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.

Perseid Meteors—2020

The Perseids meteor shower is an always popular sky event. Perhaps one reason is that it occurs during the warm summer months and can be a pleasant family event.

Perseid meteors—2020.
Perseid meteors—2020.

We found ourselves at a parking lot in Wupatki National Monument—an International Dark Sky Park. Two other groups of two were also there but the parking area is big and maintaining distance was easy.

Photographing a meteor shower is always about trade offs. If you shoot with an ultra-wide lens the meteors are small and you will likely miss some of the dimmer ones. But the wide angle view ensures that you cover a large portion of the sky.

Another option is to shoot with a lens that is in the “normal” range or even a telephoto. The disadvantage is the field of view is greatly reduced while an important advantage is that the lens will capture the dimmer meteors.

The Lens Aperture Area versus Angular Coverage Trade
Because meteors appear in random location across the entire night sky, one might think that an all sky camera would pick up the most meteors. But this is not the case. Wide angle lenses mean short focal lengths and short focal lengths have smaller physical lens apertures, so collect less light. Thus, there is a trade between lens technology to collect a lot of light and angular coverage…

Another factor in meteor capture is where to point. If one points closer to the radiant then the angular velocity of a meteor decreases and the longer focal lengths are not impacted as much.

For several years I shot with wide-angle and ultra-wide-angle lens (28mm, 24mm, and 16mm). More recently, I been shooting with 50mm and 85mm lens. Last year, with the 85mm lens I captured one (1) meteor. But the detail was great!

This year I shot with a 50mm lens. This is an old, legacy lens: Nikon 50mm Ć’/1.8 AI manual focus.

We set up the camera on a star tracker, dialed in the settings, and then let it go taking continuous shots at Ć’/2.8, 30 seconds, and ISO 1600. The camera was pointed with the radiant in the lower left corner. Also visible in the composite is Andromeda Galaxy (M31) in the upper right. Meanwhile, we pulled out the camp chairs and leaned back to stare at the sky for a few hours.

We saw a few dozen meteors in about 2-1/2 hours and the camera with its smaller FOV captured considerably fewer. As the Moon rose above the horizon we packed it all away and drove home. Reliable reports indicate that meteor activity picked up considerably in the pre-dawn hours. We were happily asleep at that time.

Perseid meteors (full crop)—2020.
Perseid meteors (full crop)—2020.

The first image is a stack of the handful of shots containing meteors and downsized for this posting. The second image (full-size image), on the other hand, is a full-size crop of two meteors showing how much detail can be found when using a fast lens with a narrow field of view.

Comet C/2020 F3 (NEOWISE)—VIII

Comet C/2020 F3 (NEOWISE) is growing dimmer in the evening sky although is still visible in binoculars. Longer exposures are now necessary to reveal the fan-shaped tail.

Comet C/2020 F3 (NEOWISE) in the evening sky.
Comet C/2020 F3 (NEOWISE) in the evening sky.
Comets C/2020 F3 (NEOWISE), C/2019 U6 (LEMMON), and C/2017 T2 (PANTARRS).
Comets C/2020 F3 (NEOWISE), C/2019 U6 (LEMMON), and C/2017 T2 (PANTARRS).

The second image is a wider view that shows that Comet C/2017 T2 (PANSTARRS) and Comet C/2019 U6 (LEMMON) are also visible albeit both are very small and faint. M53, a globular cluster, and M64, a spiral galaxy, are also visible and labeled. A full-size version of this image (~2.1 MB) is also available.

These images are a stack of five images each 120 seconds at Ć’/4, 85mm, and ISO 400. The shooting location was Sunset Crater National Monument, an International Dark Sky Park.

Comet C/2020 F3 (NEOWISE)—VII

The waxing Moon is getting brighter in the evening sky and this makes it more difficult to see Comet C/2020 F3 (NEOWISE). In fact, I was unable to see it with the unaided eye but both binoculars and long-exposure photographs easily brought out the comet.

Comet C/2020 F3 (NEOWISE) above Grand Canyon.
Comet C/2020 F3 (NEOWISE) above Grand Canyon.

On the other hand, the presence of the first-quarter Moon illuminates the inner canyon while the comet is faintly visible above.

The image is a composite. The first image is on a fixed tripod to get a sharp result of the moonlit canyon. The second image is on a tracker to get sharp points for the stars and comet. The two images are then combined. Camera settings are 24mm, Ć’/4, 120 seconds, ISO 400.

Thunderstorm with lightning near Grand Canyon.
Thunderstorm with lightning near Grand Canyon.

As a bonus, a late evening thunderstorm developed just west of Page and moved to the northeast while producing a lot of lightning. Although no cloud-to-ground strokes were noted, the lightning easily illuminated the cloud from the inside.

Sunset with crepuscular rays over Grand Canyon.
Sunset with crepuscular rays over Grand Canyon.

Second bonus: there was a nice sunset, too.