Instruction manual

Note: temperature is measured using the built in temperature sensor in the RoboFocus controller. The

temperature readings are in raw temperature counts (the counts are close to twice the absolute temperature

in deg. Kelvin, with 32F=0C=273K=546 counts approximately), or in F, or C.

We have supplied a temperature compensation dataset that was taken with an 8in. f/10 LX200 under test

conditions. Your setup will almost surely have different values for all the data; however, it will give you

some idea of how the data might look. As noted below, you can inspect the file using RFCP, Notepad, or

Excel. Except to experiment, do NOT use this file to operate your telescope as it will surely produce

incorrect results.

Note: When using the internal temperature sensor either in training or in operation, we recommend setting

the duty cycle (configuration screen) to zero or 10% to reduce heating of the sensor (see Duty Cycle

discussion in previous chapter). The controller should also be mounted vertically with the power switch

down to reduce heating of the sensor by the electronics. See the discussion below.

Manual Temperature Coefficient

As noted above, you can manually enter a temperature coefficient and then begin compensation. But how

do you know what to enter? There are several ways:

• You might know other people with the same telescope who have already measured the coefficient by

training their system

• You may already know the coefficient for one setup (e.g., at f/10), and can easily calculate the new

coefficient for a new setup. For example, if you use an f/6 reducer, the coefficient would be 6/10 x the

f/10 coefficient.

• You have focus data at several temperatures and can easily calculate the focus change per degree.

To enter the values, simply open the temperature compensation screen, pick Slope Setup mode, and type in

the value desired (be sure to get the sign correct).

Temperature Compensation Training.

The basic idea of training is to gather data on how the focus of the telescope changes as temperature

changes. Thus, you want to train during an evening (or more than one evening) when the temperature is

either likely to change, or is at least at a different temperature from that experienced in previous training

sessions. You would normally want focus measurements from at least three substantially different

temperatures, and with at least a half dozen focus position measurements at each temperature. Training can

extend over several sessions of using the same optical setup (lenses, cameras, Barlows, etc). A typical

training process would be as follows:

• Use the View/Training to open the training window.

• If you have previously trained using the current optical setup, open the relevant file (if not, start a new

file). When you open an existing file, the RFCP will take the stepsize (microstep per step) setting used

in the earlier training and send it to the RoboFocus controller so that the new data will fit the old.

• Focus the telescope

• Click on the GetDataPoint button. This will send a command to the RoboFocus unit to get the current

temperature and focus position, which are put into the new data boxes. If you like the new data and

want to add it to the dataset click the “add to dataset” button. You can have up to 600

focus:temperature measurements in each data set.

• Each time you enter or edit a piece of data, the system automatically recomputes the best-calculated fit

for the focus vs. temperature relationship. The coefficients in this equation are displayed in the

“position calculator” in the main temp comp window. Correlation coefficients and expected error

given the spread in the data) are displayed in a window at the bottom of the window (you can resize the

window to make this go away).

• You can click on this or any other piece of the data, which will move the data into the editing box

where you can edit the data, replace the old entry in the data set, or delete it.