Optec, Inc.
199 Smith Street ∙ Lowell, Michigan 49331 ∙ U.S.A.
www.optecinc.com
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Revision 10 –8/31/2012
Generic Information
The following information applies to all Alnitak Astrosystems devices.
Choosing brightness settings
The brightness range has been designed to accommodate a variety of telescopes and
filters. The low end should be used for normal wide band imaging filters, and the upper
end for narrow band filter such as Ha, OIII, and S2. Experiment with various setting for
each filter. Current imaging practice is to adjust the brightness level to give mid-range
ADU values (around 30000 for a 16 bit camera) with short exposure times. We suggest a
2 second exposure for wideband filters. Narrow band filters will require longer exposure
times (and higher brightness settings) to reach acceptable ADU values.
Caring for your Product
Very little maintenance should be required beyond gentle cleaning of the diffuser (the
white plastic that the light shines through). We suggest cleaning the diffuser with a soft
optical cloth after blowing off any particles to minimize scratching. Heavy soiling may
require gentle rubbing with a glass cleaner or mild soap and water.
Flat fielding strategies
We have found that it is best to take darks at night so that there is no risk of light leaks in
the optical path. With these devices, there’s no rush to get all your filters exposed at
twilight, so don’t scrimp on exposures. Remember that the noise levels decrease as the
square root of the number of exposures, so a master flat of 36 frames will have half the
noise of a master flats consisting of 10 frames.
Don’t forget to take a set of dark frames of the same exposure length (and temperature) as
the flat frames. No bias frames are needed if the flat and darks are of the same exposure
length. For short flat field frames (<10s) you may find that simple bias frames are
adequate for dark subtraction. In all cases, make sure you dark (or bias) correct your flat
field frames before using them to flat field your images.
You can find out more about flat fielding on our website: www.alnitakastro.com.
