Starizona's MicroTouch autofocuser is ASCOM compatible and can work with most autofocus software. By far the most popular software is the freeware FocusMax, which is included with the MicroTouch autofocuser. FocusMax controls the MicroTouch, quickly and easily bringing your telescope to focus. FocusMax works in conjunction with a camera-control program, either MaxIm DL or CCDSoft. Since MaxIm is by far the most popular software, it will be used for these instructions.
Overview of the Focus Process
The first time you use FocusMax, it needs to characterize your imaging system. The focus parameters the software uses are dependent on the actual mechanical focuser being used, the telescope optics, and the camera. Fortunately, FocusMax will learn everything it needs to know automatically with no user input necessary! The basic steps are outlined below, with details given in the following sections.
- Launch FocusMax and MaxIm DL
- Connect the MicroTouch autofocuser
- Manually focus the telescope
- Run a First Light Wizard to characterize the system
- Autofocus the telescope
- Image the universe!
Launch the Software
At this point, your telescope should be aligned and the camera connected in MaxIm DL. Begin by launching FocusMax. The first time you use FocusMax, it will display the ASCOM Focuser Chooser where you can select the focuser being used. If you don't see the Chooser, click on the System tab at the bottom of FocusMax and press the Select button.
When the Chooser appears, find MicroTouch Focuser on the pulldown list and select it.
If you are using Windows 7, there is a quirk involved with the Chooser. Before clicking the Properties button in the Chooser, you must move the Chooser window away from the center of the screen, otherwise the Properties window appears behind the Chooser and there is no way to get to it and the program must be closed with the Task Manager.
Click on the Properties button and the Properties window appears. Make sure it is set to USB2 under COM port and click OK. Click OK in the Chooser and FocusMax will connect to the MicroTouch focuser.
To verify the focuser is connected, click on the Focus tab at the bottom of FocusMax and make sure the red Position number at the top matches the number displayed on the MicroTouch hand control.
In the future, you can start an imaging session by simply launching FocusMax. This will automatically open MaxIm DL and connect to your camera and to the focuser.
To start, you need to roughly focus the telescope. This gives FocusMax a good starting point to learn the system. To do this, begin taking continuous 1-second exposures in MaxIm DL. You can then see changes made to the focus in almost real time.
Use the red In and Out buttons on the MicroTouch hand control to focus the telescope. Try to make the stars visible in the image as small as possible. The fainter stars should be almost perfect pinpoints when focused.
Once you've reached focus, it is helpful to reset the MicroTouch's position counter to the default 30000 position. This gives you the maximum range for focusing, but also gives you a reference position if you remove the MicroTouch motor and use the focuser manually for, say, visual observing and then replace the motor for a later imaging session. To reset, press the Mode button on MicroTouch hand control until the display shows “Reset Position?” Hold the Set button for 3 seconds and the position will flash then return to the “Mode: Idle” setting and will show 30000 for the position.
Finding a Focus Star
For FocusMax to learn your imaging system, it needs to focus on a relatively bright star. However, it will be more accurate if the star is not too bright. A 4th magnitude star is about perfect. Since such stars are too faint to have proper names, pointing to one with a goto telescope is usually done manually. A 4th magnitude star is faint but readily visible to the naked eye from most locations, so centering one in a finderscope or Telrad should be pretty easy.
Roughly center the star in the image in MaxIm DL. Be sure to stop the continuous exposures in MaxIm DL once the star is centered.
First Light Wizard
The first time you use FocusMax, it will show a warning that the telescope cannot be focused until FocusMax characterizes the system. It gives the option of running a First Light Wizard. Click on this option to begin the Wizard. If you don't see this warning, you can simply go to the Wizard menu at the top of FocusMax and select First Light.
FocusMax will recommend that you point to a 4th magnitude star and manually focus the telescope, which you have already done. Press OK.
FocusMax now asks what system you want to use to save the profile it will create. For most purposes, you can simply choose MySystem, which is the default choice. If you will be using more than one imaging setup (for example, imaging with an SCT in both HyperStar configuration and at the back of the scope at f/10), you will need to save more than one profile. You can create profiles with appropriate names before running the First Light Wizard and they will be available on the list of choices.
After choosing the system name, FocusMax displays several windows and gives you the chance to rearrange them. You will see the main FocusMax window, a Log window, and a V-Curve window. You would also like to see the images that will be taken in MaxIm DL, so you might move the FocusMax windows so the imaging area in MaxIm is visible. Once ready, press OK and FocusMax will go to work.
How the Magic Happens
At this point, FocusMax takes over and does everything automatically. It finds the star you chose to focus on and takes a subframe around that star. It will begin by determining the proper focus range. It starts moving the focuser in small increments and measures the change in the size of the star. If the changes are too small, you will see the step size between exposures increase. Eventually you will see the star becoming larger as the telescope is driven out of focus. If you look at the Log window, you will see the current measured size of the star getting bigger. Once the size is larger than 40 pixels, the focus range has been determined.
Now FocusMax moves the focuser back through focus and out the other direction by the same amount just determined. There will be a few seconds pause while the focuser moves and in the main FocusMax window you will see the red position numbers changing.
Once on the other side of focus, FocusMax begins constructing a V-Curve. This is a plot of star size versus focus position and is shown in the V-Curve window. An exposure is taken at the start position and the size of the star is plotted in the V-Curve window. The focuser then moves slightly toward focus, another picture is taken and the new (smaller) size of the star is plotted. Over the course of a number of images, the telescope will go through focus and out the other side, creating a V-shaped profile in the V-Curve window.
When the V-Curve is finished, FocusMax plots the best-fit lines to the V-shaped graph. In this way it determines the best focus point (the intersection of these two lines).
As the last step in the First Light Wizard, FocusMax will autofocus the telescope. The program begins by moving the focuser to a predetermined out-of-focus position (which it learned from the V-Curve process). Several images are taken to allow for slight variations in star size due to atmospheric turbulence. Once an average value is determined, FocusMax knows the exact position of best focus from the V-Curve. There is a pause of a couple seconds while the focuser is moved to the best focus position and a last, perfectly focused image is displayed.
In the main FocusMax window, you will see a profile of the focused star (which should look like a tall skinny spike). Below this window is displayed a value called the Half Flux Diameter, which is effectively the size of the star in pixels. The value of this number is dependent on the optical system, camera, and seeing conditions. For a typical HyperStar setup, the number will probably be in the 2-pixel range. Eventually you will get a feel for what number you should expect from your system on a good night.
FocusMax now shows a Profile window with the parameters it determined from the First Light Wizard. It will ask if you want to run another V-Curve. This is almost never necessary, but if you run multiple V-curves FocusMax will take the average value of the multiple runs in the stored Profile. At this point you can close the Log, V-Curve, and Profile windows.
The First Light Wizard is a one-time procedure unless you change some part of your imaging system. Now, whenever you want to autofocus, all you have to do is click the Focus button at the bottom right of the main FocusMax window.
In the case of a HyperStar setup where you have a wide field of view and fast focal ratio, there will almost always be star that FocusMax can use right in the field of view of your target. In this case, simply press the Focus button and FocusMax will find an appropriate star in the image to focus on. The entire focusing process takes less than 30 seconds!
There are two common instances where FocusMax can fail to autofocus. One is when there is no star bright enough to focus on. This sometimes happens with narrow-field telescopes. The other possibility is that the brightest “star” in your field of view, and the one that FocusMax chooses is really the core of a bright galaxy. In this case FocusMax might actually focus, but it will be inaccurate since the core of the galaxy isn't really a point source like a star.
When this happens, there are a couple options. In the case of FocusMax grabbing the wrong “star”, you can press the Select button (next to the Focus button) and FocusMax will let you choose the star to focus on. When you press Select, a full-field image is displayed and FocusMax asks you to click on the star you want to use. After clicking on the star, press OK and FocusMax will now autofocus on the star you picked.
Worst-case there simply won't be a bright enough star to focus on. When this happens, you can drive the telescope to a nearby brighter star (which does not necessarily need to be visible to the naked eye) and focus on that star. Then drive the telescope back to your target. This might also be necessary when imaging through a narrowband filter, such as an H-alpha filter which lets through very little starlight.
MicroTouch software download including latest version of FocusMax
Capturing Images with MaxIm DL tutorial
Processing Images with MaxIm DL tutorial
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