Table of Contents
Advertisement
4. tips and tricks
choosing a Suitable Guide Scope
Thanks to its sub-pixel guiding accuracy, the StarShoot Solitaire does not
require telescopes with a very long focal length or large aperture. As a rule
of thumb, when imaging with digital SLRs or CCDs (pixel size between 5 and
8 microns), in general the guide scope should have at least about half of the
focal length of the imaging scope. We recommend using refractors instead
of slow catadioptric reflectors (e.g. Schmidt & Maksutov-Cassegrains with f/
ratio of 10 and upwards), since focusing by movable primary mirror can eas-
ily lead to exposure trailing even if the tracking performance looks apparently
good. Moreover, there are cases where high magnification is not always an
advantage, due to lower brightness and increased sensitivity to atmospheric
turbulence (seeing).
Guiding Speed Adjustment
The StarShoot Solitaire automatically adjusts the exposure time according to
the guide star's brightness: shorter for bright stars, longer for dim ones. This
also affects the frequency of corrections to the mount: bright stars allow for
continuous position control, which also ensures that all sorts of tracking errors,
including the component resulting from periodic error and atmospheric turbu-
lence, will be easily guided out. Bright stars are best to compensate for the
most erratic periodic errors, or with guide scopes having a shorter focal length
than that of the main optics. In this case, we advise using a moderate guiding
speed (0.15 - 0.5X) with HIGH aggressiveness.
On the other hand, fainter stars imply a less frequent correction of tracking
errors: this makes them not as suitable for mounts with an irregular periodic
error. However, long exposure times required by faint stars could come in
handy to minimize the influence of bad seeing. Here we suggest a very low
guiding speed, best if no higher than 0.25X with MILD aggressiveness.
Medium brightness stars (visual magnitude between 3 and 6) generally yield
best performance.
Search for a Suitable Guide Star
Note: The telescope must not be touched during calibration, otherwise the
relevant parameters can not be calculated correctly. During calibration and
autoguiding it is also important not to place the control paddle in your hand or
the camera could move. Instead, place the control paddle on a secure surface
such as a tripod accessory tray.
If the search for the guide star fails, you can manually move the guide scope
looking for a brighter star. If the camera does not manage to find a sufficiently
bright star, a position-adjustable guide scope will help. If you are using an off-
axis guider, the pick-off prism and tube can be moved and/or rotated to find
a brighter star.
12
Mount calibration
Note: The telescope must not be touched during calibration, otherwise the
relevant parameters may not be calculated correctly. Please also ensure that
the control paddle is not moved during calibration!
Once calibration is complete, the parameters are permanently stored into the
StarShoot Solitaire's internal memory for later use, provided that the following
precautions are taken into account:
• Always guide on stars lying in the same side of the sky (with respect
to the local meridian) as where the calibration was performed. For
example, if you calibrated east of the meridian, you should choose a
guide star east of the meridian.
• Do not remove and reinstall the camera on the guide scope after
calibration, or your calibration settings will be compromised.
• Do not move or rotate the camera after calibration, or that too will
compromise your calibration settings.
If any of these things are done, the mount must be calibrated again.
It might take a relatively long time for the calibration process to finish, espe-
cially with short focal length guide scopes (under 500 mm).
It is also advisable not to use too dim a star for calibration, otherwise just a
few thin clouds or a little dew on the lenses could cause the star to be lost and
jeopardize the final result of this important process.
Autoguiding and Aggressiveness
The higher the aggressiveness, the larger and more rapid the corrections to the
mount are. So if the aggressiveness is set to HIGH, the autoguider corrects for
nearly all of the guide star movement that deviates from it's position. Ideally,
this should result in perfect tracking. But other factors like mount vibration,
wind, and poor seeing can make the autoguider "chase" the guide star move-
ment under high aggressiveness. So depending on your mount, guidescope
and outdoor conditions, you may need to adjust the aggressiveness accord-
ingly.
HIGH values are suitable when using small refractors featuring a focal length
1,5-2 times smaller than the main instrument. MILD values are for guide
scopes of about the same focal length and LOW ones are best in case of very
long guide scopes or off axis guiding (typically SCTs).
During autoguiding, the tracking error graph for X and Y should stay as smooth
(straight) as possible. It is advisable to start off with default values for aggres-
siveness and guiding speed. Later, if needed, both parameters can be fine
tuned to achieve the best possible setting between your StarShoot Solitaire
and your telescope.
If the tracking error graph is showing significant movement in both the X and Y
axis, the autoguider is likely overcorrecting, and the guiding speed should be
13
Advertisement
Table of Contents
