Hydrogen Alpha Filter
Components
First Things First
The first thing a light ray hits
in a Ha system is some sort of Energy Rejection Filter
or ERF. The ERF's are usually made of red glass that
is polished optically flat.
The ERF function is to block any
unwanted ultraviolet and infrared (if coated) wavelengths. This helps to
protect filter from deteriorating and stops excessive heat from knocking
the filter
off band.
Ray trace through a rear mounted hydrogen-alpha
system
After the light passes through the
telescope in a rear mounted design, it must be straightened
prior to striking the filter. Ha filters must contend with the incident angle of light passing through
them.
The sun’s apparent diameter is half a degree. Straight light enters the
scope as well as a multitude of other angles of light. Rear mounted filters require near
straight light to come on band. A combination of aligned lens in the
telecentric position are
used to straighten
out the rays.
Instrument beam being straightened to telecentric
beam (f/30)
A Telecentric system typically
consist of a divergent lens, usually a 2x barlow, a spacer and some sort of convergent doublet sold by AP or TeleVue. A
telecentric
adds about 3x magnification to the system which enlarges the image size. They also
reduce vignetting.
Light exiting the doublet should be at around f/30 (depending on the
aperture of the ERF) to ensure the entire disk of the sun is on band.
Next, things heat up!
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
