.Topics:

  Why test for better optics?

  Rested eyes see more!

  terminator test

  scintillation test

  "snap technique"

  Abbe-orthos versus Plössls:

  "Maxwell Gap"

   (begin at the beginning)
 
 

  (Return to "Astronomy News..."--Mars 2001)

  (Return to, or go to, "The Perfect Telescope")

  (Return to "The Perfect Telescope," Part 6: Eyepieces...)

  (Return to "The Perfect Telescope," Part 8: selecting eyepieces)

  (This way to the "library index")
 
 
 
 
 
 
 
 
 
 
 
 

To heighten the senses:
(This is why we search and test for the best eyepieces, filters and Barlows!)

(The night of nights and the week of weeks--October 1998)
 The weeks of October 5 and October 12, revealed rare good seeing in the area, and especially at the park on Saturday night, the 10th. There were comments that Jupiter was Hubble-like on that occasion. The good seeing lasted less than an hour, but it was stupendous--9.5! Nick Lawrus was there to say goodbye, and presented his 8 and 12 mm Brandon oculars and a 40 mm Plössl to the club. David Lord, Paul Schofield, Gary Bloom, Herb Knapp, Professor Lon Hill (with students from BCC), Noah McBurnett, Arno van Werven and Dennis Clift were among those present. (It was Nickís last night before he and his wife moved to California for work.)

 It turns out, there were valid reasons for the good seeing, as pointed out by Fred Schaaf in the monthly planetary observing section of Sky and Telescope, for that month, October 1998, pages 90-95--a must read. From the article and others to be mentioned, we could conclude that such fine seeing is much more rare than might be imagined--maybe only once or twice in a decade, or a lifetime!

[From the log--this was a week-long event, so I will begin five days before the trip to the park.) On 10-5-98, from a viewing site in the city, after seeing a vague gray line that seemed as though it might be the Encke division (in retrospect, the "Encke minimum," a graying of a region of the "A" ring, just inside the "Encke division, or gap"), briefly flickering in and out on several nights, the week of 9-30/10-1, the .2 arc-second gap might have been in view (a crisp line) for a few seconds, about one hour before Saturn crossed the meridian. I was using a 17 mm Vixen eyepiece on a 1.8x Televue Barlow, at 147x, on a Lumicon/E&W, 1/16 wave diagonal, and also at 213x with the Barlow in front of the diagonal. The telescope was an Astrophysics 6.1-inch f/9 apochromat. (Because Saturn is a high power object, and because a relatively low power was used, it would seem to suggest such minute detail could not have been seen, but on checking the October 1998 issue of S and T, referenced in the previous paragraph, I learned that Saturn was at opposition two weeks later, on October 23rd, and the disc was 20" for the first time in 21 years, since Feb. 1977. (re: Robert C. Victor, S and T, February 1977, page 290.)]

 Supporting information: According to another S and T article by Thomas Dobbins and William Sheehan November 2000, pages 117-121, Saturn would have been ideally positioned for best viewing early in October of 1998. The Dobbins/Sheehan article points out that viewing fine detail on Saturn is most desirable in the weeks previous to, and following, opposition. The viewing at opposition is less ideal because the sun is striking the "particles" in the rings at a 90 degree angle, and there is a resultant loss of contrast (more glare) due to lack of shadows, which would only be present when there is a slight angular displacement between us, the Sun and the ring system.

[From the log: 10-10-98 (Saturday night): I and my telescope were at the park with Paul Schofield and the gang, and for a 30-45 minute period, with Jupiter passing through the meridian, the festoons, red spot and white spots were extraordinary. It seemed that Paul's 7.5 mm Ultrascopic (186x) provided the crispest, most transparent, view. It was the best view I had seen of Jupiter since looking through Dr. Frank Denniston's f/9 12-1/2 inch Springfield reflector in 1958. (The October 1998 issue of S and T, page 93, with the foldout "folded up," facing page 90, third paragraph, bottom left-hand column indicates, Jupiter was at opposition 2 weeks before, on 9-16.)]

 More supporting information: Fred Schaaf's October 98 article, page 90, left hand column, says October provides the crispest viewing of the year, in most parts of the country, and November brings increased cloud cover. That night and that week in October of 1998 were extraordinary for good reason, and we were fortunate to be at the park, on the "night of nights."

 Factoring all this together, October 1998 was an opportunity that may only come once in a complete revolution or more of Jupiter and Saturn. I hope that doesn't mean it will be 21 years before we see such things again, but it may be so, and those who were there will always remember that night.

 (The reason I had enough information and enough determination to track this information down is, that by some good fortune, I was in place to observe both events and remembered how remarkable Saturn looked at 400x, in an 8-inch Schmidt-Cassegrain, as it approached the meridian, at 20 minutes before midnight, on February 1, 1977. February is not blessed with October's sometimes near perfect weather, but that night the "celestial canopy" was dead calm, as the moment came and went.)
 
 
 
 

(from the log:)

10-16/17-98, at 3 a.m.:
 With Saturn an hour past the meridian, Enceladus was barely visible with the Televue diagonal and 17 mm Vixen (Plössl) eyepiece at 82x. With the Vixen on the Barlow (147x), it was still there, winking on and off at the upper limit of the 6 inch refractor. I switched to the Lumicon 96% diagonal and it was just the slightest bit easier to see. This is the first time I have seen Enceladus with this telescope. (It was passing through greatest western elongation at 3 a.m. EDST--west is on the left with this setup. Dione was positioned at 10 O'clock, and Tethys at 4 O'clock. It rained hard earlier in the evening, and the seeing was about 6+ on a scale of 10. (Enceladus, Saturn's nearest moon at mag 11.7, was noticed at 82x, while comparing the Lumicon and Televue diagonals for light gain and glow. It probably would not have shown up at 147x, and it could only be seen with averted vision. It will be interesting to see what the new Lumicon flat, with what looks like a gold tinted coating, received today, will show? (The new flat was installed in the Lumicon diagonal the afternoon of 10-17-98!)
 

10-17-98--10:00 p.m.:
 The new "gold" flat for the 1-1/4" Lumicon diagonal shows relatively blacker sky right up to the edge of Jupiter's globe, and the bands standout more colorfully but with a slight loss in crispness. The new flat is designed to loose light at the blue end of the spectrum. That could prove to be a problem on faint objects, such as Enceladus, but it improves contrast on Jupiter's bands. Saturn and Jupiter appear a mellow yellow, with much less "skyglow gray," and haze in the foreground than before. It seems to be especially good for cutting through city smog! A lot of the glare and harshness has been eliminated! The original (prior to 2000) 2-inch Televue flat worked something like that. I may go back and try it again, but this way I have one diagonal for sharpness, and one for contrast. (Seeing is poor--5 out of 10.)
 

10-18-98--12:00 a.m.
 Using the new Lumicon flat, Saturn is beautiful but seems slightly less crisp than would be ideal. The area around the planet is darker than before, but I do not see Enceladus. That will require greatest eastern or western elongation, and it may take a few days for such elongation to coincide with a meridian crossing of the planet. At 12:23, I still do not see Enceladus, but in the 20 mm erfle, with 2.6x Barlow, at 170x, Saturn was superb. (Seeing is 5 out of 10--poor.) (As of 3 a.m., the flat for the 2-inch Televue diagonal has been changed back to the original, 10-year old flat.)
 

10-18-98-- 9-11:59 p.m.:
 I just finished shimming the extension tubes and diagonals where needed, and everything is parallel and concentric! The 3" extension was perfect, but there are still slight problems with the snugness of the 1-1/4" extension tubes and the 1-1/4" Lumicon diagonal, requiring careful positioning and tightening of the set screw. However, everything is very good overall, and the new Lumicon flat seems to out perform the Televue flat on the festoons of Jupiter. The Lumicon is noticeably less bright, but I can "see into" the belts more easily. The new Televue flat will have to be tested again to see which is really best.

 The coating on the new Lumicon flat reflects 88% of the light at 440 nm (middle blue--cobalt), at a 45 degree incident angle, and 96% at 510 nm (blue/green--cyan) to 680 nm (crimson to H-Alpha). The Lumicon coating (enhanced aluminum with mag. fluoride overcoating) falls to 72% in the visible violet versus 84% with a conventional coating. The older Televue flat seems to be brighter and must be about 93, 88 and 84% (vs Lumicon's 96, 88 and 72%). The newer (replacement) Televue flat may be very much the same as the original). The Televue flats present the most glare, but is intensely clear. In some ways, you can see more with either Televue than with the Lumicon, but in other ways the Lumicon is more pleasing and cuts through the haze better? (The best formula for a coating might be 98--red, 96--green and 80%--violet.) That would be most, and much, like the present Lumicon formula, but the violet end would be about 6-8 points brighter. This would seem an ideal balance between the sharpness of  pure white and the dulling effects of the blue/violet end scattering laterally in the haze and turbulence. That would be about half-way between the standard Televue and the enhanced Lumicon formula, but a bit brighter than either at the peak visual null.
 

10-20/21-98--8:00 p.m.:
 The seeing is extremely steady with some haze, but generally it is close to a 9 overall (a 9, for this site, in the city). Jupiter is dazzling and about 35 degrees above the horizon. Both diagonals were used during the evening, and the "Encke division" may have winked a couple of times when Saturn was only 45 to 50 degrees up. Moving to Jupiter, a very small, almost black, dark spot was visible on one of the bands. (The magnifications used ranged from 147x to 375x, with good results, but Jupiter suffers more than Saturn when the power is increased above 40-45x per inch of aperture. Less than the usual amount glow was seen around either planet, and there was only the slightest turbulence. (At 8:30, it was time to call Paul Schofield, and fill him in on what was happening.)

 Saturn was superb through the new Lumicon, but it was more dazzling "in-line." Jupiter was also best in the Lumicon but all combinations were excellent. The advantage of the Lumicon is that it has less brilliance and allows the mottled red details in the belts of Jupiter to be more easily made out. At 12:58 a.m., Enceladus (11.7 m) appeared in the northwest about 30 or 35 degrees above the point of greatest elongation.
 

10-21-98
 I received the 82A filter and the 7.5 mm Ultrascopic (186x) in the mail at about 2:00 p.m. During testing and comparison, I found the Ultrascopic showed almost no glow around Saturn, and the 13 mm Televue Plössl, on the 1.8x Barlow (193x), seemed to have twice as much glow, at nearly the same power. The 17 mm Vixen Plössl, on the same Barlow, seemed more transparent (less glow), but an accumulation of oily film on the Televue Plössl's field lens, might have been a factor, and the Vixen is a year newer and cleaner than the Televue. The background with all eyepiece and Barlow combinations was slightly darker with the Lumicon flat than with the 2" Televue.
 

10-22-98:
 For the last three weeks, there has been a dramatic improvement in the seeing conditions! Around the first of the month, I noted a small dark spot on one of Jupiter's bands, but did not make note of it until the 21st. It was so small I supposed few other amateurs had seen it. It was remarkable in its blackness, and less than 1 arc-second across. It is less than half as large, and almost as black as a transit shadow. When asked, at a later date, other members of the local astronomy club were unaware of it.)

 The week of 10-5, there was a clearing on Jupiter's belts, and white spots appeared near the equator that had not previously been noticed. At the time, it just seemed the seeing was improving, but it might have been something new--another sighting I did not record at the time. Now the white spots appear regularly. What I saw that week seemed to support the conjecture that there had been a change in the seeing, related to the end of El Niño and the beginning of La Niña.

 (After thinking about the glow around Saturn in the 13 mm Televue Plössl, on the 1.8x Barlow): The Televue field lens, though normally protected (covered) from dew and dust, had not been cleaned in the 19 or 20 months since its purchase. The Barlow and 17 mm Vixen also looked a bit lack-luster, but all seemed clean by unaided visual inspection.

   An oily film can settle on a lens, and not be noticed until it is removed. After cleaning, the three were brighter and clearer when held up to the light. The eyepiece/Barlow combinations will probably now be closer to the performance of the Ultrascopic.
 

10-23--98--9 p.m., and 10-24--4 a.m.:
 The seeing is poor (unsteady), but I compared the 7.5 Ultrascopic to the 17 Vixen and 13 Televue, on the Barlow anyway. The glow around bright images was about the same as before. I also tested the 2.7x Barlow with the 20 mm Meade Research Grade Erfle. In spite of wind and severe turbulence, I could see the small "dark spot" on Jupiter. Various festoons that I had not seen from this sight prior to the last few weeks were easily visible. Comparing notes to those of a month ago, there are minor belts close to the poles that could barely be seen. Now these belts stick out like a sore thumb?

 As to the issue of why more detail is visible this time of year, even on a poor night! I recently joked to Paul Schofield that the lens was growing a new skin, and there may be something to that! This is the period leading up to the most important stress peak of the year. (Stress peak: Every year at this time, the felt tape that lines the Astro-Physics dew tube shrinks for about three weeks, making the tube difficult to reverse and mount for storage. After the first of November the dew tube goes back to fitting normally. This seems trivial, but there are numerous other phenomena occurring at this time of the year, discussed and explained in another section of the "archive"--Under Southern Skies.) (download requires approximately 3 minutes at 28.8k.)

10-27-98:
A way to find M 36, M 37 and M 38 with an equatorial mount. M 37: place Betelgeuse, .75 degrees east of the cross hairs; M 36: place delta Orionis .75 degrees east of crosshairs; M 38: place the crosshairs just west of halfway between zeta and epsilon Orionis. After establishing the initial position, and using an eyepiece with about a one degree field of view, .swing north along the declination axis to crossover each cluster.
 

10-29--7:30 to 9:30 p.m.:
 The seeing has been poor for three days, but tonight is the 8th day of the harvest moon, the best night of the year to count the craters on Plato's floor. The sky is clear, but it is cool, and there is considerable turbulence- -less than 6 on a scale of 1 to 10. However, 10 craterlets can be positively identified. A new picture is in the file for same. There were three other possible craterlets, but, they could not be confirmed. However, the same two or three were seen and drawn last November, and the November before.
 

10-30-98--7:20 to 9:10 p.m.:
 Plato again, but the seeing is not much better than last night. At 9 days, there are 9 craterlets and a hint of 2 others, but the 2 others cannot be confirmed as more than ridges or craggs ("white spots"). At 9:15, I turned to Jupiter, using 209x to 464x. (The image was poor, but held its own at 464x.) The small "dark spot" on Jupiter was easy, but vague, with the 2-inch Televue diagonal, while the Lumicon showed more color and contrast by a good margin. (The "dark spot" seemed to be something new.) By 10:00 the turbulence had settled, but the haze was still quite bad. (The seeing is a 7.5 for steadiness and a 6 for transparency.)

 At 11:12 p.m., Saturn looked surprising intact at 464x and 558x. Increasing power to 672x, using two Barlows and a 6 mm Omcon Abbe-ortho, the globe and rings still held together, but were unresolved and gauzy (dishwater gray). (The seeing wasn't great, but there might have been a glimpse of the "Encke division" in the magnification range just under 400x.)

 (A problem arises: The 7.5 mm Ultrascopic is dark in the background without the Barlow, versus the others with the Barlow, but it becomes much more critical and unforgiving with the diagonal and Barlow combination. The 30-year old, 12.7 mm Criterion symmetrical beats them all (for low background illumination), on the Barlow, and is as dark as the 7.5 mm Ultrascopic, without the Barlow. However, logic would suggest it may be the lower light transmission of the much older "symmetrical" versus the high throughput of the newer eyepieces that is the "fooler." Sometimes coatings that transmit less light present a cleaner and relatively more pleasing image. (Confusing results: Viewing "in-line," the 7.5 mm Ultrascopic, with the 1.8x Barlow (335x), shows almost no glow in the background around Saturn, but there seems to be unacceptable glow using either the Lumicon or the Televue diagonal.)
 

10-31-98:
 The seeing was good tonight (8 overall by 9 p.m., with the moon just past first quarter--10 days old). I went to the park early and was home by 10:00. On returning home, my scope seemed to work better than the 6-inch Brandon refractor at the park, but the Brandon has more depth and imagery (the flat field effect of an f/15 focal ratio).

 On arriving home, I set up the scope and did another drawing of Plato, counting 10 craterlets at 193x, even though the moon was an hour closer to the western horizon by that time. The seeing approached the best possible from this location--almost a 9. Then I began to study the glow problem with short focus eyepieces, with Saturn as a test object. (The "Encke division" was out of reach at 174x , 186x, 193x, 362x and 484x! By this time, I suspected I did not see it on the two previous occasions. If you cannot confirm such a sighting it is best to assume it was not there, and it will have to wait for another day.)
 

11-1-98--10:00 p.m.:
 The seeing is very good, but the image of Jupiter through the 7.5 mm Ultrascopic on the Barlow at 335x is inferior to the Clavé with two extensions at about 330x. The glow with the 7.5 mm Ultrascopic was excessive. Inspection with a 7x loop revealed at least 40 "particles," some quite large, between the middle lens and the field lens. Disassembly, cleaning and reassembly, left only 5 or 6 small white specks inside the lens system. There was about a reduction by half of the illumination in the field immediately around bright objects! (A second cleaning was needed, because there was a diffraction spike on Sirius after the first effort.)

 At 12:25 a.m., the "Encke minimum," not the "division," was easily visible in the 7.5 mm Ultrascopic, on the Barlow, at 484x, and similarly at 325x, with the 12 mm Clavé. However, the description of the divisions in the rings by Richard Whalen of Clearwater, with a 5.7 inch Ceravolo Mak-Newt. seems out of the reach of this 6-inch scope. The seeing was about a 7, murky, but steady. Within 5 minutes, the steadiness was replaced by a river of turbulence in a cloudless sky. By 1:00 a.m., it was steady again, and the seeing was close to 7.5 overall.
 

11-2-98:
 The "mysterious dark spot" is in view for the first time in several days. It is offset to the south of the "red spot," and trails it by 1.4 hours, and it is about three hours ahead of the much larger white spots. The seeing is overcast but steady (7-8), and the Barlow assisted, 7.5 mm Ultrascopic is performing better at 335x, with only one fairly noticeable speck in the inner lens. Using the 82A filter on the Vixen and Barlow at 180x, helps just the slightest bit.
 

11-9-98--6:55 p.m.:
 While testing the 7.5 mm Ultrascopic again, "the mysterious dark spot" was in view, and appears to be oval-shaped, the longest axis being parallel to the equator, and the dimensions being minute, possibly less than about .4 by .6 arc-seconds. (Tonight I made a more accurate measurement of "the dark spot's" location and added the information to the entry for the sightings on 11-2-98. The "dark spot" trails the red spot by 1.4 hours, but is one zone closer to the South Pole.)

 (Efforts to estimate the size of "the mysterious dark spot" over the most recent 2 weeks culminated at 6:55 p.m. on 11-9-98: It is oval-shaped, the long axis being parallel to the equator, and the dimensions are about .4 by .6 arc-seconds. Occasionally, the size has seemed to vary, or there were was another spot(?), the second, more difficult to see than the first. (size update 11-9 98--7:00 p.m. to 8:25 p.m.)

 At 8:48 p.m., two of Jupiter's moons are "near-graze" (approximately 2 arc-seconds) and approximately 70 arc-seconds east of the planet. Then it rained! (I am still not satisfied with the 7.5 mm, but I have learned a lot from it regarding cleaning techniques and background illumination problems at short focal lengths, and I will continue studying it as the opportunity arises.
 

11-12-98--6:10 p.m.:
 There is definitely another "dark spot," and it appears markedly elongated or hyphen-like. It appears to be .4" by .8" versus .4" by .6" for the more visible spot, and trails it by one hour and 15 minutes, at almost the same longitude as the more pronounced and permanent dark spot on the northern edge of the NEB. The "NEB spot" appears to be dark brown, and is easily seen with the 20 mm Erfle, on the 2.7x Barlow, at 160x or 170x. The "lesser dark spot" is on almost the same latitude line as the "mysterious dark spot," but 2 or 3 degrees to the south, and about 1 hour and 15 minutes behind (20 degrees). (Further, it is 8-10 minutes ahead of, 40 degrees south of, and smaller than, the more permanent spot, near the north edge of the North Equatorial Belt.)
 

11-16-98:
 Based on observations of Jupiter at the park, in the C14, on 11-14-98 (350-400x), I need to adjust the estimated dimensions for the three spots. The hyphen-like spot was in view, and it appeared to be a straight line about .3 by 1.0 arc-seconds, and the red spot and white spots were not in view. (Estimates based on this reckoning are: "mysterious dark spot" = .35" by .7" (STB DS#1); "lesser dark spot" (STB DS#2) = .30" by 1.0"; "NEB dark spot" = .5" by 1.3" arc-second.)
 

11-17-98--a.m.
 The Leonids did not materialize tonight, and for the two nights they were nothing like they were predicted to be. It was interesting and the biggest shower I have seen, but none has ever panned out per its publicity. However, in a dark sky, it must have been impressive, at least the first night, but no "storm!"
 

11-21-98--6:30:
 The great red spot and "the mysterious dark spot" (STB DS#1) are in view. The really interesting thing about the dark spot, is its remarkable contrast versus other markings on the planet. It is several time darker and more pure, almost artificial, very much like a transit shadow, but smaller.
 

11-24-98:
  It turns out, the dark spots and white spots have been reported by Dobbins and Parker in October 1998 S and T, page 116, and in January 1999, page 130. There is a picture in the January issue, also showing the "NEB spot." From the picture and article, I will have to change the designations. The "lesser spot" is longer than the "mysterious spot," and is labeled STB DS #2. Apparently, it formed, and was first reported, not long before my uncertain initial sighting, around November 1st, and probably about the same time I first noted seeing STB DS #1, 10-22-98.

 The darker spot, STB DS #1, was first seen by Dobbins on July 19. Dobbins also estimated the small spot, DS#1, to be about 1/2 the size of a transit shadow. (STB DS #1 is the darkest marking on the planet, albeit quite small.) In addition, Dobbins and Parker, viewing from Ohio, using a C14, on July 27, reported that most of the SEB was split in two. (I noticed a change in appearance, but supposed that it had probably been there all along. There was a similar split in the NTB in early October, and again, I assumed it was nothing new, and that it appeared at this time because of the improved seeing conditions.)
 
 

Abbe-orthos versus Plössls:

11-06-00
 (13 days before the nearest opposition of Saturn since 1976)
   I set the 6-inch f/9 Astro-Physics up early this evening with 2.4x on the Barlow and the 17 mm Vixen--197x on the Lumicon high contrast diagonal. I could see three or four craterlets on Plato, but it was like a pan of sizzling grease. Maybe not quite that bad, but the craterlets are actually "walking around" on the floor of the ringed plain. I gave up on the Moon at 8:40, and turned the scope to the east to look at Saturn. By 9:00, it was in the clear, and the seeing was not too bad--a 7.0 to a 7.5, but still "sizzling."

   The target was anything named for Johann Franz Encke, at 9:30, I increased the Barlow power to 2.8x and used the 17 mm Vixen--230x. The "Encke minimum" was visible at 9:50, but only so, because I knew where it was supposed to be. (The "Encke division" was not visible!) Using the extra power was premature, so I went inside till after 10:00, intending to stick it out until Saturn was high overhead, just after midnight. At 10:30, I returned to put the 13 mm Televue Plössl in the eyepiece holder, yielding 297x. There was no apparent gain from this, but it is said you cannot see the "Encke division" with much less than 300x power, in fine seeing.

   At 1:37 a.m., the morning of the 7th, and 297x, Saturn is dazzling, and the "minimum" is easily visible, but probably only to an experienced observer, and the image still suffers from the turbulence! I think there will be no conclusive sighting by this observer of the "Encke division" (a.k.a. Encke gap) this year.

   It's 2:07 a.m., and I just made a discovery. I have been going back and forth inside, and looking at the sketches of Saturn in the November 2000 S and T, pages 119 and 120. The seeing is no better than it was an hour or two ago (7 to 7.5), maybe worse, but you can still see the "Encke minimum." The discovery is a matter of recognizing something that was visible all the time, but you have to know to look for it. "It" is the "Maxwell Gap," and it is near the outer edge of the "crepé" ring ("C" ring), just in from where it joins the "B" ring. (Only the narrowest possible strip of gray of the "crepé" ring can be seen between the "Maxwell Gap" and the "B" ring.) The "Gap" is visible (not the narrow gray strip), but difficult, in the 250-280x range (5 mm University Optics (UO) Abbe-ortho/6-inch f/9).

   It is easier to see illusive detail, such as the "Maxwell Gap" on the shady side of the planet. This is confirmed by the drawings on page 120 (referenced above). The S and T article is written by Thomas Dobbins and William Sheehan, noted planetary observers and historians. In the final section, on page 121, Dobbins and Sheean report on the observations of Audouin Dollfus. Dollfus found the brightness of the rings, at or near opposition, when there is little or no shadow, makes sighting fine details much more difficult. The drawings on page 120 show the rings and divisions on the sunny side of the planet as appearing somewhat washed out when compared to the shady side. Recognizing the glare and the reduced contrast on the sunny side is a test of the observer's skills. If the observer doesn't notice the difference in contrast and brightness between the two sides, he/she probably won't be able to separate the "Gap" from the almost nondescript gray background. A trick to help sight the "Maxwell Gap:" Do not look for its presence--look for its absence! Take a few moments to relax, clear your mind, and close and rest your eyes, then look for something that isn't there, and you will have a better chance of seeing it! (A precondition: If the seeing is not transparent enough to make the "crepé" ring easily visible, it will not be close to possible to see the "Maxwell Gap," a very tough test for contrast and clean surfaces, in a fine 6 inch telescope.)

   It is much easier above 300x! At 349x--4 mm UO Abbe-ortho. The "Gap" can now be seen on both sides of the planet. (No light scatter from a Barlow lens, on this test, please!) The seeing is getting worse, possibly down to a 7, and Saturn is about 20 degrees west of the meridian. The air cells are behaving as though the mist from an atomizer is periodically being sprayed in the field of view--an apparent effect of peak sunspot activity.

   At 420x, using the 6 mm Omcon Abbe-ortho on a 1.8x Televue Barlow, Saturn is still relatively crisp and beautiful, but "Maxwell" is a "washout." The best power in a 6-inch telescope is about 350x, and the min/max, is 280/380x. Repeating the test on a better evening will confirm the sighting, and the conditions could certainly be better. This is surely a severe test for a 6-inch telescope, and may only be possible in such moderate sized instruments near, but not very near, opposition.
 

11-08-00
 (11 days before the nearest opposition of Saturn since 1976)
  (1) Since the first night of testing eyepieces, I have switched the test from the Lumicon diagonal to the old style Televue 2", with a 93-95% coating. The Lumicon presents an image similar to what you would see through a number 82A light blue filter, but with much less light being scattered into (and dirtying up) the background as is usually the case with a filter. (With the Lumicon style coatings, there is better contrast on Jupiter and on "Maxwell's Gap," but observations of Mars in 1999, indicate the low sensitivity to blue light reduces contrast on the ruddy red surface dramatically.)

   With the latest test, the comparison between the 7 mm UO Abbe-ortho and the 13 mm Televue Plössl, on the 1.8x Barlow, provided a more equal outcome, with a slight advantage in imagery and darkness in the field to the Abbe-ortho. Interestingly, I would say, the Abbe-orthos, on the f/9 APO, do not look as sharp or as pleasing on the Barlow as some other designs. The Brandon seemed to be "pleasing" on and off the Barlow. (There is something "comfortable" about the Brandons. They seem to be less affected by poor seeing than other eyepieces.) Beyond that, an advantage of the Abbe-orthos seems to come above about 45x per inch, say at about 280x, versus whatever Barlow combination you have to put together to get up to that power range with the Televue or Clavé Plössl, but it seems less advantageous against the Brandon. (This advantage to the Abbe-ortho applies most to symmetrical images, and with not much fine internal detail, such as Saturn or a double star. On an object like Jupiter and Mars, the Abbe-ortho is more likely to fall short of the mark set by the Televue Plössls and the hybrids. However, the Abbe-orthos will show as much internal detail as most other Plössls. It takes the best to beat the orthos, even at their weakest point!)

   I decided, the first night of the test, that, along with the Televue 4-element Barlow, something like a Radian would surely not do well above 300x (50x per inch), because of the added reflections related to the extra glass, but with more recent testing on the Televue diagonal, that seemed less likely, and other reports indicate the Televue Radian like the Televue Plössl is extremely crisp. My conclusion is, the Abbe-orthos I used are noticeably less desirable on a Barlow than off, and the greatest difference or advantage to the Abbe-orthos is seen using the Lumicon diagonal. (A note about that: The best result on the Lumicon, with any eyepiece shows up on Jupiter, but it is less of an advantage as the seeing improves. Further, it is no help on the moon, but a significant detractor on anything red, such as surface markings on Mars or the reddish markings, in the equatorial belts on Jupiter.)

   That sounds obvious, but there is something between the lines (something between the lens--not just a pun!)--all that glass--the "girdling" and "bulging" effect on the light cone by a multi-element lens, versus the degraded light cone produced by poor seeing conditions results in a more degraded result than when using a simpler eyepiece design. "Simpler is better, when the seeing is poor!" Complex lenses are less tolerant of poor seeing, skyglow and related light scatter! That is, simple designs are more "accommodative" toward poor seeing, while complex lenses tend to suffer. The more glass, a bad image, related to poor seeing and turbulence, passes through, the more, the resulting degradation, versus the same eyepiece in good seeing.

   This is just more data to add to the mix, and I find I have said it before, visa vis the issue of eyepiece color error and an APOs natural tendency to spread out the spectrum, no matter what you do or how fine a lens it is. I recently mentioned to a well know optician (i.e., an apo guru) that Saturn looks much crisper with a light green  (#11) filter, and he said that was because of the inherent spherochromaticism of a moderately short (f/9) APO. He also said, "if you don't want to see that (in a refractor), get an f/15 APO."

   All this suggests, filters play a much more complex role with an APO. I wonder if the #11 filter would help with the "Maxwell Gap" (a black ring on a dull gray background), and on which diagonal, and if so, would it help detect the "Maxwell Gap" with a Newtonian design, or would there be a benefit from a decidedly different filter, such as the #8? This is a situation like the, "I don't know what it is, I just like the Abbe orthos," phenomenon. What I mean is, so many factors are involved, and the differences in how filters, eyepieces and Barlows work on different scopes is so illusive, the conventional notion of simply asking which eyepiece will give the best result, is short of the mark, as regards realizing how refined the technique of choosing which eyepiece will give the best result must be. That says, if you really want to do planetary studies, and get the process and the image, "nailed," the color divergence, characteristic of an APO refractor, tends to add to the problems of getting the most crisp image, and a specialized, high-end, long-focus (f/9 is ideal) Newtonian or a Mak/Newt may better fit the description, "the perfect telescope."
 

11-11-00
  (8 days before the nearest opposition of Saturn since 1976)
  Another for instance: For me, and while I tend to dislike filters, I am thinking that very subtle filters #85, #11 and #82A, have a carefully chosen place in the process. And some filters, possibly the #8, that works so well on a Newtonian, are not quite as effective on an APO. Also, I see a unique benefit from each of the different diagonals- -one which transmits the blue end more than the Lumicon or the Televue, may be the best on Mars. The new 99% Maxbrite/Everbrite, true white, broad-band dielectric coating may be far and away the best of all on Mars (need info). However, and to pose another question, I cannot help recalling how badly the 6-inch f/15 Brandon achromat (1/16 wave P-V) worked, vs the Schofield 6-inch Newtonian, on Mars, in good seeing conditions, during the 1999 opposition. Both instruments were using a number 21 filter, and the f/15 refractor burned out with almost no noticeable detail, while the Newtonian showed Syrtis Major and other markings nicely and plainly. (There was no sighting of the "Maxwell Gap" on this date. but there was still a hint of shadow showing on one edge of the planet.)
 

11-15-00
  (4 days before the nearest opposition of Saturn since 1976)
   A possible explanation for some eyepieces seeming to be "just right," that unexplainable something that draws the eye and the mind to them even though they are not as sharp as other designs: The human nervous system is affected by stress, and at the same time, it can correct some types of errors (e.g., refractive--color shift). If an eyepiece converges color less than ideally, the stress on the eye to accomodate refraction errors can be a source of fatigue, at an almost subliminal level, and the error may not be noticed, because the nervous system adapts quickly. What appears to be good correction, may be "fixed" ("accommodated") by the eye and the brain. However, when an eyepiece is well corrected, the stress level is lower, and the improved performance, may be hard to quantify, but the image is easier to study. (A compound effect: With less stress, the effect of easier viewing adds to the body's energy, and any added sense of ease and satisfaction will heighten sensitivity and increase stamina, allowing just that much more to be seen.)

   With something less ideally color corrected, but still close, the brain will accommodate, and we won't know the color is less than perfect, because mother nature (and the brain) says, "hey...fixing subtle variations and aberrations is my job--you are not supposed to see minute color errors!" (Beyond that, and probably more important, the notes in the section on "resonant imagery," in The Perfect Telescope, suggest that loosing a little of the finest and most challenging detail at the diffraction limits of a particular telescope will show up (reveal fewer residual errors, and be less challenging to the central nervous system and motor centers. It will also be more forgiving of imperfections of the eye, such as, mild astigmatism.)

    While they may not be as well corrected as the 3-element APO, long focus achromats, do not require the same degree of accuracy from the eyepiece. That suggests that short focus refractors are critical no matter how fine, or sophisticated and expensive, the objective lens.

A speculation: Some observers with younger and/or more perfect eyes might not notice some of the more critical constraints of the apochromat. Maybe that is why the 5-element design of the Celestron Ultima and the Antares seems so desirable. It was noted that the Antares 15 mm hybrid, versus the Televue 13 mm Plössl, seemed to work "better" on one occasion, and yet it was hard to demonstrate any advantage on another occasion. Consider that under some circumstances, especially when the optics are not fully stabilized, or the seeing is poor, or the observer is fatigued, the hybrid design, with higher correction, related to the extra lens element, might seem less fatiguing to the nervous sytsem than even the best 4-element Plössl. ***

Maybe we can say the Antares or the Celestron Ultima may, in some circumstances, seem to work "better" or present a more pleasing image (i.e., characterized as transparence and imagery: "whiteness") than the Televue Plössls, but is it sharper, or as sharp, in the best of circumstances? Further, it may be that the Radian would be easier on older eyes, as far as astigmatism and wearing glasses and eye relief are concerned. The 15 mm Antares and the 18 mm Celestron Ultima are quite desirable (above f/6), eye relief wise, using a Barlow lens, on a Newtonian, and the Abbe-orthos and the Radians each have advantages over the other, and may still be the best answer for observing with an APO. (What has become apparent, concerning the 5 mm Radian being sharper than the 5 mm Nikon ED Abbe-ortho, is consistent with what has been shown with the noteworthy superior sharpness of the 18 mm Radian vs the 18 mm UO Abbe-ortho, at the Winter Star Party, in 2000 (Re: Paul Schofield). Balance that against the Televue Plössl's claim of being as sharp as the Radian. Does that mean the Televue Plössls and the Antares and Celestron Ultima hybrids are sharper than the UO Abbe-ortho, but the Abbe-ortho has better contrast and imagery, especially on something like Saturn or double stars? It probably does, but there is obviously more study to do! To put things in perspective: While there is not much difference, the Pentax, Nikon and Zeiss ED orthos transmit slightly more light and are a bit sharper than the more mundane University Optics orthos. (For the money the difference is miniscule.) (However, it is an optimal situation, like using a telescope of larger aperture, when first class eyepieces transmit just slightly more light than their best competitors.). Further, the high end orthos will also perform slightly better (sharpness and transmission) than the UO orthos versus the Antares, Ultima and Televue, when the seeing allows the hybrids and the best Plossls to come into their own--matchless resolution. Unfortunately, some of the high end ED orthos are out of production, and will have to be found on the used market, when and where possible!)

More on Eyepieces and Barlow Lenses

   As "opposition" comes closer, you can still see a touch of a shadow on one side of Saturn, infringing on the rings, just as they pass behind the planet. However, as was mentioned earlier, and as pointed out in the article in Sky  and Telescope (Dobbins and Sheehan, November 2000), it becomes harder to see subtle changes in markings and contrast, such as the "Maxwell Gap," as the day of  opposition approaches, and the shadow shrinks, because of the increased glare.

12-15-00
(The "terminator test:" a test for sharpness and accuracy)
   I ran a test of U. O. Abbe-orthos vs Televue Plössls on Jupiter, Saturn and the moon tonight at 150x to 400x, with the 6-inch f/9 APO. The field is darker and the orthos are very uniform and pleasing to look through, but they could not match the 13 mm Televue Plössl, on a Barlow lens, at resolving patches of very small and densely packed craterlets and peaks near the terminator of the Moon, or on bringing out detail in the belts on Jupiter. Using the Plössls, craterlets and other changes in the surface appeared to be deeper and more defined than when using the orthos. (The difference in the sharpness of the two designs is hard to pin down unless the seeing is good, and unless there is a highly detailed image to evaluate.)

   The Abbe-orthos are well corrected for color, and that is one of their principle advantages, because of the possibility of color problems affecting resolution in the APO. So, with an APO, the task is to find the best color correction, without loosing detail! (The slight loss in sharpness, with the Abbe-orthos, becomes more apparent above 230x, and especially when using a Barlow lens, while the Barlow seems "more friendly" to the Televue Plössl, and to hybrid eyepieces, such as the Takahashi, Ultima and Antares. (Similarly, and paradoxically, when the "seeing" is poor, the increased dimensionality, or "resonant effect," related to the loss of sharpness, becomes an advantage.)

   The testing completed thus far, suggests that marginal seeing and the difficulty in coming up with a repeatable standard/test, masks the problem of marginal performance (i.e., resolution) with both telescopes and eyepieces. That is, when two scopes are compared, less-than-ideal seeing may limit image quality enough that, in the range of about 40x per inch of aperture, or more, it is difficult to demonstrate a difference in performance, where one is known to be measurably superior ( e.g., 1/4 vs 1/8 wave). (One of the phenomena that comes from this is, the weaker eyepiece or telescope may seem to provide more pleasing images when the seeing is poor, because the minute misty effects and micro turbulence (worse in poor seeing), revealed by the sharper eyepiece or telescope, will not be seen in the less crisp instrument.)

  Another revelation: The older 17 mm Vixen Plössl fell short! It fell into the category with the UO and Omcon Abbe-ortho and the Galoc--pleasing, but not "crisp!" The effect is like dealing with what might be called Schmidt-Cassegrain-like diffraction losses. The seeming "nailed" quality of the Abbe-orthos is actually a limitation (with marginal losses above approximately 1/4 wave), which seems to provide a more uniform and nicely finished image. (Many eyepieces, available today, are not good enough to "see into" the finest cracks and edges of the Lunar surface!)

   Interestingly, the limitations of the Abbe-ortho make star testing and double star images more perfect, instead of appearing a bit "ratty" (.i.e., ragged and irregular), as they should. One of the more desirable qualities of Abbe-orthos is "near textbook perfect" diffraction images--the seeming "perfection" comes from not being sufficiently accurate to show the most minute imperfections in the image. (To do the "terminator test," when turbulence is at a minimum, find a well defined, or "buckshot-like," crater field, or a cluster of pin-point outcroppings, and use magnification in the range of 35 to 40x per inch. I find that the occasional gravel-like patch along the terminator makes the best and the easiest test for sharpness and accuracy. The abruptness and elevation of the outcroppings, and the openness (i.e., a test for clarity) of the spaces between peaks shows the limits of the lens, mirror or eyepiece under test. You have to look at the right object, at the right time, at the right magnification to make a conclusive evaluation! This started out as a search for the sharpest eyepiece, however, with a refractor or compound reflector, the "terminator test" readily shows the subtle difference in resolution between in-line viewing and viewing with the aid of a star diagonal. It is more difficult to see the difference, but it will also work when comparing high quality diagonals in an effort to find an image closest to the in-line view.)

   The Radians may be a breakthrough design (but some say are heavy and bulky, with lateral color), and the Televue Plössls may be "best of breed" (i.e., sharpest, but vignette above f/15, while some of the hybrids have potential at the same level of excellence. The crispness, improved eye relief, image scale and 51 degree FOV available with the Antares (15 and 20 mm fl, with 11 and 14 mm eye relief) and the Celestron Ultima (18 mm fl, with 13 mm eye relief), when used with a tele-negative amplifier (Barlow lens), may be a cost effective alternative to the 57 degree field and 17-20 mm eye relief of the Televue Radian.
 

12-16-00
  Finding a repeatable standard/test by which to demonstrate the difference between 1/4 wave and 1/8 wave performance is a challenge! (The initial testing here was done using a 6 mm Omcon Abbe ortho. The 7 mm and 5 mm, University Optics Abbe-orthos were used to establish a working range and verify results. Under 35x per inch of aperture, it is harder to pick a winner, but in the range above that magnification, the test becomes more revealing!)

   The last quarter terminator was fantastic in the orthos--contrast was incredible! However, there is twice as much detail with the Televue Plössl. "Twice" is an exaggeration, but at the extreme limits of the test, it is difficult to verify the exact difference in the detail revealed with even that much difference in sharpness. This is also a severe test of observing skills! If the observer is not in relatively good health or hasn't been aware of detail that fine, he/she may not be prepared to just sit down at the focuser and reproduce these results. (For test purposes, the oft scorned Moon is an excellent source of fine markings!)

  This is as difficult a test for the observer as trying to see the "Maxwell Gap" in Saturn's rings. The difference in the performance of the two eyepiece designs is slight but important, and 38-40x per inch is needed for the test to be ideally revealing, but it will show up! It may be necessary to go back and forth a dozen times or more to be sure you are seeing what you think you are seeing, and the seeing conditions will have to be "steady as she goes" at 40x per inch! The better the "seeing," the more precise and certain the test result, and having a telescope capable of 1/8 wave P-V performance will make it easier to demonstrate and compare the high end performance of the best eyepieces. (If the test is conducted with a 1/4 wave telescope, or if more than about 42x per inch of aperture is used, the test will be less sensitive and revealing, possibly inconclusive.)
 

     12-17-00
(The "scintillation test," another test for sharpness)
 The next test subject was a 12.5 mm Omcon Abbe-ortho against the 13 mm Televue Plössl and a 12 mm Clavé Plössl, all three on a Televue Barlow lens. Before beginning the test, I wondered if using the ortho on the Barlow might or might not widen the gap in performance. (In some tests, it has seemed that Abbe-orthos do poorly on a Barlow lens.) The first thing noticed is that, in the early evening (often the best planetary viewing is at the end of twilight), with Saturn and Jupiter about 30 degrees above the horizon, at 35x per inch (210x) the Abbe-ortho does, in fact, deliver a more pristine and settled image; however, finer atmospheric ripples can be seen when using the Plössls. Again, the limitation may seem advantageous! The more forgiving eyepiece is arguably better in poor seeing, or, at almost any time, to show off objects such as double stars and Saturn, especially for the "Maxwell Gap." (With the short-focus Abbe-orthos, not needing a Barlow for the high power range, unlike the Plössls, provides an advantage (contrast-wise) on  subtle details, such as the "crepé ring." Paradoxically, the tendency for the less crisp eyepiece to look "cleaner" (i.e., a "weakness") in turbulent seeing conditions makes the symmetry and fine edges of Saturn a good test with which to demonstrate accuracy--the better eyepiece seems less desirable! Philosophically, the "scintillation test" is a negative test! Instead of looking for markings and detail you are looking for turbulence and disruption of the image.)

   The difference in sharpness becomes more obvious, after swapping the eyepieces in and out a few times, and then taking a break for a few minutes, or going inside for a snack. When returning to the eyepiece, after a break (rest), the observer's sight may be keener. With practice, it may be apparent, at a glance, which eyepiece brand or design is in the holder without looking at the markings on the barrel--the eyepiece with the finest "edges" should show more atmospheric activity and scintillation. This test and the occasionally seen fields of tiny "buckshot-like" craterlets and outcroppings along the Moon's terminator ("terminator test"), can be used to compare sharpness in any two eyepieces or telescopes. Of course, for both tests, it will be necessary to have or make every facet of the test equal and ideal, to get useful data. Example: the magnification should be the same on "A" and "B" to within 2 or 3%, and the seeing conditions should be 8 or better, for at least part of the test, and if it is a telescope test, the apertures should be the same to make a reasonable comparison, and to reasonably estimate wave front performance (especially for surface smoothness). Comparing instruments of different apertures and designs is interesting, and sometimes the results are surprising, but it will prove nothing, and it will not yield much more than bragging rights.
 

12-27-00
  After the latest tests on the 16th and 17th, I was convinced the Abbe orthos were not terribly crisp. So, I decided to compare a 12.7 mm symmetrical from Criterion to the 13 mm Televue Plössl and the 12 mm Clavé Plössl. These three eyepieces could be adjusted in the draw tube of one or the other of the Barlows to provide about the same magnification. For another test, to be done at the same time, I wanted to compare the 8 mm Brandon to the 7.5 mm Ultrascopic.

   Each eyepiece, or each eyepiece-Barlow combination, on Jupiter, while it was positioned near the meridian, seemed to perform about equally well. However, the Ultrascopic (hybrid) and the Brandon were noticeably brighter than any of the other three (12.7 mm Criterion symmetrical, 13 mm Televue Plössl and 12 mm Clavé Plössl), on the Barlow. I was surprised to see the 7.5 mm Ultrascopic was brightest and possibly sharpest, but it did seem to show a little color on the edge of Jupiter's globe. (All testing was done with the image in the center of the field--I was not looking at other qualities, just how sharp were they in the very center of the field.) During the test, the small dark spot in the North Equatorial Belt came into view. This spot is difficult to see in anything less than good seeing, but if you know it is there, you can see it with about 160-180x in a 6 inch telescope. On this occasion, it appeared about the same in all five eyepieces, between 174x and 220x. Of course, the seeing was about 6, maybe worse--the turbulence was bad! (Increased turbulence tends to make scopes of the same size, but different quality, seem be about equal in performance!)

   I decided to bring the 12.5 mm Omcon Abbe-ortho into the test at this point. The long and short of it is, with the scope not fully cooled down, the Abbe-ortho showed the "NEB dark spot" up more pleasingly than the others, and it may be because it is slightly less accurate, and has the best eye relief of the test group.

   As the scope stabilized and Jupiter passed right overhead, I settled exclusively on comparing the 12.5 ortho to the 13 mm Televue. This time, with going back and forth, it soon became apparent, at about 220x, with the seeing still choppy, that color definition in the bands was less ruddy and more vibrant through the Televue Plössl, and as the conditions improved, the "NEB dark spot" became blacker in the Televue, but did not seem to change for the better in the Abbe-ortho. The seeing worsened again, and the session had to be ended.
 

1-06-01
(The "snap technique": the finest detail...the payoff!)
   The eye and the nervous system are most accurate and most sensitive (i.e., accommodative) when rested frequently, and not fixated on an image for extended periods. (The eye begins to lose sensitivity for fine details after less than a second of observing. If you look quick and rest, you will see more!) By looking away and resting the eye for 10 or 15 seconds, then, looking back for just a second, the sharpest eyepiece will be more likely to stand out, and show the most detail. (This is best revealed at powers above 35x per inch, up to just over 40x per inch.) When an image is dwelled on for more than an instant, the brain's motor centers begin to lose their "edge" (i.e., desensitize), and it will be more difficult to see minute differences in detail. (When first looking into the eyepiece, the motor centers try to "snap" the image, and all its detail, into focus--the best (i.e., most crisp) eyepiece or telescope will "snap" more quickly, so to speak! Doing the "terminator" or "scintillation test" in this manner, employs a deprivation technique, used to increase reading speed! If the eye and nervous system are overworked, fatigue might dull the senses sufficiently to make dissimilar eyepieces difficult to tell apart, in terms of image quality and sharpness. Getting control of the test will be easier if you consider the eye and the intervening medium to be part of the optic!) (Time spent fumbling and re-focusing can make test results ambiguous! A quick change tip: The process can be enhanced by adjusting the scope's focuser to suit the eyepiece which focuses the closest in. Then, without adjusting the focuser, put some kind of "stop" (e.g., a rubber band) on the barrel of the other eyepiece to keep it from sliding in past the point of focus. The test can then be more nearly parfocal, and it will be easier to compare in less time!)

  These results show that the best and easiest test for sharpness (i.e., accuracy) is at moderately high power, on the Moon's terminator (shortly after the first, or just before the last quarter--9-10 days gibbous). (As mentioned in the notes for the 16th and 17th of December, it takes close to 40x per inch (38-40), but not much more, in good seeing, to conclusively decide which eyepiece or telescope is sharpest. This is not to suggest any virtue in competing with other amateurs as to who has the best equipment. However, making comparisons, in this manner, may be the only way to ferret out a weak component, and get good results.)

  Conclusions: You can never sell an Abbe-ortho short! It may not keep up on the most severe resolution test and the field is narrow (40 degrees), but  the light throughput, flat field, contrast, color correction, desirable eye relief and the tendency to form a clean, smooth diffraction pattern when there is none, produces a pleasing image, in ordinary seeing conditions, while the sharpest Plössl and hybrid eyepieces probably won't have much chance of demonstrating their superior resolution. (The downside of the Abbe-ortho may only be important to the most critical observer. Some hybrids and Plössls are amazingly sharp, but most reasonably good quality Abbe orthos cannot be equaled for contrast and pleasing images ("imagery")- you need both types (designs) to do it all!)

  More conclusions: The tendency for a less crisp eyepiece to form a more perfect (i.e., cleaner) and pleasing image is like the tendency for an obstructed telescope to have a resonant, or warmer, image. The pleasant, warm, "well coupled" effect provided by well made, obstructed telescopes makes them easier on the eye, but under the best conditions, like the "softer" eyepieces (e.g., ortho), discussed here, they may not quite provide the exquisite detail of a fine lens or a less obstructed mirror. (The confusion in all the testing comes when, a refractor and reflector, of about the same aperture, are compared, and the reflector seems to be gaining ground as the evening wears on. This happens because, as the seeing improves, the reflector has time to stabilize thermally. If the reflector seems to be superior after several hours, it was always superior--it just needed more time to settle in! (Because of the negative effects of the secondary obstruction and because of the "temper" of the glass, Newtonian reflectors need better conditions, and they need more time to reach their best "figure," and show what they can do.)

    Another comparison that may cause some confusion, when testing for accuracy and sharpness: The sophisticated and refined nature of the catadioptric (Mak-Newt) and the compound catadioptric (Schmidt-Mak or Schmidt-Cass.) designs give them an advantage (i.e., rapid stabilization) over the Newtonian and the refractor. And, similar to the comparison between the refractor and the Newtonian, the Newtonian will tend to overtake the catadioptric as the evening wears on. With the Schmidt-Cass. design, the instrument will stabilize and work its best right out of the box (almost every time). First the refractor, then the Newtonian will close on, and/or exceed the performance of the Schmidt Cass. (Because of the large size of the secondary mirror, and because the compound catadioptric design is optimized to "settle" and reach its best "figure" in just a few minutes, there will be almost no improvement in the compound instrument, as the evening wears on, and the prime focus instruments come into their own.)

A closing note (You can see more than you think): Not to overlook an important tool: For an instant, the "snap technique" allows the eye to sharpen and reveal more detail than would ordinarily be seen. Of course, we like to just gaze at the Moon or stars and enjoy the view, but when you are looking to see something difficult to see/detect the snap technique may bump up the effective aperture just a bit, and reveal some illusive detail that others will not see on that occasion. The "snap technique" lets you see more no matter which eyepiece you choose!

  (Return to the beginning of this section)

  (Return to "Astronomy News..."--Mars--2001)

  (Return to "The Perfect Telescope," Part 6: Eyepieces)

  (Return to "The Perfect Telescope," Part 8: selecting eyepieces)

  (Return to or go to "The Perfect Telescope")

  (This way to the "library index")