Back in December 2018, we featured some spectacular wide-field, deep-sky images by Diego Cartes Saavedra in Chile. All the images were taken with his Tele Vue-76 APO refractor and Tele Vue TRF-2008 0.8x Reducer/Flattener. This combination achieves a 380mm focal length at f/5, ideal for imaging large swaths of deep sky. You can still read the original blog at Tele Vue-76: Imaging the Southern Hemisphere. At the end of that post, we wished Diego continued success in his astrophotographic journey. Ever since, we’ve followed his progress through his postings on the AstroBin imaging hosting platform for astrophotographers. We felt it was time to “catch up” with him and post some of his latest captures in this gallery blog.
NGC 6188 ─ The Fighting Dragons of Ara (Hubble Palette)
Prior generations of supernovae explosions spread dust and gas in this complicated region of space. Continued explosions compressed this material and sparked the formation of new massive stars. Stellar winds from these stars intricately sculpted the region into areas of glowing gas, reflection nebulae, and dark clouds of dense matter. The resulting dark, dusty lanes conjure up images of two dragons. Light from open cluster NGC 6193 illuminates the large blue reflection nebula where the dragons face off. The dense, blue object at the lower-right is pk336-00.1 (also NGC 6164 & NGC 6165) ─ an emission nebula formed from the expanding outer layers of a giant, hot, O-type star at the center. Around this compact object is the faded outer ring of reflected blue dust from earlier shedding events. This image was awarded an AstroBin “Top Pick” nomination.
Sharpless 2-308 (Bicolor palette)
Like a ghostly apparition suspended against the blackness of space, many see the grinning face of a Porpoise in this nebula. Sharpless 2-308, also Porpoise Nebula or Gourd Nebula, in Canis Major is a bubble of gas formed as the bright central star in the image shed outer layers of hydrogen gas. Stellar winds from the star are causing the gas to collide with slower-moving shells from earlier in the star’s evolution. This forms the shape of the nebula that we see today. “This is the first time I attempted to capture this nebula. Its light is mainly OII[I], but Hα frames also revealed some nebular clouds in the field. It is a very big target, so it is perfect for small refractors.” Diego’s effort in creating this image resulted in his being awarded an AstroBin “Top Pick” nomination.
M17 ─ Omega Nebula (Hubble Palette)
The Omega Nebula, also known as M17 or Swan Nebula, is a “stellar nursery” similar to the more famous Orion nebula. However, it’s seen “edge on” from Earth instead of “face on” as the latter. Ultraviolet light from a cluster of stars in the nebula causes the surrounding hydrogen-rich gas to glow. Diego says he processed this image using Pixinsight’s Colormask script by following a tutorial by Chuck Ayoub. Diego tells us how he’s improved his imaging over time:
I think my processing has improved over time, but also I have tried to improve the quality of the images, increasing the exposure times of the subframes, the total integration time, and being more strict on the precision of the guiding.
What is the “Hubble Palette”?
Several of the images here are marked as being in the Hubble Palette and you may be wondering: “what is the Hubble Palette?”
Similar to how Red, Green, and Blue (RGB) light can be combined to form color images on a television screen, astro imagers can use filter sets tuned to particular wavelengths (colors) of light to produce natural-looking or false-color images of a celestial object.
Professional astronomers are more interested in finding out what an object is made of and how it evolved into its present configuration. This takes a backseat to creating natural-looking RGB images. By imaging with filters tuned to the emission lines of specific light-emitting gasses, false color photographs are created that reveal the composition and evolution of nebulae. This often conveys a sense of dimensionality not present in an RGB photo of the object. Widely distributed, eye-grabbing, false-color nebulae images from the Hubble Space Telescope (HST) inspired amateur astronomers to use a filter set that produced similar results.
The HST contains dozens of filters that can be used in many combinations, but the amateur astronomy community adopted the most eye-pleasing of the filter sets for nebulae use as the “Hubble Palette.” This filter set is listed below by the color channel commonly assigned in the final image, the atomic emission line that creates it, and the position of the emission line on the spectrum.
- Red = Sulfur II (deep-red spectrum)
- Green = Hydrogen-alpha + some Nitrogen (red spectrum)
- Blue = O III (blue-green spectrum)
It may be surprising to learn that two of these emission lines look “red” to our eyes. These filters are known as “narrow band” because they attenuate any light beyond the emission wavelengths they are designed to pass.
Rosette Nebula (Hubble Palette)
The Rosette Nebula (NGC-2237 or Caldwell 49) is an emission nebula and star-forming region in the constellation Monoceros (the Unicorn). It is comprised mostly of hydrogen gas. An open star cluster (designated NGC 2244), formed from material in the nebula resides in the center. Energy pumped out by massive blue-white stars in the cluster excites the gas in the nebula to glow. We can see the cluster clearly in the center because strong stellar winds from the massive stars are sweeping dust clear of the area. In Diego’s image, the narrowband Hubble Palette filters reveal various layers of material within the heart of the Rosette. The resulting dimensional quality draws the viewer from the ruddy edges of the nebula into the aqua-colored center and then out the “back” aperture of the structure.
IC 4628 ─ Prawn Nebula in Scorpius (Narrowband Hα)
The Prawn (also known as IC 4628 or Gum 56) is an emission nebula and stellar nursery rich in hydrogen gas in the constellation Scorpius. The clumps of stars in the nebula were likely formed there. Open cluster NGC 6231 is visible in the lower-right-hand corner. “This image was made using only the information captured using a Hα filter,” says Diego. This allows him to bring out the details inside the nebula.
Meet the Tele Vue-76
Diego’s backyard imaging setup has been upgraded with a beefier mount since his last appearance here but the imaging train is exactly the same. It consists of the compact Tele Vue-76 APO refractor with Tele Vue TRF-2008 0.8x Reducer/Flattener in the 2″ drawtube. Spacers are connected between the TRF-2008 (T-thread) and ZWO 7x36mm Filter Wheel (EFW) to achieve 55mm backfocus to the camera on the other side of the filter wheel. The camera is a ZWO ASI 1600MM Cooled Pro monochrome camera. The Tele Vue-76 ring mount on the ivory telescope tube is attached to a Tele Vue AVT-1011 adapter that connects to the plate on the iOptron CEM70G EQ mount. The AVT-1011 also allows for focus knob clearance above the mounting plate.
The Tele Vue-76 is a 76-mm diameter objective, 480mm focal length, f/6.3, APO (Doublet) refractor that combines compact size with APO optical performance and 2″ eyepiece capability. The maximum field-of-view is a binocular-like 5.5° with our 41-mm Panoptic (11.7x) or 55mm Plössl (8.7x). The 5.0° field-of-view of the 31mm Nagler (15.5x) is another option for wide-field/self-finder use. The 2″, 10:1 dual speed, rack-and-pinion focuser features dual tension adjustment screws on the drawtube and dual lock screws on the end-ring. The OTA includes a sliding metal dew shield and screw-on metal lens cap. Available tube colors are ivory or evergreen using tough, durable, powder-coat instead of paint. A custom-fitted padded case with room for accessories is included. The power range and field afforded by this scope allows you to explore astronomical, spotting, and birding targets with the same instrument.
Model TRF-2008 0.8x Reducer/Flattener was specifically designed for use with the Tele Vue-76 and Tele Vue-85 refractors. It can also be used with any 400-600mm doublet refractor with 2″ focuser. It is the simplest way to start in astrophotography with your scope and a camera that can be mounted to a T-thread. It converts the Tele Vue-76 to a 380mm, f/5 and the Tele Vue-85 to a 480mm f/5.6 telephoto lenses respectively, for fast, wide, flat field photography. More information on our website (mobile site).
Statue of Liberty Nebula (Hubble Palette)
Also known as NGC 3576, this image features loops of gas blown by the stellar winds of young stars intertwined with the dust from old exploded stars. While the nebula was discovered by William Herschel in 1834, the appellation “Statue of Liberty Nebula” is a recent suggestion (2009) by Dr. Mazlin of the Star Shadows Remote Observatory. The “Statue” is formed by the shape of the dark matter in the nebulosity at the center of the image. This image was awarded an AstroBin “Top Pick” nomination.
We hope that you enjoyed this gallery and we wish Diego Cartes continued clear skies for imaging with his Tele Vue-76!
- Our first blog on Diego Cartes from 2018: Tele Vue-76: Imaging the Southern Hemisphere
- Tele Vue-76 webpage (mobile site)
- TRF-2008 0.8x Reducer/Flattener works with any 400-600mm doublet to create a better scope for imaging (mobile site).