18
Manual: Cool-Ceramic Safety Herschel Prism Mark II
The Herschel prism for Advanced Users
Solar photography in calcium light
In the dark blue spectral range, around
400 nanometres, photospheric flares
in the vicinity of sunspots, which can
only be observed visually in white light
near the edge of the sun, can also be
made visible further towards the centre
of the sun. To do this, the contrast of
flare areas near the edge is dramatically
increased with the Baader calcium filter
# 2961590
. This filter, with a half-width of
about five nanometres, only lets through
the emission lines of calcium.
To use this very narrow band filter, you
should replace the ND3 filter with a wea-
ker filter to achieve a sufficiently bright
image. Try the ND1.8 first before trying even weaker filters if necessary. The Solar
Continuum filter and any polarising filters must also be removed.
Please note:
Since the human eye is virtually blind in the spectral range below
420 nm, visual observation is not possible. Only cameras can be used as sensors –
preferably astronomical cameras or video modules.
It is a mystery to us why competitors offer "CaK" telescopes for visual use, while
every tanning salon is legally obliged to warn against looking directly into UV-A radiati-
on. Nothing else happens when one visually observes the calcium line below 400 nm.
To take advantage of the high quality of the Baader calcium filter in combination with
a Herschel prism, the refractor objective should also be of high quality (apochromatic).
Simple double-lens achromatic objectives are usually very poorly colour-corrected in
the blue spectral range, so that no sharp images can be obtained in this spectral range
with them.
Infrared pass filter
While focal photography of the whole sun has few problems with air turbulence
(seeing) due to short exposure times and low magnification, projection photography
presents a different picture. The larger the equivalent focal
length, the longer the exposure time. This greatly increases the
susceptibility to seeing effects.
Seeing effects are wavelength-dependent
– stronger in the short-wave spectral range
(blue), less in the long-wave spectral range
(red). Therefore, it can be worthwhile – espe-
cially when shooting with video modules and
long focal lengths – to use a very dark red filter
to completely block the short-wave part of the
spectrum. Ideally suited is the Baader IR pass
Calcium-line-image of the sun. Monochrome camera at
Celestron ED80/600 with Herschel prism, ND1,8-filter und
Baader Calcium-filter
# 2961590
