Optical: systems and elements – Compound lens system – Telescope
Reexamination Certificate
2000-05-08
2001-12-04
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Compound lens system
Telescope
C359S820000
Reexamination Certificate
active
06327081
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to a focuser for controlling the focus of a telescope and, more particularly, to a temperature compensating focuser compensating for changes in ambient temperature.
Particular telescope configurations, such as the Cassegrain configuration, which include primary and secondary mirrors, are susceptible to temperature drift effect on the back focuser. It is not uncommon to experience up to a 0.010-inch temperature drift for each 0° C. in temperature change. Because telescopes are used during nighttime hours when temperature changes are often extensive, it is possible for the telescope to experience significant focus drift especially during long exposure periods. It is not unusual during an observation session, for the ambient temperature to change by at least 10° C. within the time span of a few hours. Applications which require exact focus, such as CCD imaging or film astrophotography, typically also frequently require long exposure periods. By way of example, a typical RGB exposure sequence can last one hour. The change in focus due to the temperature is a serious problem for these telescopes resulting in frequent focusing before exposures and bloated stars during long exposures.
Although Cassegrain-type telescopes are exceptionally sensitive to temperature drift, other telescopes would exhibit such drift to a greater or lesser extent.
SUMMARY OF THE INVENTION
The present invention provides a temperature compensating focuser and method for use with a telescope having a focus which changes with ambient temperature. In particular, the invention is useful with a telescope having a body supporting a primary focus optic and a secondary focus optic which define a focus and wherein the body changes relative spacing of the focus optics with changes in ambient temperature.
A temperature compensating focuser, according to an aspect of the invention, includes a lens support establishing a focus of the telescope and a temperature sensor. The focuser further includes a control that is responsive to the temperature sensor for adjusting the lens support in response to changes in temperature sensed by the temperature sensor.
A temperature compensating focuser and method, according to another aspect of the invention, includes a temperature sensor adapted to measuring temperature at the telescope body and a support for one of the focus optics. A motor is provided for adjusting the support to modify a distance between the focus optics. A control is provided which receives input from the temperature sensor and produces an output to the motor to maintain the distance between the focus optics, notwithstanding changes in temperature at the telescope body.
A temperature compensating focuser, according to another aspect of the invention, includes a temperature sensor adapted to measuring the temperature at the telescope body and a support for one of the focus optics. A motor is provided for adjusting the support to modify the distance between the focus optics. A control is provided which receives an input from the temperature sensor and produces an output to the motor. The control has a learning mode to establish a temperature coefficient of the telescope. The control further includes a control mode to adjust the motor in response to the temperature sensor and a temperature coefficient determined during the learning mode.
According to yet another aspect of the invention, a temperature compensating focuser includes a temperature sensor measuring temperature at the telescope body and a support for one of the focus optics which is moveable with respect to a base. A motor adjusts the support to modify the distance between the focus optics. A control is provided which receives an input from the temperature sensor and produces an output to the motor. The control establishes a relative position of the support with respect to the base and includes a memory for storing a relative position of the support and a temperature value sensed by the temperature sensor when power is removed from the control. The controls adjust the support according to relative position and temperature values and memory and temperature sensed by the temperature sensor when power is restored to the controller.
A method of compensating the focus of a telescope includes providing a lens support establishing a focus of the telescope, sensing ambient temperature and adjusting the lens support in response to change in sensed ambient temperature.
A method of compensating the focus of a telescope, according to another aspect of the invention, includes measuring temperature at the telescope body, adjustably supporting one of the focus optics in a manner that a distance between the focus optics can be adjusted. The method further includes maintaining the distance between the focus optics notwithstanding changes in temperature at the telescope body.
A method of compensating the focus of a telescope, according to another aspect of the invention, includes measuring temperature at the telescope body and adjustably supporting one of the focus optics in a manner that a distance between the focus optics can be adjusted. The method further includes establishing a temperature coefficient of the telescope in a first mode and adjusting the distance between the focus optics during a second mode. According to this aspect of the invention, the adjusting is in response to the temperature at the telescope body and a temperature coefficient determined during the first mode.
A method of compensating the focuser of a telescope, according to yet another aspect of the invention, includes measuring temperature at the telescope body and adjustably supporting one of the focus objects in a manner that a distance between the focus objects can be adjusted. The method further includes establishing a distance value between the focus objects that corresponds to a temperature value at the telescope body. The method further includes storing the distance value and the corresponding temperature value and adjusting the distance between the focus objects according to the stored distance value and temperature and a current temperature at the telescope body.
Although the present invention is illustrated in use with a Cassegrain-type telescope, it should be understood that its principles may be applied to other telescope configurations that exhibit temperature drift. The present invention may be built into the overall structure of the telescope or, advantageously, provided as a field installable add-on kit to existing telescopes.
These and other objects, advantages and features of this invention will become apparent upon review of the following specification in conjunction with the drawings.
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OPTEC, Inc.
Robinson Mark A.
Spyrou Cassandra
Van Dyke, Gardner, Linn & Buckhart, LLP
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