25167Re: H-alpha filters
- Mar 17, 2004I just wanted to mention that Astrodon Tru-Balance H-a filter is
parfocal with the LRGBs and unblocked clear filters. It was designed
at 6 nm FWHM, but provides ~90% optical throughput. The key for me
was to provide an H-a filter that did not require a focus change.
BTW, I have comparisons on my web site of the 9.5 nm (Schuler) vs the
original 3.5 nm FWHM (Custom Scientific) H-a alpha in the emission
filter page. In this FWHM range, I do not see any deleterious impact
of the wider 9.5 nm filter letting more broadband light in other than
the aesthetic issue of more and brighter/fatter stars that are
actually a better match to the RGBs. Have you tried blending in H-a
into the RGBs and see a tiny white bullet inside a larger colored
star? The S/N is higher for the Schuler because it's throughtput is
80% compared to 72% for the narrow 3.5 nm CS H-a. The S/N
improvement simply comes from the throughput. Now, people have a
choice between the more recent SBIG/CS 10 and 4.5 nm H-a filters and
my Tru-Balance H-a that all have ~90% throughput.
--- In email@example.com, "Ron Wodaski" <ronw@n...> wrote:
> 1. Yes, this is normal. The Ha filter is a pretty thick sandwich,
> be parfocal with thinner, simpler filters.
> 2. I occasionally can find a guide star, but I use a guidescope
> much more flexible with an Ha filter.
> Ron Wodaski
> author of The New CCD Astronomy
> -----Original Message-----
> From: remi lacasse [mailto:rmi.lacasse@s...]
> Sent: Monday, April 01, 2002 6:57 AM
> To: ccd Newastro; SBIG user group
> Subject: [ccd-newastro] H-alpha filters
> A few months ago I received my H-alpha filter from SBIG.
> It is the Standard type and I would like to ask 2 questions to
> the group or to those who have used the same type filter before:
> - I am using an ST-10E with the filter installed in the empty slot
> of the CFW-8 but the focus point is very different from the
> other filters. Is this normal?
> - Is it possible to use (find) a guide star and if so what is the
> magnitude through the filter? Or will I need an external way to
> when using the filter?
> Thanks in advance
> Rémi Lacasse et/ou Lise Charlebois
> Lat. 46 deg.
> Long. 74 deg.
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