Tele Vue-NP101is: Imaging the Skies Over Southwest Florida
The lead-off image of this post is certainly an eye-grabber! It is one of the most unique interpretations of the Rosette Nebula (NGC-2237 or Caldwell 49) in Hubble Palette filters we’ve seen. Most striking, the usual Hubble Palette aquamarine color surrounding the central cluster is cobalt blue! The typical outer ring of yellows and burnt ochre now has a deep-orange hue. This color manipulation was done while maintaining the filamentary wisps and dark protostar Bok Globules in the nebula, along with a jet-black sky background. The resulting dimensional quality of this image draws the viewer from the ruddy edges of the nebula into the blue-colored center and then out the “back” aperture of the structure.
In the middle of the Covid pandemic, stuck at home, I decided to resurrect an interest in astronomy, and in particular astrophotography.
This image is from a great collection of Tele Vue NP101is images posted by Linwood Ferguson on SmugMug. At the top of this SmugMug page is stated the motivation for his astro imaging: “In the middle of the Covid pandemic, stuck at home, I decided to resurrect an interest in astronomy, and in particular astrophotography”. In this blog, we present a gallery of Linwood’s NP101is images.
The next pair of images are studies of the Horsehead (Barnard 33) and Flame (NGC-2024) Nebulae. The first image is what we are accustomed to in a broadband filter image: a red cloud of glowing hydrogen gas dominates the background with a dark concentration of dust, that has the distinctive appearance of a horse’s head, is in the foreground. To the left is a bright nebula interlaced with dark branches of light-absorbing dark gas — the Flame Nebula.
With the next image, broadband data is mixed with narrowband data to produce a hybrid photo. The prominent hues behind the horse-head are now yellows fading into reds, oranges, and greens. Wispy veils and structures are much more evident here due to the contrast of hues.
We asked Linwood how he got started in astronomy and astrophotography and here’s what he told us.
I was interested in astronomy in my early teens and had a chance to observe the March 1970 total eclipse in person with my tiny refractor, but never pursued astronomy afterward as I was busy with my education. I then briefly tried again in the late ’90s, but work took much too much time, and I again gave up. Covid (and retirement), perversely, presented an opportunity to actually spend the time necessary to get into the hobby properly.
We were curious as to how he gravitated towards the Tele Vue-NP101is scope for imaging.
I started with a terrestrial camera and lens, and while it was a terrific lens, better than many similar size refractors, the difficulties in using a terrestrial camera in high light pollution areas led me to a mono camera and a need for a similar length refractor. I spent a lot of time digging on the Internet, and asking some knowledgeable retailers, and settled on the NP101is. It supported a full-frame environment, had an easily adapted focuser for a motorized system, and had a very rigid, threaded, wide imaging train. I also already had all Tele Vue eyepieces so I anticipated (and got) high optical quality.
Meet the Tele Vue-NP101is Photo / Visual APO Refractor
Al Nagler took Petzval’s portrait lens concept and patented a fast telescope version for the purpose of testing eyepieces (the 5”, f/4 Multi-Purpose Telescope). By 2001, the NP101 (Nagler-Petzval) scope was the ultimate culmination of 30-years of refinement toward optical perfection for the “multi-purpose” concept. However, we did not rest on our laurels: with the CCD imaging revolution challenging telescope optics beyond anything ever placed at the focal plane, we were determined to make the NP series optically, mechanically, and functionally as perfect as possible for imaging on chips with up to 50-mm diagonal, without penalty to its near-ideal visual operation. The resulting Imaging System version of the NP101 is a 4-element, 2-group (Nagler-Petzval) design, with a 101-mm objective diameter, 540-mm focal length (f/5.4), APO refractor with a robust 2.4″ focuser with built-in tilt compensation. The NP101is produces a whopping 5.3° image circle at prime focus. Maximum visual field-of-view is likewise huge: 4.9° with 55-mm Plössl (10x) or 41-mm Panoptic (13x).
We asked Linwood what impressed him the most about the NP101is after having experience using it. He told us: “it was boring”!
That it was boring. That may sound strange, but so many things in this hobby (like mounts) seem to require continual tweaking, after-market add-ons, long threads looking for help on Cloudy Nights, and seemingly every night some new gremlin injecting itself into my images. The NP101is just worked, it did its thing, there were no surprises. The field stayed flat, as I added weight there was no sag or tilt, no surprise reflections. Just nice small stars, leaving me time to fight the rest of the gremlins so prevalent.
The iconic Heart Nebula (IC 1805 or Sharpless 2-190) imaged below, is an emission nebula that glows mostly in ionized hydrogen light from the radiation provided by giant stars in the open cluster, Melotte 15, at the center of the nebula. Stellar winds from these stars are eroding “dust pillars” visible in the central part of the “heart.” The structure at the top-right of the Heart is also known as the Fishhead Nebula (IC 1795).
The Heart Nebula was shot using the Hubble Palette narrowband filter set: Hydrogen-alpha (Hα), Oxygen (OIII), and Sulfur (SII). Linwood’s image is unique because he didn’t take the well-traveled path of mapping Hα to green, OIII to blue, and Sulfur to red. His mapping is to make Hα the red: this gives the outer parts of the nebula a “natural-looking” reddish-hue of hydrogen gas. The typical Hubble Palette mapping would give the interior of the nebula a blue to green glow with the outer edges being brown to yellow.
Linwood Ferguson’s Tele Vue-NP101is Imaging Setup
Above is Linwood’s backyard setup in southwest Florida. Occasionally he images from a dark site in the Everglades. We asked him about the software used to control and image with this impressive portable setup.
After experimenting with APT and Voyager, I settled in on Nighttime Imaging ‘N’ Astronomy (N.I.N.A.) as a session manager; it is flexible and under very active development. I also use PHD2 for guiding, and Pixinsight for processing. I am using an Off-axis Guider on the NP101is despite the short focal length as it lets me move the entire imaging and guiding setup to my SCT unchanged. I currently use a Paramount MyT and so also use TheSkyX for underlying mount control and modeling.
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