Ha Filters

Has anyone had a chance to compare the Coronado Ha filters to the older
Daystar units? Do they perform equally as well or are there differences? I
understand that these filters have a shelf life and degrade as time passes.
Is this correct?

Hi there. You posted:

Has anyone had a chance to compare the Coronado Ha filters to the older
Daystar units? Do they perform equally as well or are there differences? I
understand that these filters have a shelf life and degrade as time passes.
Is this correct?

They are comparable for units of comparable passband width. These filters
don't exactly degrade very much, but the older DayStars had internal blocking
filters on either side of the central etalon which lasted from 15 to 20 years
before having to be replaced (mine cost about $300 to replace). Supposedly,
DayStar is now using materials which do not degrade as much as the older
units. The Coronado units are located in front of the telescope, so they are
more stable with temperature variations than the DayStars, which often have to
be either tilted slightly or heated in a very tightly-controlled oven.
However, in any but the smallest aperture, the Coronado filters are also more
expensive than the DayStar units, since the entire etalon has to be placed in
front of the telescope instead of in a much smaller portion of the light cone
near the focal point. The DayStar filters require a focal ratio of f/30 or
longer in order to function well, while the Coronado filters will function
with much shorter focal ratios. Reviews and comparisons are available at the
Cloudynights web page: http://www.cloudynights.com Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

Hi there. You posted:

Has anyone had a chance to compare the Coronado Ha filters to the older
Daystar units? Do they perform equally as well or are there differences? I
understand that these filters have a shelf life and degrade as time passes.
Is this correct?

They are comparable for units of comparable passband width. These filters
don't exactly degrade very much, but the older DayStars had internal blocking
filters on either side of the central etalon which lasted from 15 to 20 years
before having to be replaced (mine cost about $300 to replace). Supposedly,
DayStar is now using materials which do not degrade as much as the older
units. The Coronado units are located in front of the telescope, so they are
more stable with temperature variations than the DayStars, which often have to
be either tilted slightly or heated in a very tightly-controlled oven.
However, in any but the smallest aperture, the Coronado filters are also more
expensive than the DayStar units, since the entire etalon has to be placed in
front of the telescope instead of in a much smaller portion of the light cone
near the focal point. The DayStar filters require a focal ratio of f/30 or
longer in order to function well, while the Coronado filters will function
with much shorter focal ratios. Reviews and comparisons are available at the
Cloudynights web page: http://www.cloudynights.com Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************