Re: [APML] Tech Pan/Ha filter focusing

[<cschur@cybertrails.com>]

Scott, it wont be quite that simple.  On a camera lens, the Ha focus is
something like 1/2 to 3/4 the way from infinity to the IR mark on the
lens.  Youd have to try several positions, develop the film and determine
the best position for each lens.  For a 4 inch scope, it better be faster
than f/4 or you wont get much of anything becasue the filter is very dark,
roughly equivelent to a wratten 92.  Were talking several hours of
exposure even then!  For focus, Id recomend a ronchi grating at the
cameras prime focus with a bright white star to get the Ha focus point
established.

Chris

> Hey Tech Pan Junkies,
> This question may have been addressed before, forgive me if it has and
> for being too lazy to search the archives.
>
> I assume one day the weather will actually be clear again and I'll be
> able to shoot some film. I just ordered a 48mm Ha filter to use prime
> focus with my 4" scope. Can I use my IDAS filter to focus and then just
> replace it with the Ha filter and achieve accurate focus?
>
> Any help would be greatly appreciated.
>
> Thanks,
>
> Scott Hammonds
>
>
>
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