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Air Spaced Doublet - What is the benefit?

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#51 Ian King

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Posted 05 April 2021 - 05:58 AM

Just to chime in on this - I purchased a 1990 Vernonscope Brandon 94mm Triplet with the Christen lens and it definately does have a cemented lens.

Since thermal stress is a function of length, I am as doubtful as Jon on this.


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#52 jimhoward999

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Posted 05 April 2021 - 10:27 AM

What is the largest cemented lens you know of?

 

Jon

Pretty small.   3” is the biggest I’ve worked on.   I think I have heard of 4”, but never seen it.   



#53 csrlice12

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Posted 05 April 2021 - 11:02 AM

If a cemented lens fails, air gets in 

If an oiled lens fails, air gets in 

If an air spaced lens fails...it's probably due to human error.


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#54 Bomber Bob

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Posted 05 April 2021 - 11:22 AM

A. Jaegers sold achromatic cemented objectives up to 6" aperture back in the day...



#55 vahe

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Posted 05 April 2021 - 12:41 PM

If a cemented lens fails, air gets in 

If an oiled lens fails, air gets in 

If an air spaced lens fails...it's probably due to human error.

 

If an air spaced lens fails......it's probably due to human error or worse you have fungus growing in the air space particularly if the lens is stored in humid climate.

.

Vahe


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#56 Thomas Marshall

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Posted 05 April 2021 - 03:20 PM

Wow!

So much I didn't know I didn't know.

Lol! That happens to me all the time on CN's.


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#57 daquad

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Posted 06 April 2021 - 12:52 PM

A. Jaegers sold achromatic cemented objectives up to 6" aperture back in the day...

Bob, most of the lenses Jaegers sold were cemented doublets.  However their 3-1/4" f/15 (which I used to own), 4-1/8" f/15 (which I own) and all of their 6" f/5, f/8, f/10 and f/15 objectives were air spaced.  (I used to own the 6" f/5 and the 6" f/15.)

 

I also made scopes with the 110 mm/1069 mm f.l. and the 5" f/5.  Both were cemented and I did not care for the CA, although the 110mm was sharp.  The 5" RFT had too much SA for my taste.  I still have the 1981 Jaegers catalog, and as far as I can see the 5" f/5 was the largest cemented objective they made; it should have been air spaced.  The air-spaced 6" f/5 delivered perfect Airy discs, despite the large color blur.  

 

Dom Q.



#58 Bomber Bob

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Posted 06 April 2021 - 05:03 PM

I still have the 1981 Jaegers catalog, and as far as I can see the 5" f/5 was the largest cemented objective they made; it should have been air spaced.

 

I was referring to a 1966 edition of the Jaegers catalog... and, those that Jaegers sold -- not necessarily made.


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#59 daquad

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Posted 08 April 2021 - 06:45 PM

I still have the 1981 Jaegers catalog, and as far as I can see the 5" f/5 was the largest cemented objective they made; it should have been air spaced.

 

I was referring to a 1966 edition of the Jaegers catalog... and, those that Jaegers sold -- not necessarily made.

Oh.




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