Re: [APML] Medium format wide field scopes

["Shekhar Borde" <shekhar@prodigy.net>]

> 
> Actually, with narrow band filters, you can image with a singlet lens 
> (chromat). You don't even need an achromat. Wolfgang Lille in Germany has 
> taken some really outstanding H-alpha images of the sun with a 13" single 
> element chromat lens.
> 
> Roland Christen
>

Roland,

Is this true for just red (H-alpha) or is that true for the entire visible
spectrum?  Is the problem with an uncorrected scope that it can 
focus accurately within narrow passbands across the entire visual 
spectrum, but it cannot focus different wavelengths together? 

In other words, if I use a 400-410nm filter on this scope, will the star
sizes be as good as the ones using a 650-660nm filter?

Shekhar
  


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