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Rick
Post Laureate


Reged: 04/12/05
Posts: 3285
Loc: Tokyo, Japan
Cemented vs. Air-spaced triplet design
      #1277838 - 11/30/06 08:10 PM

Just wonder if there are any pros/cons that would give one design any advantage over the other? Takahashi seems to use cemented objectives in their TSA and TOA while other makers seem to favor air-spaced for their triplets.

happy holidays,
Rick


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Mike Clemens
Frozen to Eyepiece


Reged: 11/26/05
Posts: 6707
Loc: Alaska, USA
Re: Cemented vs. Air-spaced triplet design new [Re: Rick]
      #1278057 - 11/30/06 10:01 PM

The TOA is wide air spaced, no cemented elements.

Mike

--------------------
http://www.pbase.com/mclemens1969/tec_200_observations


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spaceydee
Postmaster


Reged: 04/16/04
Posts: 17311
Loc: Where the Kittens Are
Re: Cemented vs. Air-spaced triplet design new [Re: Mike Clemens]
      #1278089 - 11/30/06 10:19 PM

That's what I thought!

--------------------
Dee
space-scientist
student violinist
Nexstar8i,SV80S,80/9D,FC100,94 Brandon,TMB92SS,GM8
8" f/7 Discovery,12.5" Portaball, PST



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Rick
Post Laureate


Reged: 04/12/05
Posts: 3285
Loc: Tokyo, Japan
Re: Cemented vs. Air-spaced triplet design new [Re: spaceydee]
      #1278147 - 11/30/06 10:57 PM

I'll have to reread the Japanese sales literature but I thought I recalled it saying the TOA uses two ED elements and one crown, all cemented, while the TSA has one ED and two crown, all cemented.

Irregardless, is there any pro/con of one design over the other?

thanks,
Rick


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Bill McHale
professor emeritus


Reged: 11/07/04
Posts: 582
Re: Cemented vs. Air-spaced triplet design new [Re: Rick]
      #1278168 - 11/30/06 11:20 PM

Well, each has advantages....

The air spaced can use all spherical elements and still get very good control of the various abberations. With modern optical fabrication equipment, it means that it is probably easier to mass produce the air spaced elements.

The cemented Triplet on the other hand needs to have at least some of its surfaces be aspherical to control all the abberations (at least in the fast designs that are currently being made; you might be fine in an f/12-f/15 design). On the flip side though, some of the surfaces can be figured with looser tolerances than the air-spaced design. I think the the cemented triplet might be generally easier for the amateur to make.

--------------------
Bill
186,000 MPS, its not just a good idea, its the law.


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snart
professor emeritus


Reged: 04/07/05
Posts: 636
Re: Cemented vs. Air-spaced triplet design new [Re: Rick]
      #1278547 - 12/01/06 09:40 AM

Cemented lenses stay in alignment better than air spaced lenses and are easier to align when required. They also transmit more light that air spaced lenses and have fewer problems with ghosting and scatter. Air spaced lenses, as previously stated, have the advantage of being able to control various aberrations better since they have many more degrees of freedom for the designer to work with.

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Paul Stone
member


Reged: 10/20/05
Posts: 22
Loc: London and Dublin
Re: Cemented vs. Air-spaced triplet design new [Re: snart]
      #1278666 - 12/01/06 11:03 AM

I read somewhere that although cemented lenses have advantages , the main problem is that you can't use glasses with different thermal properties (which rules out most triplets except maybe the new mysterious TMB Brick ).

Also I'm 99.999% certain that the TOA's and TSA are air spaced.


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Refractor6
Post Laureate


Reged: 10/20/04
Posts: 3653
Loc: Vancouver B.C. , Canada
Re: Cemented vs. Air-spaced triplet design new [Re: Paul Stone]
      #1278746 - 12/01/06 11:51 AM

On this French link it is stated that the TSA-102 is of an air-spaced design:


http://translate.google.com/translate?sourceid=navclient-menuext&hl=en&u=http%3A%2F%2Fwww%2Eoptique%2Dunterlinden%2Ecom%2Fhp%5Ftsa102%2Ehtm


---------------------

Stan

Takahashi FS-102 NSV
Antares 152 f/8 prototype
Antares 152 f/6.5
Antares 127 f/6/45 prototype
Orion 9x63 mini giants
Pentax 20x60 PCF WP


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Mike Clemens
Frozen to Eyepiece


Reged: 11/26/05
Posts: 6707
Loc: Alaska, USA
Re: Cemented vs. Air-spaced triplet design new [Re: Refractor6]
      #1278807 - 12/01/06 12:30 PM

I dont recall any current cemented high end APOs. I was advised against buying a 1992 cemented triplet 6" AP f/12 once due to my living in Alaska with the big thermal swings that a scope goes through.

> Cemented lenses stay in alignment better than air spaced
> lenses and are easier to align when required.

How? Heating?

--------------------
http://www.pbase.com/mclemens1969/tec_200_observations


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davela
scholastic sledgehammer


Reged: 12/19/06
Posts: 887
Loc: Pasadena, CA, USA
Re: Cemented vs. Air-spaced triplet design new [Re: Mike Clemens]
      #1317122 - 12/22/06 04:17 AM

Air spaced triplets allow more surfaces to be "bent" for aberration correction - this is critical in fast-wide optical designs. Lenses over about 2" do not lend themselves well to cementing, especially of they are going to be temperature cycled a lot as in a scope.

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