A H-alpha etalon filter with no integrated Barlow, fit for use on SCTs, Maks, or refractors of F/15 to F/30 focal ratio.   From the [url=http://www.daystarfilters.com/downloads/QuarkFlyer.pdf]original Quark flyer[/url]:  "Due to variation in the end user application, we cannot specify the precise FWHM of the filter. Instead, units of 0.8 - 0.6 Å are classified as PROMINENCE and units of 0.5 - 0.3 Å are classified as CHROMOSPHERE".