Obsidian Optics 16" Primary

The heart of Natasha is a 16" thin (1 3/8") f/4.5 mirror I commissioned from Mark Cowan of Obsidian Optics in February 2003.  It took a full 12 months and much angst (on both our parts!) before the mirror was completed and delivered.  Here are the specs on it:  http://www.obsopts.com/specs/SN0322.htm  

Wow! Over 1/20th wavefront and a Stehl of 0.997!!!  Now, I don't  place much stock in Foucault-derived test results.  I also am not particularly impressed by Peak-to-Valley wavefront ratings as opposed to Strehl ratios, so from here out I'll only cite Strehl.  Obsidian's Foucault test-derived Peak-to-Valley wavefront results could not be reproduced by a NOVAC buddy of mine (thanks again, Mike!), but he did estimate the Strehl at a still superb 0.96-0.97+ by both the Foucault and Lateral Wire Test.  

When I sent the mirror to Galaxy Optics for coating (see below), I paid for John Hudek to do his basic testing to reconfirm this and instead he opted to do a full Zygo laser interferometry test.  This rated the mirror at 0.88+ Strehl, but may have been pulled down by some test stand induced astigmatism, since this is thinner than the mirrors Hudek usually works with.  Even at 0.88 Strehl it exceeds the  interferometry-based threshold optical shops such as Galaxy and Torus seem to use as the minimum standard for their own production mirrors.  (Remember that the interferometer measures 3000+ discrete points across the entire surface of the mirror, whereas Foucault tests measure ~6 narrow zones and try to extrapolate a description of the entire parabola from this-- hence the "statistics wars" between the interferometer and Foucault camps.)  Hudek did an artificial star test at 600X and found the image to be clean and crisp.  That's good enough for me!

The polish on the mirror was the best I've ever seen-- a green laser shining through the uncoated parabola produced no side scatter!  This seemed like impressionistic support for Obsidian's claim to be doing "state of the art" Zambuto-style micropolish (http://www.obsopts.com/techniques.htm).  I was also impressed by the absence of any turned down edge on the mirror (OK, so the Foucault tests do show a measly 6 Angstroms of TDE...), which impelled me in the direction of a "no mirror clip" design so as not to marr this superb figure.

Then came the decision on how to have the mirror coated-- standard, semi-enhanced, or enhanced.  I did a lot of research on-line.  Even using conservative "worst case" figures for enhanced coating performance (i.e., that it degrades from 96% to 93% reflectivity within a few months), that still makes the effective diameter of the mirror (measured as optical aperture multiplied by reflectivity) at least 2/3 of an inch greater using enhanced coatings.  The potential downsides seemed to be inconsistent application of the coating (varying thicknesses that degrade the wavefront accuracy of the mirror), and the possibility of increased scatter of light in the image.  The reports of problems with poor coating quality seemed to be either relatively old or coming from vendors who only apply enhanced coatings on a part time basis. 

I was drawn to Galaxy Optics   (http://www.galaxyoptics.com/GlassAndOpticalCoatings.html), since the proprietor John Hudek uses enhanced coatings on all of his products.  It seemed to me that, as a mirror maker, he would take a double loss if erratic coatings were to deface his work, so he must have this enhanced coating process down right!  Galaxy Optics has an expensive coating setup that deposits a thin multi-layer enhanced coating to a standard and level of consistency good enough for NASA and the U.S. military-- which do systematic and serious Quality Assurance inspection and testing on their optics-- to send mirrors in for recoating.  If it's good enough for NASA, it's good enough for me!  Hudek's "C-1" coating is 96% reflective with three dielectric layers and a quartz overcoat that promises great durability.

Antares Optics 3.1" Secondary

I know that there is a fairly heated debate about how important the optical quality of the secondary mirror is, with one school of thought maintaining that because it is close to the focal point, it is of lesser importance than the primary.  The other school maintains that it is equally important to have a high quality secondary, especially given the impact of a turned down edge (not uncommon among inexpensive, low surface accuracy secondaries) and the fact that optical performance is already degraded by an additional 40% due to the obliquity of the mirror.  I subscribe to the latter school, and feel that hooking a premium primary like the Obsidian to a mass-produced and randomly purchased secondary is an almost surefire way to degrade the view, assuming good seeing and collimation. 

I "discovered" Antares Optics (http://www.antaresoptics.com/SecEM.php) back when they marketed their wares on Ebay to the exclusion of Astromart, and in fact encouraged them to give Astromart a try.  I like the fact that they sell enhanced (nominal 98%) reflectivity pieces and provide a Zygo interferometer print of each piece after coating (which is important since some pieces are inevitably marred in the high temperature dielectric coating process.)   I've bought a series of secondaries from first Mannie and then Frederick at Antares, and have been happy with them.  Looking at the price list, I noticed a curious phenomenon.  While I understand that it is proportionally harder to make increasingly flat secondaries, the price premium from Antares does not reflect this,  e.g., a 1/30th surface wave certified mirror does not cost even twice what a 1/15th wave one does.  Based on my understanding of the process of producing secondaries, it should be costing more than twice as much, not less than double! (Now, don't take this as a request to charge me more the next time, guys!)

With this in mind, I ordered a 3.1" Pyrex certified 1/30th wave, 1/200th RMS (root mean square--RMS-- is arguably as good a measure of a secondary's flatness as Strehl is of a primary's parabola) secondary from Antares.  When it arrived, I was surprised to discover a ~2mm hole in the coating.  When I emailed an image of the defect to Antares, the company president (Fred Koch) responded in near real-time by agreeing to send me me a 1/40th wave, 1/250th RMS piece, and by personally inspecting it and performing a fresh Zygo interferometer test to ensure that it was good.  Now that's customer service, and the mirror is a worthy companion to the Obsidian primary!  Assuming a reasonable level of support from the 18 point cell and a good job of collimation (about which I am fanatic), I could have 1/10th wave on the wavefront accuracy at the eyepiece.

I haven't yet had the weather needed to do a extended run of high magnification tests of the scope... but at 600X, planetary and stellar images look pinpoint.  That's pretty good performance in my book-- nearly twice what Frankenscope rendered on comparable nights.

Tuthill 80mm SuperFinder

I had planned to install a 9 power 60mm Tuthill finder (anyone remember Roger's unique products???) I'd gotten from a friend a couple of years ago.  Ironically enough, at the "Almost Heaven Star Party" in June another friend sold me an 80mm Tuthill SuperFinder for next to nothing (thanks, Bill!).  80mm is my favorite aperture for a finder for a 16" scope, since it is large enough to show a fair number of Deep Sky Objects in its own right.  (I once did a partial Messier Marathon from dark skies using just my 80mm finder.  The wide FOV made it a spectacular experience.)  Coupled with a 25mm Erfle crosshair eyepiece, the Tuthill yields about 20X and a 5 degree field of view, I believe.  It's a fraction of the weight of the 80mm finder on Frankenscope (which is an Apogee "Ganymeade" ST80 scope in a homemade and heavy quick release mount)!

Rigel Quikfinder Reflex Sight

I've always favored having both finder refractors and zero magnification reflex sights on my scope.  Some nights I never even uncap the finder, if I'm just doing planetary observing or public outreach viewing.