Reflections and Absorbtions

[Dom543]

This is my first attempt to look for color and contrast in reflection and dark nebulae.

Unfortunately the contrasts of the captures are fainter at daylight than were while sitting out there under the moonless sky. Please try to look at the images in a darker environment.

First, dust illuminated by the orange glow of Antares (off the image to the left) and blue reflections of Rho Ophiuchi surrounding dark bayous of Barnard 44.

To my best knowledge 22 Scorpii is the double (triple?) star in the upper left, Rho Ophiuchi is the triple star in the lower right and IC4603 is the nebulosity in the lower center.

Next is a frame shifted closer towards Antares and showing dark lanes of Barnard 44. The bright star is 22 Scorpii.

Unfortunately, at this point, I am not able to bring out more of the otherwise abundant blue reflections around the brighter stars. It washes into the background. Trying to shift the hues to emphasize blue more turns the orange glow into green.

As said, this was a first try. Any suggestions are welcome.

The equipment used was a Nikkor 180mm f2.8 lens with UV/IR cut filter, Lodestar x2C and LodestarLive v.0.11.

Clear Skies!

--Dom

(I have to post this without reviewing it, due to fading internet connection. Apologize for typos and other errors.)

[Paul81]

Hi Dom,

It may be worth un-ticking auto-align of the colour channels and slide the blue channel (by selecting blue and then adjusting the brightness) a little to the right - might help bring out blue a bit more.

Paul

[Dom543]

Thank you Paul! Here is my second iteration from yesterday night.

This is a slightly wider field of view with a 135mm SMC Takumar lens at f2.5. (The subscription is inaccurate, I forgot to update from the night before.)

I also include a screen capture that shows all my settings. I increased the contrast of the blue channel to 0.7 from 0.5 base used originally for all channels. As you see, I also fiddled with the hue and maxed out the saturation. I am a color extremist...

You can also see my red-and-black windows color theme that I use for real-time astro observations.

Clear Skies!

--Dom

[Dom543]

Here is my third attempt to capture more of the elusive blue reflections.

This is with a wider angle 85mm lens stopped down to f2.8.

The wider field also includes Sigma Scorpii at the bottom right.

But I excluded Antares and M4. Antares is too bright and destroys the balance.

The globular doesn't show well on this scale against the bright Milky Way background.

I also rotated the image to have North at the top. This is a mean stack of 5x20 sec exposures.

I am not sure, if this is any better than the second attempt.

As said, reflection nebulae are challenging.

Clear Skies!

--Dom

[Paul81]

Hi Dom,

I agree they are quite challenging, I have tried a few in the past and got the brighter bits but never quite got a hold of the fainter whisps. I wonder if any filters might help, I'd need to goggle around on that one!

Paul

[Dom543]

I found a source for surplus laboratory filters and bought 40nm wide blue and 20nm wide orange bandpass filters.

The orange picked up no signal except for the brighter stars. This means that what looks orange on the image is not orange by its spectrum but a mixture of light of other colors. This is not unexpected but interesting to know.

The blue filter did pick up some of the blue reflections around the brighter stars. This far I was not able to add this to the full spectrum frame as refocusing is needed, when changing filters.

Focusing is tricky and time consuming with narrowband filters and fast optics. For my particular frame superposition technique, this has to be done, while stacking is suspended. If too much time passes before resuming stacking, the registration stars may have drifted too far for the algorithm to re-accept them. I don't have a permanent setup, so my alignment and tracking is never perfect. I may be able to improve my refocusing skills but this far I wasn't sufficiently motivated in the lower 30's temperatures after 1 am...

I would still be interested to hear any input or suggestions regarding capturing reflection nebulas.

Clear Skies!

--Dom

[Dom543]

I had a chance to buy at half price a set of LRGB filters that are parfocal with the NB filters that I have already owned. This makes swapping filters between consecutive frames in a stacking run painless. To test the opportunities that the use of the new filters opened up I revisited one of my favorite challenges, the colorful Antares/Rho Opiuchi complex of reflection absorbtion and emission nebulas.

My earlier captures of this area were made with just a single UV/IR cut filter. All I could do was to tweak the brightness and contrast of the three color channels and the hue setting. With the new filters I can now add more of some of the desired but underrepresented colors to highlight the main features of the target area.

Below is my new favorite. It is a mean stack of three blue filtered frames, five luminosity (UV/IR cut filter) and two red filtered frames. All exposures are 20 sec each. The main goal was to capture more of the elusive blue reflection nebulosity while maintaining the color balance. In particular the unique orange reflections originating from dying Antares.

Even though the above image is my current personal favorite, for demonstration purposes I also include a crop from a screen cupture made during a different experiment. This differs from the previous one in that the two red frames were replaced by four H-alpha frames. The objective was to better capture the HII emission nebula SH2-9 around Sigma Scorpii (the brightest star on the lower right). The brighter red double "eyebrows" above Sig-Sco are the result of capturing more of the H-alpha emissions. (On it's own Sh2-9 is rather faint.)

The cost of replacing the wide band red with the narrow "far-red" wavelength of H-alpha was the shift of the nice orange areas to become pink. After thinking a bit, this was to be expected. As I said in an earlier post, the orange is not the result of a single spectrum orange radiation. It is a mix of a wider spectral band, whose wave lengths average out to end up to yield orange. If we replace the wide band of all the reds contributing to this feature by a single narrow band from the far longest end of the red wavelength spectrum (H-alpha), then the average will shift to longer wavelengths, i.e. to more reddish from orange.

The relatively large number of frames stacked is the result of my lack of experience with this technique. If one overdoses one of the colors at the beginning of the stack, the only real-time way to correct it later is to "dilute" it by adding more luminosity frames. With filter swapping and all, it currently takes me about 5 minutes to live capture-compose such an images. It's longer than taking a snapshot but still vastly shorter than the time astro-photographers spend on producing their images. And it's fun to wait to see in real time what changes the addition of the next frame will make...

By the way, doing these things by sum-stacking is easier and yields faster results. A good way to start experimentation. But the quality of the final images is less satisfactory due to their noisy texture that I am not able to smooth out.

Clear Skies!

--Dom