#1  
Old 30-07-2019, 08:02 AM
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Merlin66 (Ken)
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Long focus lenses - Surplus Shed

https://www.surplusshed.com/pages/item/L3920D.html

Surplus Shed have a special running at the moment on long focus lenses- 2500 to 4000+mm with apertures of 150mm.
These sound ideal for anyone considering building a spectrohelioscope.
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  #2  
Old 28-08-2019, 05:04 PM
Wavytone (Nick)
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Also 102mm f/8.8 doublets, mounted
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Old 28-08-2019, 05:17 PM
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Merlin66 (Ken)
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Nick,
The singlet long focus lenses are ideal for spectrohelioscope applications.
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Old 29-08-2019, 03:36 PM
Wavytone (Nick)
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Hi Ken,

I’m well aware singlets are preferred for that application - and suitable lenses are hard to find.

It was more that I was surprised to see SS had what appears to be a fairly respectable refractor objective that might interest someone keen to make a scope.
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Old 29-08-2019, 03:39 PM
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Merlin66 (Ken)
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Nick,
Misunderstanding....

Surplus Shed have been selling large achromatic doublets for the past few years. I had a 90mm and 70mm objective which were OK.
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Old 18-09-2019, 01:35 PM
Wavytone (Nick)
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Hmm... If I was into grinding glass one of those singlet lenses could be a candidate to construct a 150mm Hamiltonian scope.

What stops me is that an ordinary f/8 newtonian is simpler to make and perfectly achromatic.
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