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Stacking filters ???

Started by Eblanken, 07/14/2003 06:41AM
Posted 07/14/2003 06:41AM Opening Post
Hello all,

I just purchased Lumicon UHC and H-Beta filters to add to my collection: Lumicon O-III and the nice colored set that comes as part of the Celestron eyepiece kit.

My question is: "Having noticed that the UHC and H-Beta have external threads, but no internal threads, Is there a reason that these filters should never be stacked ?"

I know that the Lumicon filters are achieved with special coatings instead of (or in addition to) the optical glass substrate coloration (if any), but was wondering if I put the UHC into the diagonal or barlow and then put the O-III or the H-Beta downstream in the eyepiece, would I get a better rejection of unwanted light or would I create some odd "multiple reflection" senario like a Fabre-Porro (sp?)interferometer.

Another question, "Can I use the H-Beta filter with my full aperature solar filter to get some extra detail on the Hydrogen cell granularity (of the Sun's surface) like the cool, but expensive H-Alpha filters that come with the Energy Rejection Filters ?"

Any opinions and/or experience ?

Posted 07/14/2003 07:08AM #1
Hello again,

Another related question, "If I use a wideband filter for the SCT exit aperature, will that 'stack' O.K. with any or all of the much narrower band filters ? For example, I also have polarizing filters and the Celestron LPR filter.

Thanks in advance,


Posted 07/14/2003 07:14AM #2
Hi Ed.
You'd end up with a "net" filter with rejection characteristics being the *sum* of both single filters. Place both rejection curves on the same wavelength scale, and you'll have their net bandpass curve.

Since the H-beta and OIII filters are essentially "line" filters (strong or full rejection of most wavelengths other than their targeted bandpass peaks), when they're combined with a narrowband or broadband nebula filter, the "weaker" or broader-bandpass filter is essentially nullified -- neither filter is enhanced nor "helped" by the combo.

Best wishes.