TheSkySearchers

I just brought this over from the old place. I suggest we make this sticky?

http://www.brayebrookobservatory.org/Br ... PIECES.pdf

My vote is yes for a stickie, but let me ping the other CoAs to get some additional buy-in. A quick question, is this public domain information? BTW, this is an awesome informational reference.

Cheers,
JT

JayTee wrote: ↑Sun Oct 27, 2019 3:50 am My vote is yes for a stickie, but let me ping the other CoAs to get some additional buy-in. A quick question, is this public domain information? BTW, this is an awesome informational reference.

Cheers,
JT

Yes, it is public domain. The link is direct to Chris Lord's website and is open access!

Thanks for bringing it over nFA. This reference is must have/read for anyone who is into EPs.

You had me wondering what was going on Bigzmey, I was sure I had pinned this a long time ago

Lady Fraktor wrote: ↑Mon Feb 03, 2020 9:52 pm You had me wondering what was going on Bigzmey, I was sure I had pinned this a long time ago

Somehow missed the post earlier. Also, figure out it is good to bump it for more exposure.

Here's Lord's eyepiece evolution tree: It was a jpeg originally, but it is so big that it works better as a pdf. Zoom in and navigate around the tree.

Very interesting resource notFritz. Thank you.

Interesting article but way too technical for me, a few thing stood out :
on page 44
" It is also quite inappropriate for example.
equipping an f/10 Schmidt-Cassegrain
with an f/6.3 focal reducer, or an f/4
Dobsonian light bucket with a coma corrector, and then using an 8 element
ultra-wide angle eyepiece. Unless that
is, it is your purpose to loose as much
light as possible and drive image quality
already perilously close to the diffraction
limit, well below it."
I have done these things and with the focal reducer on a F10 SCT using a Panoptic 27mm I would agree the result was not wonderful but I also manage to borrow a 21mm Ethos that I coupled it with my F4.5 Obsession and Paracorr II......I cannot comment on distortion but the sharpness, edge to edge, in the views were excellent!

The other thing what court my attention is the "Pretoria" eyepiece. Someone asked, on another forum, if there are "telescope correcting" eyepieces available and my response was that I don't think so because the market for it would be too small, I was wrong but right about the market because they are not available anymore. Then the name?! Pretoria is the administrative capital of South Africa, why name a eyepiece after it?

The name is from the design inventors.

https://myscienceshop.com/product/digi ... /tmkpdf029

Pretoria has been a site for observatories so that’s likely the reason I’d guess. If I recall correctly Harvard University had a southern observatory station at Pretoria as did John Herschel?

PS I found the answer! in another article : "Finally, there is an alternative to the Paracor. It’s called the Pretoria eyepiece. It was designed in the early 1980s by H. W. Klee and M. W. McDowell of the National Physics Research Lab in Pretoria, South Africa."

Here is the article: https://astromart.com/reviews/telescope ... stigmatism

notFritzArgelander wrote: ↑Fri May 22, 2020 9:01 am The name is from the design inventors.

https://myscienceshop.com/product/digi ... /tmkpdf029

Pretoria has been a site for observatories so that’s likely the reason I’d guess. If I recall correctly Harvard University had a southern observatory station at Pretoria as did John Herschel?

The Harvard University southern Station were originally in Peru but were moved to Bloemfontein in 1927. It is called Boyden and is 25 Km outside Bloemfontein. I have access to the observatory and have done some of my best viewing with the 15" Obsession from there.
here is a photo of some famous people taken at Boyden in 1952 : In the centre we have Jan Hendrik Oort and Georges Lemaître

PS the Metcalf telescope, depicted on our club badge, were used to take photographic plates for Harvard University at Boyden, it is still being housed there.

This is an excellent work by Chris! Quite comprehensive and a lot of research on his part. Is Chris a member here?

WilliamPaolini wrote: ↑Thu May 27, 2021 12:33 am This is an excellent work by Chris! Quite comprehensive and a lot of research on his part. Is Chris a member here?

I'm not aware if he is.....

WilliamPaolini wrote: ↑Thu May 27, 2021 12:33 am This is an excellent work by Chris! Quite comprehensive and a lot of research on his part. Is Chris a member here?

Unfortunately he is not. The treatise is available from his Brayebrook Observatory site.

As an Erfle-gatherer, and see how some are better than others, I reckon there is common labelling, such as with Plossls/ symmetricals.

Some "Erfle" eyepieces could be Zeiss Astroplantakular, Kaspereit, original Panoptic, Konig, Bertele or whatever. All "Erfle", easier to put on a barrel or label & more widely known than the true longwinded name.

Ex-military is a separate fan base for optics, as other things.

Erfle is a pretty adaptable type of the eyepiece designs.
The Ur-design has the symmetrical convex/convex middle lens, two lens materials out of five are the same.
The Astro-Planokular has an asymmetrical convex/convex middle lens, and just three different glass materials in its five lenses. Optimized for the observatory grade refractors.
The Zeiss binocular eyepiece, a derivate of Erfle, has two positive focus lenses between the doublets, both of them with different glass materials.

The modern wide field designs (tactical optics) employ a higher level of complication in the material choice and in the variety of the lens surface curvatures,
https://spie.org/publications/pm92_1124 ... iece?SSO=1
https://spie.org/publications/tt82_83_eyepiece?SSO=1

Other examples are the bull's eyes from Leica, Rodenstock (also in my collection), Zeiss, and the Swiss WILD Heerbrugg (also in my collection),
http://web.archive.org/web/200701271148 ... de/F30.htm

The design of the Swarovski 20x S W (f=23mm) spotting eyepiece (in my arsenal) goes back to the Zeiss binocular eyepiece, a derivate of Erfle.

Best,
JG

PS: The SPIE.org page is on maintanence 14 - 15 August, 2021

You might like this information, too:
https://www.telescope-optics.net/eyepiece_raytrace.htm

Don Pensack wrote: ↑Sat Aug 14, 2021 4:26 pm You might like this information, too:
https://www.telescope-optics.net/eyepiece_raytrace.htm

The Erfles, and some other eyepieces are desribed by the Zeiss designers in

DIE FERNROHRE UND ENTFERNUNGMESSER
Dr. Phil., Dr.-Ing. E. H. Albert König, and Dr. Rer. Nat. Horst Köhler
3rd enlarged edition, Springer-Verlag Berlin and Heidelberg, 1959

reprint on my bookshelf,

JG