Planewave Instruments: Auto-Focus with ACP & PWI3

[Brad Vietje]

MANY thanks to Bob Denny and the good folks at Planewave for putting their heads together to allow ACP to use Planewave's PWI-3 software to make auto-focus runs. We've had lots of problems with FocusMax, but the PWI Auto-Focus routine is superb. I like everything about the PWI-3 platform.

Here's a screen shot that shows tonight's first focus run... A very interesting feature is that the entire field is divided into a 3x3 array, and a separate V-curve and focal position is calculated for each segment, so you can see if there is any residual miss-alignment of the image train. The yellow highlighted area shows that our system currently does have a slight tilt from upper left to lower right. This probably results from our last filter swap-out back in April. There is a fair amount of play in the "secure fit" connections between filter wheel, auto-guider, and focuser, so if these components are not held perfectly flush against their mating surfaces, a little tilt can be introduced -- or even a little lateral translation is the set screws are not tightened evenly. The optional graph shows the focus positions, and to the left are the 9 segments, and a separate V-curve can be displayed for each.

The PWI software is very easy to use, and very user-friendly; thanks for making it an option for use with ACP!

Clear skies,

Brad Vietje
Newbury, VT
Northern Skies Observatory/ Northeast Kingdom Astronomy Foundation web site: www.nkaf.org

[Bob Denny]

Thanks Brad - Kevin Ivarsen of Planewave was the key ... not only did he add the API to PWI needed for external programs to use PWI focus, but he also wrote and tested the code needed for ACP to make use of it (thanks to ACP's open architecture and his excellent skills).

[Peter Prendergast]

Actually your tilt is within spec. I spoke to Richard Hedrick about this and he and others have said if the error is less than 80 microns your fine. Keep in mind the focus "plain" if you will, is often 120 microns wide.
Peter