Is there some kind of RANKING ???

Started by BABOafrica, 05/21/2011 03:01AM
Posted 05/21/2011 03:01AM Opening Post
I have very little practical experience but I've been reading a lot on eyepieces lately. There seems to be an overall ranking (in descending order):

1) Televue Ethos

2) Televue Nagler

3) Baader Hyperion

4) All the rest

Is this an exaggeration?

Clear skies dusk to dawn
Joe

In lumine tuo videbimus lumen.

8O Home-made 10” Dob / Home-made 4” refractor

EPs: Konig 32mm (1.25") / Zhumell WF 30mm (2") / Nagler 13mm T1 / Orion Sirius Plossls 25 & 10mm / Zhumell Plossl 9 mm / Meade MA 9mm
Posted 05/21/2011 06:37AM #1
Joseph:

Every discussion of eyepieces should begin with a quote from page one of Jean Texereau's classic work: "How to Make a Telescope", first published about 60 years ago:

"It is not usually made clear, that these elements,
objective and eyepiece, are by no means comparable in
importance. The astronomer's hopes are almost wholly tied
to the size and quality of the objectve. The objective of
even the smallest telescope, because of its larger
dimensions, the severe optical requirements it must meet,
and the difficulty of its construction, completely
overshadows the eyepiece."

There are lots of good eyepieces out there. To enjoy the view, one does not need to invest hundreds of dollars in each eyepiece, there are very good eyepieces available for $50 and even less. For example the TMB Planetary eyepieces do a good job even in a moderately fast scope, have a comfortable 12mm of eye relief, a nice 58 degree AFoV and cost about $65.

There are quite a variety of attributes that are important in an eyepiece and depending upon the object and the telescope, some capabilities are more important than others.

A list might look like this, no particular order:

- Cost... needs no explanation, some very competent eyepieces can be had for $50... Some very competent eyepieces can be had for $500... The cost depends on what combination of capabilities one chooses.

- Focal length... this is how eyepieces are measured..

- Transmission/Throughput: the efficiency of the eyepiece, this can range from about 85% to about 98%. This depends on a number of factors but the quality of the coatings are very important.

- Scattered light: eyepieces vary in how much light is not quite where it should be, a bright object might have a glow around it. This is related to the design and again the quality of the coatings.

- Eye relief: the distance from the eye lens to the image. This can vary from about 3mm to 20mm or more, this is the distance between the eyepiece and observer's eye, if it is too short, it will be uncomfortable and your eyelashes may contaminate the eye lens of the eyepiece. Generally one wants at least 10mm of eye relief.

With simple eyepieces, Plossls, othos, Kellners etc, the eye relief is about 70%-80% of the focal length of the lens, a 10mm eyepiece will have maybe 7-8mm eye relief, a 5mm might have only 4mm or even less. Short focal length eyepieces that have lots of eye relief are generally what is termed, "negative-positive" eyepieces because the consist of a tele-negative (Barlow-like) front section followed by a longer focal length magnifying or positive section. The first common negative-positive eyepieces were the Naglers.

- On-axis resolution/sharpness: Most eyepieces are very sharp on-axis, that means if the object is centered in the eyepiece, the eyepiece will not cause visible aberrations.

- Off-axis aberrations: This where things get tricky and expensive. In slow scopes, F/12 for example, most eyepieces are sharp and clean right up to the edge, the field stop. Erfle's for example, at F/13, provide pinpointy stars right up to the edge. In fast scopes and moderately fast scopes, F/4-F/5-F/6-F/7, most eyepieces are not so sharp near the edge, the stars are no longer pinpoints but rather can be rather messy looking. Commonly this shows itself as astigmatism, the stars will not focus to a point. This lack of off-axis sharpness is often combined with aberrations of the objective, coma in a Newtonian, field curvature in a refractor or SCT. Also, normally the wider the field of view, the greater the off-axis aberrations...

- Apparent field of view, how big is the view, this is what people pay for... A 32mm Plossl is a pretty nice eyepiece, provide a pretty nice 50 degree AFoV in an F/5 Newtonian and can be purchased for $60. A 31mm Nagler is a very nice eyepiece, is huge, weighs about 2 lbs, costs about $600 and can provide an essentially perfect 82 degree AFoV even at F/4... People pay money for this...

There are general catagories of AFoVs;

Narrow: 45 degrees and under... Othos, Kellners, monocentrics, Ramsdens, Huygens, etc. Some are very good eyepieces on-axis.

Normal: 50 degrees, Plossls and Plossl like eyepieces.

SuperWide (SWA): 65-70 degrees. Lots of choices here. Erfles, Konigs are the original SWA designs. The Televue Widefields were probably the first improved SWAs and the TV Panoptics are the standard for comparison, "It's nearly as sharp off-axis as a Panoptic in a fast scope" is a common statement.

UltaWide (UWA): Lots of choices here but there were no simple 82 degree eyepieces. The Naglers were the first in terms of a market force and over the years they have been refined. The originals are still very good and they are the Standard which others are compared to. An owner of an F/4 Newtonian often owns an eyepiece case full of Nagler because Naglers are rated down to F/4 (and a Paracorr to correct the coma.)

There are others that are quite good. Early on in the game, Meade essentially copied the Nagler design. The Meade Series 4000 UWAs are very good eyepieces. The newer series 5000 UWAs, the ES 82 degree eyepieces are more affordable than the Naglers while providing reasonably well in a fast scope.

The Super Ultra Wides: (SUWAs my name for them) The Ethos's and the Explore Scientific 100 degree AFoV eyepieces. Again, the Ethos's are the standard... sharp to the edge in a fast telescope. It seems the Explore Scientific was copied off the Ethos, there is an Xray floating around the net that shows them side by side... it is pretty obvious who designed and who copied.

A bit of history: About 30 years ago, TeleVue transformed the amateur eyepiece market with the original Naglers. These were 82 degree eyepieces that were free from off-axis aberrations even in an F/4 telescope. It is this combination of a UWA, Ultrawide Field of view combined with ability to operate effectively at F/4 that made the Naglers and now the Ethos's so valuable and effective. They are negative-positive designs are provide wonderful views in just about any telescope...

About the list... One cannot make a list without specifying the object, the telescope and what the observer feels is important.

A list of UWAs and SUWAs has the Naglers and Ethos's at the top...

A list of SWA probably has both the Panoptics and the Pentax UWs at the top, many giving the nod to the Pentaxes.

A list of planetary eyepiece might be quite different depending on the telescope and the mount.

As far as the Hyperion/Stratus lines go, these are essentially the same eyepieces. In my experience, I would put them somewhere near the middle of the list, they are not particularly sharp off-axis, no mistaking a Hyperion for a Nagler or Panotpic....

A final thought: It has been said that eyepieces are a religion, certainly there are a lot of thoughts and opinions. But if you start with a budget and a scope, there are will be some obvious choices. And while fancy eyepieces provide fancier views, simple eyepieces show as much detail and are a whole lot more affordable.

Nuff said for one night...

Jon






Attached Image:

jonisaacs's attachment for post 140801
Posted 05/21/2011 11:09AM | Edited 05/21/2011 11:22AM #2
Joseph Babendreier said:

I have very little practical experience but I've been reading a lot on eyepieces lately. There seems to be an overall ranking (in descending order):

1) Televue Ethos

2) Televue Nagler

3) Baader Hyperion

4) All the rest

You need to ask "ranking for what purpose." I would probably agree with your ranking
for wide-field observing under very dark skies. If I were flying 2000 miles away for a
week of observing under perfect skies with a big dob, I'd probably take a case full of
Ethos and Naglers.

But in reality 95% of my observing is done in the backyard from a moderately bright
location. Here I am mostly interested in planetary / lunar / double stars with
small scopes. So I personally place a great deal of importance on high performance
per dollar, optical purity, small size, and low weight. I like to have a full set
available with many focal lengths, so I can fine-tune the magnification to the seeing.
I also find, as a practical matter, that eyepieces get banged around from time to time
-- maybe once a year the cat will knock over the observing table, or sleepy 4 AM
astronomer forgets to latch eyepiece case befor carrying it inside, etc. A full set of
orthos makes for small light case, whereas a full set of Ethos are big, heavy, and
expensive.

So my personal ranking looks like this (descending order):

(1) UO Orthos (very high quality per dollar, small, rugged, many focal lengths, easily replaced)

(2) Ultima, Ultrascopic, Masuyama (getting hard to find / replace)

(3) Pentax SMC orthos (excellent optically, very small & light, hard to replace)

(4) Nalger Zoom, Nagler Type 6, small Panoptics (bigger, heavier)

(5) all other Naglers, big Panoptics (larger, heavy)

(6) Zeiss Abbe Orthos (best optically, too precious for nightly use)

(7) Ethos (fabulous wide view, but too big, too heavy, too expensive for 95% of my observing)
Posted 05/22/2011 02:05PM #3
Joseph Babendreier said:

I have very little practical experience but I've been reading a lot on eyepieces lately. There seems to be an overall ranking (in descending order):

1) Televue Ethos

2) Televue Nagler

3) Baader Hyperion

4) All the rest

Is this an exaggeration?

Clear skies dusk to dawn
Joe

Your 1 and 2 I will buy...more or less. For one thing "how good is an eyepiece" is a subjective thing. For another thing, you've left a WHOLE LOT out. How about TV Panoptics? How about Explore Scientific's 100-degree wonders? How about William Optics' Uwans? Etc., etc., etc.

Uncle Rod

Time on your hands?
Waste it with Uncle Rod's Astro Blog!

http://uncle-rods.blogspot.com/