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John K
scholastic sledgehammer
Reged: 12/26/05
Posts: 797
Loc: Vernon BC Canada
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I was just playing around with a image of M13 and decided with the help of Wins stars 2 to simulate eyepiece fields of view.anyhow here you are just for fun.The scope in question is a 15 f5 dob FL 1900.The magnification vary s from 146X to 172X. 
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RASC Member (Okanagan)
Home built 15"F5 Obsession clone
Bushnell 76mm Modified Dob (Little Richie)
Celestron Skymaster 15x70
Howie Glatter laser pointer/Blug
Astronomik filters OIII UHC
Televue Eyepieces 31mmNagler,32mmPL,15mmPL,13mm Ethos,11mm PL,2X Barlow
10mm Speers Waler
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JSeay86
super member
Reged: 04/26/09
Posts: 129
Loc: Norman, OK
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That's a very nice figure. I very much like the way my 13 T6 frames M13, but the Ethos looks very appealing... Now if I could just win the lottery.
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Jared
Orion XX12 Dob
Ten Acre Observatory
Edited by JSeay86 (10/08/09 02:18 AM)
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kaaikop
scholastic sledgehammer
Reged: 07/13/08
Posts: 764
Loc: North of the Montreal nebula
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Nice work! 
From a RASCal to another 
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Benoit, RASC Montreal
-C9.25 on EQ6 Pro - C6/ED80 on Portamount
-TV Plossls, Radians, Nags, Pans, UO Orthos.
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Arizona-Ken
sage
Reged: 08/31/08
Posts: 304
Loc: Scottsdale, Arizona
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Nice job, but you could also add a 68-70 degree AFOV (Sieberts, Hyperions on the budget end, Pans on the high end).
Arizona Ken
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"Considered as a collector of rare and precious things, the amateur astronomer has a great advantage over amateurs in other fields ... the amateur astronomer has access at all times to the original objects of his study; the masterworks of the heavens belong to him as much as to the great observatories of the world. And there is no privilege like that of being allowed to stand in the presence of the original."
--Robert Burnham Jr, Burnham's Celestial Handbook
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ibase
Carpal Tunnel
Reged: 03/20/08
Posts: 1527
Loc: Manila, Philippines 121*E 14*N
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Great!  Thanks for posting.
Best,
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Hernando
Nexstar 8/CG-5 ASGT; WO Megrez 102ED SV
Antares 6" 1529;WO ZS66SD;Orion ST80
WO:2"Dielectric,Binoviewer 8to32mm's,SCT Crayford 2-spd
Hyperion 8-24mm Zoom,21mm; WO 7.5-22.5mm
TV Naglers 5T6, 9T1, 12T2; Panoptic27
BO/TMB 2.5/3.2/4/6mm;UO HD 5;BGO 6;Meade-RGO 7;UO-V 9/12.5
Brandon 16mm;Ultima18;TV 2x,3x barlow&8/11/15/20/32plossl
Aspheric31;Siebert36-OB;Paragon40;Meade56Smoothie
C-f/6.3FR;OIII,UHC,SkyGlow,U-block,8" S-flter
GLP/Telrad/MRF/9x50RACI
NexImge;Canon RebelXS
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hfjacinto
Almost got me
Reged: 01/12/09
Posts: 2068
Loc: Union,NJ
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John,
That is very nice but it isn't reality, the FOV in the Radian is generally what the eye can see. The other 82 and 100 degree views entail you looking up and down to see the whole view. A more correct representation would be the M13 in the center and the stars up a circular wall (like a cup), they are visible yes, but only when you look for them.
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C9.25 ASGT 9*50 MM Finder,FT Focuser & 2" Diagonal
Meade LXD 75 6 Inch SNT w 9*50 MM Finder
5,6,9,14.5 MM Zhummel Planetary EPs
13,17,21,24,31,36 MM Baader Hyperion
6.7,8.8 MM Meade UWA & 11 MM Nagler T6
Planetary, OIII and Narrowband Filters
Thousand Oaks Dew Control w Kendrick Heaters
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Darenwh
Pooh-Bah
Reged: 05/11/06
Posts: 1219
Loc: Covington, GA
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Quote:
That is very nice but it isn't reality, the Radian is generally what the eye can see. The other 82 and 100 degree views entail you looking up and down to see the whole view. A more correct representation would be the M13 in the center and the stars up a circular wall (like a cup), they are visible yes, but only when you look for them.
It is possible to see the whole field of view with 82 degree and 100 degree eyepieces. Not everybody has to 'look around' to see the whole field once they get used to the larger AFOV eyepieces.
Your statement would indicate that when you walk outside and look around without a telescope that you are only able to see a 60 degree field of view. This is simply not true. The eye is able to see a larger field of view than 60 degrees.
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Daren
Covington, GA
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BillP
Post Laureate
Reged: 11/26/06
Posts: 3922
Loc: Vienna, VA
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Great job! What this tells me though is that I really need to get a 15" Dob!!!!
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Bill Paolini
XT10i Dob---TSA-102 S-APO---APM80/480 S-APO--- P.S.T.
TMB Supermonos---Meade UWAs---TV Panoptic---AT Titan II ED
To your own eyes be true...
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hfjacinto
Almost got me
Reged: 01/12/09
Posts: 2068
Loc: Union,NJ
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Daren,
I am not an optician, but your statement is incorrect. If I look straight ahead the FOV is limited to between 50 and 60 degree. That is generally the most the eye can see. Everything else is peripheral. If you want to see more than the 50-60 degrees you must:
1) Move your eye
2) Move your head
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C9.25 ASGT 9*50 MM Finder,FT Focuser & 2" Diagonal
Meade LXD 75 6 Inch SNT w 9*50 MM Finder
5,6,9,14.5 MM Zhummel Planetary EPs
13,17,21,24,31,36 MM Baader Hyperion
6.7,8.8 MM Meade UWA & 11 MM Nagler T6
Planetary, OIII and Narrowband Filters
Thousand Oaks Dew Control w Kendrick Heaters
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Darenwh
Pooh-Bah
Reged: 05/11/06
Posts: 1219
Loc: Covington, GA
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So have you ever used peripheral vision while using your telescope? I use it quite often when trying to see faint details and very faint objects. Seems to work well for that...
Peripheral vision: Side vision. The ability to see objects and movement outside of the direct line of vision. Peripheral vision is the work of the rods, nerve cells located largely outside the macula of the retina. The rods are also responsible for night vision and low-light vision but are insensitive to color. As opposed to foveal (central) vision.
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Daren
Covington, GA
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hfjacinto
Almost got me
Reged: 01/12/09
Posts: 2068
Loc: Union,NJ
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Daren,
You and I are saying the same thing. I agree your eye can see more than 60* (it is just peripheral vision). What I am also saying is that Peripheral vision is just that, it is peripheral, you can see it, but it does not look like the pictures above. M13 looks pretty much the same in each eyepiece, once you pass the 60* mark the stars are not directly in front of your eye, they kind of move up to the side. Can you see them, yes, but they are peripheral to the center of view. I personally don't like it. The pictures while "correct" are not correct in the way the view looks to your eye.
While I am typing this, do I notice that a door is on my left and a fax machine is on my right, can I tell you what each looks like yes, can I focus in on the fax machine and tell you the colors of the keys, no it is too far to the right to allow me to focus. The screen is what I am looking at, that is the clearest part of my vision.
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C9.25 ASGT 9*50 MM Finder,FT Focuser & 2" Diagonal
Meade LXD 75 6 Inch SNT w 9*50 MM Finder
5,6,9,14.5 MM Zhummel Planetary EPs
13,17,21,24,31,36 MM Baader Hyperion
6.7,8.8 MM Meade UWA & 11 MM Nagler T6
Planetary, OIII and Narrowband Filters
Thousand Oaks Dew Control w Kendrick Heaters
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gnowellsct
professor emeritus
Reged: 06/24/09
Posts: 729
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Quote:
Quote:
That is very nice but it isn't reality, the Radian is generally what the eye can see. The other 82 and 100 degree views entail you looking up and down to see the whole view. A more correct representation would be the M13 in the center and the stars up a circular wall (like a cup), they are visible yes, but only when you look for them.
It is possible to see the whole field of view with 82 degree and 100 degree eyepieces. Not everybody has to 'look around' to see the whole field once they get used to the larger AFOV eyepieces.
Your statement would indicate that when you walk outside and look around without a telescope that you are only able to see a 60 degree field of view. This is simply not true. The eye is able to see a larger field of view than 60 degrees.
You're not talking about the same thing. All you have to do is look a screen full of print. Concentrate on one word. Now how many of those words can you actually read at once? Only four or five, I'll warrant. Yet you do have a much larger field of view at the same time.
When you're staring at a screen full of words and see that you can only read (without moving the eye) a few words at a time, we're getting into some kind of zone, it's not that everything else is true peripheral vision, but there is a high intensity zone, and then a lesser intensity zone. It may be that when looking at the center of an eyepiece fov you can detect (without much detail, the way you are conscious of other words on the screen but can't read them without redirecting the eye) other objects in the fov, and that is useful, because as you train yourself at a telescope you can develop a sense of what kinds of peripheral signals might bear further scrutiny. But on the other hand it is also true that "taking in the full field" has different senses. If you are looking dead center at an Ethos you will *not* be getting as much detail from objects near the edge, even half way to the edge, as you will when looking directly at them and recentering your gaze.
So both positions are correct: you can see the whole field, the way I am conscious there is a couch and chair in the corners of my fov as I write this. But I also can't "see" couch or chair in any detail, in the sense that the other post was raising; they are just shapes. If I look directly at them I seen grain in the chair, stitching on the couch, etc.
I've tried to test how much of my fov is actually usable. I have done it on computer screens and by staring at brick walls to see how much of the wall I actually resolved in high detail. My intent has been to see how that "I can read the word at the center" zone applies in other situations. And in fact if one is looking at minute details in the brick the same zone is apparent. My best guess is that it is a few arc minutes at most. This means that our area of focused concentration could be accommodated in a super mono.
That being the case, whether one wants 100 degrees or 70 is some kind of aesthetic decision. I prefer XWs because of my sense of "a complete field directly in front of me" even though within the terms I have set above I *still* have to "look around" to get everything there is to see. So the way I think of it, I have to look around a 70 degree field, and look around even more in a 100 degree field.
Of course, often lost in these considerations is that the same field is accessible in a 70 degree eyepiece at lower magnifications. The Ethos 13 offers the same fov as a Nagler 17T4 (82 degrees) and an XW20 (70 degrees). If I'm gong to boost my magnification to get the fainter stars etc. I'm not sure, personally, taht I want 100 degrees of that; I'm happy with the same field at 20mm, and don't mind losing some field at 13 or 14mm.
But that's just me. Obviously the Ethoi have a lot of delighted users. And there are other ways that this matters. For example I can only see a few words at time on a computer screen, but I like a wide screen. I'm not sure that I need a super-wide screen, or that I even want one. But it's a similar idea.
Greg N
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"Aperture will get you through times of no money better than money will get you through times of no aperture."
featuring selected astrojunk:
bunch o' widefield eyepieces
bunch o' narrowfield eyepieces
couple o' Barlows
couple o' scopes
couple o' mounts
couple o' tripods
and a pier 'n' stuff
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2925
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Quote:
John,
That is very nice but it isn't reality, the FOV in the Radian is generally what the eye can see. The other 82 and 100 degree views entail you looking up and down to see the whole view. A more correct representation would be the M13 in the center and the stars up a circular wall (like a cup), they are visible yes, but only when you look for them.
This is so right! Last night I was trying to split a very close double that was very dim at the magnifications I was using. The field was so dark I could hardly see the field stop. When you are really concentrating on one object rather than just going "ooh!" then the field of view is irrelevant - you want your eye to be as relaxed as possible and to have the best light transmission.
And your statement about the "cup" effect is often overlooked - you don't see what this diagram suggests - it's like looking at a plate vs a shallow saucer vs a soup bowl vs a mixing bowl.
-drl
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BillP
Post Laureate
Reged: 11/26/06
Posts: 3922
Loc: Vienna, VA
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Quote:
I am not an optician, but your statement is incorrect. If I look straight ahead the FOV is limited to between 50 and 60 degree. That is generally the most the eye can see. Everything else is peripheral. If you want to see more than the 50-60 degrees you must:
1) Move your eye
2) Move your head
I'm no optician either, but by medical definition direct vision of the human eye is only the central 13 degrees of the FOV. Everything outside of the 13 degree mark is handled by peripheral vision which is vision outside the macula (i.e., center) of the retina. Peripheral vision for a single unobstructed eye (i.e., no nose in the way) is between 140-150 degrees (so even the Ethos is not exploiting what we are capable of). You should be able to see the peripheral area without moving your eye or head, it will be much less distinct though then the direct vision of the macula in that central 13 degree area.
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Bill Paolini
XT10i Dob---TSA-102 S-APO---APM80/480 S-APO--- P.S.T.
TMB Supermonos---Meade UWAs---TV Panoptic---AT Titan II ED
To your own eyes be true...
Edited by BillP (10/08/09 11:32 AM)
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2925
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I like to think of it in terms of sitting in a movie theater. People who are comfortable with ultrawides probably prefer sitting up close. A 100 degree FOV amounts to sitting in the first three rows! I prefer to be able to see the edges of the screen as clear black lines while concentrating on the center. It really is the identical problem, without the complication of a finnicky exit pupil.
-drl
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Plan9
sage
Reged: 01/28/08
Posts: 309
Loc: Northern VA
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Just felt an overwhelming desire to jump into this discussion. I've actually done a bit of work in the area of human vision; Bill and Greg are getting pretty close on this. Going somewhat from memory, your actual best vision (resolution and color) is in a small region (the fovea) on the order of a degree or two! Around that, you have a few more degrees (parafovea) where you have improved light sensitivity, but reduced color vision (more rods, fewer cones - this is what brings about the effectiveness of averted vision). Beyond that, your vision degrades quickly in terms of color and acuity (resolution), so peripheral vision is more a matter of awareness of surroundings and sensitivity to motion (e.g., so you don't crash into things as you walk). I think Bill P's number for field of view are about right, but fundamentally, you have to move your eye around to really see any detail. Your eye is capable of moving on the order of about 45 degrees off-axis, so you can really see clearly over a zone of about 90 degrees - but only by moving your eye around. Beyond that, you have to swivel your head.
The amazing part is that the human visual system is geared to doing this all the time, without much awareness on your part. Even if you stare at one spot, microtremors and microsaccades are jiggling around your visual field so it's really impossible to keep 100% steady (and you you would actually stop seeing anything if you could - cells in your retina adapt-out light levels that don't change). Normally, your eye is making saccadic movements to scan out a scene and give you the impression you're seeing everything in high resolution. My impression is that people doing astronomy have learned some additional control (using averted vision), and perhaps are more aware of how far they're having to move their eyes.
An interesting, though disconcerting, thing to try is to look at the sky and fixate hard on a single star (no telescope). If you can really suppress your desire/reflex to move, you'll find after a few seconds that the visual field starts to gray-out at the edges and virtually everything outside of the center just disappears. I suspect this is because visual acuity away from the fovea is too low for involuntary eye movements to maintain the image, but I don't know for a fact.
Now, what this has to do with eyepieces - most people can probably take in the view of a 100 deg eyepiece, but to really see detail, your eye needs to swivel over more than its comfortable 90 deg range - I suspect that individual variation might play a role here (some have a wider range, others narrower). To really cover the field, you have to move your head.
Interesting topic.
Bill W
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Celestron 6SE
Celestron Onyx 80 EDF
Vixen Porta Mount
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Mike Hosea
Post Laureate
Reged: 09/24/03
Posts: 3924
Loc: "Metrowest" Boston
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Quote:
So both positions are correct
Yes and no. This comes up from time to time. For the position that "seeing" is "detected in the visual field" rather than "resolved", we have an objective standard. Your eye doctor will apply it when he measures your visual field. For the position that "seeing" is somehow "resolving" to a certain degree, we have only hand-waving and subjectivity about where to draw the line. The quoted 60 degrees is arbitrary, 70 degrees is arbitrary, 30 degrees is arbitrary. It's just dealer's choice. Greg mentioned "seeing" words, as in being able to read them. This is an excellent example, but notice that this extends only over a few degrees. Now wouldn't it be silly if somebody tried to use that as the definition of "seeing" for the purposes of selecting eyepiece AFoV? TMB Supermonos are as wide as anybody should ever need because well over half your acuity is lost before the AFoV even reaches 20 degrees.
Speaking of which, there's a nice graph depicting acuity by field angle here . Notice that there's no obvious place to draw the line on "seeing" and "detecting". It simply depends on how much acuity you require for your definition of "seeing".
Coming back to the original subject here, you may not have a big enough computer monitor to simulate a 100 degree AFoV with a circular image and still be able to focus on it (it will tend to be rather close to your eye unless the image is fairly large). The easiest way to get a gist of it is to select a fixed viewing distance from the monitor and display a large astronomical image that has been cropped to have a calculated width. The relationship is simply
viewing_distance * 2 * tan(AFoV*pi/360) = image_width
where I'm assuming the tan function accepts its input in radians. If you use a calculator in degree mode, just replace "*pi/360" with "/2".
Obviously the image will be rectangular, so use your imagination, or if you're savvy, crop it to a circular image. Doesn't really matter if it's clipped on the top and bottom.
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Mike
Stuff that I use:
- 7" f/6.7 home-built Newt, eq platform, Pentax 40XW and 5XO, Tele Vue 13E and 2x Barlow, ZAO-II 6mm
- 120mm f/8.3 home-built grab-n-go Newt with 7-21mm Nikon Zoom
- Canon 15x50 IS and Eagle Optics 12x50 Ranger binoculars
Edited by Mike Hosea (10/08/09 01:30 PM)
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hfjacinto
Almost got me
Reged: 01/12/09
Posts: 2068
Loc: Union,NJ
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I have to say I learned a lot.
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C9.25 ASGT 9*50 MM Finder,FT Focuser & 2" Diagonal
Meade LXD 75 6 Inch SNT w 9*50 MM Finder
5,6,9,14.5 MM Zhummel Planetary EPs
13,17,21,24,31,36 MM Baader Hyperion
6.7,8.8 MM Meade UWA & 11 MM Nagler T6
Planetary, OIII and Narrowband Filters
Thousand Oaks Dew Control w Kendrick Heaters
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Jim Curry
sage
Reged: 10/29/07
Posts: 431
Loc: Maine
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>I'm no optician either, but by medical definition direct vision of the human eye is only the central 13 degrees of the FOV. Everything outside of the 13 degree mark is handled by peripheral vision which is vision outside the macula (i.e., center) of the retina<
And that's why I've migrated to 40-45 deg. Abbe's for most observing except when trying to capture open clusters or other large fov objects. More and more the ethoi sit unused. The 31n makes for a great finder ep.
Jim
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Vixen 140 refractor
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2925
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Quote:
viewing_distance * tan(AFoV*pi/360) = image_width
This is missing some factors of 2 but it doesn't directly apply in any case - we're talking about solid angles on the celestial sphere whose diameters are measured in angles (the apparent field of view). These solid angles are perceived as flat apertures (disks) up to about 60 degrees - perhaps more - after that the brain registers the field of view as a solid angle in space rather than an aperture in a plane, with more and more sensory dissonance as the field gets wider because the field stop is not directly perceived. With an extreme wide field one has the confusing situation of an arcuate field populated by magnified objects which may be moving - this goes completely against how we expect objects in the distance in a wide field of vision to behave. The "wow" factor people often get is actually the visual system reeling under contradictory information. The more aware you become of it, the less "wow" and the more "ugh" you experience. I find that I cannot even look though an Ethos without being dizzy and 80 degrees is a stretch that I usually won't go if there is any work involved in holding the head steady.
-drl
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Mike Hosea
Post Laureate
Reged: 09/24/03
Posts: 3924
Loc: "Metrowest" Boston
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Yep, I saw that and put the factor of 2 back in there as you were writing. I had the factor of two inside the tan() already (using 360 instead of 180). It was lunch time, you see, so I hit send and then dashed off to lunch without checking it. Came back after lunch and saw the error immediately.
Well, simulation is simulation, never perfect. There is always something wrong. The little circles from a distance are flat, the angles are actually all small, and the eye resolves them, edge-to-edge, too well. Not a great simulation. So, how do we improve it? I was just fixing the over-resolution problem and the small angle problem to some extent, but there's always a next step. We could forget about the computer monitors and print a large astro photo, curving the surface to keep the distance to the eye about the same. Next we could print it on the inside of a sphere. Somewhere along the line it just gets a lot easier to try the eyepieces than to rig the simulation. I'll admit that I think it's slightly more pleasant to pan around with a smaller apparent field of view, say 60-65 degrees, for the reason you describe, but I don't think it's a question of having a more "advanced" reaction because of knowledge or awareness. I also don't think it's that big of a deal, but I respect that it's a big deal to you, hence, by probable extension, to some other folks as well.
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Mike
Stuff that I use:
- 7" f/6.7 home-built Newt, eq platform, Pentax 40XW and 5XO, Tele Vue 13E and 2x Barlow, ZAO-II 6mm
- 120mm f/8.3 home-built grab-n-go Newt with 7-21mm Nikon Zoom
- Canon 15x50 IS and Eagle Optics 12x50 Ranger binoculars
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turtle86
professor emeritus
Reged: 10/09/06
Posts: 656
Loc: Red Sox Nation
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Great work and thanks for posting. It is interesting that going even from 82 to 100 degrees makes a very significant difference. There was a similar simulation by Televue when the Ethos first came out but I like yours better.
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turtle86
professor emeritus
Reged: 10/09/06
Posts: 656
Loc: Red Sox Nation
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Ultimately, this strikes me as the "short answer." The limit to the area the human eye can resolve at a high level is going to be much less than the 70, 82, or 100 degrees offered by Pentax or Televue EP's. The question then becomes how much "context" we want around the object being observed. (OTOH, for very large objects like the Veil or Andromeda, it would seem that even 100 degrees isn't really enough!) I myself tend to prefer 100 degrees, because then for me the EP seems to disappear and the view takes on that proverbial (cliched?) "spacewalk" aspect. Sure, I have to move my eye around a bit to take it all in, but I like it. At the same time, I can fully understand why others might not. We are very fortunate indeed to have so many wonderful choices today.
Quote:
That being the case, whether one wants 100 degrees or 70 is some kind of aesthetic decision.
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PJF
professor emeritus
Reged: 05/06/04
Posts: 667
Loc: UK
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Quote:
The magnification vary s from 146X to 172X.
This doesn't seem to be represented in your image, which is surely essential for such a comparison. The object (M13 and surrounds) is the same size in each of the four views, which means the AFOVs are not to scale.
Full disclosure: I'm having a few days off and my appreciation of the facts is filtered through beer.
Ooh, and I must press this button again:
The 13mm Nagler is not an 82mm AFOV eyepiece; it's somewhere between 78 and 79 degrees if memory serves. The 12mm Nagler offers more magnification and more TFOV - truly, er, majestic! 
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Peter
10x50 binocs
ED80 'frac
6" f/12 Maksutov
6" f/6 Newtonian alt/az
10" f/4.3 Newtonian alt/az
Bryce
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turtle86
professor emeritus
Reged: 10/09/06
Posts: 656
Loc: Red Sox Nation
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Facts are often best filtered through fine beer or single malt scotch...
Quote:
Full disclosure: I'm having a few days off and my appreciation of the facts is filtered through beer.
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John K
scholastic sledgehammer
Reged: 12/26/05
Posts: 797
Loc: Vernon BC Canada
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Well here is an exercise we can all try.I would like to here you views after this one.
Take a toilet paper roll and walk out side.Look through the paper roll at a subject and then without it.Witch is a more pleasing view to your brain.You are still focusing on the same part of the subject but the extra unfocused and irrelevant information,is to me much more pleasing.I think we are using the info that our brain receives weather we think we need it or not.
But that's just my view.
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RASC Member (Okanagan)
Home built 15"F5 Obsession clone
Bushnell 76mm Modified Dob (Little Richie)
Celestron Skymaster 15x70
Howie Glatter laser pointer/Blug
Astronomik filters OIII UHC
Televue Eyepieces 31mmNagler,32mmPL,15mmPL,13mm Ethos,11mm PL,2X Barlow
10mm Speers Waler
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scoping
super member
Reged: 01/05/09
Posts: 150
Loc: Jacksonville,Fl
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Here is easiest way for me to get the sensation of the Ethos, Nagler and other eyepiece fields without using my telescope.
Go outside look at the sky and close one eye. Presto Ethos field. Now form a circle using your middle finger and thumb. Hold this circle to your eye, can you say Nagler. Now use your index finger. Maybe a Radian? Find a paper towel tube and you have a Plossl field.
This is by no means scientific and individuals with short fingers may not be able to reach the Ethos line.
Mark Kaupas
20"F5
13 Ethos
22 Nagler sold
21 Ethos ordered
31 Nagler
2x Barlow
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2925
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This is harmless in itself but utterly false and misleading. A Plossl is about like a fist held at your nose tip.
DRL
No Ethoses
No Naglers
No Radians
No Panoptics
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8271
Loc: Beatrice, Nebraska
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Quote:
Here is easiest way for me to get the sensation of the Ethos, Nagler and other eyepiece fields without using my telescope.
Go outside look at the sky and close one eye. Presto Ethos field. Now form a circle using your middle finger and thumb. Hold this circle to your eye, can you say Nagler. Now use your index finger. Maybe a Radian? Find a paper towel tube and you have a Plossl field.
This is by no means scientific and individuals with short fingers may not be able to reach the Ethos line.
Mark Kaupas
20"F5
13 Ethos
22 Nagler sold
21 Ethos ordered
31 Nagler
2x Barlow
Subject: 10 inch diameter large dinner plate held with the center directly in front of your eye:
100 degrees (Ethos): dinner plate at distance of 4.2 inches from your eye.
82 degrees (Nagler): dinner plate at distance of 5.75 inches from your eye.
68 degrees (Panoptic): dinner plate at distance of 7.4 inches from your eye.
50 degrees (Plossl): dinner plate at distance of 10.7 inches from your eye.
toilet paper tube 4.25" x 1.75": approx 23 degree true field of view (a little less than a bad HM or Ramsden eyepiece).
Personal Eyepieces: No Ethos (but have used two plus one other 100 degree eyepiece)
No Naglers (but have an 82 degree Nagler-like Meade 14mm Ultrawide, and two variable Speers Walers (81.4 deg. and 76.4 degree AFOV)).
A 24mm Panoptic
30mm, 15mm, and 10mm Ultrascopics, two 25mm Plossls (in binoviewer), 20mm and 10mm Plossls, a 6.4mm Meade "SuperPlossl", and one old but loved 6mm Brandon Orthoscopic.
Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org
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Peter9
scholastic sledgehammer
Reged: 10/30/08
Posts: 799
Loc: Yorkshire - Born & Bred
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Where did you learn all this technical stuff. 
Peter.
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Some of the pleasure I get from life I owe to Astronomy.
Astronomy does not owe me a thing.
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Nexstar 8se
150mm Helios Newton Reflector EQ 3 G.E.M.
6.3mm 10mm Plossls. Celestron 25mm & 40mm E.Ps. 8mm x 24mm Baader Hyperion Zoom. 2x Barlow. 9x50 R.A.C.I Finderscope. G.L.P and Bracket. Dew Shield. Home made Solar filter. Home made H.C Holder.(Great Asset). Maplin's 12V 17ah Auto Start Unit.
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hfjacinto
Almost got me
Reged: 01/12/09
Posts: 2068
Loc: Union,NJ
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The toilet paper roll just doesn't work. I agree with David. And I still stand by my first post a flat depiction in no way shows what the EP shows. I have looked through 100* FOV eps and the view is not as above, M13 looks like M13 and stars are on the side.
I have my personal EP's also listed.
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C9.25 ASGT 9*50 MM Finder,FT Focuser & 2" Diagonal
Meade LXD 75 6 Inch SNT w 9*50 MM Finder
5,6,9,14.5 MM Zhummel Planetary EPs
13,17,21,24,31,36 MM Baader Hyperion
6.7,8.8 MM Meade UWA & 11 MM Nagler T6
Planetary, OIII and Narrowband Filters
Thousand Oaks Dew Control w Kendrick Heaters
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scoping
super member
Reged: 01/05/09
Posts: 150
Loc: Jacksonville,Fl
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Quote:
Quote:
Here is easiest way for me to get the sensation of the Ethos, Nagler and other eyepiece fields without using my telescope.
Go outside look at the sky and close one eye. Presto Ethos field. Now form a circle using your middle finger and thumb. Hold this circle to your eye, can you say Nagler. Now use your index finger. Maybe a Radian? Find a paper towel tube and you have a Plossl field.
This is by no means scientific and individuals with short fingers may not be able to reach the Ethos line.
Mark Kaupas
20"F5
13 Ethos
22 Nagler sold
21 Ethos ordered
31 Nagler
2x Barlow
Subject: 10 inch diameter large dinner plate held with the center directly in front of your eye:
100 degrees (Ethos): dinner plate at distance of 4.2 inches from your eye.
82 degrees (Nagler): dinner plate at distance of 5.75 inches from your eye.
68 degrees (Panoptic): dinner plate at distance of 7.4 inches from your eye.
50 degrees (Plossl): dinner plate at distance of 10.7 inches from your eye.
toilet paper tube 4.25" x 1.75": approx 23 degree true field of view (a little less than a bad HM or Ramsden eyepiece).
Personal Eyepieces: No Ethos (but have used two plus one other 100 degree eyepiece)
No Naglers (but have an 82 degree Nagler-like Meade 14mm Ultrawide, and two variable Speers Walers (81.4 deg. and 76.4 degree AFOV)).
A 24mm Panoptic
30mm, 15mm, and 10mm Ultrascopics, two 25mm Plossls (in binoviewer), 20mm and 10mm Plossls, a 6.4mm Meade "SuperPlossl", and one old but loved 6mm Brandon Orthoscopic.
Clear skies to you.
Could not see any stars through the dinner plate
Might have been a large cloud.
Mark Kaupas
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helpwanted
Carpal Tunnel
Reged: 07/04/07
Posts: 2636
Loc: Phoenix, AZ
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if you can see the entire fov with a 70deg ep with direct vision, you can still see the same 70deg within the 100 deg of the Ethos with direct vision... you just have extra fov left in your peripheral vision... so the ethos give you the best of both worlds.
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2925
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Quote:
Where did you learn all this technical stuff.
Peter.
Well it all started in a biker bar outside Santa Fe New Mexico, me and this guy named Chainsaw got into an argument about eyepieces, and as I was getting ready to slug him I noticed - "hey, that's about like my 15mm Plossl..." - stupid move. When I got out of the hospital, I vowed never to argue about eyepieces with bikers again.
-drl
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ibase
Carpal Tunnel
Reged: 03/20/08
Posts: 1527
Loc: Manila, Philippines 121*E 14*N
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hmmm  all these may yet explain why most times I prefer the 70ish views of my Hyperion 8-24mm zoom to my 82Naglers. YMMV rules.
Best,
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Hernando
Nexstar 8/CG-5 ASGT; WO Megrez 102ED SV
Antares 6" 1529;WO ZS66SD;Orion ST80
WO:2"Dielectric,Binoviewer 8to32mm's,SCT Crayford 2-spd
Hyperion 8-24mm Zoom,21mm; WO 7.5-22.5mm
TV Naglers 5T6, 9T1, 12T2; Panoptic27
BO/TMB 2.5/3.2/4/6mm;UO HD 5;BGO 6;Meade-RGO 7;UO-V 9/12.5
Brandon 16mm;Ultima18;TV 2x,3x barlow&8/11/15/20/32plossl
Aspheric31;Siebert36-OB;Paragon40;Meade56Smoothie
C-f/6.3FR;OIII,UHC,SkyGlow,U-block,8" S-flter
GLP/Telrad/MRF/9x50RACI
NexImge;Canon RebelXS
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j3ffr0
sage
Reged: 07/06/08
Posts: 422
Loc: Virginia
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Nice job and thank you.
The Ethos and the Nagler sure look good. Seems to confirm my preference for 65 degree or better AFOV. I don't really notice a huge difference when switching between Naglers and Pans. However, I do feel a little constrained when switching between anything > 65 degrees down to 50 degree or lower EPs.
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10" Dob, 127mm Mak, 120mm f5 achro, PST
35, 24 Panoptic; 16, 13, 9, 3-6 Nagler
15, 10, 7.5, 5, 3.8 Ultrascopic
20, 15, 9, 6 Expanse
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John K
scholastic sledgehammer
Reged: 12/26/05
Posts: 797
Loc: Vernon BC Canada
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All my examples are just for a general reference and not to be taken literally as I don't care about exacts.I just like to observe deep space, and I know what I like to observe with.
John
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RASC Member (Okanagan)
Home built 15"F5 Obsession clone
Bushnell 76mm Modified Dob (Little Richie)
Celestron Skymaster 15x70
Howie Glatter laser pointer/Blug
Astronomik filters OIII UHC
Televue Eyepieces 31mmNagler,32mmPL,15mmPL,13mm Ethos,11mm PL,2X Barlow
10mm Speers Waler
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starrancher
professor emeritus
Reged: 06/09/09
Posts: 565
Loc: Northern Arizona
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Quote:
Well it all started in a biker bar outside Santa Fe New Mexico, me and this guy named Chainsaw got into an argument about eyepieces, and as I was getting ready to slug him I noticed - "hey, that's about like my 15mm Plossl..." - stupid move. When I got out of the hospital, I vowed never to argue about eyepieces with bikers again.
-drl
    
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LXD75 AR5
LXD75 SN8
Series 4000 Plossls
Misc. other stuff
Fort Rock , Az .
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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So why do people put picture windows on their houses?
So you can look farther to the left and farther to the right and see a bigger picture?
An Ethos eyepiece is a lot like a picture window. It doesn't upset me that I have to move my eye to concentrate on the field edge on the left or right. Why does that upset you? Do you feel you are paying for something you don't use? In practice, you use it. Does that wide field bother your sensibilities because you like to see a black edge to the field all the time and be aware of it all the time? Why do you feel that way? What's wrong with only being able to see the entire edge simultaneously by concentrating on peripheral vision? It doesn't prevent you from looking at the edge with central vision concentration if you choose.
Does having several fields of view of normal eyepieces all in one, overlapped, bother you? Why does it bother you? Because it's not like the eyepieces you use?
Or does it bother you that some company has produced an eyepiece you can't afford? Is that the reason you don't like it?
After years of using ultrawides, my first view of space through the 13 Ethos was like loosening my belt a notch after a big meal. It was less restricted and a lot more open. Not perfect (I think it has too much eye relief), but a big improvement over the ultrawides (82 degree).
I got to thinking about it later and realized I wouldn't even mind having an eyepiece with a 200 degree field that was so wide I couldn't see the edge with peripheral vision.
I probably wouldn't use the whole field of view, ever. And it wouldn't bother me at all to not even be able to see the edge. Why would that bother you?
There can be valid reasons to prefer a narrower field in some circumstances (such as an obnoxiously bright star in the field when you're trying to look at details in a faint galaxy--a star that would be outside the field of view in a narrower eyepiece).
But it sounds, and I've heard and read it all, like the major objections to the wider field of an Ethos or Explore Scientific are psychological, not visual. That's fine. After all, we relate to the world in a psycho-social manner.
But all discussions of vision are a red herring. If someone simply said, "I don't like it and that's that," or "I'll never pay that much for an eyepiece," it has more meaning than trying to rationalize a physiological reason for the dislike.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2925
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The bottom line is that these eyepieces are for gawkers, not observers. Gawking isn't bad, I do it all the time, but for real observing they are just not very good. The entire idea is silly after 70 degrees.
And ultrawides are not like picture windows - they are like peepholes into magic large angle world.
-drl
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8271
Loc: Beatrice, Nebraska
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Quote:
The bottom line is that these eyepieces are for gawkers, not observers. Gawking isn't bad, I do it all the time, but for real observing they are just not very good. The entire idea is silly after 70 degrees.
And ultrawides are not like picture windows - they are like peepholes into magic large angle world.
-drl
That may be your own personal opinion, but it can not even remotely be considered a factual statement. Indeed, what you have said here is potentially insulting. I do not usually "gawk"; I OBSERVE (and have been doing so for the past 40 years). I *observe* variable stars. I *observe* detail in small planetary nebulae at powers that are near or beyond the usual 50x per inch maximum recommendation. I *observe* globular star clusters and even have done some sector counting at rather high power. I *observe* and study galaxies at moderate to high power to detect star-like nucleii or hints of inner spiral structure. I *observe* the planets at high power for hours of time.
Guess, what eyepieces work best for me for a lot of this? Answers; the 5-8mm Speers Waler (76 degree AFOV), followed closely by my 8.5-12mm Speers Waler (81.4 deg. AFOV), my 14mm Meade Ultrawide (82 degree AFOV), and my 24mm Panoptic (68 degree AFOV). I have seen the 15th magnitude central star in M57 with my 5-8mm 9-element Speers Waler using my 9.25 inch SCT. In my 10 inch f/5.6 Newtonian, the 5-8mm SW rapidly gained my appreciation when observing globular clusters, as it allowed me to tailor the power to the specific cluster and still see the whole thing. I first resolved the stellar-like core of M5 into its tiny components using that 5-8mm eyepiece and a 2.5x Powermate at 446x. I did some of my early variable star work in my old 10 inch using the 14mm Meade Ultrawide (101x, 49.5 arc minute true field), as it allowed me to zero-in on faint long-period variables in rich star-fields while still getting the proper comparison stars in the field of view. I am considering replacing the old Ultrawide with the new Explorer Scientific 14mm 100 degree eyepiece, as it is more light efficient than the older Meade while providing me even *more* field of view. A friend of mine's 20mm Nagler and 2x Powermate is also a dynamite combination on M5 (BTW, that is a grand total of *10 elements* used). I don't need that combination anymore now that I have the 8.5-12mm Speers Waler (8 elements), as it gives me a similar combination, but the former combination is still impressive. With small planetaries, I will use the wide-field eyepieces for both locating and observing them. A few weeks ago, I was hunting and *observing* 14th and 15th magnitude galaxies using that old Meade 14mm Ultrawide. When going after the finer detail in planetaries or resolving the tightest double stars, the first eyepiece I often reach for is the good old 5-8mm Speers Waler (and sometimes the 2.5x Powermate as well). For the planets, I have a 4-element 6.4mm Meade "superplossl", but it rarely gets used anymore, as the 5-8mm gives me better performance, a much wider field, and the ability to tailor the power again to seeing conditions. Two weeks ago, my friend with his 8 inch f/5 and I with my 9.25 inch SCT both spent almost three hours on Jupiter, and much of the time, we were using either his 100 degree ES 14mm and his 2x Powermate or our 5-8mm Speers Walers. The views were beyond incredible, allowing us to study the fine detail in the equatorial belts, inside the Red Spot, and the finer spots and whorls in the polar regions
In short, the statement that a wide-field eyepiece somehow is not for "observers" is total and unvarnished hogwash! I could continue to cite concrete examples of the observations I have made using wide-field eyepieces, but I feel I should have more than made my point by now. If you personally do not like wider-field eyepieces for cost reasons or other preferences, that is fine. However, it would be best if one did not make a statement that may infer that a person can only be judged as an observer by the choice of their eyepieces. That is just plain wrong. Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2925
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What can I say - to me the view is always better in as simple an eyepiece as is consistent with the object involved. For planets and the Moon there is just no point in using wide field complex designs. For dim objects, ditto. If you really need a wide field to find things, I guess that's different. The more I try my ultrawides the more I don't use them at all. Yes they make pretty pictures and group portraits but most of the time they are just annoying and excessive and you know the view is dimmer and less sharp than it could be. So you just don't use them.
Real observing involves both patience and a plan of attack. Using a multi-element eyepiece is just not a good plan of attack because it's guaranteed to have less contrast, less sharpness in the middle, and less light transmission overall, no matter what else one wishes to believe. You might as well argue with gravity. Other things equal, more lenses means less performance, unless you are talking about the single isolated fact of a wide field with good edge performance. That's a good thing to have but it's really a small part of real observing.
-drl
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Shawn H
Carpal Tunnel
Reged: 05/16/07
Posts: 2954
Loc: Southern France 43°56'N-4°50'E
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Right or wrong, FOV was always a determining factor in my ep choices! IMHO the larger the FOV the better, for non driven Dob owners! 
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18" David Lukehurst truss Dobson with Sky Commander flash 4 DSC's & Moonlite CR2 focuser & Astrocrumb filter slide
Orion xt10i fully flocked with Telrad on 4" risers & Feather Touch focuser & huge Boston Red Sox decal
The original Orion StarBlast & 15x70 Celestron Skymaster binos & Ethos & Naglers & Dobs oh my!
Orion Ultrablock narrowband filter & Astronomik OIII line filter
Tele Vue 2x Barlow & Antares 1.6x (2") Barlow
CATSEYE collimation tools, TeleGizmos Dob covers
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8271
Loc: Beatrice, Nebraska
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One of the things that really convinced me of the value of some of the better wide-field eyepieces happened just after moonrise one night. A friend of mine and I had just finished some variable star magnitude estimates when the moon came up. My friend stuck his 14mm Meade Ultrawide into his 12.5 inch f/4.8 Portaball (109x) and pointed it at the moon. I took one look in and was instantly hooked. It was perhaps one of the best views of the lunar surface I had ever seen. One uses a wide-field eyepiece on the moon to see more of it. I don't regret the view of the moon in my wider-field eyepieces, as it lets me see most of the entire lunar disk at considerably higher power. It *is* like looking out a spaceship window.
Quote:
Real observing involves both patience and a plan of attack. Using a multi-element eyepiece is just not a good plan of attack because it's guaranteed to have less contrast, less sharpness in the middle, and less light transmission overall, no matter what else one wishes to believe. You might as well argue with gravity. Other things equal, more lenses means less performance, unless you are talking about the single isolated fact of a wide field with good edge performance. That's a good thing to have but it's really a small part of real observing.
Sigh... and people wonder why I don't go on the eyepiece forum very much....
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org
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russell23
sage
Reged: 05/31/09
Posts: 416
Loc: Upstate NY
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Quote:
Just felt an overwhelming desire to jump into this discussion. I've actually done a bit of work in the area of human vision; Bill and Greg are getting pretty close on this. Going somewhat from memory, your actual best vision (resolution and color) is in a small region (the fovea) on the order of a degree or two! Around that, you have a few more degrees (parafovea) where you have improved light sensitivity, but reduced color vision (more rods, fewer cones - this is what brings about the effectiveness of averted vision). Beyond that, your vision degrades quickly in terms of color and acuity (resolution), so peripheral vision is more a matter of awareness of surroundings and sensitivity to motion (e.g., so you don't crash into things as you walk). I think Bill P's number for field of view are about right, but fundamentally, you have to move your eye around to really see any detail. Your eye is capable of moving on the order of about 45 degrees off-axis, so you can really see clearly over a zone of about 90 degrees - but only by moving your eye around. Beyond that, you have to swivel your head.
The amazing part is that the human visual system is geared to doing this all the time, without much awareness on your part. Even if you stare at one spot, microtremors and microsaccades are jiggling around your visual field so it's really impossible to keep 100% steady (and you you would actually stop seeing anything if you could - cells in your retina adapt-out light levels that don't change). Normally, your eye is making saccadic movements to scan out a scene and give you the impression you're seeing everything in high resolution. My impression is that people doing astronomy have learned some additional control (using averted vision), and perhaps are more aware of how far they're having to move their eyes.
An interesting, though disconcerting, thing to try is to look at the sky and fixate hard on a single star (no telescope). If you can really suppress your desire/reflex to move, you'll find after a few seconds that the visual field starts to gray-out at the edges and virtually everything outside of the center just disappears. I suspect this is because visual acuity away from the fovea is too low for involuntary eye movements to maintain the image, but I don't know for a fact.
Bill W
Bill,
This is fascinating and I tested it last night. I put M-27 in the center of my field at 21x magnification and I concentrated on staring at it without moving my eyes. It was unbelievable -- after a few seconds the nebula just began to disappear as if someone was turning a light off by turning it down and then off with a dimmer switch.
I did it a number of times on a number of objects and it happened every time. Several times I was able to get the object I was observing to completely disappear. As soon as you start moving your eye again the object pops back into view.
One other thing I noticed when I did this - when M-27 disappeared it was from the outside in until even the very center light was gone.
Thanks for sharing this information.
Dave
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turtle86
professor emeritus
Reged: 10/09/06
Posts: 656
Loc: Red Sox Nation
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Excellent post! 
Quote:
That may be your own personal opinion, but it can not even remotely be considered a factual statement. Indeed, what you have said here is potentially insulting. I do not usually "gawk"; I OBSERVE (and have been doing so for the past 40 years). I *observe* variable stars. I *observe* detail in small planetary nebulae at powers that are near or beyond the usual 50x per inch maximum recommendation. I *observe* globular star clusters and even have done some sector counting at rather high power. I *observe* and study galaxies at moderate to high power to detect star-like nucleii or hints of inner spiral structure. I *observe* the planets at high power for hours of time.
Guess, what eyepieces work best for me for a lot of this? Answers; the 5-8mm Speers Waler (76 degree AFOV), followed closely by my 8.5-12mm Speers Waler (81.4 deg. AFOV), my 14mm Meade Ultrawide (82 degree AFOV), and my 24mm Panoptic (68 degree AFOV). I have seen the 15th magnitude central star in M57 with my 5-8mm 9-element Speers Waler using my 9.25 inch SCT. In my 10 inch f/5.6 Newtonian, the 5-8mm SW rapidly gained my appreciation when observing globular clusters, as it allowed me to tailor the power to the specific cluster and still see the whole thing. I first resolved the stellar-like core of M5 into its tiny components using that 5-8mm eyepiece and a 2.5x Powermate at 446x. I did some of my early variable star work in my old 10 inch using the 14mm Meade Ultrawide (101x, 49.5 arc minute true field), as it allowed me to zero-in on faint long-period variables in rich star-fields while still getting the proper comparison stars in the field of view. I am considering replacing the old Ultrawide with the new Explorer Scientific 14mm 100 degree eyepiece, as it is more light efficient than the older Meade while providing me even *more* field of view. A friend of mine's 20mm Nagler and 2x Powermate is also a dynamite combination on M5 (BTW, that is a grand total of *10 elements* used). I don't need that combination anymore now that I have the 8.5-12mm Speers Waler (8 elements), as it gives me a similar combination, but the former combination is still impressive. With small planetaries, I will use the wide-field eyepieces for both locating and observing them. A few weeks ago, I was hunting and *observing* 14th and 15th magnitude galaxies using that old Meade 14mm Ultrawide. When going after the finer detail in planetaries or resolving the tightest double stars, the first eyepiece I often reach for is the good old 5-8mm Speers Waler (and sometimes the 2.5x Powermate as well). For the planets, I have a 4-element 6.4mm Meade "superplossl", but it rarely gets used anymore, as the 5-8mm gives me better performance, a much wider field, and the ability to tailor the power again to seeing conditions. Two weeks ago, my friend with his 8 inch f/5 and I with my 9.25 inch SCT both spent almost three hours on Jupiter, and much of the time, we were using either his 100 degree ES 14mm and his 2x Powermate or our 5-8mm Speers Walers. The views were beyond incredible, allowing us to study the fine detail in the equatorial belts, inside the Red Spot, and the finer spots and whorls in the polar regions
In short, the statement that a wide-field eyepiece somehow is not for "observers" is total and unvarnished hogwash! I could continue to cite concrete examples of the observations I have made using wide-field eyepieces, but I feel I should have more than made my point by now. If you personally do not like wider-field eyepieces for cost reasons or other preferences, that is fine. However, it would be best if one did not make a statement that may infer that a person can only be judged as an observer by the choice of their eyepieces. That is just plain wrong. Clear skies to you.
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russell23
sage
Reged: 05/31/09
Posts: 416
Loc: Upstate NY
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Quote:
What can I say - to me the view is always better in as simple an eyepiece as is consistent with the object involved. For planets and the Moon there is just no point in using wide field complex designs.
If you have a manual adjusted scope, then the wide fields are helpful because they allow you to adjust the position of the scope less frequently. In addition, wide fields can be very useful in helping to nicely fram an object.
Quote:
For dim objects, ditto. If you really need a wide field to find things, I guess that's different. The more I try my ultrawides the more I don't use them at all. Yes they make pretty pictures and group portraits but most of the time they are just annoying and excessive and you know the view is dimmer and less sharp than it could be. So you just don't use them.
This depends not just on the number elements in the eyepiece but also upon the quality of the coatings and lense grinding. I've looked through a 4 element 26mm plossl that had a dimmer image than an 8 element 20mm Pentax XW. Perhaps Zeiss orthos beat out the Pentax XW's, but I think some here might say that is not such a certainty.
In addition you also have to remember that some people use eyeglasses. Every short FL 4 element eyepiece I'm aware of has eye relief way too short for use with eyeglasses. When you start adding elements not only do you have the ability to increase AFOV, but you also add the ability to increase the eye relief at short FL.
Quote:
Real observing involves both patience and a plan of attack. Using a multi-element eyepiece is just not a good plan of attack because it's guaranteed to have less contrast, less sharpness in the middle, and less light transmission overall, no matter what else one wishes to believe. You might as well argue with gravity. Other things equal, more lenses means less performance, unless you are talking about the single isolated fact of a wide field with good edge performance. That's a good thing to have but it's really a small part of real observing.
What is "real observing"? Is observing only "real" if you make detailed notes of what you saw? Is observing only "real" if you make sketches? Is observing only "real" if you record magnitude estimates? What makes observing "real" as opposed to "gawking"? To be "real" you must have a plan of attack when you go out each night? A list of objects? Stated objectives?
To researchers publishing work in the pages of astrophysics research journals, the observing amateur astronomers are doing could be considered "gawking". I'm quite familiar with astronomy research as I have published a number of papers in astrophysics journals over the last decade. My most recent paper used the Ks-band Tully-Fisher relation to investigate the value of the Hubble Constant:
http://arxiv.org/abs/0812.1288
In order to conduct that research I used 2MASS K-band photometry which provided near-infrared magnitudes of spiral galaxies. I also needed rotational velocities derived from hydrogen linewidths and/or optical spectra. I didn't actually make any of these observations myself. I used the online published data.
My point is that what constitutes "real observing" is very much a matter of perspective. To someone conducting research, it would be possible to say that most backyard observing is "gawking". But I don't see it that way. Real observing is whatever suits the needs, interests, and purpose of the person doing the observing.
The work I've published I've done as an independent researcher not associated with any research institution. When I picked a major at college I decided not to become a professional research astronomer because I was afraid if I did, I would never do backyard observing. In this age of data available online it is possible to do both -- and I would never denigrate the efforts of any backyard astronomer as not "real observing" or merely "gawking".
Just my 200 cents.
Dave
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turtle86
professor emeritus
Reged: 10/09/06
Posts: 656
Loc: Red Sox Nation
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Dave,
Thanks for your perspective on all this. As you suggest, one shouldn't presume that there is only one "correct" way to observe. At the same time, I for one couldn't less whether someone deems my own observing as mere "gawking." While I am very passionate about astronomy, ultimately for me it is a hobby that is supposed to be fun, and no one is going to take that away from me. As you also suggest, one shouldn't presume that an EP is necessarily inferior for a given purpose just because it has more glass. Just too many other considerations involved, including the object involved, coatings used on the lenses, type of scope and mount, and so on. If others get more out of observing by using eyepieces with simpler designs and narrower FOV's, then more power to them, just so long as they don't try to rain on my parade.
Edited by turtle86 (10/11/09 11:42 AM)
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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This repartee reminds me of the same discussions about the use of coma correctors--specifically the Paracorr:
Those extra 4 elements must, somehow, reduce one's view of details in planets and deep-sky objects.
In fact, using an in-out comparison, fainter stars were seen WITH the Paracorr in my scope than WITHOUT. What I presume that means, because there is certainly SOME light loss occurring, is that tightening focus by elimination of coma made more difference to the visibility of faint stars than the tiny light loss.
I spent an entire night from dusk to dawn comparing the 7 element Nagler Type 6 (formerly the sharpest eyepiece I'd ever owned) to the 9 element 13 Ethos. On every globular, small planetary nebula, faint galaxy, and Jupiter, fainter and smaller details were visible in the Ethos. Startlingly so, in the case of Jupiter, which was in technicolor in the Ethos and somewhat gray in the Nagler. I presumed, because the Nagler was a very sharp eyepiece, that the difference was light transmission, with the edge going to the eyepiece with more elements. Tom Trusock disagreed with me, as he felt the 13 Ethos was actually sharper.
These two examples point out that adding elements doesn't necessarily cost you anything at the eyepiece, and can gain you quite a bit of sharpness and improvement in the view.
Since I always observe all night when I go out, and since I always record what I see (my log is nearing 11,000 observed objects, about which I try to record as much detail as I see), I also discovered that the wider field of the 13 Ethos meant that, in most cases, I didn't even have to change to lower powers to find an object. The 45' field in my scope was large enough to find nearly everything. Not changing eyepieces when finding definitely saves time and gives me more observing time at the eyepiece.
Here's a typical example of my recorded observations, taken at random from my log (this is M56): "small,moderately bright,relatively loose structure,core large,fully-resolved,cluster is not round,outliers double apparent size of cluster,core area appears slightly oval (rotational flattening?),brighter stars form fan shape that is the most distinctive feature of this globular, in rich field".
Funny thing: my ability to see details in an object is completely unrelated to the size of the field of view. My ability to see other objects in the same field, however, is.
Abell 426 displays a lot more galaxies in a larger field than in a smaller one. And having everything in tight focus means I can trust that that faint smear at the edge of the field is a galaxy and should be identified, logged, and described (as opposed to being an out-of-focus, comatic, star). Do I bring it to the center to observe it and do I use higher powers on small objects? Of course I do. But the field size is a very important element in finding and identifying the objects in the field.
Individual stars in NGC206 and hundreds of stars in M14 have been visible in the 13 and 8 Ethos eyepieces that were invisible in eyepieces with 3 to 4 fewer elements. Could there be eyepieces with narrower fields and fewer elements that would also have shown me stars fainter than magnitude 17 in my 12.5". For sure. But those narrow, pinched, fields of view tend to rob the objects of context.
Tracing striated nebulosity away from M17 for several fields of view, M16 swam into view, and for the first time I realized that they were both merely brighter patches in one large nebula. This was an observation I had never made before with other eyepieces because the smaller fields of view made the context of each nebula (i.e.its field) less important to observe. In fact, in talking about this observation with other experienced observers, it is a very uncommon observation--what made it apparent was the large field of view at medium power that made the field part of the observing experience.
I suppose, because I am not doing measurement of any object, that I am merely gawking and not observing. Well, call it what you will. I'm just going to continue to do it because I like teasing out faint details in the objects and writing about them.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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helpwanted
Carpal Tunnel
Reged: 07/04/07
Posts: 2636
Loc: Phoenix, AZ
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hey Don, what ep do you find you use the most? what magnification does it product?
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Quote:
hey Don, what ep do you find you use the most? what magnification does it produce?
The 13 Ethos produces 140X in my scope. It seems to be nearly optimum for most mid-sized (5-20') deep sky objects.
For the small stuff, the 8 Ethos at 228X seems great, while for large stuff, either the 31 Nagler (59X) or 22 Nagler (83X) works fine.
But, considering the type of objects I've been viewing recently, the 13 spends 90% of the time in the focuser.
When I had an 8" scope, that high a magnification would have been too dark, and I found a slightly lower magnification closer to optimum (101X).
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Mike Hosea
Post Laureate
Reged: 09/24/03
Posts: 3924
Loc: "Metrowest" Boston
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Quote:
What I presume that means, because there is certainly SOME light loss occurring, is that tightening focus by elimination of coma made more difference to the visibility of faint stars than the tiny light loss.
That's the argument Al Nagler's been making for years, and it makes sense. We're talking off-axis, of course. But generally, as you probably know, I think transmission as a factor in object/detail visibility is over-emphasized. I think, rather, that it's about contrast, and contrast may be affected by the apparent field of view through scatter in the eye itself, so I'm saying that there are other factors that might be responsible for what people see.
A simple test that might help is to keep the same eyepiece in and to mask the aperture down by a calculated amount to simulate a loss of transmission of a few percentage points. Preferably a buddy would do the honors while you weren't looking, so that you wouldn't know whether the mask was in place or not.
Unfortunately, to reduce transmission by only a few percentage points, the aperture masks will need to be somewhat precise and precisely placed. It would be easier to modify/introduce a central obstruction to simulate lower transmission. With the central obstruction approach, contrast is slightly reduced, too, so the test has a negative character, i.e. it has the potential to say more about what you can't see, transmission-wise, than what you can. Nevertheless, I think it might be worth a try, especially if you're the kind of person who believes the effect on transmission of introducing a few lenses should be obvious.
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Mike
Stuff that I use:
- 7" f/6.7 home-built Newt, eq platform, Pentax 40XW and 5XO, Tele Vue 13E and 2x Barlow, ZAO-II 6mm
- 120mm f/8.3 home-built grab-n-go Newt with 7-21mm Nikon Zoom
- Canon 15x50 IS and Eagle Optics 12x50 Ranger binoculars
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sixela
Postmaster
Reged: 12/23/04
Posts: 10848
Loc: Boechout, Belgium
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Quote:
For dim objects, ditto.
For sim small objects. For dim large objects, if you have a limited FOV, you're sometimes either stuck with choosing to frame it properly (and using too little magnification for optimal detection of smaller contrast detail) or choosing the correct magnification and not seeing all of the object (or not enough context to even sketch it).
And yes, it happened to me with an object recently with a 70° AFOV eyepiece, though I can't remember which one without delving in my logs. 13mm Ethos: too little magnification. 10mm XW: too little field.
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400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
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gnowellsct
professor emeritus
Reged: 06/24/09
Posts: 729
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Quote:
Does having several fields of view of normal eyepieces all in one, overlapped, bother you? Why does it bother you? Because it's not like the eyepieces you use?
Or does it bother you that some company has produced an eyepiece you can't afford? Is that the reason you don't like it?
Don:
These things get debated because their is a social need to debate. Eventually we pass on to other things (haven't seen the go-to vs non-go-to in a while).
The arguments about Ethos vs other eyepieces is no different than GEMs vs alt-az or "true apos" vs "less good apos" vs ED doublets vs achros etc.
And you're surely aware that folks who've popped for all or most of the XW line have enough dough to get into Ethos if they like.
So the questions you are asking pertain more to why it is that people adopt religious affiliations to various equipment brands. I don't know, but I do know that I'm also guilty, but I try to keep it in perspective.
There are, here and there, BTW, 1.25" 45-50 degree addicts out there who won't have anything to do with a 68 degree eyepiece!
Anyhow I'm sure that we can take a more philosophical view. Some people like to say "no" to ethos with the same vigor that Bush No. 1 said he didn't like broccoli. Myself, if I'm offered a view in an Ethos I don't say no, but I find it does not suit my aesthetic. Anyhow Internet argument is just that, passionate displays of feeling for things that are not of real importance in the great sweep of time.
But it's better than watching television!
regards
Greg N
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"Aperture will get you through times of no money better than money will get you through times of no aperture."
featuring selected astrojunk:
bunch o' widefield eyepieces
bunch o' narrowfield eyepieces
couple o' Barlows
couple o' scopes
couple o' mounts
couple o' tripods
and a pier 'n' stuff
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Greg,
I guess I grew up with nothing. I think I may like everything in the astronomy field a little bit because everything is better than what I started out with.
I was asking the questions so that people would look at their own comments and evaluate WHY they made the comments they did. Perhaps so they would take that more philosophical view.
I prefer ultrawides, but I never turn down a look in someone else's scope because they have a Plossl or Orthoscopic.
I like GoTo and manual and PushTo.
I like apos and EDs and reflectors and SCTs and MCTs.
I like Pentax and TeleVue and Explore Scientific and Meade and Celestron and others.
I enjoy observing most of all, and the equipment is secondary. I'm glad I can afford whatever I want (astro gear is pretty cheap compared to my other hobbies), but I obviously couldn't always.
But I'm happy with a 5" scope and 1.25" Plossls or a 16" with Ethos eyepieces. Just give me a night under the stars and my internal battery is charged for a long time.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Mike Hosea
Post Laureate
Reged: 09/24/03
Posts: 3924
Loc: "Metrowest" Boston
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Quote:
Sigh... and people wonder why I don't go on the eyepiece forum very much....
I am not a "real observer", and so I personally could not be offended by being called, instead, a "gawker". However, I am a little bit offended on David's behalf, since, by all accounts, he is a real observer, if anyone here is. I always appreciate your contributions here, David.
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Mike
Stuff that I use:
- 7" f/6.7 home-built Newt, eq platform, Pentax 40XW and 5XO, Tele Vue 13E and 2x Barlow, ZAO-II 6mm
- 120mm f/8.3 home-built grab-n-go Newt with 7-21mm Nikon Zoom
- Canon 15x50 IS and Eagle Optics 12x50 Ranger binoculars
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gnowellsct
professor emeritus
Reged: 06/24/09
Posts: 729
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Quote:
Greg,
I was asking the questions so that people would look at their own comments and evaluate WHY they made the comments they did.
I think people like to argue and loudly proclaim their views about things that have no consequence in real life! I also like observing. But it's fun to bug the Ethoi-addicts!
There's also a little bit of pulling-off-the pedestalism. I mean Televue is so dominant in eyepieces that it's always TV this TV that etc. So out of cussedness some people like to take that on.
But let's be fair: by all accounts, Al Nagler helped spur a revolution in eyepiece design: I wonder if any of the eyepieces we use today, including my beloved XWs, would have been engineered if he had not paved the way. He really sort of laid out the challenge of using the best glass and the best optical programs to achieve astounding results.
I'm sure the phenomenal progress in camera optics is linked to widefield eyepiece progress in important ways. But the fact is that we have more neat stuff at better prices than any other time in the history of amateur astronomy.
I was picking my way through UGC catalog galaxies in Cygnus and consider that something of a feat: usually I say we amateurs are working off the 19th Century NGC catalog, but looking at UGCs puts everything on the line about what modern astronomy can do for visual: the eyepieces, the scopes, the computers, the databases. Pretty amazing.
Until I hear otherwise from someone who knows a lot about eyepiece design--Chris Lord's well reputed article ends with the advent of the modern widefield era--I'm going to have to give Al Nagler credit for being one of the leading designers that led other eyepiece designers to try their hands at wider fields and higher prices.
So there's a bit of Al Nagler in my XWs, that's what I think.
Now that we have that out of the way, I'd like to go back to saying, "well, they're OK if you really MUST have a space walk effect, but some of us prefer..."
Greg N
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"Aperture will get you through times of no money better than money will get you through times of no aperture."
featuring selected astrojunk:
bunch o' widefield eyepieces
bunch o' narrowfield eyepieces
couple o' Barlows
couple o' scopes
couple o' mounts
couple o' tripods
and a pier 'n' stuff
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2925
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The is nothing wrong with gawking at star fields in an ultrawide - no insult is given or intended. I spend half of my telescope time gawking. But the other half is spent in zen-like concentration with as little in the light path as needed.
-drl
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2925
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As a solution to a SPECIFIC and DIFFICULT problem, namely how to get a wide field of view with sharp stars at the edge of a fast telescope, the ultrawide designs are amazingly successful. As a solution to the problem of acutally SEEING THINGS at the limits of optics and perception, they are far from optimal
-drl
Quote:
Quote:
Greg,
I was asking the questions so that people would look at their own comments and evaluate WHY they made the comments they did.
I think people like to argue and loudly proclaim their views about things that have no consequence in real life! I also like observing. But it's fun to bug the Ethoi-addicts!
There's also a little bit of pulling-off-the pedestalism. I mean Televue is so dominant in eyepieces that it's always TV this TV that etc. So out of cussedness some people like to take that on.
But let's be fair: by all accounts, Al Nagler helped spur a revolution in eyepiece design: I wonder if any of the eyepieces we use today, including my beloved XWs, would have been engineered if he had not paved the way. He really sort of laid out the challenge of using the best glass and the best optical programs to achieve astounding results.
I'm sure the phenomenal progress in camera optics is linked to widefield eyepiece progress in important ways. But the fact is that we have more neat stuff at better prices than any other time in the history of amateur astronomy.
I was picking my way through UGC catalog galaxies in Cygnus and consider that something of a feat: usually I say we amateurs are working off the 19th Century NGC catalog, but looking at UGCs puts everything on the line about what modern astronomy can do for visual: the eyepieces, the scopes, the computers, the databases. Pretty amazing.
Until I hear otherwise from someone who knows a lot about eyepiece design--Chris Lord's well reputed article ends with the advent of the modern widefield era--I'm going to have to give Al Nagler credit for being one of the leading designers that led other eyepiece designers to try their hands at wider fields and higher prices.
So there's a bit of Al Nagler in my XWs, that's what I think.
Now that we have that out of the way, I'd like to go back to saying, "well, they're OK if you really MUST have a space walk effect, but some of us prefer..."
Greg N
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8271
Loc: Beatrice, Nebraska
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deSitter posted:
Quote:
As a solution to the problem of acutally SEEING THINGS at the limits of optics and perception, they are far from optimal
And you have yet to conclusively prove this. Let's look at just one factor: light loss through coated optics. With multi-layer coatings, the light loss per surface can go as low as 0.2 percent. With each lens element, we are probably looking at a light loss of around 0.5 percent in each lens to be a little more realistic. In a 4-element eyepiece for example, you would be looking at about a two percent light loss. From variable star visual observations, the human eye has some difficulty in consistently measuring a difference of 0.2 stellar magnitudes (16.8% difference in light intensity) and is usually incapable of seeing a light intensity difference of much less than about 0.1 stellar magnitudes (9% intensity difference). Assuming 0.5% light loss per element, just to get past that bare minimum 9% potential threshold of possible detection, you would have to use at least 10 more elements in the eyepiece than in a simpler design, and to get to the more common 0.2 magnitude difference, you might need as many as whopping 34 more elements than in a more light efficient eyepiece design. Thus, the *difference* between light throughput of simple vs. more complex eyepiece designs ends up being somewhat less significant. While the light loss through the optics is definitely a factor, it can be much less of a factor that some here would argue that it is. Considering the many other factors involved in faint object detection (eye sensitivity, dark adaptation, local seeing conditions, experience, etc.), it is clear that the light loss issue for some wide-field eyepieces is often way overblown. Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2925
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What is to prove?? This is what I find just crazy-making - we learned as kids that the main problem in optics, leaving aside convenience and specialized applications, is to get the best possible image from the least number of surfaces, because every surface encountered robs and scatters light and does not bend it perfectly - EVERY optical surface is a big withdrawal from the optical error budget. I am not claiming anything at all disputable or controversial - with the one exception of having sharp edge stars, a 9-element or 11-element design cannot begin to compete with a 3-element or 4-element one at the place where serious observing occurs, right on axis and right inside the sweet spot.
We were also taught as kids to optimize our observing technique - to learn patience and how to "see", vs. just looking. I think the reason is - in those days, amateurs were told they could still do useful scientific work - and indeed they still can - but we've come to think of ourselves as mere spectators, lazily pushing around our Dobs with their huge mirrors and massive wide angle oculars. This sort of observing is easy, fun, and rewarding. But I like the challenge of testing the limits of my eyes and my scope and have spent a lot of time learning the patience to see very dim things, very close things, and very detailed things. That sort of patience is just wasted on a complex design - the eye position is uncomfortable, the image milky from excessive glass scatter, dim from reflective loss, not as sharp as the objective can deliver because of accumulating surface errors.
My admitted prejudice comes from the time I inhabited - when amateurs were practically expected to take observing seriously and not treat it as just a pleasant, passive pastime.
-drl
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2925
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Ok let's give an example because I thought this was obvious but it's not I guess..
I put a 6mm Ortho in my 5" f/9.3 refractor and point it at the Trapezium - immediately I see E and F with direct vision. Now I put in a 6.7mm UWA - they are still there, but not with anything like the immediacy of the Ortho. So I try a 6.4mm Plossl of standard design - there they are, even more obvious than with the better eyepiece, the Ortho. I put in a 12.5mm Ortho + a PowerMate - still there, somewhat less sharp and dimmer. A 12.5mm + Barlow - missing. Well E flickers in and out of direct vision - F is missing. A 40mm Plossl + 5x TeleXtender - same as with the PowerMate, just a hair off the simple eyepiece.
I can go on and on with these lens combinations between orthos, superwides, ultawides, Plossls, Barlows.. and the result is always the same - the best view of these dim objects is in the simple design - they stand out better pretty much as some direct function of number of lenses. Now it's only on the objects that test the telescope that these differences are apparent, but there, it's so obvious that it's beyond numbers.
Now hunting like this is qualitatively different than just enjoying the view, something I like as much as anyone. That's why I have a whole set of wide fields.
-drl
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8271
Loc: Beatrice, Nebraska
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deSitter wrote:
Quote:
What is to prove??
You have yet to prove your statement: "the ultrawide designs are amazingly successful. As a solution to the problem of acutally SEEING THINGS at the limits of optics and perception, they are far from optimal". I will grant that the wide field (not "the Ultrawide, as that is a Meade re-engineering of an early Nagler design), may or may not be optimal. However, I would strongly contend that if they are not optimal (and that is not certain), the better ones are certainly not very far off optimal. My own experience pushing the limits of deep-sky observing has shown this to be true.
You are basically bashing all the wider-field designs based on poorly-conceived logic and not enough hard facts. All you really have is that you don't like using them for what you term "serious" observing. That is fine, but that is *your* personal choice. It may not be the choice of others and the reasons you gave to back up your choice may not be accurate as I demonstrated in my example. There is so much variation in design or production run quality that the items you cite as reasons may in fact not be nearly large enough to condemn the wider field designs wholesale as you have done.
Quote:
My admitted prejudice comes from the time I inhabited - when amateurs were practically expected to take observing seriously and not treat it as just a pleasant, passive pastime.
Gad, there you go again insulting people! There *are* serious people today doing serious "work" with both wide-field and simple eyepieces. Amateur Astronomy has been both a pleasant pass-time and a serious hobby for decades, and it continues to be that way. You have proven nothing.
--------------------
David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org
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russell23
sage
Reged: 05/31/09
Posts: 416
Loc: Upstate NY
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I think the best way to truly make these comparisons would be to compare 4 vs 8 element designs with identical coating and lense grinding specifications.
My 20mm XW provides a brighter image than a 26mm Sirius plossl -- that despite the fact that the 20mm XW has 8 elements and a smaller exit pupil.
Perhaps a pentax Ortho should be put against a Pentax XW to see how much - if any - difference the human eye can detect. Based upon David K.'s earlier post it seems unlikely that all other things with coatings and grinding being equal, that the effects of extra elements would be detectable.
Dave
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Mike Hosea
Post Laureate
Reged: 09/24/03
Posts: 3924
Loc: "Metrowest" Boston
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Quote:
However, I would strongly contend that if they are not optimal (and that is not certain), the better ones are certainly not very far off optimal. My own experience pushing the limits of deep-sky observing has shown this to be true.
Danny argues in absolutes. Is x - y > 0 ? Yes or no. End of argument. If you take the right seat out of a Ferrari, I have no doubt that it will go faster. Where we disagree, probably, is whether taking the right seat out is worth doing. I mean, how you going to pick up chicks in your Ferrari without a right seat?
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Mike
Stuff that I use:
- 7" f/6.7 home-built Newt, eq platform, Pentax 40XW and 5XO, Tele Vue 13E and 2x Barlow, ZAO-II 6mm
- 120mm f/8.3 home-built grab-n-go Newt with 7-21mm Nikon Zoom
- Canon 15x50 IS and Eagle Optics 12x50 Ranger binoculars
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star drop
Guilty as Charged
Reged: 02/02/08
Posts: 16141
Loc: Snow Plop, WNY
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For those of us that use reflecting telescopes I think that the multi lens argument about light loss is a fickle point. How many of us have their mirrors re-coated with high reflectivity coatings every year or even every five years? My telescope came with standard 88% reflectivity coatings in 1988. Now I am contemplating having my 25" re-coated after 21 years. A few weeks ago I performed the dreaded shine a flashlight from behind the mirror test and confirmed for certain what I had been noticing for the past five years while observing. So while my telescope may be providing perhaps 50% - 60% total reflectivity I still enjoy the views. If I am happy now that could mean that with new coatings I would be happy viewing with an eyepiece that has approximately 80 elements assuming a .5% loss for each individual element.
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Ted
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nyc_nurse
sage
Reged: 07/29/09
Posts: 252
Loc: nyc
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Interesting points made on all sides. Taking out the amount of light loss due to more elements is there a way for us to judge empirically if a simpler design does indeed show better detail on-axis? There seems to be a lot of tools available, at least to professionals and to manufacturers, that would enable if not a definitive answer then more supportive evidence than an observer saying that they see more detail in one vs the other. I like to assume, however incongruous it might be, that the complex designs have the benefit of more sophisticated computer models. But that might be just wishful thinking on the part of this TV consumer.
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Sam P.
www.agirlandaguy.blogspot.com
Pentax 7X50
TV-102 APO w/ (Starbeam - on backorder  )
Ash Gibraltar w/ SkyTour DSC
NZ3-6, N9T6, N13T6
TV 20 Plossl
Pan 24, 35
Pentax XW10, XW14
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hfjacinto
Almost got me
Reged: 01/12/09
Posts: 2068
Loc: Union,NJ
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Quote:
If you take the right seat out of a Ferrari, I have no doubt that it will go faster. Where we disagree, probably, is whether taking the right seat out is worth doing. I mean, how you going to pick up chicks in your Ferrari without a right seat?
They can sit on your lap, have you not seen the fast and the furious 2?
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C9.25 ASGT 9*50 MM Finder,FT Focuser & 2" Diagonal
Meade LXD 75 6 Inch SNT w 9*50 MM Finder
5,6,9,14.5 MM Zhummel Planetary EPs
13,17,21,24,31,36 MM Baader Hyperion
6.7,8.8 MM Meade UWA & 11 MM Nagler T6
Planetary, OIII and Narrowband Filters
Thousand Oaks Dew Control w Kendrick Heaters
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Quote:
For those of us that use reflecting telescopes I think that the multi lens argument about light loss is a fickle point. How many of us have their mirrors re-coated with high reflectivity coatings every year or even every five years? My telescope came with standard 88% reflectivity coatings in 1988. Now I am contemplating having my 25" re-coated after 21 years. A few weeks ago I performed the dreaded shine a flashlight from behind the mirror test and confirmed for certain what I had been noticing for the past five years while observing. So while my telescope may be providing perhaps 50% - 60% total reflectivity I still enjoy the views. If I am happy now that could mean that with new coatings I would be happy viewing with an eyepiece that has approximately 80 elements assuming a .5% loss for each individual element.
 
Try enhanced coatings. Then you can use anything in the focuser that you want--all at the same time!
I've proven to myself that sometimes adding glass increases what I can see through the eyepiece. Through the years I've also proven to myself that viewing with a telescope that has more elements and a larger secondary has no noticeable effect on the limiting magnitude I can see in the scope. If a purist thinks that using a refractor with monocentrics gains him a tiny bit of detail, so be it. Me, I'll just get a slightly bigger scope and use those zillion element ultrawidefields.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Mike Hosea
Post Laureate
Reged: 09/24/03
Posts: 3924
Loc: "Metrowest" Boston
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Quote:
But that might be just wishful thinking on the part of this TV consumer.
Obviously the diffraction-limited zone tends to be wider on a fast scope. But at any rate, it's not usually an exclusive proposition. After reading a half-dozen conversations like this, where the virtues of less glass are extolled, you'll probably end up buying at least some decent, simpler designs to try out, just to see for yourself. Would sir like to try a UO HD orthoscopic?
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Mike
Stuff that I use:
- 7" f/6.7 home-built Newt, eq platform, Pentax 40XW and 5XO, Tele Vue 13E and 2x Barlow, ZAO-II 6mm
- 120mm f/8.3 home-built grab-n-go Newt with 7-21mm Nikon Zoom
- Canon 15x50 IS and Eagle Optics 12x50 Ranger binoculars
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nyc_nurse
sage
Reged: 07/29/09
Posts: 252
Loc: nyc
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Quote:
Would sir like to try a UO HD orthoscopic?
A most affirmative yes. I juggled the idea of 4 UO HD ortho EP's for planetary work but the cost was too close to a new Nagler zoom, which I settled on because of the "simple" yet complex design of having 4 EP's in one. I have no problem taking in the entire 82 degree FOV of the 13 Nagler but prefer a smaller field for planetary/double views - in fact the zoom's 50 degrees is plenty big enough for me at the magnifications I get.
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Sam P.
www.agirlandaguy.blogspot.com
Pentax 7X50
TV-102 APO w/ (Starbeam - on backorder )
Ash Gibraltar w/ SkyTour DSC
NZ3-6, N9T6, N13T6
TV 20 Plossl
Pan 24, 35
Pentax XW10, XW14
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FirstSight
Post Laureate
Reged: 12/26/05
Posts: 3870
Loc: Raleigh, NC
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If it comes down to a choice between simpler, three-element eyepieces with itty-bitty fields of view that give the advantage of perhaps transmitting a smidgen more light and a tad better chance of glimpsing the faintest of fuzzies, VERSUS generously wide fields of view that I can get pleasurably immersed in but possibly lose just a smidgen of light through all those element-to-element interfaces and thus render a few of the faintest of fuzzies invisible to me, I'll take the widefield EVERY TIME.
But that's just me, I don't claim this is a perspective everyone should universally follow. Personally, I simply don't get enough pleasure in trying to view objects through orthoscopics (or even plossls) to compensate for the sensation of viewing them in what amounts to a virtual broom closet to my sensibilities.
But hey - whatever floats your boat is fine with me, if chasing n-th magnitude remote galaxies that only Hubble and a relative handful of hard-core observers have ever seen and you think orthoscopics give you an appreciable advantage toward joinng the club of those with that accomplishment, or that an orthoscopic gives you a better chance of seeing one extra subtle festoon on Jupiter that my complex widefields purportedly fail to catch - GO FOR IT WITH MY SINCERE BLESSINGS, and I look forward to your observing report.
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Chris M., aka "First Sight"
Orion XT12i Dob with Moonlite CR-2 focuser
WO Megrez 90 refractor on UniStar Light mount
Nikon 10x50 Binoculars
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turtle86
professor emeritus
Reged: 10/09/06
Posts: 656
Loc: Red Sox Nation
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Today's lens coatings are so good that any loss of light by having "extra glass" in a good wide-field EP is negligible at best and not even worth quibbling over with larger aperture scopes so readily affordable now.
Quote:
I've proven to myself that sometimes adding glass increases what I can see through the eyepiece. Through the years I've also proven to myself that viewing with a telescope that has more elements and a larger secondary has no noticeable effect on the limiting magnitude I can see in the scope. If a purist thinks that using a refractor with monocentrics gains him a tiny bit of detail, so be it. Me, I'll just get a slightly bigger scope and use those zillion element ultrawidefields.
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gnowellsct
professor emeritus
Reged: 06/24/09
Posts: 729
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Quote:
Interesting points made on all sides. Taking out the amount of light loss due to more elements is there a way for us to judge empirically if a simpler design does indeed show better detail on-axis? There seems to be a lot of tools available, at least to professionals and to manufacturers, that would enable if not a definitive answer then more supportive evidence than an observer saying that they see more detail in one vs the other. I like to assume, however incongruous it might be, that the complex designs have the benefit of more sophisticated computer models. But that might be just wishful thinking on the part of this TV consumer.
Some of the complex designs actually have been measured to have high light loss, including the TVs and 14mm Meade UWA which came in somewhere around 89 to 90%. The XWs in yellow green are 96%. That leaves very little "room at the top" for a simple eyepiece to make a detectable difference. And these are eight lens designs, some of them anyhow, so if you go the distance in terms of glass quality, coatings, etc., it becomes an overstatement to say, as is the wont of my fellow Pentaxian addict Drl, that glass sucks light out of the eyepiece.
I think that it is more likely that the wide fields "lose light" by spreading it in ways that make the faintest stars at the margin disappear. I noticed in my Nagler 17T4 that in my preferred position there is actually a circular pool of kidney bean that is very very very very faint, but there. I think that as we position our eyes to take in some of these widefields we get effects that we may interpret to be light pass through but are not in fact that.
In any case detecting faint stars is something of an art, and time consuming. Trying out an XO5 vs an XW5 would probably best be done on Jupiter or Saturn, rather than in faint star detection. I just don't think an XO 5mm or a ZAO II 4 or 6mm is going to walk away from an XW5mm in a faint object contest.
Since the faintest objects at the margin actually wink in and out of view as seeing distributes the light to the invisibility threshold and then allows it to reconcentrate and momentarily get stronger, there is always going to be subjective issues to these tests of light throughput at the margin. The best you can hope for is a Palomar glob which is detectable with one eyepiece and not detectable with another, after repeated switching. But the point is because faint objects wink in and out, and there are variations in high atmospheric clouds etc., these tests really can't be performed very well.
But you can use eyepieces over a long period of time and figure out which ones you like, and when, at long last, you encounter a design that kicks a** and that you want to convert to that.
I tried using my Super Mono 10 for faint object detection and ended up getting rid of it. It turns out that part of what you need for faint object detection is *context.* That is, it is easier to "see" that "something is there" if you have enough field around the object so that when you use the paddle you have some context as to what is moving and there really is a soft light patch there that moves when you make the scope move. If the field is too narrow it constricts that. So I concluded I was better off with an XW10 than a Super mono 10. Jury is still out on the ZAO II, but I'm going to have to use these eyepieces for a long time, barring penury. I really like the magnification the ZAO II 16mm gives on my C14 (233x) so it has a niche.
regards
Greg N
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"Aperture will get you through times of no money better than money will get you through times of no aperture."
featuring selected astrojunk:
bunch o' widefield eyepieces
bunch o' narrowfield eyepieces
couple o' Barlows
couple o' scopes
couple o' mounts
couple o' tripods
and a pier 'n' stuff
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Darenwh
Pooh-Bah
Reged: 05/11/06
Posts: 1219
Loc: Covington, GA
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I am beginning to think the only way we are going to decide this once and for all is a shoot out between two eyepieces.
Lets say a 13mm Ortho vx a 13mm Ethos with a field stop added to stop it down to the same FOV as the Ortho.
This way, a count of faintest stars visible in same FOV in same telescope by a few experienced observers and you have it once and for all.
Will the Ethos show more stars or as many as the ortho? Who has the set and when can this be done.
I would love to be there but Georgia seems to be on a cloud and rain run and I don't really get much time to participate in something like this any ways.
Perhaps if the group getting ready to do the 5" refractor compairison could do a side by side in each scope of these two eyepieces we could really get a final verdict...
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Daren
Covington, GA
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gnowellsct
professor emeritus
Reged: 06/24/09
Posts: 729
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Doh! The field of view on the wider field eyepiece will necessarily have more stars, UNLESS it is masked down with an artificial field stop.
You're not really interested in number of stars in any case. It's the faintest stars that are of interest, they can be compared to a photometric study (Luginbuhl and Skiff's book has a few). The trick is to have the observers do positional sketches of all the faintest stars they see in order to do a positive ID of them.
Any ol piece o' glass can bring in an 8th mag star.
Greg N
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"Aperture will get you through times of no money better than money will get you through times of no aperture."
featuring selected astrojunk:
bunch o' widefield eyepieces
bunch o' narrowfield eyepieces
couple o' Barlows
couple o' scopes
couple o' mounts
couple o' tripods
and a pier 'n' stuff
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Jim Romanski
scholastic sledgehammer
Reged: 01/02/05
Posts: 842
Loc: Guilford, Connecticut
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Quote:
you want your eye to be as relaxed as possible and to have the best light transmission.
When I was taught about the nature of light and seeing things I was not taught about light transmission but rather about contrast. Light transmission is important for seeing dim objects but contrast is what allows you to see anything. That is why filters work. All filters reduce light transmission. They do so selectively but they all reduce it. So why do they help us see things…contrast.
Theoretically, and typically, an eyepiece with fewer pieces of glass should allow more light transmission. If all other things were equal then they’d give better contrast as well. But that is never the case. Many things contribute to contrast such as eyepiece baffling, glass type, glass smoothness, chromatic aberration correction, image sharpness and of course coatings. I’ve had older cheap eyepieces (Kellners, Plossls, Orthos, etc.) all of which have fewer elements than my more expensive wider field eyepieces with many more lens elements. But on head to head comparison on planets and the moon I’d rather use my Radians and Naglers (Didn’t have the Ethos back then). Granted I only had older inexpensive versions but if the number of glass elements were the only reason for better contrast then they would have outperformed my more complicated eyepieces and I would have kept them. Instead I’ve given almost all of them away to beginning astronomers to learn on.
Now I don’t doubt that a well made simple design can give a superior image at its center as compared to a more complicated design. But I don’t believe that it just automatically does so because it has a simpler design. Most of the other things that can impair contrast like the ones I mentioned above must be equal or better in order to see the difference.
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Jim
17.5" Dob "Project"
13.1" Coulter
8” Cave
NP 101 on a CG-5
25x100 binos
Naglers, Ethos, etc.
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Jim Romanski
scholastic sledgehammer
Reged: 01/02/05
Posts: 842
Loc: Guilford, Connecticut
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Quote:
Real observing.
Real observing? What do you call the observer searching for supernovas? What about the ones looking for comets? There are many types of observing that I would consider “real observing” that don’t involve looking at precise detail at high magnification. A comet hunter would want the widest field they could get. And they would want an eyepiece that was very well corrected so that the objects just entering the field didn’t all look like comets…same with the supernova hunter. And on the Moon when I’m looking for the Hadley Rille I want to see as much field as possible. Why? It’s easier to find things with you have context and can see a larger view. In fact I always want a large field of view when I look at the Moon. It’s a very large object. The only times when I don’t need as much field are planets and perhaps planetary nebula.
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Jim
17.5" Dob "Project"
13.1" Coulter
8” Cave
NP 101 on a CG-5
25x100 binos
Naglers, Ethos, etc.
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12211
Loc: Los Angeles
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Quote:
I think that it is more likely that the wide fields "lose light" by spreading it in ways that make the faintest stars at the margin disappear. I noticed in my Nagler 17T4 that in my preferred position there is actually a circular pool of kidney bean that is very very very very faint, but there.
regards
Greg N
This is one Nagler I owned that I did not like. I found that when my eye was perfectly positioned behind the eyepiece I could see a ring of reduced light around the periphery of the field--not quite a kidney-bean shaped blackout, but always there, and especially visible if the whole field was filled with Milky Way.
I did not see that effect in the 22T4 or the 12T4 or the 16T5, but it was always there. It looked like classic vignetting, but since longer focal lengths displayed none, it wasn't from the scope.
Only one other eyepiece I've owned has such a noticeable dimming of the edge--the 35mm 1.25" 5-element "Pseudo-Masuyama" (aka Super Plossl)eyepiece (from several brands).
If I were a betting man, I'd say the eyepiece itself did not have full illumination at or near the edge.
Now what I saw was lateral--near the edge. What you've described is in the center, and that, I believe, would result from having your eye centered, having a small pupil diameter in the eye and a large exit pupil from the eyepiece. I bet it was most noticeable on the Moon, too.
You don't say in what type of scope, but I'd bet either a Schmidt-Cassegrain or a sub-8" reflector with a secondary size chosen for full illumination of a 1/2" field. In other words, if you look for it in the daytime, it'll be easier to see. You've perfectly described the effects of secondary shadow in the image.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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sixela
Postmaster
Reged: 12/23/04
Posts: 10848
Loc: Boechout, Belgium
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Quote:
I mean, how you going to pick up chicks in your Ferrari without a right seat?
You mean "how do you observe wide objects at close to optimal detection magnification for the details when at the optimal magnification the object doesn'fit in the field of a narrow AFOV eyepiece"?
Mhhh..picking up chicks sounds a lot nicer.
It's pointless to argue with deSitter - he picks tests designed to favour non wide field eyepieces and then simply dismisses any observing style that doesn't fit that model as irrelevant. It's not a proof of anything but circular reasoning.
Nobody in his sane mind would pick a Nagler over an ortho for looking at the trapezium in M42 only. What's good about an Ethos is that you can often use enough magnification to detect E and F *and* still see more whisps of nebulosity extending very far away from it, all without moving the scope or losing context.
Sketching large objects is a pain in the lower back without a wide field. With an ortho, you never seem to get the location of your field stars vs. the other star and the location of small details right, or the proportions exactly right, because you can't see it all at once at the magnification the object deserves or needs. In effect, you have to do what photographers do when they make mosaics.
Of course, you *can* use low magnification, get your reference stars on the sketch, and then start navigating, going back to lower magnification to get the orientation of a small detail just right when the high mag view has too few field stars to do it well, but forgive me for thinking that it's like flogging yourself on the back and telling yourself it doesn't hurt.
And there's no hard rule that makes photons count the number of air-glass transitions and nothing else: Pentax XOs have one more lens group than orthos but the excellent coating and baffling makes a 5mm handsomely outperform all 5mm orthos except the Zeiss ones (ubt including the old Pentax ones!).
And on Jupiter, some nights ago, I actually picked a Zeiss-barlowed Pentax XW as the eyepiece of choice. Yes, it has lots of lens groups and "too much glass", but the added eye relief actually helped to reduce the glare caused by the reflection of Jupiter on the eyeball (even at 400x in my scope I have an exit pupil close to 1mm and Jupiter can be darn bright), and the excellent coatings means that even the barlowed combination almost feels like a simple eyepiece design (and the scatter around Jupiter is markedly less present than in e.g. a T6 Nagler).
That night I could also use an ortho and Pentax XO with a filter to reduce that irritating glare (I have both at similar effective focal lengths to my barlowed Pentax XW) and I actually tried it -- and would have expected to prefer it, because I only happened to use the XW because I had been gawking at deep sky objects.
But I couldn't achieve the same depth of colour that I could with the unfiltered Pentax XW (even though the detail was still there, with a complex group of three barges playing with each other in the NEB, the subtle tone differences weren't as vivid and the festoons close by didn't seem quite that blue anymore).
Guess what? I used the Pentax XW because that night it worked better, somehow. I don't like to be guided by religious fervour above all else.
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400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
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sixela
Postmaster
Reged: 12/23/04
Posts: 10848
Loc: Boechout, Belgium
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Quote:
Interesting points made on all sides. Taking out the amount of light loss due to more elements is there a way for us to judge empirically if a simpler design does indeed show better detail on-axis?
It even depends on the scope. Star test an f/4 with an ortho and you'll be amazed at the amount of spherical aberration in the star just outside of focus. And yes, from experience that's just enough to have effects on the in-focus image, even though you can see it less obviously there.
To quote Roland Christen, just to show you I'm not dreaming:
Quote:
Try different eyepieces if the refractor is faster than f10, you may see different contrast effects. Plossls and some Orthos tend to add undercorrection to the image. When you find the eyepiece that gives the most equal out-of-focus images, use it in your observing. Hint - multi element eyepieces like the Naglers have the best spherical correction for fast scopes.
Yes, Rolando's not a man of many dogmas (even though he obviously really likes refractors, I could never ever catch him displaying the irrational exuberance some of his customers display).
I must confess that in fast scopes, you can usually find a good barlow (like the Zeiss one), an ortho, and find a spacing in which the combination works better at not displaying on axis spherical aberration than even a Nagler or Radian, but in my experience anything without an obvious negative field lens group is doomed to more SA (and that includes unbarlowed Plössls, orthos, monocentrics but excludes the Pentax XOs).
Of course, deSitter will retort that we shouldn't be using fast scopes at all if we're serious (even though I seem to remember he's had encounters with a Meade SN8, a simple eyepiece design torture bench par excellence). But that's exactly what I'm doing by using a Zeiss barlow, and I still have one less piece of glass than someone with an SCT and a star diagonal between me and the object.
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400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
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Darenwh
Pooh-Bah
Reged: 05/11/06
Posts: 1219
Loc: Covington, GA
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Quote:
Doh! The field of view on the wider field eyepiece will necessarily have more stars, UNLESS it is masked down with an artificial field stop.
Doh! That is what this line from my post was saying. You should really finish reading the post before commenting.
Quote:
Lets say a 13mm Ortho vx a 13mm Ethos with a field stop added to stop it down to the same FOV as the Ortho.
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Daren
Covington, GA
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gnowellsct
professor emeritus
Reged: 06/24/09
Posts: 729
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Quote:
I bet it was most noticeable on the Moon, too.
You don't say in what type of scope, but I'd bet either a Schmidt-Cassegrain or a sub-8" reflector with a secondary size chosen for full illumination of a 1/2" field. In other words, if you look for it in the daytime, it'll be easier to see. You've perfectly described the effects of secondary shadow in the image.
This was on M56 if memory serves. Small not too bright dob. I would say that it was a 2ndary shadow effect but as I moved my head in and out I could see the darkness move and shift positions. Classic kidney bean in some positions, shrinking towards the center as I moved away.
It was a C14. GN
--------------------
"Aperture will get you through times of no money better than money will get you through times of no aperture."
featuring selected astrojunk:
bunch o' widefield eyepieces
bunch o' narrowfield eyepieces
couple o' Barlows
couple o' scopes
couple o' mounts
couple o' tripods
and a pier 'n' stuff
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gnowellsct
professor emeritus
Reged: 06/24/09
Posts: 729
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Quote:
Quote:
Doh! The field of view on the wider field eyepiece will necessarily have more stars, UNLESS it is masked down with an artificial field stop.
Doh! That is what this line from my post was saying. You should really finish reading the post before commenting.
Quote:
Lets say a 13mm Ortho vx a 13mm Ethos with a field stop added to stop it down to the same FOV as the Ortho.
Doh! I issued a Doh! when it wasn't necessary!!! GN
--------------------
"Aperture will get you through times of no money better than money will get you through times of no aperture."
featuring selected astrojunk:
bunch o' widefield eyepieces
bunch o' narrowfield eyepieces
couple o' Barlows
couple o' scopes
couple o' mounts
couple o' tripods
and a pier 'n' stuff
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PJF
professor emeritus
Reged: 05/06/04
Posts: 667
Loc: UK
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Quote:
I am beginning to think the only way we are going to decide this once and for all is a shoot out between two eyepieces.
Nah, too much wriggle room there. The way to end it is we buy Harleys and wear ugly tattoos and ludicrous facial hair.
deSitter wrote:
Quote:
...I vowed never to argue about eyepieces with bikers again.
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Peter
10x50 binocs
ED80 'frac
6" f/12 Maksutov
6" f/6 Newtonian alt/az
10" f/4.3 Newtonian alt/az
Bryce
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2925
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Quote:
Some of the complex designs actually have been measured to have high light loss, including the TVs and 14mm Meade UWA which came in somewhere around 89 to 90%. The XWs in yellow green are 96%. That leaves very little "room at the top" for a simple eyepiece to make a detectable difference. And these are eight lens designs, some of them anyhow, so if you go the distance in terms of glass quality, coatings, etc., it becomes an overstatement to say, as is the wont of my fellow Pentaxian addict Drl, that glass sucks light out of the eyepiece.
Yes the primary image munger in complex eyepieces is, thanks to multicoatings, not light loss even though it is there - by "loss" I'm not just referring to brightness but the entire image. The main loss in heavy glass is from optical error accumulation. You can even see this in a cheap filter. The next factor is milkiness caused by both bulk scatter in heavy glass and surface narrow-angle scatter coming from the same multicoatings that make complex eyepieces possible.
As for fast scopes, I have an f/4.5 and and f/4 so I voted with my arms. Other things are not always equal. Even in those, when doing concentrated observing I prefer my Orthos which are not great at the edge (not as bad as the ray traces would suggest however). The coma is so bad it doesn't matter anyway.
I do have my wide fields and coma corrector for star fields and clusters.
-drl
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hfjacinto
Almost got me
Reged: 01/12/09
Posts: 2068
Loc: Union,NJ
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The Kecks and almost all professional scopes do not use eyepieces. Imagine the ep needed for the Keck, if your F ratio is correct, a 13 MM Ethos would exceed your 7MM exit pupil and that would give you 26,923 magnification. I can tell that is just too much power for NJ, maybe not between Umatilla and Astatula, but in NJ I have a hard time using 250X
We would probably also need a paracorr.
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C9.25 ASGT 9*50 MM Finder,FT Focuser & 2" Diagonal
Meade LXD 75 6 Inch SNT w 9*50 MM Finder
5,6,9,14.5 MM Zhummel Planetary EPs
13,17,21,24,31,36 MM Baader Hyperion
6.7,8.8 MM Meade UWA & 11 MM Nagler T6
Planetary, OIII and Narrowband Filters
Thousand Oaks Dew Control w Kendrick Heaters
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