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Eyepiece Size History

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24 replies to this topic

#1 BobH

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Posted 23 January 2012 - 07:32 AM

Was there any particular reason why the earlier eyepieces were .965" in diameter?

#2 cuir

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Posted 23 January 2012 - 08:21 AM

Interesting question... Wiki's got no info on the origins of that barrel standard.

I'll take a wild guess that the biggest microscope manufacturer of the last century used it out some practical reason not remembered by anyone, and others copied the size for interchangibility.

#3 Pollux556

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Posted 23 January 2012 - 08:23 AM

I think it was a standard in japanese optics.

#4 Astrojensen

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Posted 23 January 2012 - 02:51 PM

It was the standard eyepiece size of Carl Zeiss, Jena from 1897 to 1995. Since Carl Zeiss, Jena telescopes were widely copied or at least served as strong inspiration for Japanese companies in the 1930'ies and after WW2, this eyepiece size somehow became the Japanese standard as well.


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Thomas, Denmark
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#5 Blake Andrews

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Posted 23 January 2012 - 03:48 PM

I will see if I can find a link. As I recall, the barrel size was dictated by material available. This was the diameter of gas piping of the day.

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Blake

#6 ed_turco

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Posted 23 January 2012 - 04:04 PM

OK, read this :)

After WWII, the US sent experts in many fields so the Japanese could develop their industries and compete on the world stage in a non-military way.

The Japanese were told that the eyepiece diameter standard was 1" or 25.4mm. Somewhere in the process, the numbers were garbled to 24.5mm, and eyepieces were made to that standard.

What could anyone have done to correct this error except leave it alone?

For those who doubt this 1" standard, look at any Alvan Clark refractor . . .
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#7 jrbarnett

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Posted 23 January 2012 - 04:22 PM

Don't think so, but funny. Zeiss has offered 0.965" format eyepieces since the late 1800s. More likely the Japanese chose to copy Zeiss when Japan began to develop its native optics industry. Note the format originated for microscope eyepieces.

Regards,

Jim

#8 Eddgie

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Posted 23 January 2012 - 05:23 PM

As others have mentioned, German and French optics used 24.5mm barrels for a very long time.

If I were to hazard a guess, I would say that the reson is that things like this often start with what the supply line can provide.

Since France has been metric since the 1600s and Germany went metric in the 1870s, my guess is that the TUBING that was used for eyepiece turrents had 25mm inner diameter.

And when your vendor has 25mm ID tubing, and you choose to use it for your eyepiece holder, then it is necessary to turn down another peice of tubing so that it will fit, and shaving .5mm off is pretty easy since the invention of the metal lathe around 1750.

Of course this is simply supposition, but often these things have practical anwsers based on supply chain. These people didn't MAKE their own tubing. They bought it from speciaist companies, and they machined it to fit their needs.

And the simplest approach would be to start with a 25mm inner diameter tube for the eyepeice holders, and turn down peices for the eyepiece barrels so they would fit.

And I agree that when the Japanese entered the telescope making enterprise, they went with the standard eyepeice size at the time.

And even modern eyepeices are not REALLY 1.25".

Modern eyepeices are actually 1.245" We call them 1.25 inch because that is the size holder they fit in.

And using THAT convention, what we call .965" eyepieces might better be called 25mm eyepeices, because that is the size of the holder that they fit into....
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#9 Jon Isaacs

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Posted 23 January 2012 - 07:15 PM

Modern eyepeices are actually 1.245" We call them 1.25 inch because that is the size holder they fit in.



Actually I think if you sit down with a micrometer and measure some eyepieces, you will find a significant variation in the barrel diameters.

As far as the 0.965 inch barrel size, it actually began when Christian Huygens was discussing his eyepiece design with Aloysius P. Nagler. Aloysius was pushing for the 2 inch format, suggesting that in the future, widefield eyepieces would be popular with the coming shorter focal length scopes. Huygens however felt that the 0.965 inch format was sufficient.

Jon
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#10 Paul G

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Posted 23 January 2012 - 07:24 PM

Modern eyepeices are actually 1.245" We call them 1.25 inch because that is the size holder they fit in.


Not always. :) I bought a Baader/Zeiss binoviewer from the first production run, they still said Carl Zeiss Jena on the center hinge. (Mods: this is my photo of my binoviewer, used by Company 7 with my permission)

Posted Image

The ZAO I's were a VERY tight fit in this BV, sometimes fitting and sometimes getting stuck. The culprit was German precision. The inside diameter of the eyepiece holder was exactly 1.25" and the outside diameter of the eyepiece barrel was exactly 1.25". Whether it fit or not was temperature dependent, differential expansion and all. Roland machined out the eyepiece holders of the binviewer a few thousandths and it worked just fine (anondizing gone of course) Baader changed the eyepiece holders for the second run.
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#11 Astrojensen

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Posted 24 January 2012 - 04:10 AM

Since France has been metric since the 1600s and Germany went metric in the 1870s, my guess is that the TUBING that was used for eyepiece turrents had 25mm inner diameter.

And when your vendor has 25mm ID tubing, and you choose to use it for your eyepiece holder, then it is necessary to turn down another peice of tubing so that it will fit, and shaving .5mm off is pretty easy since the invention of the metal lathe around 1750.

Of course this is simply supposition, but often these things have practical anwsers based on supply chain. These people didn't MAKE their own tubing. They bought it from speciaist companies, and they machined it to fit their needs.

And the simplest approach would be to start with a 25mm inner diameter tube for the eyepeice holders, and turn down peices for the eyepiece barrels so they would fit.



I don't think this is so. The eyepiece holders I've seen on all old telescopes are actually machined from a considerably larger block, so that they could turn threads on one end to fit the focuser, diagonal, etc. Many older telescopes had a push-fit adapter for small (perhaps 0.965") eyepieces for medium to high power, typically 25mm to 5mm focal length, and larger thread-on eyepieces from 30mm and up to maybe 50mm or 60mm with the same threads as the push-fit adapter. The focal plane of the larger threaded eyepieces (often huygenians) were placed so that it was almost parfocal with the smaller eyepieces in their adapter.

But WHY the 24.5mm size was chosen remains an unsolved mystery. It would have made MUCH more sense to use 25.4mm, one imperial inch, as standard, if they were after a standard pipe size to use for eyepiece barrels. Or why not just 25mm, to go with the metric system?

And 24.5mm was not even a universal standard in Europe. Britain used 1.25"/32TPI R.A.S. standardized eyepieces, There was both a 30mm and 31mm size used by some German makers well into the 1970'ies. Some early Clavé eyepieces were made with 27mm barrels, one Paris inch. Yes, there was such a thing as Paris inches, in the country that invented the metric system.

Lichtenknecker and Vixen both share the same M36.4x1 adapter thread, used for thread-on diagonals and long-focus eyepieces. Where the heck did *that* one come from and why do they both share it???? It's such an odd number that two companies sharing this particular thread size on their telescopes can hardly be a coincidence.


Clear skies!
Thomas, Denmark

#12 bgavin

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Posted 24 January 2012 - 10:58 AM

If I were to hazard a guess, I would say that the reason is that things like this often start with what the supply line can provide.

Since France has been metric since the 1600s and Germany went metric in the 1870s, my guess is that the TUBING that was used for eyepiece turrets had 25mm inner diameter.

This was my first thought, also.
Materials at-hand.

#13 Monoeil

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Posted 24 January 2012 - 11:52 AM

You are right, Clave eyepieces were produced with a 27mm or a 50mm sleeve.

Even if France was the first to use the metric system, ASTM rules are still used there for some industries like oil. :smirk:
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#14 ed_turco

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Posted 24 January 2012 - 04:41 PM

Jim: Please don't consider this a "gotcha." I have the deepest respect for your comments and can only wish that mine were as good.

There is, or was, a .917" standard for microscope eyepiece diameters.

And, the eyepieces for my club's 8" Alvan Clark were all 1.0", until replaced.


:bow:

#15 Astrovelo

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Posted 13 February 2013 - 11:29 AM

Interesting stuff. I have a Cooke 3.25" Photovisual telescope with an objective dated 1895. The push fit eyepieces have an OD of 30mm (1 3/16"). So I wonder if the tube was made elsewhere.

This size is a bit of a pain as modern 1.25inch eyepieces are just 1mm or thereabouts too big. I have an adapter, tailormade by Broadhurst & Clarkson, to take their RAS eyepieces (but I couldn't afford to buy these with my pocket money in the 60's when I had the adapter made!) So the only off the peg solution I can find is to put a RAS/1.25" adapter into this, but I wonder if I'll end up with vignetting. Alternatively, I could get a new adapter made.

#16 Sarkikos

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Posted 13 February 2013 - 12:21 PM

As far as the 0.965 inch barrel size, it actually began when Christian Huygens was discussing his eyepiece design with Aloysius P. Nagler. Aloysius was pushing for the 2 inch format, suggesting that in the future, widefield eyepieces would be popular with the coming shorter focal length scopes. Huygens however felt that the 0.965 inch format was sufficient.

Jon


:funny:

#17 csrlice12

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Posted 13 February 2013 - 12:56 PM

Tired of his carnival life selling tickets to the Hall of Mirrors; Little Johnny Dobson makes a life altering discovery........

#18 Starman1

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Posted 13 February 2013 - 03:58 PM

If you see a lot of "classic" telescopes, you realize that many of the eyepieces were made for the scope at the time the scope was made. I've seen diameters of 22.0, 23.8, 24.5, 25.4, 30.0, 31.75, 32.0, 35.0, 2", 2-3/16", 3", 4" and others I can't remember off the top of my head. I think some of it was the sizes of lens available, the sizes of tubing available, the lack of mass-manufacturing, and the idea of early manufacturers that a telescope had to be delivered with a complete set of eyepieces for the customer to use.
A lot of these early eyepieces were Huygens, Ramsden, Kellner, and other types now long obscured by the depths of history. The standardization on specific sizes came later. The 2" size wasn't new when recent eyepiece companies started making it, and neither will be 3" or 4" if we start getting some choices in those sizes (imagine the price for a 4" Ethos!! Eek!).
but there has been a distinct trend toward wider apparent fields, and that has gone a long way toward determining the popularity of larger eyepiece barrels.
I just wish there could be a little more standardization in outside diameters of 2" eyepiece barrels. My buddies at Parks measured 50 different eyepieces and got 50 different diameters, and a few weren't even round (!).
In case you wondered why your filter didn't fit.

#19 leonard

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Posted 13 February 2013 - 04:45 PM

Hello


>>>>>> (imagine the price for a 4" Ethos!! Eek!). <<<

:jawdrop: Eekkkk , imagine the weight !!!!!!!

#20 Sean Cunneen

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Posted 14 February 2013 - 01:20 PM

I have a set of eyepieces by Warner and Swasey that date from 1905, both 1.25" and 2" barrels. Prior to 1895, you see barrels of every different size. Post 1911, barrel diameters start to become more standardized as machinery processes changed to the mass-production style. .965" eyepieces come in vogue in the 50's and 60's because of Japan's influence as mentioned above.

#21 csrlice12

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Posted 14 February 2013 - 02:05 PM

Hello


>>>>>> (imagine the price for a 4" Ethos!! Eek!). <<<

:jawdrop: Eekkkk , imagine the weight !!!!!!!


Just mount the eyepiece and insert a scope and focuser to the barrel end........ :lol:

#22 csrlice12

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Posted 30 December 2013 - 08:29 AM

Let's just face it....there's a lot of different sizes because most eyepieces were fairly custom hand-made up until the mid 19th century. It has really been global expansion that has been narrowing down the field (so to speak). I have no doubt in earlier times, the person building a scope/eyepiece (few could purchase a finished scope/eyepieces) was limited to what was at hand.....and we're still visiting Home Depot for our astro needs.....

#23 Augustus

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Posted 05 February 2017 - 05:52 PM

neither will be 3" or 4" if we start getting some choices in those sizes (imagine the price for a 4" Ethos!! Eek!).
but there has been a distinct trend toward wider apparent fields, and that has gone a long way toward determining the popularity of larger eyepiece barrels.

We already have 3" eyepieces from ES, Siebert, and Masuyama.



#24 noisejammer

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Posted 06 February 2017 - 02:51 PM

I've seen a couple of weirdies too - the 7" f/15 photographic refractor (dates to around 1900) at the Johannesburg observatory is about 50 mm. I suspect the visual back is an afterthought but it comfortably predates my first visit to the observatory (35 years ago.) There's exactly one eyepiece that fits it - an Erfle.

 

I have no idea why 50 mm was chosen - perhaps the eyepiece was surplus and it's just coincidence that 2" became common. The scope has 90 mm of available back focus... making a diagonal a pipe dream.



#25 Peter_D

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Posted 12 January 2019 - 01:34 PM

Very interesting thread! I only recently became aware of the variation in eyepiece diameters when I acquired my first ortho - a 1.25 inch 9mm Perl Royal. I wanted to see how it barlowed but the barlow lens doesn't fit in its thread and it doesn't even fit in the barlow (latter point was more of a curiosity because a focal length of 4.5mm is outside my telescopes' limits). Measured the ortho and it's 31.77mm (1.250787 inches) in diameter.

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Edited by Peter_D, 12 January 2019 - 01:36 PM.



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