Manual

EasyFocus User Manual

Installation

Installation of the EasyFocus is covered in this section.

To make the best use of your EasyFocus you will likely want to attach a piece of velcro to its back and then also attach a mating piece of velcro onto one of your tripod legs or onto the tripod head. This way you can simply stick the EasyFocus onto the mount, cable it up, and be ready to use the EasyFocus as quickly as possible. In this document however, the components are shown simply laying on a table for clarity.

Power

The EasyFocus requires a DC power source in the range of 9-18V and accepts a standard 5.5mm by 2.1mm power plugs. Any power supply capable of supplying a few hundred milliamps of current should work fine.

The EasyFocus is protected from reverse polarity and requires that the power plug be tip positive and ring negative.

Interfacing to the PC

The EasyFocus is interfaced to the PC using the provided serial cable. The female DB9 connector plugs into your PC and the four positions 4-conductor RJ22 plug is inserted into the EasyFocus.

Serial communication is at 9600 baud with one stop bit and no parity. The ASCOM driver for EasyFocus takes care of setting the serial port parameters correctly when you connect to the EasyFocus.

Figure 1: EasyFocus shown with its serial cable attached

Interfacing to the Focusing Unit

You interface your focus motor to the EasyFocus using the supplied DB9 patch cable. The DB9 patch cable is a 10-foot long piece of 9-conductor ribbon cable with a male DB9 connector on one end and a female DB9 connector on the other end. The male end of the patch cord plugs into the EasyFocus and the female end plugs into your focus motor.

The proper motor wiring for the EasyFocus is shown in the following table.

EasyFocus Motor Wiring

Male DB9 Pin	EasyFocus
1	Coil 1+
2	Coil 1-
3	Coil 2+
4	Coil 2-
5	+12V
6	Gnd
7	Gnd
8	Gnd
9	+12V

Figure 2: EasyFocus connected to DB9 patch cable

Usage

Operation and adjustment of the EasyFocus are described in this section.

Operation

There are two ways to control the focus motor. You can use the EasyFocus hand controller or you can use the EasyFocus serial line focusing commands. In this section, we only cover using the EasyFocus hand controller. For information on the EasyFocus serial line focusing commands, see Appendix A.

As shown in Figure 4, two red buttons are used to control the focus motor using the EasyFocus hand controller. The In and Out buttons move the focus motor in or out respectively. Since the meaning of In and Out is different for different configurations the direction that the focus motor turns when either the In or Out button is pressed can be changed. When the EasyFocus is first powered up, the LED will flash for 3 seconds. If in that 3 seconds you press and hold the in button, and then release it when the LED lights and stays lit, then the direction that the focus motor turns when either the In or Out button is pressed switches roles. This change is permanently stored in non-volatile memory and you need to make this change only once as it will be remembered across power cycles of the EasyFocus.

The in button has one other function, and that is if you hold the in button down when the EasyFocus is powered up, then all of its internal non-volatile memory is reinitialized to their default values. When the LED lights, just release the in button and the EasyFocus will boot normally.

When you first press either the in or out button the motor will step exactly once in the desired direction and the LED will flash off and then back on once. If you continue to hold the button for one more than one second, then the motor will step in the desired direction until you release the button. This way you can accurately step the motor only one step at a time manually if you desire to do so.

When the EasyFocus powers up successfully, the red LED will light and stay lit. The only time you will see it flash is if you enable temperature compensation focusing.

Figure 4: Control elements of the EasyFocus hand controller.

Adjustment

The EasyFocus requires no adjustments. It will work with just about any unipolar stepper motor without having to make any special provisions other than to make sure that the motor is wired to the EasyFocus correctly.

Safety

Whenever the motor starts moving due to a serial line command, a 15-second timer is started in the EasyFocus firmware. If the motor is not stopped before the timer expires, then the motor is automatically stopped. It is therefore impossible to move the motor for more than 15 seconds via a serial line command.

ASCOM Driver

Installation

You must first install ASCOM before installing the ASCOM driver for EasyFocus. Once you have installed ASCOM, then download and run the installation instructions for EasyFocus. The installation instructions are available here. Download the zip file, extract it to a temporary directory, and follow the directions in the README text file.

Port

The serial port that will be used to communicate with the EasyFocus is chosen using the ASCOM properties dialog box that is shown in figure 5. Using the drop-down combo-box that is labeled, ‘Serial Port,’ you can choose the correct serial port to use when communicating with the EasyFocus.

Please refer to figure five in the rest of this section where all of the different properties that can be set in the ASCOM properties dialog box are discussed in detail.

Figure 5: EasyFocus ASCOM Properties Dialog Box

Basics

There are a number of basic properties that can be set for EasyFocus using the ASCOM driver’s properties dialog box. This dialog box is displayed whenever you click on the ‘Properties’ button in the ASCOM driver chooser dialog box. Each of these basic properties is described here.

Max Increment

This is the maximum number of steps allowed in one move operation. If possible, you should set this so that your auto-focusing software can make the longest step it needs to in a single step.

Most focusers don’t have a limited range of motion, but some do like the crayford style focusers. If your focuser does not have a limited range of motion, then a good starting value to try is 5,000.

If you know that your focuser has a limited range of movement, then the best thing to do is figure out how many steps your focus motor can move. Your maximum increment value should represent no more than one-half of the maximum range of movement of your focuser. For example, if at your limits the focuser is at position 31,500 and 28,000, then the range is 3,500 so try using a maximum increment value of 1,750 to start with. Keep in mind that when the EasyFocus is used for the first time the initial position the focus motor is 30,000.

Max Step

This is the maximum step position permitted. If any attempt is made to send a command that would move the focus motor greater than this position, it is rejected. Enter the value you want to use using the text box.

Min Step

This is the minimum step position permitted. If any attempt is made to send a command that would move the focus motor less than this position, it is rejected. Enter the value you want to use using the text box.

Focuser Position

Sometimes it is convenient to be able to set the current position of the focus motor to some absolute position. You can do this by entering the position that you desire into the text box labeled ‘Current Position’ and checking the check box labeled ‘Enable.’ When you close the dialog box by clicking ‘OK’ the position of the EasyFocus will be set to the value entered in the text box.

Focuser Advanced

The properties described here allow you to control some of the more advanced features of the EasyFocus.

Mode

This controls whether or not the motor is half-stepped or not. Simply choose the Full or Half radio-button.

Frequency

The frequency combo box controls how many steps per second the focus motor will make when moving. Simply select the value you want.

Temperature Compensation

You can activate or deactivate temperature compensation using the ‘Status’ combo box. This is the only way that temperature compensation can be enabled or disabled. You can enter two different temperature coefficients and choose which one to use. This is done simply for convenience in case you image with two different setups. Choosing the temperature coefficient to use (A or B ) is done using the ‘Use’ combo box.

When temperature compensation is active, the LED on the EasyFocus will blink continuously on for a second and off for a second. Additionally, when temperature compensation is active, the In and Out buttons on the EasyFocus are disabled as well as any serial commands that would interfere with temperature compensation focusing were they allowed to be active. This includes disabling the setting of any EasyFocus parameters via the serial port as well as all of the focus serial commands.

Temperature compensation works by sampling the ambient temperature once a second. If a temperature difference between the current reading and the previous reading is detected, then the focus motor is moved in or out a certain amount depending on the value of the temperature coefficient.

The absolute value of the temperature coefficient is the amount to move the focus motor in steps per one-half degree centigrade of temperature difference. The sign of the temperature coefficient determines whether or not to move the focus motor in or out if the temperature falls. A positive temperature coefficient means move the motor in as the temperature falls while a negative temperature coefficient means move the motor out as the temperature falls.

For example, a value of +5 for a temperature coefficient would move the motor in 5-steps for every one-half degree of centigrade that the temperature falls. Similarly, if the temperature rises, then the focus motor would move out 5-steps for every one-half degree centigrade that the temperature rises.

In figure 6, this concept is illustrated by showing that the temperature coefficient is simply analogous to the slope of a line. In most cases, the change in the focus of a system is well approximated by a linear line over the limited temperature differences usually encountered during a typical night of imaging. If the performance of your system is non-linear, then temperature compensation focusing will not likely work.

To determine what your coefficient value should be, you simply have to gather focusing data over a period as the temperature is changing. Then the data gathered can be used to perform a simple linear regression, which will in turn allow you to determine your temperature compensation coefficient. Some programs (like FocusMax for example) include wizards that will automatically gather this data for you. Refer to your programs manual for more information.

Figure 6: Graph showing the difference in effect of a positive and negative coefficient

Practical Considerations

Focuser Quality

The quality of your telescope focuser will be one of the most limiting factors in your ability to achieve accurate and repeatable auto-focusing results. If your focuser exhibits any of the following characteristics, then your chances of successfully auto-focusing your telescope are greatly diminished:

The focuser sags under the weight of the camera and is not parallel to the focal plane of the telescope.
The focuser slips under the weight of the camera, and cannot be locked into place after focus is achieved.
The focuser has excessive backlash that cannot be compensated for in a predictable manner.
The focuser exhibits mirror shift as is the case for some kinds of commercially available Schmidt-Cassegrain design telescopes.

If your focuser suffers from any of the above mentioned anomalies, then you will need to correct them before expecting to get good auto-focusing results. You can usually do this by simply upgrading your focuser. In some cases a focuser can be adjusted and tuned in order to get better performance.

Mount Quality

Your mount must be stable, track well and be able to be polar-aligned without the polar alignment slipping over time, or you will have an almost impossible task achieving good auto-focus results. An unstable mount will result in blurry star images during auto-focus runs that will result in false readings. A mount that cannot track well will not be able to keep a star in the field-of-view long enough to achieve auto-focus. A mount that cannot be polar-aligned with a quarter degree of the true pole in each axis, and maintain that alignment indefinitely will not only not work for astrophotography, it will not be able to achieve auto-focus either.

Camera Coupling

Your camera must be firmly coupled to your focuser and it must not sag, slip or otherwise move in order to achieve good auto-focus results as well as stay focused during the exposure of a photograph.

Critical Focus Range

All telescopes have a range of positions where an image will achieve best focus. The size of this range is called the critical focus range.

Using the formula:

Critical Focus Range = 0.000088 x (Focal Ratio) ²

We can calculate what the critical focus range is for various focal ratio telescopes.

Focal Ratio	Critical Focus Range
10	0.22352 mm
8	0.143053 mm
6	0.080467 mm
4	0.035763 mm

What we should notice about this table is that the faster the telescope, the smaller the critical focus range becomes. In practical terms, your focus motor should be able to position your focuser repeatable and accurately ½ the distance of the critical focus range, or it’s doubtful you will be able to achieve good auto-focus results consistently and repeatably.

You can use a ruler or calipers to measure how far your focuser moves in millimeters for a given number of steps. Simply measure how far your focuser is in or out with respect to some reference point that does not move. Next, move your focuser a given number of steps (say 100 or 1000) and measure how far your focuser is in or out with respect to the same reference point. Subtract these two measurements and then divide it by the number of steps to determine what distance your focuser moves per step.

For a Schmidt-Cassegrain telescope and other similar telescopes, you can focus the telescope with an eyepiece, and then move the focuser out 100 steps. Now pull the eyepiece out of the focuser until the image is sharp. Measure the distance the eyepiece was moved out and divide it by 100. This gives your step size in mm.

Appendix A

EasyFocus Serial Commands

Command	Returns	Remarks
:C#	Nothing	Initiate a temperature conversion; the conversion process takes a maximum of 750 milliseconds. The value returned by the :GT# command will not be valid until the conversion process completes.
:FG#	Nothing	Go to the new position as set by the ":SNYYYY#" command.
:FQ#	Nothing	Immediately stop any focus motor movement.
:GC#	XX#	Returns the temperature coefficient where XX is a two-digit signed (2’s complement) hex number.
:GD#	XX#	Returns the current stepping delay where XX is a two-digit unsigned hex number. See the :SD# command for a list of possible return values.
:GH#	00# or FF#	Returns "FF#" if the focus motor is half-stepped otherwise return "00#"
:GI#	00# or 01#	Returns "00#" if the focus motor is not moving, otherwise return "01#"
:GN#	YYYY#	Returns the new position previously set by a ":SNYYYY" command where YYYY is a four-digit unsigned hex number.
:GP#	YYYY#	Returns the current position where YYYY is a four-digit unsigned hex number.
:GT#	YYYY#	Returns the current temperature where YYYY is a four-digit signed (2’s complement) hex number.
:GV#	DD#	Get the version of the firmware as a two-digit decimal number where the first digit is the major version number, and the second digit is the minor version number.
:SCXX#	Nothing	Set the new temperature coefficient where XX is a two-digit, signed (2’s complement) hex number.
:SDXX#	Nothing	Set the new stepping delay where XX is a two-digit, unsigned hex number. Valid values to send are 02, 04, 08, 10 and 20, which correspond to a stepping delay of 250, 125, 63, 32 and 16 steps per second respectively.
:SF#	Nothing	Set full-step mode.
:SH#	Nothing	Set half-step mode.
:SNYYYY#	Nothing	Set the new position where YYYY is a four-digit unsigned hex number.
:SPYYYY#	Nothing	Set the current position where YYYY is a four-digit unsigned hex number.
:+#	Nothing	Activate temperature compensation focusing.
:-#	Nothing	Disable temperature compensation focusing.