Inside a Rear Mounted Ha Filter
After passing through the ERF,
telescope and Telecentric lens the light rays are properly prepared to enter the filter.
A combination of anti-reflection,
blocking, polarizer and trim components are combined with a
mica etalon to reduce the light to only the Ha emission line
needed.
The mica etalon is an amazing creation! A
super thin, hand cleaved piece of optical mica is coated to
produce the etalon.
Here is the description used by permission from
DayStar Solar Filters:
"At the heart of rear mounted
DayStar style filters is a Fabry-Perot etalon crystal. We actually coat
the Mica crystal to use the perfectly parallel surfaces of fine grade
Mica. So the very thin 0.010 - 0.030mm cleaved crystal is its own,
stand-alone etalon. The crystal grows in the ground naturally with
perfectly flat layers measuring 10Å thick. We cleave the crystal.
That-is, cause it to split between its layers to generate a perfect,
untouched surface. This is a delicate process, because the material
often splits across a layer boundary and causes a steppe.
This steppe in material causes a
10Å jump in transmission at that point. We can also only use crystal of
the highest natural homogeneity. Non-homogeneous mica crystal will
cause slight variants in the transmission wavelength through different
areas of the filter aperture. These fluctuations usually range at
0.02-0.05Å, if present. Only mica crystal with perfect natural
homogeneity is used for University(PE) grade etalon crystals. Most
observers can't discern a 0.02 - 0.05Å fluctuation across the aperture.
However, in academic studies or in photographic tiling, these uniformity
issues can be critical.
They are then coated using a
protected process in an optical thin film coating process, then tested,
qualified and mounted in BK-7 glass using a special optical couplant. The solid spacing of the etalon crystal with no air gap allows it to
maintain structural integrity and uniformity needed for rear mounted
applications. "
For more
information see:
http://www.daystarfilters.com/introduc.shtml
Why Ha? |
The View |
What you see |
The Chromos |
Ha Emission |
Bandwidth |
Main Designs |
Ha Components | Rear Filters |
The Etalon |
Front Filters |
Coronado filters |
DayStar Filters |
Solar Spectrum Filters
