Telescope Accessories

Focus Max Setup

Setting up your MoonLite Hi-res Stepper Motor Focuser to run with FocusMax

This tutorial will guide you through the initial setup of FocusMax (FM) and its "First Light Wizard". Once completed, you should be capable of "nailing" precise focus. It does not include all the advanced features of FM. There are plenty of internet resources available for advanced features including the FocusMax User Group on Yahoo.

Important - This tutorial is specific to a MoonLite Crayford style Hi-res Stepper Motor Focuser only. The numbers provided match our resolution. Also, our focuser will not be damaged by running beyond the focuser limits. Other types of focusers, such as rack and pinion, could be and probably would be damaged if focus limits are exceeded.

This tutorial assumes the following:

  1. You have a MoonLite, Crayford style Hi-Res Stepper Motor Focuser and Controller
  2. You have downloaded and installed the latest version of ASCOM
  3. You have downloaded and installed the MoonLite Focuser Installer
  4. You have downloaded and installed the latest version of Focus Max

Start FM, click on "Jog" and try to move the focuser 1000 steps on either side of your current position. Watch the knob opposite your motor and if it moves, you are ready to start.

Zero the focuser.

To be honest, this step isn't absolutely necessary but I like to do it for 3 reasons:

  1. It makes the upcoming number game easier.
  2. It allows me to seat my focuser all the way in so my OTA fits in my travel case.
  3. If the drawtube ever slips, I know where to start.

1" of travel = 6135 full steps (you may see this a few times)

Our goal here is to seat the drawtube all the way "in" and set the position in FM to zero. So how do we do this? Well that depends on which controller you have.

If you have the Digital Read Out (DRO) controller, use the full step buttons and run your drawtube all the way in. Notice the position does not go below zero. If, after seating the drawtube, the DRO is still reporting a positive position, press the 1 and 4 buttons simultaniously to zero the controller. Check FM and it should also show a position of zero.

If you have the MoonLite Mini Controller (mini), you will have to use FM to zero your focuser. Use the Jog feature in FM to send your drawtube inward. If seated and FM is still reporting a positive position, you can "zero" FM by clicking System, Setup (under Focuser) put the number "0" in Current Position, check the Set box, and click OK.

At this point your drawtube should be seated against the focuser base and the FM position should read "0".

Finding focus.

1" of travel = 6135 full steps

I need to present this in two ways:

  1. SCT
  2. Refractors and Reflectors

Note: For this initial focus step I like to use a bright star, mag 2 or brighter.

If you have a Schmidt Cassegrain Telescope we will refer to your mirror focuser as your "primary" focuser. Since your MoonLite has only around 1" of travel, our goal here is to focus somewhere near the center of its travel. So first, we must move your MoonLite to the center point. You can do this by using the formula: 1" of travel = 6135 steps. So, for example, if you purchased a MoonLite SCT focuser with the .95" travel drawtube, your focuser range is from 0 - 5828. Half of this range is roughly 2900. In this example, we would use FM to jog the focuser drawtube "out" to position 2900. With your imaging software running, use your primary SCT focuser to bring a star to focus.

Refractors and Reflectors
With your imaging software running, use the Jog feature in FM to bring the star to focus.

Example: My TSA 102 f/8 has a drawtube with 4.5" of travel. I slew to Betelgeuse and took a .1 second image. As expected, I was way out of focus at the zero point. So much so, I didn't think it would even show in a screen shot. I instructed FM to Jog out to 7000 steps and took another image:

After several more jogs and images, I came real close to focus at 13000 steps:

If you remember the formula (1" of travel = 6135 full steps) I am in focus about mid way of my drawtube travel. Also note that I am using one of the two supplied spacers that came with my Tak. You too will have to determine the spacing of your imaging train. Depending on your setup, FM will need 1000 +/- steps on each side of focus to work properly.

If you are satisfied with your focus, it's time to slew to a mag 4 star and center. Pick a star well above the horizon where the seeing is the best.

Setting up some initial numbers:

With a mag 4 star centered and roughly in focus, we're just about ready to run our first V-curve. But before we do, we have to enter some initial parameters:
In FM, click on the System tab and under Focuser, click on Setup. This will open your focuser settings window. Here is what we recommend as a starting point:

  • Max Increment - 3000 (This is almost 1/2" of travel and should be plenty)
  • Min Step - 0 (This will allow you to send the draw tube all the way in for transport)
  • Max Step - For this, use the formula: (length of drawtube travel in inches x 6135) - 500. For example, a 2" travel drawtube would be (2 x 6135) - 500 = 11770. This will prevent you from exceeding the outward travel of the drawtube.
  • Current Position - Leave this alone and make sure the box is "NOT" checked. FM already knows your current position.
  • Make sure "Full" mode is selected and set Frequency at 125.
  • Click OK

      We are now ready to run the "First Light Wizard"

      With your imaging software running, and a mag 4 star centered and mostly focused, Click Wizard/First Light in FM. Follow the prompts and let it rip.

      Keep an eye on the log file for any issues. One issue that I have had is the star is too weak or off frame. To fix this, go to the Setup tab in FM and increase the frame size (from 100 to 300) and/or the Exposure (from .11 to .2). Don't be afraid to play with a few of these settings.

      When your first V-curve finishes, it may not look real pretty. Don't worry about it, we can always delete the bad ones.

      Run several V-curves and then Focus. Delete any bad ones and run some more. Your PID should get smaller and smaller. You will want at least 12 for a good model. This was my fifth V-curve on a night of average seeing.

      At this point I would click Focus in the lower right FM window. When focus is complete, I'd hit Next in the First Light Wizard window to run another V-curve. Under the System Profile window, you can toggle the "Y" to "N" and watch what is does to your "Mean" results. Run a lot of V-curves, delete the bad ones, save the best ones.

      When done, save the profile. From here on all you have to do to focus is center a mag 4 star and select "Focus".

      Clear skies.