PARTS LIST
Light Pollution Imaging Filter in Filter Cell
Spectral Transmission Chart
Plastic Case
The Light Pollution Imaging Filter for the Rowe-Ackermann Schmidt Astrograph
(RASA) 8 improves image contrast by selectively blocking wavelengths of light
strongly emitted by certain sources of light pollution. These sources include
high and low pressure sodium-vapor streetlights, mercury-vapor streetlights,
and natural airglow caused by oxygen in the atmosphere. The filter only blocks
narrow sections of the spectrum instead of wide regions; this helps to retain
image brightness and color balance. Specific emission lines from nebulae, such
as H-α (656nm), H-β (486nm), OIII (496nm and 501nm), and SII (672nm), are
highly transmitted, so emission nebulae won’t be dimmed.
LIGHT POLLUTION
IMAGING FILTER, RASA 8
#93614
The included spectral transmission chart indicates the transmission measured
for the filter you received.
INSTALLING THE FILTER IN RASA 8
The Light Pollution Imaging Filter replaces the RASA 8 optical window. This
maintains optical performance, as no extra piece of glass is added to the fast
optical system. The optical window is removed along with its cell, and the filter
is installed using its own cell.
WARNING: When removing the optical window and installing the filter, avoid touching optical
surfaces or you may leave fingerprints. Handle the filter and optical window by their cells only.
1. Carefully grasp the knurled edge of the optical window cell within the RASA
8 lens group cell, and begin rotating it counter-clockwise. If the edge of the
optical window cell cannot be grasped initially because it is too recessed, use
the notches in the knurled surface of the cell to begin rotating it. Completely
unthread and remove the optical window cell. The optical window can be
stored in the filter case when the filter is in use.
2. Install the Light Pollution Imaging Filter by threading its cell into the lens
group cell of the astrograph. The notches in the edge of the filter cell should
be facing outward. Do not over-tighten, the filter cell should only be threaded
until it stops turning.
Notches on filter
face outward
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