From: "Richard F.L.R. Snashall" 
To:  atm{at}shore.net
Reply-To: "Richard F.L.R. Snashall" 




Guy Brandenburg wrote:
>
> I have a projector lens that I purchased really cheaply a few years ago,
> intending to make a finder scope. It looks like the lens is plastic for
>
>
> It occurs to me that I could perhaps lengthen the focal length with the
> equivalent of a barlow lens, which, I understand, is simply a negative
> lens, preferably an achromat. I imagine that I will have to play around
> with this to get it to work at all.
>

If the original lens is not achromatic, would an achromat help here at all?
 Maybe a single lens would be better... you measured the focal length...
maybe you want to refine it a bit first by measuring at different
wavelengths.

                Rick S.

> Any suggestions?
>
> Guy Brandenburg
>
>
>
>

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