ACP has built-in support for the free FocusMax autofocus tool, written by Larry Weber and Steve Brady, as well as the PlaneWave PWI focusing tool provided with PlaneWave's mount/telescope systems. If you have a focuser that has an ASCOM driver, you can use FocusMax or PWI together with ACP.
Do not attempt to use ACP's autofocus features until you can achieve reliable automatic focus virtually every time with PWI or FocusMax at any place in the sky. Plan to spend some up-front time getting familiar with your auto-focus tool. Both programs are sophisticated programs with lots of features.ACP offers several ways to control autofocus, however if you have multiple filters it is recommended that you configure ACP with focus offsets and use periodic autofocus in your observing plans. See Using Filters. Alternatively, (or in addition to periodic autofocus) you can force autofocus to be done during observing at specific points in your observing plan (e.g. at filter switches) via the #autofocus directive. See Getting Started below.
ACP's unique adaptive autofocus feature monitors focus quality and refocuses your imager only when needed. At present this depends on MaxIm DL's half-flux diameter measurements. This measurement is not reliable enough when the image(s) contain large extended objects (galaxies, nebulae), so if you are an astro-imager, we recommend against depending on adaptive autofocus.
If you are using FocusMax, it has two places where a Chooser window appears. One is for selecting the focuser type; the other is for selecting the telescope type. In this step you are selecting the telescope type. If you can't find the ACP Hub, you are probably looking at the focuser Chooser (which should be set for your specific focuser type). 
In FocusMax, select the Open menu, Options (the last menu item in FocusMax). In the Options window (shown at right) turn on Send log text to ACP. This will cause FocusMax's logging to be included in your ACP run logs, very handy when diagnosing focus problems! Close the Options window. PlaneWave provides this automatically, so you don't have to set any options.Once you have ACP and FocusMax set up per the preceding section, using autofocus with ACP is easy. It is recommended that you include periodic autofocus in your observing plans (#afinterval), but you can force ACP to refocus any time you want. You can also set it to run when your FWHM gets above a certain value (adaptive autofocus). Just a hint: Some people focus way too often. Try reducing the frequency of your autofocus runs.
We've found that starting FocusMax by hand, when you start ACP, is best. It doesn't matter which one you start first (ACP or FocusMax). Just start FocusMax yourself. ACP's logic for selecting a nearby "bright" star can use a file of known bad bright star locations. If the file BadBrightStars.txt exists in ACP's config file folder (Public Documents\ACP Config), ACP will read its list of RA/Dec coordinates. If any candidate stars lie within 5 arc minutes of a coordinate set in that file, those stars will be ignored. Use this to prevent ACP from using stars you discover are ill-suited for autofocus (doubles, in crowded field, etc.).
The format of the BadBrightStars.txt file is plain ASCII text. A semicolon starts a comment; the semicolon and everything to the right on the line is ignored. Blank lines are OK and are ignored. A live line consists of a right ascension value, a TAB, and then a declination. In other words, the file is tab-delimited. The RA and Dec values may be in decimal or sexagesimal, and a wide variety of sexagesimal formats are OK. Example:
; ; Bright stars list ; 21:34:09.1 +12:54:21 7.48954218 -2.0873106
ACP run logs include the RA/Dec of the selected star for autofocus, so if you suspect a bad star caused a focus failure, you can get the RA/Dec of the star, then go take an image at that location. If the star is indeed bad, add it to your list. It's hoped that people will share their bad star discoveries via the DC-3 Dreams Communication Center.