Observing the night sky with binoculars 1. Asterisms, nebulae, clusters, and other low power objects for binocular viewing. Double stars. Variable stars. Objects viewable with binoculars & filters. 2. The limits of binocular viewing: Alberio. Horsehead. Detail on the Moon. Jupiter. Titan. Rings of Saturn. At the end, a long series of notes from Jack Eastman on the subject, followed by a summation that partially duplicates the notes. 3. How to hold binoculars for a steady view. This file consists of e-mail & newsgroup posts. Although this re-posting is pushing the limits of electronic propriety, the very public nature of the original messages, and the 'not for profit' nature of this site, seem to grant enough of a license. Besides, "it's easier to seek forgiveness than to ask permission". As always: on-line information sources should be 'believed with caution'. ========================================= 1. Wide field astronomy: objects of choice. ---------- The Pleiades or Hyades, all three parts of the Veil, the Rosette, the sword of Orion, N. America nebula, M33 & M101 face on spiral galaxies, emission 'complexes' IC 1396 in Cepheus & IC 1848 in Cassiopeia. 12 x 50: M51 with two bright components --------- 1) Barnard's Loop 2) Rosette Nebula + NGC 2244 3) California Nebula 4) North American Nebula 5) Pelican Nebula 6) Kemble's Cascade 7) Double Cluster 8) Sudor Ophiuchi 9) Coathanger 10) M7 11) M8 12) M24 13) M44 14) M45 + nebula 15) IC 1396 16) IC 4665 17) IC 4756 18) Stock 1 19) Stock 2 20) Melotte 20 21) Ruprecht 56 22) Ruprecht 64 23) B 168 24) B 111 25) B 119a 26) Cr 69 + Sh2-264 27) Cr 132 28) Cr 135 29) Cr 463 30) Cr 464 There are also many objects that are nice to see in the same field together such as: M46, M47, and NGC 2423; M31, M32, and NGC 205; NGC 2451 and NGC 2477; or the three main components of the Veil. The outer arms of M42 meeting in a complete loop as they sideswipe NGC 1980. Southern objects like the Vela Supernova remnant and Eta Carina. ---------- Wide field Galaxies: --M33 almost fits into an 0.8-degree field, but it is at best ill framed unless the field is 1.2 degrees or more. This object is notoriously hard to find in an 8-inch SCT under light pollution, probably because of the limited field. --M31 requires 3.2 degrees or more to fit the whole thing, but it shows a magnificent view in a 2-degree field, or even in a 1.5- degree field, with M32, M110, and the central bright region all showing together --------- Nebulae: --M42 The faint outer extensions require a 1.2-degree field or more. --M8 needs at least 1.2 degree to fit the whole thing. --IC 434 (the Flame Nebula in Orion) requires at least 1.2 degrees to fit the whole thing --The Rosette Nebula, bigger but much fainter than M8 or M42, 1.5-degree field. --NGC 2264 is a monstrously big nebula with a bright, coarse cluster embedded at one end. Hard to see without a filter. It is at least two degrees across, but seems to fade out into infinity at the end opposite the cluster. --The Veil Nebula is actually quite easy to see with a nebula filter, and under dark skies much of it remains fairly easy when you take the filter away. The Veil is composed of many disjoint pieces, and the entire thing just fits into the 3.2-degree field --The North American Nebula (NGC 7000) is possibly even bigger than the Veil. Unlike the Veil, it tends to be amorphous and disappointing if you try to pan over with a smaller field, except maybe the Gulf area. ----------- Open Clusters: --The Double Cluster (NGC 869 and NGC 884), 0.8-degree field, but looks much better at 1.2 degrees, and better still at 1.5. --M48 is a bright, very coarse cluster that maybe fits in an 0.8- degree field but is hard to pick out from the background even in a 1.2-degree field. --NGC 752 in Andromeda and IC 4756 in Serpens are rather similar clusters, about a degree in size, composed of fairly faint stars for such big clusters. IC 4756 is quite a bit richer, but also in a much more crowded part of the sky. OK in a 1.5-degree field, better in a bigger field. --Stock 2 is a striking cluster composed entirely of bright stars and about 1 degree in diameter. Because it is quite sparse and in a crowded part of the sky, it is indistinct in anything less than a 2-degree field. --M7 is one of the most magnificent clusters in the sky, over a degree in diameter, looks good in a 1.5-degree field and better in a 2-degree field. A little too dense, and with stars too faint, to get full appreciation in hand-held binoculars. --Collinder 399 (the Coathanger, Brochi's cluster) is not a true cluster, but a very striking asterism of 10 stars ranging from mag 7 to mag 5. It is 1.5 degrees from end to end, requiring a 2-degree field. --M44 and M45 fit (barely) into a 2-degree field, but require a bigger field to appreciate them fully. M44 is quite a bit smaller than M45, but it is also rather coarse and straggly, and so requires a larger background frame to make it stand out. Most of their stars are fairly bright, so larger apertures are not called for, unless you want to see the nebulosity in M45. --The Hyades and the Coma Berenices star clusters are composed primarily of very bright stars, ...show best in 7X binoculars. The Coma star cluster is just a bit too big to show well in the 5-degree field of most 10X binoculars, but the Hyades do fine in a 5-degree field. ---------- Galaxy fields: --M81 and M82 ...a 1.2-degree field. --M65, M66, and NGC 3628 ...almost fit in an 0.8-degree field. --M95, M96, M105, NGC 3384, and NGC 3389,... fainter and more scattered than the M65 family.... barely fit into a 1.5-degree field; magnificent at 2 degrees. ----------- --The central Orion area, including the sword and the belt, 7-degree field to fit the whole thing, 3 degrees fits the whole belt, 2 degrees just about fits the sword, which would might still be the most splendid 2-degree field in the sky. --Sagittarius Milky Way is magnificent at every power and different at every power. 2 degrees just fits M8 together with M20 (the Trifid Nebula). It also just fits M24, the small Sagittarius star cloud. --Objects that are too big even for binoculars, such as the whole constellation of Orion, the Big Dipper, or the Great Rift in the Milky Way stretching down from Cygnus. And objects that cannot be taken in in their entirety even with the naked eye, including the Milky Way and night sky as a whole, which can be seen only in the mind's eye, or from outer space. - Tony Flanders ---------------- The Messier list for the Zeiss 10mm MiniQuick: > M31 hard because of the bright background > M42 easy > M45 easy > M35 not too difficult to see fuzzy patch > M36 hard to see fuzzy patch > M38 hard to see fuzzy patch > M37 harder to see fuzzy patch > M41 relatively easy > M47 hard to see but the sky was better > M48 ? I think I saw it but I'm not certain > M13 not too difficult ------------------ Naked-eye objects under dark skies: M31 obvious M42 easy, but hard to separate from the various Theta Orionis M45 easy under heavy light pollution M35 obvious, a good test for reasonably dark skies M41 obvious M47 very obvious even under mediocre skies M13 faint but obvious - Tony Flanders -------------------- objects for 10 x 50: -- M13 -- M31 (Andromeda galaxy) -- M41 -- m42--great nebula in orion -- m44 -- in cancer -- m45--pleaides open star cluster with 7 bright naked eye visible stars -- M49 -- M101 followed by a trip through the MIlky Way including such interesting things as the Coathanger, American Nebula, Veil Nebula and the wonderful stuff all around the Sagitarius area. M42 is always fun along with other nebulosity in the area with a view of the Roseatte a real treat. -- ngc869/ngc884--double cluster in perseus -- the entire scorpius/saggitarius region which includes m4 (globular cluster), m8 (lagoon nebula), m20 (trifid nebula), m7 (open star cluster), m6 (open star cluster), m22 (globular star cluster), m24 (small saggitarius star cloud), m17 (omega nebula), m16 (eagle nebula, technically in serpens cauda), and many other fine objects. -- The moon -- Star cloud north of Saggitarius - actually the whole region -- Mirfak cluster in Pegasus. (A sprinkling of diamonds) -- Coma Bernices cluster -- Milky way. the Cygnus region. -- Sun, with filters --M31 is spectacular in a mag 6 sky. M31, M32, and NGC 205 all visible in the same field. M31 is a spiral galaxy spread across a three degree FOV and has a very bright core. M32 and NGC 205 are both elliptical galaxies which are satellites of M31. M32 a compact fuzzy star, and NGC 205 much larger with a much smaller surface brightness. -- NGC 5139 is a favorite in my 10 X 50 Ultima's. -- Sword of Orion (NGC 1981, M42, iota Orionis) -- Collinder 399 (Coathanger asterism) = Brocchi's cluster = Collinder 399. http://www.seds.org/messier/xtra/ngc/brocchi.html Also worth a look are the M6, M7, M13, M24, the Hyades, the Muscleman Cluster (Stock 2), the Double Cluster (NGC 869 & 884), the Christmas Tree Cluster (NGC 2264), the Helix [Helical Nebula (NGC 7293)], the North American Nebula (NGC 7000), the Pipe Nebula (LDN 1773), and Melotte 111 (Coma Berenices open cluster). Some of these will require very dark skies to be seen. Dave Mitsky ---------------------- Messier objects. In an hour or so cumulatively, spaced over the night, I went through eighty-three of them, from the Beehive and M67 all the way around to M2, M15, M30, and M39. That was easier than it sounds -- I have been through the Messier catalog more than twenty times, and can find most of them without charts, and a 70 mm binocular of modest magnification is probably the easiest instrument for a Messier survey: It is capable enough to show them all without difficulty, and has a wide enough field to make finding them a cinch..... I usually have a binocular handy when I observe, but only rarely use one much. This night was an exception. I logged 155 observations with the 14x70, more than on all the previous ones with it, put together. JR Freeman, Hawaii --------------- Celestron Ultima 7x50. -Cancer - Followed from Orion to Gemini then identified it as I swept towards Leo. M44 (Beehive) was the standout here, easily finding a large cluster of discrete bright stars. I swept towards the horizon and found Acubens (alpha-Cancri) as a guidepost for M67. This cluster was seen just to the right of Acubens, not resolving points of stars, but definitely seeing a tight patch of mist here. -Perseus ­ the concentration of stars around alpha-Persei (Mirfak). Hopping from alpha- to kappa-Persei, I was able to form a triangle within a field of view of kappa-Persei, beta-Persei and M34. This was seen as a nice small cluster of stars. Beta-Persei (Algol) is an eclipsing binary ­ I didn¹t split the double but according to Harrington it should be seen as a variable with about a 2.8 day period. I looked over to the double cluster (NGC 869 / NGC 884), very impressive each time I see them. When I first saw this, the background star density was so high, I wasn¹t sure whether these were true clusters or just focally increased star densities. Beautiful! -Cassiopeia ­ Just taking in sweeps of this rich constellation is a joy. M103 as a faint cluster just above delta-Cassiopeiae (Ruchbah). Failed to find M52 by following a line from alpha to beta-Cassiopeiae towards Cepheus. Should be just more than one FOV away from beta-Cass. -Puppis ­ Following a line from Mirzam to Sirius in Canis Major, I searched for a pair of Messiers which are actually in Puppis. M47 was easily seen as a nice tight cluster of discrete stars. M46 just to the left was seen only as a faint smudge best seen with averted vision. -Canis Major ­ Just a quick look here to find M41 which is viewed as a nice bright cluster of a large number of discrete stars. -Orion ­ M42 and M43 nebulae, splitting theta1 and theta2, I think. Following the chain up, seeing NGC 1977 with 42- and 45-Orionis split within this. NGC 1981 cluster slightly higher. Peter Huang -------------- From: "Frank Bov" the open clusters of Auriga - M36, M37 and M38 - and M35 in Gemini. The former are all in one binocular field at 7x, and with that wide field, you can scan down the Milky Way from M52 (which you will find) through Cassiopia, etc., to Canis Major/Puppis, picking out about 20 open clusters. I get a real feeling for the structure of the outer arms of the Galaxy in this region, dominated as it is by open cluster, rather than the globulars of the Ophiuchus/Sagittarius central Milky Way region. Given what you're finding, i.e. M46, you might also want to look for M1 in Taurus and NGC 7000, the North America Nebula in Cygnus. The former is a real binocular challenge, but I've succeeded in 10x50's while the NA nebula is a naked eye object that just shows detail in binos. ------------ 10x50 Bushnell Binoculars From: "Tom Luton" M31-elongated smudge, bright nucleus with pale disk, no sign of companion galaxies (M32, M110) M33-no sign, may not have swept far enough from Alpha Trianguli NGC 752- found line of 6th & 7th mag stars that 'underline' cluster, but no sign of cluster itself M38- possibly saw it, too vague to be sure M36- dim,circular smudge M37-similar to M36, slightly brighter NGC 1647-no sign (Jupiter may be too close, too bright) M78 -nebula forms Cepheus shaped asterism near Alnitak, M78 would be in 'position' of Beta Cephei, no sign of nebula NGC 2264- found central star, but no sign of others M35 - dim smudge NGC 884,869 (double cluster)- clear, many stars visible M103-elongated, narrow smudge -------- Kemble's Cascade. To find the Cascade, make an equilateral triangle, with Mirfak at one apex, the Double Clusters the 2nd apex, and a smudge to the north being the 3rd apex. The Cascade (a group on perhaps 15-20 stars in a beautiful line) comes out of the "smudge". The beautiful cluster NGC 1502 is at the foot of the Cascade. Aaron Bransky Duluth MN ========================================= DOUBLE STARS: Ten Binocular Doubles for Summer Evenings; none require a truly dark sky. Magnitudes and separations are from "Seeing the Deep Sky" by Fred Schaaf. From: "Wes Stone" 1) Epsilon Lyrae (4.6, 4.7; 208"): Most people should be able to split it without optical aid. In 8x56 binoculars, appears as two perfect white dots. 2) Zeta Lyrae (4.3, 5.9; 44"): Much closer than Epsilon, and very unequal. The primary (to the north) has a yellow tinge while the secondary is bluish. 3) Nu Draconis (4.9, 4.9; 62"): In color and brightness, the equal of Epsilon Lyrae, but the stars are much closer. Resolution is easy in any binoculars. 4) Beta Cygni (Albireo) (3.1, 5.1; 34.4"): It may be a bit difficult to split on your first attempt; remember that the secondary is toward the body of the swan. The primary is yellow-orange, the secondary blue. 5) Omicron-1 Cygni (3.8, 6.7; 107" (AL)): A double to the naked eye (with 30 Cygni); binoculars add a faint companion to the primary of this pair. The two brighter stars look yellow-orange and blue-white; the faintest sometimes appeared blue and sometimes red. 6) 61 Cygni (5.2, 6.0; 30"): One of the nearest star systems. Two orange stars of similar brightness. About as difficult to split as Albireo. 7) Delta Cephei (variable, 7.5; 41"): The primary is a famous variable. This system is a paler version of Albireo: pale yellow and ice blue. The stars are slightly farther apart. 8) Theta Serpentis (4.5, 5.4; 22"): The closest pair on this list; a good test. Both stars are whitish with a slight violet tinge, and are similar in brightness. 9) Nu Scorpii (4.2, 6.1; 41"): Unequal in brightness, and rather difficult to split. Primary (to the south) is yellow; secondary is faint and may appear gray or slightly reddish. I could not split nearby Beta Scorpii with my 8x56 glasses. 10) 15 Aquilae (5.5, 7.2; 38"): Another close and unequal pair. Primary (to the east) is reddish orange. Secondary, if it shows any color, is similar. ------------------- Double stars. Alberio in Cygnus shows a nice color contrast, and is resolvable in 10x50s if they are held VERY steady. Also a favorite is Nu Draconis, they are very close to the same brightness and it is just resolvable hand-held with no support. =============================== VARIABLE STARS: 10x50 binoculars and some variable stars-- W Ori and RX Lep for starters, then UU Aur for the first time, then tried Y Lyc but it was faint enough that it could be seen but not estimated well in the binoculars--probably a bit below 7.3. Then on to X Cnc near the Beehive Cluster..... I think some of the sequence stars in the "kite" asterism that X Cnc is in are suspect-- especially the Northern mag 61 star... you can download the "a" or "ab" wide field binocular charts for these stars at the AAVSO website. ============================================= FILTERS: --With interchangeable eyepieces on binoculars, you can put a UHC or OIII filter behind the eyepiece. Fujinon makes a "nebula" filter which fits in the eyepiece of their 7x50 and 10x70 binocs. I've tried taping Lumicon UHC and OIII filters over tripod-mounted Fujinon 10x70's. It works, but it's not quite as good as filters mounted behind the eyepiece, where the light rays are more parallel and the filter bandpass is tighter. ---I've compared the views between taped UHC's over Fujinon 10x70's and filters behind the eyepiece in a 70mm Pronto. It's a subtle difference, but you can see it.... nebula filters dim the view quite a bit. --VEIL: I have seen the Veil from a dark-sky site with 10x50 binoculars without a filter. Curtis Croulet --I saw hints of the Veil Nebula in my 4.5 mag small town skies. My method was to hold a nebula filter against one eyepiece of 11x70 binocs. I found 52 Cygni with the clear eye, then covered that objective with a hand to aid concentration on the filtered eye. Averted vision then saw some hints of the nebula. From: siop@my-deja.com --I used one of the wider band nebula filters (OIII + Hbeta) since I knew the filter probably wasn't exactly perpendicular to the optical axis. --While the presence of 52 Cygni would make the western half appear easier to find, I found the eastern part easier... probably due to the light from 52 Cygni interfering with my vision. At first, I didn't think I was seeing the eastern veil, because it seems to "make too small a circle." However, looking at photographs, it does have a tighter curvature than the western side. I can pick it up with 7 x 50 binocs, and my eyes aren't that great. I never saw the western half until one night when I wore red goggles for about a half an hour before going outside. Then it was so easy I was shocked! In fact, while I didn't expect to see it, the inside of the veil was brighter than the outside. (due to the supernova explosion clearing it out.) I'd thought that would be a purely photographic observation, and I wasn't even looking for it. In fact, I thought that I could use that effect to find the western veil the next time, but I've only seen it after wearing my red goggles. If I go out with 11 x 80's, the veil is beautiful, but I still have to wear my goggles to pick up the western, 52 Cygni, half. movac5@webtv.net (Marty) --I have a set of 10x50 binocs that the EPs are set up to take 1.25" filters on the eyecup. Things like the Veil and other objects pop out real nicely with a pair of nebulae filters screwed in. Bob May --I could see the North American nebula clearly by holding a UHC in front of the eyepiece on my 8x50 finderscope while it was very difficult to see in the eyepiece of the telescope. When an object is larger than your field of view, you can actually have the telescope eyepiece centered on it and not realize it because there is no "edge" to bring the difference from the background sky to your attention. (Same thing happens with M33 without the UHC -sandymc456@aol.comnospam (Sandy McNamara) ============================ To estimate the area of sky that a binocular will show, divide the apparent field of the eyepiece by the magnification. For example, if your binocular has an apparent field that is about the same as a standard plossl eyepiece, it has about 50 degrees of field. If it is a 10 power binocular, divide 50 by 10, to deduce your true field of view as 5 degrees. You can also take a known object, like the bowl of the big dipper, which is 10 degrees, and estimate the field by viewing the asterism. ======================================================== 2. Pushing the limits of viewing with binoculars: Alberio, Horsehead, the Moon, Jupiter, Titan, Saturn's rings. ============== a. splitting Alberio --Yes - If you look closely, you'll notice you're unable to focus Alberio down to a point, unlike the stars surrounding it. I discovered this the other night with my Bushnell 10x50's. --easy at 10x. One can even split it in a 7x50. --Yes, but I can do it only with a tripod. --I split it cleanly with a Russian 8X16 monocular with excellent optics, so splitting it with a pair of 10X50's should be easy --Yes, I use it to determine the sharpness of the pair of binocs. I could split it clean with 8x42 Leicas, and 10x50 Orion Ultrascopics ---Yes, fairly easily with my Minolta XL 10x50s - and handheld too. The colours show up well and maybe that helps. ===================== b. Horsehead nebula --I've seen the Horsehead through a pair of Fujinon 10x70's and Unitron. Be aware that both binoculars were outfitted with a pair of hydrogen-beta filters (taped in place!). The view came at the 1991 Winter Star Party. Phil Harrington ====================== c. the Moon --moon in 20x80 binoculars. I observed Hipparchus and Albategnius on the lunar terminator. Horrocks (30 km diam) was on the north edge of Hipparchus. Halley (36 km) and Hind (29 km) were near the south edge of Hipparchus. Sunlit ridges on the following side of Halley on the shadowed floor of Hipparchus gave the appearance of another 30 km crater. Finer details were visible in the walls of Hipparchus and Albategnius. Albategnius had a black (shadowed) floor when I observed it. The walls of Albtegnius were illuminated by the low sun all around the crater's perimeter, but the floor was black except for the brilliant central peak that rose high enough to catch the sun's rays. Both Hipparchus and Albategnius had the polygonal shapes characteristic of the larger lunar craters. From: lifeform@stars.end (Starstuff) ==================== d. Jupiter --tripod mounted 20x80 binoculars ...equatorial bulge was easily visible. The north and south equatorial belts could be seen with the planet's equatorial zone between them. Ganymede could be recognized by its brightness. Callisto could be recognized by its color, magnitude, and distance from the planet. I was unable to tell Io from Europa, but both were easy to see. From: lifeform@stars.end (Starstuff) ====================== e. Titan: magnitude 8 to 9 --I could see 8.3 mag stars away from Saturn, I could *not* see similar stars near the planet. As I didn't have a truly steady bino mount, the bright image of Saturn was moving around on my retina, desensitizing (I'm sure) a large region. : Bill Walsh --its possible...I just saw it last night with binoculars. It does look somewhat like a faint background star...just a tiny pinpoint of light. From: Josie Caat ======================== f. Saturn's rings --through my 10x50's Saturn appears elongated; through my 20x80's the effect is pronounced but I cannot resolve distinct rings; through my C4.5 Newtonian at 30x the rings are unmistakable. ---Saturn with tripod mounted 20x80 binoculars, the planet's strong yellow color was very prominent, especially compared to Jupiter's golden white color. Titan was easily visible. The dark gap between the ring and the planet was visible on both sides of the planet. lifeform@stars.end (Starstuff) --"Stephen M. Zumbo" wrote: I believe I can see that Saturn is different than a normal star point in my 10x50s, but I am not certain if knowing the rings are there is helping my powers of observation. My first such views were in the year or two after ring plane crossing when the ring tilt was a minus -3 degrees. I haven't taken alook this year in binos, but I know it is much brighter naked eye since the ring is at -14. --You should be able to just discern Saturn's rings with a good pair of 10x50s; Often unless you have it focused tack-sharp, the planet will appear to have ears. I routinely can see the rings [no significant detail though!] with my 15x70mm binoculars. I know what you mean about seeing what you know is there already, but try finding it, then pan around near it. Darren Hennig dhennig@sprint.ca 1998/12/29 --According to my experience, 20x is needed to barely make the rings out and 40-50x or more to view them comfortably. Paul Schlyter --I have the 9 by 63 celestrons and my eyes aren't good enough to see the rings. jeff --I have 7X50 Celstron Pros, and my eyes are not good enough to detect rings, perhaps, just a hint of elongation, though. Jim Mueller --I tried the other night in fairly unsteady air with 16x70s and saw only an elongation; no separation between rings and sphere. I think with very steady air, I could've managed a better view. Phyllis K. Lang, --I've tried it last week with my Fujinon 10x70 FMT-SX, but I couldn't see the rings. They are very fine astro binoculars (sharp and bright images), so that can't be the problem. I think 10x is just not good enough. Though there were some hints, indicating it was Saturn: - the orange colour; - the image was not quite pin-point (more like an oval); - (almost) no 'twinkling'; But you don't need a high magnification to see Saturn. I've seen it with a 32mm Plössl in my Ranger (15x), and of course a stable mount (Tele-Pod) and good eyes :-) . Ruud Schmeitz -- Bert Harless: The correct answer is "Yes you can see Saturn's rings in bino's." ....I was reminded of a story from Jack Eastman. He thought that it should be possible due to the amount of magnification and the angular size of the planet. But when he tried it he couldn't see them. He then realized that the exit pupil of 7x50's is about 7mm. Peoples eyes don't work at maximum resolution at 7mm but do at about 2mm. He made a couple of disks with holes about 14mm in the center and taped them to the front of the bino's and tried again, low and behold the rings were visible. I haven't tried this personally, but I have no doubt that it will work. I have done the same thing on my scope with an off axis aperture mask to split close doubles. Apparently only part of the resolution boost comes from negating the effect of bad air, the rest comes from stopping down the exit pupil. --Andrea Merritt In my 8x56's I can only get a hint of elongation, like looking at a close double star in a telescope. --I had my Celestron 10x50s .....Saturn for a moment. With the binoculars well supported the elongation is simply unmistakable. No, you can't really even begin to resolve the rings, but it is clear that there's something 'wrong' with this planet! Rod Mollise --Gerrit_Kooi@hpl.hp.com: I've seen the rings of Saturn clearly in 14x binoculars. The trick is to look at Saturn just after sunset, when Saturn is still invisible to the naked eye. This way Saturn is not too bright to wash out the rings. When it gets dark, Saturn looks much brighter and I cannot see the rings in my 14x bino. --The best 10x optics do show the "projections" or a definite elongation, yes indeed.... Or is eyesight the big factor at these low powers? I _easily_ detect the elongation of the planet, not just in my decent Celestron 10x50 binos, but in my el cheapo Simmons 10x50s. Rod Mollise --I too can see an elongation in my 7x50 Steiner binocs, but not in some other 7x50 or 10x50 models. Maybe we have discovered a new "star" test for binocualars. joe ======================= Saturn's rings through binoculars? Various posts from Jack Eastman. --30 Sep 1998. From: "Eastman, Jack F" Rings of Saturn at 7X. Theory says no problem, trivial. Practice: No way. The reason, I think is that although we think the world of binoculars, 'specially if we paid many bucks for 'em, they really aren't very good, as optical instruments go. Also our eyes, which operate close to the diffraction limit during the day (Arc-minute resolution, 2mm pupil) are more than likely pretty awful "wide open" at 6 or 7mm. Mine sure are! Third, (obviously) the bino needs a steady mount. On the second point it would be interesting to try and quantify "goodness". I was thinking of setting one up, at infinity focus, in front of the interferometer and looking at the transmitted wavefront. The experiment: Use my 7X or 8X glasses stopped down to a 2mm exit pupil and see what happens, and try with a little 6X18 (3mm exit pupil). I have a "calibrated milliradian" in the form of a "golf-ball" water tank several miles away, the ball part is one milliradian, 3.44 arc min. and another one farther away that subtends about 2 arc-min. I have no trouble resolving that smaller one with the naked eye in daylight. At 10X the ball of Saturn will look like about 1 milliradian, and the major axis of the rings will be 1mR at 4.6X, as will the disk of Jupiter. By the time you get back I will clarify this thing and hopefully have observational results and will try to get some time to go down to the lab and look at the wavefront through a couple of these things. FJE ====== From: Peter Abrahams. I agree that even good binoculars are not noteworthy in terms of optical quality, the thinking being, why make them diffraction limited for only 7x. And I know my eyes aren't very good with wide open pupils. But I'm not sure I agree that the rings of Saturn are impossible at 7x. I believe I've seen them...we're just talking about a visible linear extension off the tiny disk; though I'm always the first to admit to 'averted imagination' etc. Also, there are major differences in acuity between individuals, maybe due to varying levels of SA of eye; apart from myopia etc. Peter ====== Date: Thu, 01 Oct 1998 From: "Eastman, Jack F" I hope to carry out the experiment with the pupil size. I did see the rings with a 11?X80 (It might have been a 14X80) by squinting and moving my eye around so as to choke off the pupil somewhat. The rings are obvious in the finder on my Clark, 22X36, but not quite so nice with a 10X40 finder. (Pupil size again?) I didn't mean to say this observation is impossible, I hoped my discussion of the resolution of the distant water towers (3.4 and ~2 arc minutes) using the daytime adapted eye proved just the opposite, that seeing the rings would be trivial at one arcminute resolution (eye). Using 7X, Saturn's ball would subtend about 2 arcmin. (19"x7X=126", or ~2 arcmin.) The major axis of the rings is 2.4X this number, and since it is easy to recognize that 2 arcmin water tank on the horizon, I'd say Saturn at 7X is no problem. What does render the observation very difficult is the aforementioned optical quality of the eye-bino combo used at large pupil openings, perhaps exacerbated by glare from the bright planet against a black sky. Suggestion, try this in twilight. I have found splitting bright double stars, like Castor, with a big 'scope much easier, in the presence of marginal seeing, against a bright sky. .... My second sentence, "Practice: No way." That should be qualified and should say, perhaps, no way with 7X binos used in the usual way. 7X is not the problem, but all the other things are, pupil size, optics etc. My thesis is that in a perfect optical system, at 7X, Saturn's rings, and the disk of Jupiter, should be obvious. FJE ============= 05 Oct 1998 From: "Eastman, Jack F" I have no prescription for a typical 30mm bino objective, so I fiddled. In the Melles Griot catalog/database I exhumed a "Precision laser grade achromatic doublet" of 100 mm focal length, scaled it to 120mm FL, gave it an aperture of 30mm (f/4). and had at it. The P-V wavefront is ~0.77 waves and the circle containing 75% energy is 28 arcsec in diameter, 90% energy, 32 arcsec. compared to the ideal airy disk of about 9.9 arcsec. The Strehl came up .159, which is meaningless. The Strehl is the ratio of the amount of energy in the Airy disk to the ideal number. Strehl of .8 roughly corresponds to a .25 wave system, and numbers much less than .2 or so means the calculation is getting lost. Yes, as supposed, this thing is pretty awful by telescope standards. Yes, again, the prisms in the binocular will introduce their brand of aberrations, but if you are designing the "precision grade" lens, you'd include the prisms as part of the system and come close to the above results anyhow. Stopping this down to 16mm (F/7.5, 2mm exit pupil) now gives a P-V wavefront of .074 waves, and encircled energy of 16 arcsec for 75% and 32 arcsec at 90%, the diffraction disk is now 18.5 arcsec and the Strehl is .98%. MUCH improved. The size of Saturn's disk these days is about 19 arcsec. If I find my 8X30's differ greatly from the above assumptions, or if someone has a 30mm lens prescription, I'll use that and try again. In the "good old days" these calculations would have involved a day or so of work, several minutes of CPU time at $700 or so/CPU second and a week or so of elapsed time while the computer gorillas drop and/or shred your card decks and so forth. Today it was 10 minutes, doing the calculations on the PC while writing this missive on the Mac. No CPU charges, no cards to fold spindle and mutilate no computer gorillas whose noses need punching. Takes all the "fun" out of it! FJE ============ 3 Nov 1998 From: "Eastman, Jack F" ......at 15X... I stopped the Zeiss 8X30s to about 15mm (1.9mm exit pupil) and took a quick look at Jupiter and Saturn just hand holding them against a semi-solid support. Jupiter's disk was apparent and I couldn't tell that much about Saturn. The reason for such a sloppy try was due to drizzly and otherwise bad weather. I was sort of peeking between wet clouds. It went 100% overcast while I went to get a tripod and has been totally shot ever since. At the Astronomy Day open house I looked at Saturn through a friend's Canon 15X42 image stabilized binos. The rings were obvious even hand held. Releasing the stabilize button rendered them useless hand held. That feature really worked, and with a 2.8mm exit pupil, the eye aberrations were not too bad. FJE ============ 05 Nov 1998 From: "Eastman, Jack F" Last night (NOV.. 5, ~3:00 UT) I stopped the Zeiss 8X30s to about 15mm (1.9mm exit pupil) and took a look at Jupiter and Saturn with them tripod mounted. Jupiter's disk was apparent and Saturn appeared elongated, but without much more than looking like a tiny ellipse. As a control I set up my 60mm refractor at 32X to be sure the seeing was good enough for this test. It sure as hell ought to be for a 15mm aperture, but this is Denver. I stopped the 60mm to 15mm. Saturn still sort of showed the space between the ball and the ring, but it was easy to imagine I was seeing three disks in a line. 15mm @ 32X isn't much different than Galileo's telescope. Stopping to 10mm, still at 32X Saturn looked like an ellipse with a bright central bulge, or a fuzzball with short wings. Clouds finished that and I switched to Jupiter. The disk was obvious, but no detail was seen at 10mm, at 15 I imagined a dark equatorial belt. At full aperture the NEB and SEB were apparent. I doubt I really saw anything at 15mm aperture. ========================== ========================== A MORE COGENT ESSAY, SUMMARIZING THE ABOVE: Subject: Resolution of binocular - eye system From: "Eastman, Jack F" Some thoughts, and observations, on the visibility of the rings of Saturn at 7X. Theory says no problem, trivial, assuming perfect optics, including the eye. I have a "calibrated milliradian" in the form of a "golf-ball" water tank several miles away, the ball part subtends one milliradian (mr), (3.44 arc min.) and another one farther away that subtends about 0.67mr (2.3 arc- min.) I have no trouble resolving that smaller one with the naked eye in daylight. At 10X the ball of Saturn will look like about 1 mr, and the major axis of the rings will subtend 1mr at 4.6X, as will the disk of Jupiter. From this purely geometric argument it would seem trivial to see Saturn's rings at 7X where the major axis of the ring system would now subtend over 1.53mr (5 arcmin), better than 5X the resolution of the "standard" eye. I think, however, one should be cautious playing with these numbers. If one looks at the images of the relative apparent sizes of the planets, for example, on Sky & Telescope's Sun Moon and Planets, (p 103 in the Nov. issue) shows that Saturn is considerably smaller than Jupiter, although the maximum angular dimensions of each are comparable. Practice: No way. (Or so it would seem) My first astronomical instrument was the Zeiss 8X30 binos I had mentioned in earlier editions of this column. Early on I had mounted these on a tripod and with then childish enthusiasm looked at everything I could. The planets were a big disappointment, and I thought a telescope was necessary to see anything at all. After acquiring my first 'scope, (40mm Polarex (Unitron)) and looking at Jupiter and Saturn at 40X - 50X I thought anything much under 20X would not show much. The real reasons for the inability to resolve these small structures is, while we think the world of binoculars, especially if we paid many bucks for 'em, they really aren't very good as optical instruments go. Secondly, our eyes, which operate close to the diffraction limit during the day (Arc-minute resolution, 2mm pupil), are more than likely pretty awful "wide open" at 6 or 7mm. Mine sure are! (Suggestion, try this in twilight. I have found splitting bright double stars, like Castor, with a big 'scope much easier, in the presence of marginal seeing, against a bright sky.) On top of all of this,the retina's resolution gets poorer in low light, the effect of "bigger pixels". ( Roger Clark in his book Visual Astronomy of the Deep Sky discusses this effect) On the first point it would be interesting to try and quantify "goodness". I was thinking of setting a bino up, at infinity focus, in front of the interferometer and looking at the transmitted wavefront. While I have no prescription for a typical 30mm bino objective, I fiddled around with the computer analysis of a "typical" 30mm f/4 cemented achromatic objective. From the Melles Griot catalog/database I exhumed a "Precision laser grade achromatic doublet" of 100 mm focal length, scaled it to 120mm FL, gave it an aperture of 30mm (f/4). and had at it. The P-V wavefront is ~0.77 waves and the circle containing 75% energy is 28 arcsec in diameter, 90% energy, 32 arcsec. compared to the ideal airy disk of about 9.2 arcsec. The Strehl came up 0.159, which is meaningless. The Strehl is the ratio of the amount of energy in the Airy disk to the ideal number in a perfect image. Strehl of 0.8 roughly corresponds to a 0.25 wave system, and numbers much less than 0.2 or so means the calculation is getting lost. Yes, as supposed, this thing is pretty awful by telescope standards. Yes, again, the prisms in the binocular will introduce their brand of aberrations, but if you are designing the "precision grade" lens for a prism binocular, you'd include the prisms as part of the system and come close to the above results anyhow. Stopping this down to 16mm (F/7.5, 2mm exit pupil at 8X) now gives a P-V wavefront of .074 waves, and encircled energy of 16 arcsec for 75% and 32 arcsec at 90%, the diffraction disk is now 17.3 arcsec and the Strehl is 0.98%. MUCH improved. The size of Saturn's disk these days is about 19 arcsec. (I used a wavelength of .55um for the Airy calculations, the aberration and wavefronts were at the lens' design wavelength of .587 um.) The punchline here is that the binocular, as well as the eye will perform very poorly "wide open" and the light from one of these planets won't make the eye "stop down". In addition,irradiation and glare from a bright nearly point image will further hide the real shape of the object. I propose the following observational experiment: Use the 7X or 8X glasses stopped down to a 2mm exit pupil and see what happens, and try with a little 6X15 (2.5mm exit pupil). The observations. Saturday,Oct 10/98, ~6:00 or so UT (Midnight, local) I made the following observations of Jupiter and Saturn. The instrument was a 7X35 monocular, made from a very tired 7X35 widefield bino. I don't remember the make (I misplaced the backplate with the name on it) It has an 11 deg. field and fully coated optics. I stopped the objective to about 14mm (2mm exit pupil) and braced it against a solid support. The disk and moons of Jupiter were unmistakable (I even imagined I could detect the major equatorial belts). Saturn did appear elongated, I wasn't sure if I could detect the space between the ball and ring or the ball bulging from the ellipse of the ring. This was difficult. Again referring to the apparent sizes of these objects as pictured, this difficulty comes as no surprise. The diffraction disk, at this aperture, is comparable with Saturn's disk and I'm sure helped wash out this finer detail. I then stopped it down to about 10mm. The result seemed to be about the same. At 10mm the resolution should be noticeably poorer due to diffraction. (NOV.. 5, ~3:00 UT) I stopped the Zeiss 8X30s to about 15mm (1.9mm exit pupil) and took a look at Jupiter and Saturn with them tripod mounted. Jupiter's disk was apparent and Saturn appeared elongated, but without much more than looking like a short line or possibly a tiny ellipse. As a control I set up my 60mm refractor at 32X to be sure the seeing was good enough for this test. It sure as hell ought to be for a 15mm aperture, but this is Denver. I stopped the 60mm to 15mm. Saturn still sort of showed the space between the ball and the ring, but it was easy to imagine I was seeing three disks in a line. 15mm @ 32X isn't much different than Galileo's telescope. Stopping to 10mm, still at 32X, Saturn looked like an ellipse with a bright central bulge, or a fuzzball with short wings. Clouds finished that and I switched to Jupiter. The disk was obvious, but no detail was seen at 10mm, at 15mm I imagined a dark equatorial belt. At full aperture the North and South Equatorial Belts were apparent. I doubt I really saw anything at the 15mm aperture. At the Astronomy Day open house I looked at Saturn through a friend's Canon 15X42 image stabilized binos. The rings were obvious even hand held, however releasing the stabilize button rendered them useless, hand held. That feature really worked, and with a 2.8mm exit pupil, the eye aberrations were not too bad. (Nov. 22, 7:00 U.T.) I again set up the 60mm refractor, this time using the 15mm and 10mm apertures at 16X and 20X. The appearence of Saturn was as the earlier observation. I then mounted, in turn, the 6X15, 7X35 monocular and the 8X30 Zeiss. With the 6X15s (2.5mm exit pupil) Saturn appeared as a short line, and did appear non stellar. Jupiter's disk was apparent, noticeably larger than the image of a star. With the 7X35, stopped to 15mm, the planet's appearence was the same as before, and with the 8X30, again stopped to 15mm the planets were maybe a bit more obvious. With the 8X30s at full aperture, there was considerable flare and although I now knew what to look for and what to expect, I'd have to say that Saturn didn't look like Saturn. The flare and irregularity of the image brought about by glare and eye aberrations masked the already difficult image. I could probably convince myself thar Jupiter was nonstellar, but again the brightness and glare probably masked the real disk. The conclusions from all of this is that, yes, one should be able to tell the shape of Saturn and Jupiter with magnifications in the range of 6X to 8X but it isn't easy. One must be careful to maximize the performance of the binocular and mitigate the brightness of the image with aperture stops which give a 2mm exit pupil, and reduce the glare. I would say that the rings of Saturn probably will not be apparent to a casual observer, but if the above precautions are taken the planet will show its shape. As the inclination of the rings increase over coming years they should become easier to detect. It helps to know what to look for and what to expect at these low magnifications. How often have we not been able to see a faint star or something in a small telescope until it is shown to us in a larger instrument. Then it becomes visible and we can't understand not having seen it before. FJE ========== > "In addition, irradiation and glare from a bright nearly point image will > further hide the real shape of the object." > This does make sense.....an image that is almost a point. But I think you > meant nearby point image, like a bright double star. ??? No, the thought here is that the glare, or more properly angular extent of blurring due to glare will be large compared to the angular size of the real image, and therefore obscure the real image. One reason why the 15X binos showed the rings of Saturn was, although the eye aberrations and such were worse at the 2.8mm pupil than at 2mm, the image was larger by virtue of the 15X and more than compensated for the poorer performance of the eye. Your point is also true. If a double star, say is 1 arc minute and we magnify it 5X it will look as if it is 5 arc minute of separation. If glare produces a 10 arc minute blur, we won't see the double star. If we now magnify it 20X with the same glare problem as before. the apparent separation is now larger than the blur, and the double is now easily seen, assuming this glare is produced after the magnification, as it would be in the observer's eye. If it is due to a crummy objective, then the blur will be magnified in proportion, and increasing it won't help. Reality is somewhere between, a certain amount of blurring by the eye and a certain amount by the telescope. The same sort of thing works for detecting the shape and/or size of an image. FJE ====================== 18 Nov 1998 I got a response from D. Buchroeder alerting me to a plethora of papers, in the Sept. JOSA-A, on the eye's optical performance. I looked over some of the papers, and was amazed at how well and how poorly the eye works. Well, in that at a 2mm pupil it seems we are equipped with 1/10th wave optics. Poorly in that the wavefront falls to about 1 wave at 4.5mm aperture and to almost 3 waves at 5.5mm! Really bad compared to the 30mm bino objective I analyzed earlier. Small wonder that stopping things to a 2mm pupil helps as much it does This last comment was from the paper by Thomas O. Salmon, Larry N. Thibos & Arthur Bradley "Comparison of the eye's wave-front aberration measured psychophysically and with the Shack-Hartmann wavefront sensor" in the aforementioned JOSA-A. My estimate of .77 waves with the bino lens was at a focus setting to minimize the wave aberration. At the paraxial focus of the bino lens, the optical path difference (OPD) is 3.2 waves P-V. add that to the eye's approximate .5 wave at the 3.75 pupil diameter, (8X), and no small wonder things look terrible! With a lower magnification, larger exit pupils, thing get even worse rather rapidly. Also, with the 30mm objective, at its paraxial focus, field curvature and astigmatism gives a P-V wavefront error in the vicinity of 20 waves at the edge of a 8-deg. full field, that of my 8X30! Makes one wonder how one can see anything at all with these things! FJE =========================================================== 3. Steadying binoculars: low tech, low budget, light weight methods to give a steady view. ------------------ http://www.deja.com/ Telescope Buyers FAQ Date: 29 Aug 1999 00:00:00 GMT 10.1. How Do I Hold Binoculars? This section was written by Jay Freeman. For most people, there is a better position. Imagine that you are holding the binocular to your eyes, with your hands positioned as just described. Now, slide your hands along the body of the instrument,toward your face, until only your pinky and ring fingers are curled around the back end of the binocular body. In this position, the binocular feels a little nose- heavy, because you are supporting it behind its center of gravity. Now curl each thumb up as if you were making a fist, and flex your hands so that the second bone in from the tip of your thumbs are pressed up against your cheekbones (counting the bone in the part of your thumb where the thumbnail is, as the first bone). This makes a quite solid structural connection between the body of the binocular, through your hands and thumbs, to your face, and markedly improves how steadily you can hold the instrument. Similarly, curl the first and middle fingers of each hand around the corresponding binocular eyepiece, to provide a little more structural connection (and perhaps also some protection from stray light). In this position, your hands are not far from where they would be if you brought them to your face to block out stray reflections while peering through a store window at night. For most people, this position leads to markedly steadier viewing, but if the binocular is especially long and heavy (say, a 10x70 or an 11x80), the out-of-balance position can be quite tiring. In that case, move *one* hand out to the objective end of its side of the binocular, so that you are supporting the instrument on opposite sides of its center of gravity, but with some structural connection between it and your face; namely, the other hand. When the hand way out there gets tired-just switch hands. ------------------------- From: Peter Abrahams Directions for holding binoculars, bracing the fingers against the forehead above the eyes. Grasp your binoculars at the eyepiece and the prism housing near the eyepiece, using the 'pinky', ring finger, and middle finger. Depending on the size of the binocular, 2 or 3 of these fingers will be grasping the prism housing, with the thumb on the underside of the prism housing, and the middle finger can grasp the eyepieces or the housing. Use your first finger to press against your forehead, just above your eyebrows. This finger can sometimes be used to grasp the eyepiece. Don't use a fatiguing iron man exertion, just use enough pressure to steady things. Squeeze the four fingers against each other. This uses hand muscles that can hold a grip for long periods of time. Use only as much force as needed, to minimize fatigue, and take breaks. This makes your head, hand, and binocular into a mechanical unit. Heavy binoculars will be out of balance with this grip. One solution is to lay back on a reclining lawn chair, pointing the binoculars more vertically. This will cause the weight of the binoculars to pass to the first fingers and your forehead. This is how I hold Fuji 16 x 70s, typical 80mm glasses, and even Orion 100mm binoculars, and I can effectively use them for some minutes before needing a break. But I can't hold them horizontally with this grip. As mentioned, you can also place one hand under the objective, to support the weight. This grip makes the binoculars much more steady. But there is still a noticeable difference in image shake between 7 power and 10 power binoculars. To me, for birding etc. I like 10x, to give me a larger bird. For astronomy, I much prefer 6 to 8x, for the steadier images; and because there are few objects in the sky of the size that will fill a 10x field, about 5 to 6 degrees. Image size is always balanced against field size, and views of the sky just don't seem to improve when increasing magnification over this range. The 'rifle sling' method is another steadying trick that involves running the strap under your elbows. This one is really tough to describe. Extend the strap to its longest length. Poke your elbows through the loop from the inside, so the strap runs under your arms. The strap runs around your neck, over your tricep, under your upper arm, to the binocular. Press your elbows down, against your sides or until your arms press against your sides. Strap length should be adjusted until it is just long enough to do this. It is fairly awkward, but not as strange as when you poke your elbows through the loop from the outside, another variation. These methods arrange things so the strap running from the binoculars is a short length that is under tension, and the binoculars, strap, arms, and body are sort of mechanically linked.....a tensegrity?? They do work, but I've never heard of anyone actually using them much. --Peter ========================= see also: http://www.lightandmatter.com/binosky/binosky.html http://www.cs2e.com/ http://freespace.virgin.net/m.poxon/tableofc.htm 12 Jan 2000 home page: http://www.europa.com/~telscope/binotele.htm