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- Explore Scientific AR 102
- Review: davejlec's Paralellogram Mount
- Annals of the Deep Sky, Volumes One and Two
- Discovery 17.5” Split Tube Dobsonian Telescope
- REVIEW OF SUMERIAN OPTICS ALKAID 16” TRAVEL SCOPE
- Astrotrac TP3065 Pier Review
- Apo-tmosphere: Gutekunst ADC Review
- Optolong LRGB Filter Testing and Comparison with Baader LRGB Filters
- First Light Review: Teeter Custom TT Planet Killer 16" f/5.4
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24mm EP Eyepiece Comparison
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Eyepiece Surfing on channel 24mm
A sultry love affair under the stars, complicated by Ocularitis Binoculus Extremis
Once upon a time there was a fellow with a newly acquired 10" F10 Schmidt-Cassegrain telescope (SCT). Being the largest aperture scope he'd had the pleasure of using, and having been outfitted with Meade's add-on 'Magellan' computer-object-locator, the heavens seemed to unfold & freely divulge their hidden splendors! With Plossls, Orthos, an a couple of Vixen LV eyepieces (EPs) in hand, astro-nirvana had finally been achieved in 1996.
This was also during the heady days of comets Hayakutake & Hale Bopp, as well as favorable apparitions of Jupiter riding high in the sky, and Saturn with its rings displayed brazenly open. Both gear & sky had met in the most wonderful conjunction, timed so very perfectly!
How could one improve on such perfection? Well, one could begin by being introduced to the internet. Surfing around the web, this same fellow eventually stumbled across a number of helpful & intriguing astro websites, including the Cloudy Nights (CN) site. This was the beginning of a very eye-opening, as well as wallet-draining adventure!
The first eye-opener in this saga seems to have been that of wider-than-Plossl EPs. The Sky & Tel advertisements displaying 68-degree and 82-degree trinkets, proudly displaying green lettering on their shiny barrels, had for years fallen on deaf eyes... but with the advent of interactive user-input shared in CN's friendly forum environs, the until now invisible hook had been wickedly baited.
Budget always seeming to be a significant factor, the first bite was on a medium focal-length (FL) 20mm University Optics 'Super Erfle', which provided a whopping ~62-degree apparent field-of-view (AFoV) with comfortable eye-relief (ER) and a marvelous 2.0mm exit-pupil (ExP) in the SCT. The views therein were astounding, and the hook was set firmly & quite deep!
Several additional budget-conscious widefields came along in the months that followed, even an affordable 'ultrawide' made its debut in the SCT's diagonal- all rendering splendid images with its 'slower' F10 optic. The ol' EP case began groaning under the increasing load, as the addiction to the glass-and-metal baubles continued gaining momentum. Yet this was when events took a sudden & drastic turn... the forum chatter began ranting in enticing terms of a "new" viewing experience, one involving BOTH eyes!
"Binoviewers" (BVers) they were called, and their internal optical mojo split the scope's primary lightcone into TWO separate pathways, one to each eye. Until this point they'd mostly been converted microscope hardware, and fairly obscure at that- at least as far as the general "market" was concerned. But now several vendors had entered the arena with what seemed to be radically delightful & functional versions! Some were somewhat "affordable", too.
The forum fixation flowed fast & furious as more of these BVers made their way into observers' hands, several folks obtaining multiple competing units for the purpose of "shoot-outs". The resulting reports offered tantalizing glimpses depicting the benefits to be enjoyed from BVer use, as well as evaluating the good, bad, & ugly of the various contenders.
Having squinted, or learned to ignore the visual input from the non-observing eye, even purchasing a bonafide eyepatch to accomodate the 'cyclops' nature of the traditional observing equipment- our fellow had spent 35 years, on-and-off, peering at heavenly glories thru one eye... as if two-eyed viewing were somehow reserved for the mundane of daily earth-bound existence. That was all about to change...
The Denkmeier family of BVers rose to the top of the heap for many, some enticed by their offering both a 'standard' and a 'premium' version, others being drawn to their handy 'Power-X-Switch' (PxS) option. Such choices posed some serious soul-searching for one, who to this point had consistently labored under the self-imposed constraint of 'budget'... this same one having grappled with the dual-headed serpent of aperture fever AND 'premium' optics, no doubt a byproduct of hanging around too close to the CN forums where these matters were unendingly discussed. With an ever-growing pool of drool that had collected beneath his computer's keyboard, a plan had begun to hatch- one that involved an exciting series of upgrades, ones designed specifically to both maximize & optimize his astro-viewing adventures!
Said plan would begin with the investment in the top-drawer 'Denk II' & PxS package, along with the vaunted 24mm Panoptic EPs in pair. The plan would eventually culminate in the acquisition of a larger scope, a primo Dob having primo optics! This would NOT be a flash-in-the-pan effort, but a long-term commitment... one built on & buoy'd by the previous 35 years of involvement in things astro. So after numerous phone conversations with Russ at Denkmeier, the credit-card came out to play... uhh, PAY!
The Denk II arrived in June of 2004, and immediately took up permanent residence in the SCT's 2" diagonal. Likewise, the 24mm Panoptics arrived a few months later & assumed yeoman's duty in the BVer! Several other pairs of 'premium' lovelies would follow- including Pentax XLs & XFs, and Vixen LVWs. The UO Super Erfle found a mate as well, and the NEW nirvana that ushered in with their use so thoroughly blew away the old 'nirvana', that 'cyclops' viewing rarely ever occurred thereafter! This was a whole new paradigm, and our fellow was so profoundly engaged in his new-found love of bino-viewing that many must've wondered about his sanity. Some wondering thusly shared the same walls & roof, though the warmth these provided was often shunned for the cold night air environment wherein the new BVer thrived... and frequently beckoned!
In particular, the 24mm Pans offered a relative 'sweet-spot' out of all the EP acquisitions! In the Denk-SCT system they provided the following optical characteristics, F-values (below) as verified by in-field measurements:
|F7.2 effective (PxS *reducer* mode)||F12.9 effective (PxS switches *out*)||F26.8 effective (PxS *magnif* mode)|
... and many were the nights where they NEVER left the scope! Other than their rather tight-for-eyeglasses ER, the Pans provided the most amazing views- as if they'd been specifically tuned for such a scope set-up.
Then one fateful day everything changed. The 'plan', which had been so carefully crafted & its results so long awaited, actually reached its culmination! Finances, calendars, & opportunity had all aligned: A used Dob had finally appeared on the market within driving distance, and a private-party deal was soon finalized. In preparation for its eventual arrival, a Newtonian PxS had even been ordered, and in May of 2007 all the pieces came together, and oh so beautifully!
Well... mostly beautifully. Yeah, the views were truly wonderful- all that had been hoped for! Yet a fly appeared in the EP ointment. The once ideal-for-views Panoptics now were getting notably less BVer time, and a pair of Vixen 17mm LVWs were hogging the show. The change in aperture & system FL resulting from use of the Dob, a 15" F4.55 affair, along with the more closely-spaced Newt PxS range, had rendered the Pans too short of legs... merely low-power sweepers. The following chart depicts the new reality, first the 24mm Pans, then the 17mm LVWs below. Again, measured in-field:
|F6.64 effective (PxS *right* switch)||F9.33 effective (PxS *left* switch)||F11.2 effective (PxS switches *out*)|
While the ability to field two-thirds of a degree on the "low" end remained attractive enough, daily (nightly?) practicality typically saw the 24mm Pans overlooked in favor of the Vixens, or even another higher-powered pair. In addition, the Pan's tight ER made other EPs, like the Vixens, all-the-more attractive for first pickin's. So the Pans languished in the EP case... a truly unthinkable state of affairs!
Eventually this conundrum burned a hole in the conscience... and $500 worth of premium glass collecting dust, rather than photons, provided plenty of fuel for that fire. A serious effort was undertaken to find an appropriate replacement for the Pans- EPs that would not concentrate such intense value in a FL so infrequently used, EPs that would offer more ER, and that would provide the closest performance to the Pans... given the other limiting criteria. And considering the fact that this FL would not "push" the envelope of extreme perception, such an optical compromise seemed much more palatable!
This is then the main purpose of this article, for which you have been dragged along to this point, dear reader.
One by one, the EPs were researched, then scavenged off the used market- a small & amateur investment in equipment evaluation that is hoped will benefit others with similar goals (and budget!) Below is the EP line-up that developed in the wake of critically eyeing the Panoptic EP's utility (prices new/used approximate, published FL not measured, published ER & AFoV user verified or estimated, compared to the Panoptic as a 'standard'):
(note the barrel undercut (UC) visible on the Meade 5k & Pan EPs)
Tal Ultra Meade 5k Meade 4k Panoptic
All of the above EPs, depending on when they were acquired, were utilized over the period of several nights last winter, viewing the 'Trapezium' region of M42 in Orion, the M45 Pleiades open star cluster, and the prominent M-clusters scattered across the Auriga region. The EPs were used 'mono', inserted into alternating sides of the Denk II BVer, two at a time for quick & easy comparing, the BVer inserted in the F4.55 Dob. Therefore, each EP was "seeing" an effective F6.64 lightcone as processed thru the PxS, including the Newtonian optical corrector (OCS).
For additional torture, several EPs (but not all were yet available) were also subjected to photons thru a StellarView 'F80' achromatic refractor, an F3.75 optic capable of reducing lesser oculars to shivering puddles of twisted & distorted shreds. As noted above, the Panoptic was used as the 'gold standard' to which & against which all the other EPs were compared thru these processes.
Panoptic: Sharp over central 75% of the FoV, decent with minimal fan-tailing (F/T) out to 90% FoV, more F/T but image still fair to the field edge- but strong pincushion (P/C) in outer field, most of all the EPs tested.
Meade 4k SWA: Sharp over central 70% of the FoV, decent with some F/T out to 85% FoV, strong F/T and some field distortion & P/C beyond 85% out to edge.
Siebert Ultra: Sharp over central 50% of the FoV, decent out to 75% FoV, outer 25% goes pretty 'soft' with F/T stars & fairly strong P/C.
Denk 'n Dob Duels
Panoptic: Tight ER for eyeglasses, can see full FoV only with guard folded down & eyeglasses pressed in tight, eye-position reasonably easy to maintain, only minimal blacking or greying-out when eye moved off-axis, but view is engaging & sharply focused to ~98% FoV, actually almost 'immersive' by its absolute sharpness! Tone of view is most "coffee-tinted" of bunch, tho still shows faint stars as well as the best. Best *snap* to folding rubber eyeguard of all EPs, easily popping up, or else popping down.
Meade 5k Plossl: Excellent ER, but modest kidney-bean & grey-out issues, slightly less-sharp on axis than other EPs, slightly behind others in consistently showing & holding faintest stars, sharpest focus to ~85% FoV, image softness & astigmatism evident beyond. Excellent rotating up/down soft rubber eyeguard.
Tal Koenig: Plenty of ER, even too much? Yet eye-position very easy to maintain, no kidney-beans or issues even when viewing off-center, view Pan-sharp across entire field, tho field noticeably smaller than most other contenders, & of medium-tone tint. The eyeguard supplied with the EPs acquired (see pix) was poor-of-fit, so i borrowed an idea from Don Pensack (CN's Starman1) for using a bike innertube section, sleeved over EP & top folded over on itself. Funky fersure, but works like a charm!
Meade 4k SWA: Very good ER, very easy eye-position & general ergonomics- much like the Vixen LVW series, not quite as wide AFoV or immersive as LVW, yet easily accessible, sharp focus to ~90% FoV, view bright & "cool" of tone, only slight astigmatism seen. Second best *snap* to eyeguard, nearly as good as the Pan's.
Siebert Ultra: Excellent ER, but slightly tricky eye-position, bright & "cool" toned view & sharp on-axis, but visibly less-wide & not as well corrected- stars begin to degrade beyond 50% FoV, quite distorted with F/T at ~80%, mush at 90% FoV, P/C quite strong. Stiff eyeguard folds down similar to LVW, but comes off EP entirely when folding back up.
On a few nights these EPs were evaluated specifically for how they rendered the 'Trapezium' region of the M42 nebula, particularly in regards to showing the 'E' & 'F' stars. All the EPs were fairly close at revealing both E&F stars on axis, 'F' less so when the seeing varied into the mediocre range... it was primarily the outfield performance that varied. Again, the EPs were installed left/right in the BVer, using the 15" Dob. Unfortunately, not all EPs were available for each session, so some of the comparisons will be subject to variations in nightly seeing.
Panoptic: E&F shown perfectly clear to nearly the edge of the FoV, only slight loss in sharpness in the outer 5%- but stars still distinct! F star seen most consistently of all the EPs
Meade 5k Plossl: E&F shown distinctly over the middle ~80% of the FoV, view loses some sharpness but still functional out to ~90%, E&F stars lost only in outer 10% FoV. F star seen slightly less consistently than 4k SWA.
Tal Koenig: E&F shown perfectly clear to nearly the edge of the FoV, only slight loss in sharpness in the outer 2%- but stars still distinct! F star seen most consistently of all the EPs, at least as good as Panoptic!
Meade 4k SWA: E&F shown distinctly over the middle ~80% of the FoV, view loses some sharpness but still functional out to ~95%, E&F stars lost only in outer 5% FoV. F star seen fairly consistently.
Siebert Ultra: E&F shown distinctly over the middle ~50% of the FoV, loss in sharpness progresses until E&F lost around 75%, by 85% of FoV many stars no longer distinct, and from 90% out the entire Trap is a barely distinguishable mess! Changing the BVer PxS to a higher magnification & longer effective system F-ratio (~F11.2) only changes the loss-in-sharpness zone to maybe 80-85%, but the outer 10% FoV still remained a "mess".
The *true* FoV changes between three of the EPs showed fairly similar steps in narrowing: Pan to Meade 4k, Meade 4k to Siebert Ultra. Also visible in comparing these EPs side-to-side in the BVer was their respective view "circles" at the focal plane, their *apparent* FoV; Again, one could "merge" the views left & right, and clearly see the overlapping "circles" & how they differed slightly in size. So if the Panoptic was taken as 68-degrees AFoV, the Meade 4k would be around 64-65* AFoV, and the Ultra around 62*.
Another consideration some may have, depending on the species of BVer used, is whether the EP has a barrel undercut, or NOT. In the case of the Denk II's self-centering EP collets, a straight barrel is much to be desired, for an undercut can mean an uneven grabbing and/or seating of either or both EPs, yielding difficult or impossible to merge views... or awkward retraction of the EPs when it comes time to swap them out. For my specific preference of use, this gives the Pan & the Meade 5k Plossl a bit of a wooden leg in this race.
As an aside, the UC of the Vixen LVW design is slightly different in form, and does not generally present issues. So this matter of barrel UC would seem to have some variance at the EP end, as well as among BVers.
While the "Tal" EP had the visibly smallest AFoV of the bunch, as well as the smallest TFoV (~tied the "Ultra"), and had the oldest & probably least ergonomic design- it really did a great job of brooming the field clean! For its limited "widefield", it pointed up stars shoulder to shoulder with the esteemed Panoptic, and was wonderfully easy to view thru... even more so than the Pan according to this observer. It was as lightweight as the Ultra, even thinner of profile, and had no wretched barrel-undercut to hang-up or get twitchy in the BVer collets! There just wasn't anything to dislike about this EP!
Ultimately, however, it was the Meade series 4000 SWA that garnered the most points with this gearhead, and further efforts soon produced three of them for BVer use. More on that later. The AFoV gave this EP the "widefield" feel closest to the Pans, as well as a *true* field respectably close thereto. Its optical performance was closer to the Pan's end of things than the other end, its ergonomics & ER were excellent... and it didn't even have that nasty barrel UC!
The Meade series 5000 Plossl would've been a decent choice, too. While its AFoV was noticeably farther from Pan territory, its TFoV was actually the best of the four... due to its slightly longer FL & correspondingly lower magnification. Its ergonomics were quite good, and its ease of view was perhaps acceptable... yet in the end its rather average optical performance nudged it nearer the bottom of the list.
The Siebert Ultra was an EP really wanting to be liked... but it just ended up being nudged out of the upper ranks in every category- sometimes by very little, and not always by *every* EP reviewed... Perhaps in a "slower" optical system it would shine a little brighter? I believe the Dob-Denk's effective F6.64 is faster than what the 3-element 24mm Ultra is rated for by Mr. Siebert, and its certainly possible that others in the "Ultra" line would make splendid performers in such a set-up. In fact, i *strongly* suspect this to be the case, as i've used his 4-element 17mm Ultras in my Denk-SCT for several years, and found them quite good in all respects! For weight & balance considerations, the Ultra line of EPs are truly leaders, tipping the scales at merely half (or less!) the weight of most other "widefield" EPs.
So why did i need *THREE* of Meade's 4k SWAs for my BVer? No, i have no "trinoviewers", and have not sprouted a third eye... that i'm aware of, anyway. No, this became a necessary step due to the fact that not ALL series 4000 SWAs were created equal. While their optics were similar, if not identical, their barrel architectures were most definitely NOT! The ones that came to me each had their always welcome "Japan" stamp, but it was located in differing places, and the upper *black* barrel sections had heights that varied significantly- enough so that using them in a BVer would be ill advised. Such was attempted, and to achieve focus & eye-level ergonomics, the shorter EP needed pulling precipitously far out of the BVer collet, such that little confidence remained that it wouldn't make a dive for its country of origin while one was busy viewing!
(note the 'Japan' stamp: Left EP on black barrel, Right EP on chrome)
Acquiring the *THIRD* one instantly created a "match", and the odd EP was subsequently sold for what it had cost. Problem solved.
For what it's worth, the same EP exercise was previously performed while acquiring the beloved set of Vixen 17mm LVWs... and for precisely the same reason- differing architectures. The same solution served, and did so equally well. Both EP types are highly desirable, and move pretty quickly on the used market.
Funny how changing one's choice of telescope can create such a shift in their preference of EPs! Yet it all makes perfect sense when looking at the numbers. My enjoyment of visual astronomy, however, has been an experience-based pursuit, so perhaps its not so surprising that "numbers" would sneak up... maybe they'd be less inclined to do so now, having walked this path?
While not being affiliated with any of the manufacturers or distrbutors of the gear mentioned above, aside from being a customer, it is my hope that this entire story, or some obscure part thereof, will be found helpful to someone contemplating EPs themselves, the potential jump into the deep end of the lake (BVer addiction), or attempting a cure for aperture fever... perilous endeavors, one and all!
That mankind can take sand & ore, convert them to glass & metal, and then assemble them in such a manner to enable breathtaking glimpses of the heavens- seeing sights hidden for all of time, until the last few generations... what a wonderful journey we're privileged to make!
I have certainly enjoyed my journey to this point, and i hope we can work toward inspiring yours, as well.