This is the Baader graph that I used to make my purchase decision:
http://www.alpineastro.com/filters/H-Alpha_filter_curve.htm

Richard



--- In Astroimaging_filters@yahoogroups.com, "ssb73q" <ssb73q@...>
wrote:
>
> Hi, I ordered and received a Baader 35nm bandpass Ha filter. While
> most are interested in narrowband Ha filters, my interest in this
> filter was to be used as a prefilter for Ha redshift spectroscopy
> work.
>
> To the eye the 35nm bandpass Ha filter passes more light than a 7nm
> filter. This is expected.
>
> I did a transmission test (Spectronic 1001 plus, +- 1nm) of the
> filter and found that the filter isn't centered on Ha, but severely
> blueshifted. This is just the opposite of what is desired for a
fast
> optical system and useless for my application.
>
> File Baader_Ha_35nm.xls in Folder Filter tests shows the filter's
> transmission.
>
> I expect to return the filter for either or a refund.
>
> Regards,
> Richard
>