Talk:Eyepiece/Archive 1

Please, give even weight to microscope eyepieces.
I was trying to use this article to research eyepiece design for microscopes. There's an extensive list of telescope eyepiece designs, but little if any references to microscope eyepiece design. I know that the amateur telescope community is large, but if microscope and telescope eyepieces are going to be combined into a single article (as they should), there should be an equivalent amount of detail provided for the former. Here is a good example of information that could be added: http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artmar01/eyepieces.html

—Preceding unsigned comment added by 169.237.3.137 (talk) 17:14, 22 April 2009 (UTC)

Splitting eyepiece types to different pages
What about seperate pages for each eyepiece design? I think it is reasonible to expect people to want to know about specific eyepieces. Currently I'm studying up on some physics and eyepiece issues and hope to write a little more to the todo list as well. Flehmen 02:00, 19 August 2005 (UTC)


 * Hi Flehmen -- thanks for adding stuff. The main concern I'd personally have about splitting it into separate articles (right now) is that they'd probably all be stubs, by wikipedia standards..... unless you're planning to write quite a full article-length thing about each one (sections, subheadings, etc).  The list was originally a list because there weren't any descriptions, but it probably would have been a group of sub-headings if there were descriptions available at the time of original writing.  How about doing it this way first?  I'll go and edit the article after writing this with the format I have in mind.  If the descriptions become very detailed, it might then be more worthwhile to split them out. Izogi 03:23, 19 August 2005 (UTC)


 * Yep, that makes sense for now. I do intend to write enough of an article on each one to make them seperate pages but I'll modify this one as time progresses and do some cut and paste while making the new ones. I should have known you could use a pipe to get rid of the &#035;. Flehmen 12:04, 19 August 2005 (UTC)


 * Sounds good to me. I'm glad you're able to write about the technical aspects of different types of eyepieces.  That's something the whole article had been missing. Izogi 21:44, 20 August 2005 (UTC)

Merging of Eyepiece lens article
I merged the "Eyepiece lens" article into this one, which has a more appropriate name since an eyepiece is more than a lens, and it has a lot more links to it.

Refactoring of focal length
I've just done some brief refactoring of the focal length section, since I thought it read a little confusingly switching between telescope and microscope eyepieces as it did. I wanted to clarify a bit more about microscope eyepieces and why they're more often expressed using magnification power, but it's not something I know a lot about so I've left it alone for now.

Can anyone comment if this is because microscope eyepieces usually remain with one microscope to the point where the actual focal length isn't very useful? That's what I'd guess the reason is, but not being someone who uses microscopes often, it's only guessing.

Izogi 03:36, 30 Mar 2005 (UTC)

Working on copyvio free eyepiece pictures and diagrams.
Just a note to let you guys know I'm still working on the artcle between things. I'll be putting up a generic eyepiece picture and working on ray-trace diagrams for the eyepieces we have at the moment. What do you think about adding a section on eyepiece projection (for CCD, film, and solar observing)? I've added a reference to barlow lenses. Flehmen Work with me 15:18, 31 August 2005 (UTC)
 * Sounds reasonable to me to an extent, although the topic of projecting might fit better into a different article (though I'm not sure what). If it's in the eyepiece article, it should probably be written so as to focus as much as possible on the role of the eyepiece, why eyepieces are important for it, and whatever else (if that makes any sense).  That's my thoughts, anyway. Izogi 06:28, 1 September 2005 (UTC)

I have put up a picture of eyepices in general and an image of the 2 inch (50.8 mm), a 1¼ inch (31.75 mm), and a 0.965 inch (24.5 mm) eyepiece types. I may start work on a few diagrams next.... if anyone else is making some let me know so I wont duplicate work. Halfblue 17:25, 5 January 2007 (UTC)

Field of view formula assumption
I've just given the Field of View section an overhaul, to try and clear it up. It's probably not finished, so if anyone wants to attempt making it clearer, go for it by all means and I won't feel offended. However, I noticed that the following formula (which I adapted from the one originally added by an anon user) never stated what units the telescope's focal length need to be measured in.
 * $$FOV_C= \frac{57.3d}{f_T}$$

In my added explanation in the article, I've assumed that $$f_T$$ needs to be expressed in mm, which would be consistent with what d was stated as needing to be expressed as. If anyone could confirm this assumption, though, I'd feel somewhat better about it. Izogi 10:22, 6 September 2005 (UTC)
 * That's correct. Good catch. I'll add a reference to my physics text in the article when I get home. Flehmen Work with me 11:51, 6 September 2005 (UTC)
 * Excellent, thanks. Izogi 05:55, 7 September 2005 (UTC)


 * I am confused. If I use this formula and calculate $$d$$ from the other parameters I get strange values. For example, if I use a telescope with a focal length of 1000mm and a $$FOV_C$$ of, say, 60° I get $$d = \frac{60*1000}{57.3} = 1047$$ which is a very out-of-place value for the diameter of the eyepiece field stop, in mm. Did I miss something? --Alexander Forst-Rakoczy (talk) 16:47, 24 August 2010 (UTC)

More refactoring of Focal Length section
I've been going through the Focal length section again to try and tidy it up further, and I've discovered that based on the previous text, I'm a bit confused about how microscope eyepieces are marketed and used. With the re-factoring, I've assumed what I think it was saying, which is that all eyepieces are referred to using a "magnification" value that would be correct if they were used in a 250 mm microscope. Because modern microscopes are 160 mm focal length, however, the user needs to multiply the eyepiece's mag value by this multiplier to get the real magnification. Am I anywhere near correct with this? I'm not sure if I understand the whole objective power thing at all. I hope I haven't confused things further, and as always feel free to edit if you know better. Izogi 06:56, 12 September 2005 (UTC)

Notable products?
I have moved these sections to talk because they seem to be promoting the features of specific products without providing 3rd party references to assert notability. The article is about eyepieces in general so jumping to specific comercial astronomical references like this may be a little off topic. I leave them here for discussion and any re-intergration of relavent material. Fountains of Bryn Mawr 07:07, 2 February 2007 (UTC)

"--Other Eyepiece Types--

''With the success of TeleVue's version of the Plössl eyepiece (with a 50° FOV), in the mid-1980's, Nagler introduced the most famous of all of the eyepieces that bears his name, the Nagler Type 1. With an apparent FOV of 82°, this type of eyepiece, with at least seven lens elements, gives its user a "spacewalk" view (the view created as seen by astronauts wearing either the old Apollo/Skylab A7L or Shuttle/ISS EMU suit "bubble helmet" and its associated sunshade cover).''

''Since then, the Nagler eyepieces have expanded to include focal lengths ranging from 2mm to 31mm, with the 31mm weighing over 2 lbs and measuring over 3 inches in diameter at its widest point. Some of the longer focal length Naglers have a 2-inch barrel, and thus are only usable with telescopes with either 2-inch focusers (for Newtonian and Dobsonian telescope users) or special 2-inch 90° right-angle diagonals (for users of refractors and modern-day Schmidt-Cassegrain variants). In addition, TeleVue has also produced the "Panoptic" eyepiece, with a 68° apparent FOV, allowing those astronomers who have a more modest budget (the current 31mm Nagler Type 5 sells for around $640 USD [as of 2006]) to experience a high-quality image with an excellent field of view.''

''Along with the Series 5000 Plössl, Meade has also introduced a Series 5000 "Super Wide Angle" (68° FOV) and Series 5000 "Ultra Wide Angle" (82° FOV), with views that rival those of the TeleVue eyepieces, but costs hundreds of dollars less. The 24mm Series 5000 Ultra Angle eyepiece is the standard eyepiece that is sold with the new RCX4000 "Advanced" Ritchey-Chrétien telescope."''

"Common eyepieces having 20mm eye relief are Vixen Lanthanum, Pentax SMC XL, and Tele Vue Radian. They are particularly suitable to be used with glasses."

"Al Nagler owner of Tele Vue Optics created a large demand in the amateur market for this eyepiece when he designed a high quality Plössl in the 1980s. In the 1980's, Meade and its rival Celestron made the Plössl (usually a 25mm or 26mm) as a standard accessory for their line of Schmidt-Cassegrain telescopes.  Since then, Celestron still produces Plössls with 55° FOV, while Meade introduced, in 2004 as part of its 5000 Series eyepieces, a Plössl with a 60° apparent FOV (to compete with Tele Vue)."

Apparent field of view only abstract?
From the article:


 * By itself, the apparent field of view is only an abstract value, but it can be used...

I disagree with this but it isn't something I can express clearly and concisely. The AFOV is itself an important value since it indicates how big the overall image appears through the eyepiece. The AFOV is the angle formed between the eye and the light from two opposing sides of the image - a wider AFOV gives a bigger (as opposed to higher power) image than a smaller one. That is a small FOV will appear to show a small "distant" "disk" through the eyepiece, while with a bigger AFOV the same disk will be much larger and the edges of the image less intrusive - with the very widest AFOV you almost feel as if you are looking "into" rather than "through" the telescope since the edges of the image are pushed out into your peripheral vision rather than the central area of view. CrispMuncher (talk) 21:39, 20 January 2009 (UTC)


 * Well I've made a stab at sorting this out and added an image to try and clarify things. I'm still not quite happy with my image caption, though, since it appears a little 'wordy'.  Feel free to try and condense it but try not to leave any pertinent details out. CrispMuncher (talk) 20:30, 25 January 2009 (UTC)

Needs some work...
This is an interesting article, and in some ways thorough, but it's also seriously flawed. The most obvious problem is that it reads like the reasonably well informed, but opinionated, ideas of an amateur astronomer rather than a professional optics manufacturer or scientist. There's lots of information, but no inline references. Comments about cost, value and performance are liberally scattered about, but without citations to support them. Telescopes are mentioned three times as often as microscopes. The section on Nagler eyepieces for example exemplifies the problems with this article; it's like listening to the thoughts of an astronomy club member rather than reading something from an optics textbook.

The external links also need to be pruned back. Almost all of the links there are basically repetitions of what's said in the article, though this time very obviously by amateur astronomers rather than professionals.

As I said before, this is an interesting article. But it could be so much better if it was morphed into something about eyepieces rather than amateur astronomers' opinions on telescope eyepieces.

Cheers, Neale Neale Monks (talk) 09:39, 22 November 2009 (UTC)

Is It Really True
Yes, refracting telescopes suffer from longitudinal chromatic aberration. How do you relate that to the focal length? Microscope objectives are very short focal length (some about 1 mm) yet they are not free from the disease. On the other hand, using glasses of two different refractive indices one can correct it only to the extent that the spectrum is folded over to itself. That is to say that it is reduced by half and becomes managed.

The article does not define the terms used accurately.Ck.mitra (talk) 13:12, 5 January 2010 (UTC)

Eyepiece Designs section
A few comments on the Eyepiece Designs section:

It might also be instructive to mention that the Nagler design is made possible only through the use of anti-reflection coatings; without them, the loss of light at each air-to-glass interface of a five-group design would produce a dim final image, with the reflected light contributing to ghost images and low overall contrast.
 * 1)  Why are the "Historical" designs of Galileo and Kepler shown only in diagrams at the end, without descriptive text?  It seems a bit silly to present an incomplete list of ten designs going back 300 years when it would be straightforward to complete the list with twelve designs going back 400 years.  (Fourteen designs, including Dolland and Herschel.)  I think most would consider the Huygens design of 1703 to be within the realm of "Historical"; the division seems arbitrary.  Moreover, the reader deserves to know the optical characteristics of those very early designs, to the same level of detail as the explanations of the others.  Discussion of the Galileo design would also serve as a good base for the mention of inverted images, a distinction that matters for terrestrial optical systems (like binoculars), and which most first-time telescope users are quite startled to discover.
 * 2)  There is another claim to the meaning of the "RKE" name given to Edmund Scientific's eyepieces, that it records the initials of the 2nd generation owner of the company, Robert K Edmund.  I haven't added that claim to the current article because I have no supporting reference, although the claim appears in various online forums.
 * 3)  The section on the Nagler design needs attention from an informed author.  Errors include:
 * 4) referring to the Ethos design as a variety of Nagler (Al Nagler himself gives it the status of an independent design)
 * 5) referring to the Ethos as Nagler's design (Nagler credits TeleVue optical designer Paul Dellechiaie with its creation)
 * 6) the statement "every Nagler has a negative doublet field lens, which increases magnification" (the negative field lens, before the focal plane, increases focal length)

4.249.0.42 (talk) 13:29, 4 May 2010 (UTC)


 * I was seeing most what you describe the last time I took a whack at trying cleaning up and improving this section. Could be made clearer. The diagrams were added piece meal in the crufty sorta wikipedia way. They bring up the need for expansion to show the full history of eyepiece development. They also bring up a big problem with the diagrams re:they have incorrect captions. Kepler did not invent the convex lens eyepiece, it was used in Zaccharias Janssen 1590 compound microscope. Galileo did not invent the negative lens eyepiece in 1609, it was already being used in the Netherlands telescopes in 1608. The Huygens 1703 date has him inventing that design 8 years after he was dead, a bit impossible. Reverted the images to the old un-captioned ones. Fountains of Bryn Mawr (talk) 14:46, 26 May 2010 (UTC)

define "field lens"
The term is used in several places but it is never defined. Are there other named lenses in an eyepiece, or is this the only one?

--jon