ASTRONOMY · ASTRONOMY TECHNOLOGY TODAY Your Complete Guide to Astronomical Equipment Volume 10 • Issue 2 $6.00 US DREAM TELESCOPES Q&A • THE VIXEN SX2 WITH STAR BOOK TEN TAKING

ASTRONOMYTECHNOLOGY TODAYYour Complete Guide to Astronomical Equipment

Volume 10 • Issue 2$6.00 US

DREAM TELESCOPES Q&A • THE VIXEN SX2 WITH STAR BOOK TENTAKING A LOOK AT THE OFF-AXIS PERFORMANCE OF PARABOLOIDAL MIRRORS

DESIGNING AN ATM 6-INCH F/15 BINOSCOPE

Astronomik L-RGB Typ2c and

Narrowband Filters

Industry News/NewProducts10 ASTROZAP

New Dust Covers

12 ASTRONOMICSExpands Astro-Tech EDT Refractor Line

14 JOSHUA BURYObserver Pro 1.1.1

16 SANTA BARBARA SCIENTIFIC Announces SM-1 Seeing Monitor plus Certification Services

19 UNIHEDRONAdds SQM -LU-DL to Its Line

Astronomy TECHNOLOGY TODAY 3

Contents

In This Issue6 Editor’s Note

The Evolution of ATT ContinuesBy Gary Parkerson

33 Astronomik L-RGB Typ2c and Narrowband FiltersNo Halos. None.By Austin Grant

47 The Vixen SX2 with Star Book TENA Solid Portable GoTo EQ Mount with a Planetarium-Style ControllerBy James Chen

55 Getting Enlightened:Taking a Look at the Off-Axis Performance of Paraboloidal MirrorsBy Shane Santi

65 Designing an ATM 6-inch f/15 BinoscopeBy Ed Connors

Issue 75 Dream Scopes Q&A

A Short Interview with Shane SantiBy Gary Parkerson

88 Astro Tips, Tricks & Novel SolutionsGet Solar Ready ... Now!By Gary Parkerson

Cover Story: Pages 33-44

Our cover features Astronomik’s latest L-RGB filters, dubbed “Tpy2c,” as well as its most popular Ha, OIII and SII narrowband filters, all contained in theseven-position filter wheel of the QHYCCD QHY9 camera ATT AssociateEditor Austin Grant used to capture thebackground image of the RosetteNebula. Austin’s final image of theRosette is actually a mosaic of fourframes, each comprised of 3.0 hoursthrough Astronomik’s Ha filter, 1.5hours through its OIII and 1.5 hoursthrough its SII, for a total of 24 hours ofdata.

ASTRONOMYTECHNOLOGY TODAYYour Complete Guide to Astronomical Equipment

Volume 10 • Issue 2$6.00 US

DREAM TELESCOPES Q&A • THE VIXEN SX2 WITH STAR BOOK TENTAKING A LOOK AT THE OFF-AXIS PERFORMANCE OF PARABOLOIDAL MIRRORS

DESIGNING AN ATM 6-INCH F/15 BINOSCOPE


Narrowband Filters

In late 2014, I made the decision tojump feet-first into the realm of mono-chrome-CCD imaging. I contacted a friendof this magazine, Bruce Morrell, with As-troFactors.com, and we decided on theQHY9-Mono with the seven-position filterwheel. Bruce didn’t lead me wrong, and that

QHY9 camera has been a rock-solid, bullet-proof addition to my imaging system. Aboutthe same time, I had to choose what filters Iwanted to put in the camera. I’ve used sev-eral different brands in the past for differentwrite-ups or product demos, but in the end,I decided to go with the Astronomik filters.

Simply put, Astronomik filters have alwaysexceeded my expectations, and I really enjoyinteracting with Gerd Neumann and theother staff over there.

When I contacted Astronomik, theyasked what type of imaging I planned ondoing, and used that information to suggest


Narrowband Filters

By Austin Grant

Image 1- Astronomik 6-nm Ha, 12-nm OIII and 12-nm SII filters (top row) and L-RGB Tyc2c filter set (bottom row).


No Halos. None.

Image 2 - Transmission curves of Astronomik’s L-RGB filters.

ASTRONOMIK L-RGB TYP2C AND NARROWBAND FILTERS

34 Astronomy TECHNOLOGY TODAY

Image 3 - 36-mm unmounted Astronomikfilters installed in filter wheel.

the best filter set for my needs. Specifically, Iwanted to do deep-sky imaging withRed/Green/Blue color filters, as well as color-mapped narrowband filters. We ended upgoing with the L-RGB Typ2c filters for thetraditional color (bottom row, Image 1). Fornarrowband, I got the 6-nm Hydrogen-alpha filter, and 12-nm Oxygen-III and Sul-fur-II filters (top row, Image 1).

Both the L-RGB Typ2c and narrow-band filters represented the latest and great-est in Astronomik filter technology at thetime. Also, Gerd suggested that I grab aCLS-CCD filter to use in place of the Lu-minance filter, if light pollution was an issue.So, eight filters later, I had all the tools Ineeded to start imaging.

The L-RGB Typ2c filters (transmissiongraph in Image 2) are advertised as beingoptimized for CCD astrophotography.What’s cool is that they are also designedaround actual tools you are likely to use. Forinstance, the passband for each color was cal-culated from the sRGB color space. This isan industry standard adopted by most man-

ufacturers of monitors, printers and imagingsoftware. You are very likely looking at amonitor utilizing the sRGB color space asyou read this. Likewise, you will probably

send files for printing that are reproducedusing that same color space.

The filters are also diffraction limitedand essentially parfocal. I got the 36-mm



Image 4 - Narrowband transmission of Astronomik Ha 6-nm filter.

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unmounted filters (Image 3), and they arrived incompact hard cases, shown in Image 1, that providedexcellent protection. They are 1.0 mm thick with ahumidity- and scratch-resistant finish.

Also, they are advertised as being halo-free since2008. Honestly, this was the only issue that con-cerned me. I’ve read stories on the forums about peo-ple being unhappy with one filter set or another, andit usually came down to coating issues or halos onbright stars. Whatever changes Astronomik made tothe filter coatings, there simply aren’t any halos. Icould not get them to show a halo or reflection arti-fact under any scenario. In fact, Alnitak didn’t evengive me trouble when I shot some test HorseheadNebula data.

The narrowband filters have properties that aresimilar to the L-RGB filters. The big difference isthat they are emission-line filters. They block out allbut the tiniest sliver of the visible spectrum, andallow for more scientific or artistic endeavors. TheHydrogen-alpha filter had a 6-nm FWHM (fullwidth half maximum) bandpass and was narrowenough to use on any clear night (transmission graphin Image 4). Under a bright Moon, I still imaged,just not in the direction of the Moon. This wouldhave been impossible with the L-RGB filters withoutcapturing a ridiculous gradient.

The Oxygen-III and Sulfur-II filters have a 12-nm FWHM bandpass (transmission graphs inImages 5 and 6). They aren’t as narrow as the Hy-drogen-alpha, but were the best offered at the time.I found that they were plenty restrictive and allowedme to image on most nights. The stars were slightlylarger than in the Hydrogen-alpha images, but thiswas easily fixed in post processing.

The beauty of the narrowband filters is thatyou can assign different colors to each filter, andmap them as you see fit. I’m fond of the modified

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Image 5 - Transmission curve of Astronomik OIII 12-nm filter.

Image 6 - Narrowbank transmission of Astronomik SII 12-nm filter.


Hubble palette, which replicates the colors assigned to each gas by released Hub-ble images and reduces the green cast. The sky truly is the limit with creative op-tions here.

The Astronomik narrowband filters areexcellent for imaging under light-pollutedskies, but the L-RGB set can work for that,too. In fact, the best advice I received was tosubstitute the CLS-CCD filter for the Lu-minance filter. Although I don’t have aridiculous amount of light pollution, I gaveit a shot. The results were higher-contrastimages, so I stuck with it. The CLS-CCDfilter has a transmission curve (Image 7)similar to Ultra High Contrast filters, but it’snot as restrictive. I found it to be an excellentsubstitute for the Luminance filter, and it dida great job of blocking the artificial lightfrom my surroundings.

As soon as I gathered a respectable num-ber of images with this filter set, I contactedAstronomik to let them know how muchI’ve enjoyed them. It was then that they in-formed me of the newest filters in theirlineup. They still offer everything that I’vereported on here, but they have also ex-panded the lineup quite a bit. They nowhave a Deep Sky RGB filter set, which pur-ports to have even better color separationand much better coatings. They also have 6-nm versions of the Oxygen-III and Sulfur-II filters. I don’t see how my results could getany better, and I’m ecstatic at how well theseAstronomik filters have worked. Still, Iadded both upgrades to my cart, so look foran update to this article after I’ve had achance to capture sufficient data to comparethose new filters.

I could go on and on about these filtersand how impressively they perform. Thequality is top notch, and I haven’t seen a sin-gle halo or coating issue in over a year ofusing them. In fact, Astronomik offers a 10-year guarantee on all filters. If you ever havean issue, they will stand by their product andcorrect the issue promptly.

But they say a picture is worth a thou-sand words. If true, here’s a few thousandwords to make the point. The Rosette Neb-ula (Image 8) is a composite mosaic of four

frames, each composed of 3.0 hours of Ha,1.5 hours of OIII and 1.5 hours of SII data.That’s a total of 24-hours of data with thenarrowband filters. I’ve still got a lot to learnin processing, but after I mapped the colorsin the modified Hubble palette and tried toalign everything, I think it turned out prettywell.

The other images are all single-frames,not mosaics. They mostly consist of about3-hours of Luminance or CLS-CCD data,and 1-hour each for the Red, Green andBlue channels. The Little Dumbbell (Image9) and M78 (Image 10) were shot with the standard Luminance filter plus RGB. I used the CLS-CCD filter for the Lumi-

nance data when capturing M51 (Image11), M63 (Image 12), and M81/M82(Image 13).

All images were shot with a QHYCCDQHY9 monochrome camera fitted with the seven-position filter wheel shown inImage 3. All astrophotos, but Image 9 of the Little Dumbbell, were shot through aSky-Watcher ProED 120 and Hotech SCAfield flattener. The Little Dumbbell was shotthrough a TPO 8-inch R-C with an Astro-Physics CCDT67 reducer. All gear was car-ried on a Software Bisque Paramount MX+.All images were captured using SequenceGenerator Pro and a Seletek system for ob-servatory control.

Image 7 - Astronomik CLS-CCD filter transmission curve.


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Documents

ASTRONOMY · ASTRONOMY TECHNOLOGY TODAY Your Complete Guide to Astronomical Equipment Volume 10 • Issue 2 $6.00 US DREAM TELESCOPES Q&A • THE VIXEN SX2 WITH STAR BOOK TEN TAKING