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Super Ramsden?

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#1 hwhall

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Posted 14 September 2009 - 10:19 AM

I had this in the Eyepiece Forum but someone suggested posting it here instead.

I recently disassembled a cheapie SR4mm eyepiece (going to use the body for a project). I expected from the name to see just 2 lenses inside but I found three. From what would be the objective end of the eyepiece, there was a field stop then a short space to a double-convex, a short space to another stop then a short space to a double-concave followed very closely by a double-convex.

I think it was an air-spaced doublet looking at a double-convex field lens. That sounds like a Kellner but isn't the negative lens instead closest to the eye in a Kellner?

At first I thought SR was Symmetrical Ramsden but with the extra lenses I thought maybe this was a Super Ramsden but that too seems to use only 2 lenses. What is a Super Ramsden really? And was this a super ramsden or something else?

Thanks!

#2 mikey cee

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Posted 14 September 2009 - 11:48 AM

SR denotes Special Ramsden. :smirk:Mike

#3 hwhall

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Posted 17 September 2009 - 12:51 AM

Okay, but a web search for "special ramsden" didn't turn up any more info than "super ramsden". :shrug:
With three lenses in it instead of two, my dissected SR just didn't seem very Ramsdenesque. :p

#4 rmollise

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Posted 17 September 2009 - 07:01 AM

Okay, but a web search for "special ramsden" didn't turn up any more info than "super ramsden". :shrug:
With three lenses in it instead of two, my dissected SR just didn't seem very Ramsdenesque. :p


Ain't nothing special about a Ramsden. "SR" is "Symmetric Ramsden," and no doubt there have been many variations on that sorry theme. :lol:

#5 hwhall

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Posted 17 September 2009 - 12:33 PM

Agreed, Uncle Rod, that they are nothing special! Hence my willingness to trash one for tinkering around.

But I now have seen three definitions for SR:
Symmetric Ramsden
Super Ramsden
Special Ramsden
They all turn up with varying frequency in web searches but almost nothing on how SR differs from the original Ramsden design. I did find one reference that claimed Super Ramsden employed special glasses to enable slightly wider field of view.

It still seems that the 3 lense design I encountered doesn't jive with any interpretation of Ramsden at all.

#6 rathbaster

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Posted 17 September 2009 - 01:40 PM

I was looking through Chris Lord's Evolution of the Astronomical Eye Piece today and noticed he included two different Ramsden's one from 1783 the other from 1790 with a closer spacing of the elements and a wider field of view. He also has an achromatic ramsden from 1849 with a 2 element achromat and a single element. This latter could be the derivation of the "SR" eyepiece.

-Joe

#7 hwhall

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Posted 17 September 2009 - 11:19 PM

Hi, Joe. Yep, that achromatic ramsden looks quite a bit like the "SR" that I took apart. The achromat was just air spaced instead of being cemented. Thanks!!

#8 John Carruthers

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Posted 18 September 2009 - 02:50 AM

SR denotes Special Ramsden. Mike



That's what my literature says too, mine look like a reverse Kelner.


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