoy is still visible in the sky in the constellation Cassiopeia. It is not as bright as it was a few months ago but can still be seen with a pair of binoculars. It is probably best viewed in the evening as Cassiopeia moves lower in the sky overnight and in the early morning hours. This makes it more difficult to see as there is more atmospheric attenuation at these lower elevation angles.

Sky map for locating Comet Lovejoy (03/22/2015) using the free and open source <a href="http://www.stellarium.org" target="_blank">Stellarium</a> planetarium software.
Sky map for locating Comet Lovejoy (03/22/2015) using the free and open source Stellarium planetarium software.

Using my recently acquired iOptron Skytracker for tracking night sky objects I took numerous exposures totaling 14 minutes (9x60s@iso1600; 10x30s@iso3200). These were then stacked in Deep Sky Stacker (DSS), a very good and free program designed for astrophotography.

Comet C/2014 Q2 Lovejoy on 03/16/2015. A faint tail can be seen extending to the upper right.
Comet C/2014 Q2 Lovejoy on 03/16/2015. A faint tail can be seen extending to the upper right.

The resulting image was then post-processed using the Astronomy Tools v1.6 actions in Photoshop.

 

Comet PanSTARRS — VII

This will probably be the final entry for Comet C/2011 L4 PanSTARRS. The comet is heading farther away from Earth each day and its brightness has diminished substantially. I have still been able to photograph it using long exposures or by stacking* many shorter exposures.

Comet PanSTARRS
Comet PanSTARRS

Here is an image from a few days ago that clearly shows the fan-shaped tail of the comet.

Comet PanSTARRS and M31.
Comet PanSTARRS and M31.

From a month ago — this stacked image shows both the comet and M31 (Andromeda Galaxy).

______________________

* I’ve been experimenting with the free Deep Sky Tracker for image stacking.