5 elements in a spotting scope? (1 Viewer)

[John goshawk]

The primary of my Opticron 66ED has five elements. My astro 72ed only two.
There both wonderful instruments, but why five elements?

Thanks John

 

[wllmspd]

Possible better correction, maybe faster and thus needs more surfaces to obtain the same level of correction?
Peter

 

[henry link]

The five elements in the Opticron consist of a fixed triplet at the front of the scope and a moving focusing doublet behind it. That's a common design in current spotting scopes. Some astronomical refactors also use triplets up front for added degrees of correction compared to doublets, but typically skip the focusing lenses and instead simply move the eyepiece back and forth for focusing as in your 72ED.

 

[John goshawk]

That's fascinating. Many thanks.
John