ZWO EAF Focuser (Updated video Autofocus routine 11/8/21)

EAF Focuser

I was at NEAF 2019 for the unveiling of the long promised ZWO EAF (Electronic Automatic Focuser), the latest component to the ASIair suite.  Designed for refracting telescopes, it works remotely with the ASIair software or manually with a hand control.  There is even the option of getting a temperature probe to have it change automatically during an evening’s imaging session. 

OUT OF THE BOX

The standard system includes a stepper motor, bracket, cable, and several couplings, spacers, and screws to fit your style refractor.  The one I tested had the option of the hand control and temperature probe.

INSTALLATION

Dave and I performed the following steps for installation on a StellarVue 100 refractor.

1.     Using an allen wrench, remove the plain focus knob on the refractor.  (figure 1)

2.     Choose the correct coupling that will fit the focuser shaft on your telescope, and put in the four allen wrench screws. (figure 2)

3.     Set the focus all the way in on your refractor, and attach the coupler onto the focuser shaft.  Be certain to tighten so no slippage occurs.When I first tested the system, I didn’t have the coupler tight enough on the focuser shaft.  It was turning, but only occasionally moving the focuser.  Tighten it down and it’s fine.

4.     Attach the stepper motor onto the shaft.  Again be certain to tighten so no slippage occurs.  The weight of the motor will hang down slightly because the coupler is flexed. (figure 3)

5.     Attach the stepper motor bracket to the telescope. Be aware that the various size screws that were included were not the right length for this application so we ended up at the hardware store to purchase two allen wrench 6/32 screws that were ¾” long. Figure 4 shows the setup but the screws weren’t tightened down yet.

6.     Attach the motor bracket to the stepper motor making certain that it is level.(figure 4)

CONNECTIONS

There are three ports on the back of the stepper motor (figure 5).

The one on the right is for power and you will need either a DC cigarette lighter adapter or an AC adapter (https://telescopes.net/store/zwo-12v-5v-dc-converter-for-asiair.html).

The center port is for the USB cable.  This connects to the ASIair box to control the focuser.

The probe on the right is for the temperature probe or hand control.

SETUP

In the ASIair app the EAF focuser should show up on the setup page (figure 6).

After you click ENTER you will see the Focuser icon tab at the top (figure 7).

  Click on that and the menu comes up. (figure 8).

  The focuser should be on, and the first thing you want to do is to set the zero point.  When you set it up the focuser was moved all the way in.  That should be zero.  Notice that on this menu you can also set the fine and coarse steps.  The default has it as 10 and 30 respectively.

If you have the hand control(figure 9) that should be used next as you focus on a bright object.

  I did this during the day on a distant radio tower to get me close for the evening session.  Select an appropriate exposure in focus mode, and on the hand controlselect the fast mode and watch the focuser move to make certain everything is tight.

Final focus of course is done at night using the hand control and a bright star.

OPERATION

Once you have your focus you really don’t need the hand control. The ASIAir focus has a generous 60,000 steps to use.  I found focus for the StellarVue at step16,197 using the L-enhance filter and 16,173 using the BaaderSkyGlow filter (figure 8).This number shows on the Focus Settings screen under current position.  Be certain to write down the focus numbers for the various filters. To switch back and forth just type in the number and click GO.  That’s all there is to it.

You may have to tweak the focus a bit, but that’s easy to do remotely.  Put the ASIair on focus mode and click on the focus icon on the right side of the ASIair screen (figure 10).

  This gives you a quick method of moving back and forth, and gives you the number as you use the fine or coarse buttons.

TEMPERATURE COMPENSATING

ZWO has not yet included the algorthim for the temperature compensating focuser into their software.  When that occurs we’ll update this article. 

With a base price of $200 (with hand controller $250), the ZWO EAF focuser is a cost effective way of utilizing the ASIair software to achieving a fast, good focus that is easy to adjust using your smartphone or tablet.

Update 11/8/21

Video to show updated EAF autofocus routine