© Baader Planetarium GmbH | 2023
7
The Light Path inside of the Herschel prism
The diagram on the right shows the path of light inside
of the Herschel prism. The sunlight enters the prism
from the left. Approximately 4.6% of the sunlight is
directed upwards at a right angle into the eyepiece or
camera for observation. Further grey filters dim
the light even more to a harmless level.
The disproportionately larger, higher-
energy portion of 95.4% of the
radiation passes through the prism
body and would form a focal point in
the "air" far outside the prism housing.
A heat-absorbing special ceramic as a closure
of the light trap ("heat cage") absorbs radiant heat – like
the heat tiles on the space shuttle – without heating the
surroundings too much. The housing, which is closed except for the ventilation slots,
reliably prevents any risk of glare. Since the "heat cage" is only connected to the prism
housing via four screws, there is practically no heat transfer to the prism itself. The ce-
ramic plate also acts as a viewing screen for the sunlight beam. Positioning the solar
image in the centre of the telescope's field of view is thus child's play.
The 2" ClickLock
®
eyepiece clamp is used to hold eyepieces or other accessories.
With a 15° turn you clamp any eyepiece bombproof – even in winter with thick gloves.
Never use Filters in front of the Herschel Prism:
For manufacturing reasons, the 2" nose piece of the Herschel prism also has a
female filter thread of M48 as it is standard to accommodate 2" filters. In the case
of the Herschel prism, however, no filters must be mounted here, as any filter in-
serted at this point will become very hot and thus be destroyed (see also the safety
instructions on page 3). Any optical accessories must be mounted after the prism
(i.e. on the eyepiece side).
Mounting on the telescope
The Herschel prism is attached to the telescope in exactly the same way as a 2" star
diagonal. Make sure that it is securely held in the eyepiece focuser.
Owners of Diamond SteelTrack
®
focusers can
also attach the Herschel prism permanently to the
focuser. This is particularly interesting for purely
solar telescopes and in public use, so that no one
can remove the Herschel prism. To do this, simply
unscrew the 2" nose piece and attach the Herschel
prism to your Diamond SteelTrack
®
focuser using
the S58 ring dovetail instead of the eyepiece clamp.