Eyepieces
UPDATES:
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talking to Al Nagler at the Winter Star Party, I learned that my old faithful tunable top Paracorr (described below) was probably one of the older photo-visual models, which vignettes slightly with the Nagler 31 eyepiece. Since it also has a set screw-- vice the newer non-marring brass clamping ring-- and I've got a couple of new-ish Naglers that I'd like to keep in good shape in case I opt to sell them, this was enough to tip me into hunting for a new visual Paracorr. I baulked (as usual) at paying retail price, and fortunately found a cooperative soul on Astromart who was willing to sell one. |
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I also bought a nearly new Nagler 26mm Type 5, since the exit pupil is more reasonable with my 24" Dob. (5.7mm vs. 6.7mm both in the Paracorr.) The magnification and field of view are pretty close-- I'll give this a good testing in the field, and if I don't find it superior to the Nagler 31 will probably flip it on Astromart |
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27mm Kellner illuminated double crosshair eyepiece. I decided I was tired of non-illuminated finder eyepieces, plus thought one could do double duty as an initial alignment eyepiece for calibrating the tracking when using my Dob Driver 2. I didn't want to get one that was 12mm because of the narrow FOV. Clearvue Optics sold a 27mm Kellner model that ironically no one else-- even Antares seemed to list. (They showed a dot reticle model instead.) As a Kellner, it shows quite a bit of distortion off-axis, but generally seems like a good eyepiece. (I am a bit surprised by how bright the laser is at even its lowest setting.) By coincidence I ended up purchasing it a scant week or so before Clearvue Optics closed its doors. |
DESCRIPTION
I find myself using what I term "the holy trinity" -- one low, one medium, and one high powered eyepiece virtually all of the time with my 16" f/4.5 scopes. This trio changes by one member for my 24" f/4.5 The members of this extended trio are:
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Nagler 31 in the Televue Paracorr, for wide field low power work. I had been using the "poor man's Nagler 31" --the Panoptic 35-- for three years, with mixed success. I kept seeing unacceptable amounts of coma, even when I added a tunable top visual Paracorr. I had always sworn just on general principle that I wouldn't buy the Nagler 31-- who in their right mind would spend over $600 on a single eyepiece? Then, towards the end of a star party, a friend brought his over to use in Frankenscope. I was surprised at how flat the field looked, but was nothing short of amazed at the effect when we put it in the Paracorr. It rendered a steamroller flat field; we amused ourselves by placing first Magnitude stars at the very edge of the field of view and noticing virtually no flaring or coma! Right then and there I knew that a Nagler 31 was in my future after all. With the Paracorr, in Natasha or Frankenscope, it gives a magnification of 67X, a true field of view (TFOV) of 64 minutes (nearly 1.1 degrees), and an exit pupil of 6.0mm -------probably a good upper end for my middle aged eyes under dark skies, but a bit optimistic for my streetlight-polluted neighborhood sidewalk where the bulk of my viewing occurs. In my 24" f/4 Brutus, this eyepiece has an overly large exit pupil-- 6.7mm, hence see the next entry. |
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Nagler 20 "Type 2" I decided to get something intermediary in focal length between the 31mm Nagler and the 14mm Meade UWA but of comparable quality. The choices seemed to be between a Nagler 22 and a Nagler 20. I decided to try the 20, which is available in two "types"-- 2 and 5. The older "Type 2" is massive-- heavy than the 31mm Nagler "grenade". The "Type 5" is smaller and some users find it to have slightly greater light throughput. After some deliberation, I opted to go with the older "type 2" which is long out of production and only available on Astromart. It is cheaper than the Type 5, any optical differences between it and the Type 5 are subtle (and a minority of users find it preferable to the newer model), and I can always pick up a Type 5 retail if I want. In practice I didn't use the eyepiece much for the first year I owned it, but then when I looked seriously at the optical stats I realized that it was a better match for Brutus's focal length than the Nagler 31, since in the Paracorr it has an exit pupil of 4.3mm to go along with its 140X power and 1/2+ degree (35 arc min) TFOV. (In the 16" Natasha, the numbers are 3.9mm exit pupil and 104X power, with a 47 arc minute TFOV.) |
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Meade 14 Ultrawide (series 4000) for general purpose viewing. I find this combination of 131X power, 39 arc minute TFOV, and 3.1mm exit pupil in the 16" scopes to make it an ideal general purpose eyepiece, and it is usually the first one into the focuser and the last one back into its case. It renders nice sharp contrasty views. In Brutus, this eyepiece has a 3.5mm exit pupil, 174X, and 1/2 degree (29 arc min) TFOV. UPDATE: I recently tested this eyepiece in the Televue Paracorr, and found that it appreciably helped to increase the diffraction-limited sweet spot! Don't know why I'd never noticed this before... possibly because it was more noticeable at f/4 than f/4.5). The new numbers for the 14 UWA in the Paracorr are 200X, 3mm exit pupil, and 25 arc min TFOV in Brutus, and 149X, 2.7mm, and 34 arc min TFOV for Natasha. |
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Nagler 3-6mm zoom for planetary and close double star splitting. With a power of 305X at the low end and 610X at the high end, this is certainly one whose use is dependent on the seeing conditions, but it has a respectable 10 arc minute TFOV at 6mm along with a 1.3mm exit pupil. (The scores at 3mm are 5 arc minutes and 0.7mm) It excels in a motor driven scope like Brutus or Frankenscope, though-- using it in a manual Dob like Natasha involves considerable "chasing" of the object if I am doing any sketching. It has exceptionally high light throughput, due to its five optical element light path. In Brutus, this eyepiece yields 406-813X (and yes, I have used ever bit of this in planetary observing!), an exit pupil of 1.5-0.8mm, and a TFOV of 7 down to 4 arc minutes. |
On the 10" LX200, I find the 22mm Panoptic to be superb. At 153X and with a 3.4mm exit pupil it is a good general purpose eyepiece. It's 27 arc minute TFOV on that scope is a nice compromise between magnification and field size. The Panoptics just don't fare as well on the faster focal ratio scopes, though, either the Pan 35 or the Pan 22, and since I've become a "fast Dob guy" this eyepiece has seen comparatively little use. I did recently pick up a second one on Astromart, though, for binoviewing.
Having discovered the superiority of the Nagler 31 over the Panoptic 35, I figured it was a cinch that the Nagler 22 would similarly trounce the Panoptic 22 in my 16" scopes. I confidently borrowed a friend's Type 4 Nagler 22 when we were observing at a dark site, and was amazed-- this time at how much worse the Nagler 22 was than the Panoptic! This just reinforces the adage of trying other folks' equipment before taking the plunge and buying.
Public Outreach eyepieces: since I'll be doing a lot of public viewing this year, I opted to set myself up with a couple of eyepieces I won't agonize over if they have their coatings sacrificed 'in the line of duty'. I bought a Clearvue Optics 30mm (Widescan III clone) that works 'OK' for the non-discriminating user-- especially in the Paracorr. I'll also use my old Russell 11 or 13mm eyepiece at the higher power end.
"Oldies but goodies": I still have a University Optics Koenig 32mm that I purchased new in ~1979, when it was the widest field eyepiece readily available. I still sometimes use it in my 80mm f/5 spotting scope. Oddly enough, the internal threads don't match the current standard--something must have changed in the past 20 years.
I also had purchased a Research Grade Meade 10.5mm orthoscopic eyepiece in this same timeframe. Getting back into the hobby, I was amused to discover that these had become collectables, and I therefore sold mine. I was stricken almost immediately by "seller's remorse", but fortunately some research suggested that Apogee's inexpensive orthos were OEM'd out of the same factory that had made the Meades decades earlier. (This was born out a bit by some of the odd focal lengths both were available in-- 10.5mm and 16.8mm, in particular.) I succeed in locating a replacement 10.5mm Apogee ortho, as well as its 7mm stable mate. (The 16.8mm eluded me, despite several "wanted" ads on Astromart.) With their relatively simple 4 element optical construction, both proved to be excellent planetary eyepieces in the 1.5X barlowed Sirius Variable Optics Filter system on Frankenscope.
Rini 62mm. OK, so the exit pupil is almost 14mm (maybe it would work for an elephant's eye) and therefore most of the incoming light is wasted, but it offers a Nagler 31-sized field in an inexpensive package that can be useful if you are in a high risk viewing situation (i.e. a public event with young food toting observers.). I've also got a Gary Russell 11mm and 13mm, and had (but sold) one of his 9mm's. Inexpensive --especially for a 2" eyepiece-- but decent performing alternatives to the premium stuff. Call me a fool, though, but I tend to use the good eyepieces even with the public...
"Homebrewed glass". When the TMB monocentric eyepieces came out, I was intrigued by their potential, but appalled by the $200 price tag. Fortunately, discussion on an Astromart forum suggested that they were not different in principle from a "Hastings triplet" that could be procured commercially. I bought a ~35mm Hastings from the Surplus Shed, and mounted it in a 1.25" diameter wooden dowel--only to find it made a mediocre eyepiece. Bausch & Lomb jeweler's loupes were reputed to contain much higher quality triplets. I was able to find them for ~$30 apiece, and bought the magnifications that equated to focal lengths of 12.5mm and 18mm. The 18mm one was relatively easy to get out of its loupe housing and put in a length of dowel; the 12.5mm one proved impossible to remove, and I ended up putting the loupe housing itself into the wooden eyepiece barrel! Both had the miniscule field of view I would expect, but blind testing by other observers confirmed that they did indeed have higher light throughput than the benchmark orthoscopics!
For binoviewing I also have a pair of Edmund Scientific 28mm RKE's (high light throughput thanks to their 3 element design), a pair of Japanese-made Meade Super Plossl 26mm's, and a pair of Harry Siebert's early 35mm wide fields.
A tale of two zoom eyepieces
Nikon 9-21 zoom. I initially purchased these eyepieces from APM-USA in 2001 as a single eyepiece set solution to my then-new binoviewers. They are 0.965" barreled eyepieces made by Nikon for use in their spotting scopes, and were given 1.25" barrel adapters by APM. I paid about $225 apiece for them on sale. I have subsequently heard anecdotally that "Hands On Optics" and Apogee Inc. have sold OEM versions of these for ~$50, but I haven't been able to verify this by comparison, and in any event, since Nikon seems to have a sizeable stable of spotting scope eyepieces, would suspect that these OEM offerings are actually of another of Nikon's many models. This was Nikon's model 7466 MC (for "multicoated"); they now have a newer model that is 7-21mm in power instead of 9-21. I purchased these in part because of their favorable ranking in a zoom eyepiece "shootout" between the Nikons, the Vixen, Orion, and pricey Leica offerings. (http://www.cloudynights.com/documents/zooms.pdf)
I discovered a couple of idiosyncracies with these eyepieces. The rotating ring that zooms the eyepieces is actually the uppermost part of the eyepiece housing (where the stock small eyepiece cup rests), rather than something mid-barrel. This meant that it took two hands to zoom the eyepiece, until it finally occurred to me after a couple of years of use to put a piece of duct tape around the barrel to make it a one-handed shift! Also, there is no millimeter scale on the eyepiece, just a magnification range for the two most popular sizes of Nikon spotting scope. I rectified this by making a paper scale and illuminated tape "needle" that could display focal length to a fraction of a millimeter accuracy-- see the "David and Goliath" image at right. Optically these are great performers, with exceptionally high light throughput for zooms, thanks in large part to their five element optical design. (Many competing zooms have 7 or 8 pieces of glass in the light path.) This renders them exceptionally good in solar viewing.
Pentax 8-24 SMC zoom. After my superlative experiences with the Nikon zooms in the binoviewing role and as solar eyepieces in the PST, I embarked on a plan to test zoom eyepieces in solar work. I therefore bought a Pentax zoom, since it was reputed to be of comparable quality to the fixed focal length Pentax eyepieces that give the Naglers a run for their money in the opinion of many experienced observers. My first impression was that this was one huge eyepiece! Optically on solar work-- which isn't a good differentiator of eyepieces, since even lousy zooms work well on the sun-- it was in a virtual deal heat with my Nikons, perhaps edging it by a whisker. In nighttime use it was a superlative performer in my 10" f/10 LX200, and could be a "one eyepiece solution" for all but low powered viewing on such a scope. Unfortunately, it didn't fare as well in the f/4.5 16 inch scopes, with coma and flare comparable to the Televue Panoptics in those telescopes. I am using it as a second optical setup for my PST, since by coincidence it is almost perfectly parfocal with the binoviewer-installed Nikons! (Focusing the PST is a bit of a pain, due to the small sized knob and its location beneath the PST housing.)
My "homemade monocentrics"-- 35mm at left, 18mm at bottom, 12.5mm at top
"David and Goliath" the Pentax 8-24 and Nikon 9-21mm zooms
Oblique view showing how large the Pentax viewing area is-- nearly large enough to contain the whole Nikon eyepiece!
