Serious problem with Acquire Star - Any ideas?

[Mike Dodd]

I'm having problems with Acquire Star in FocusMax -- it ignores nearby stars, slews across the sky to a faraway target star, but misses that by a huge amount, and ends up pointing at my trees -- causing the plate-solve and autofocus to fail. I've asked about this in the Yahoo FocusMax group, but I'd like hear what folks here think.

Last night I was imaging IC443 with ACP. At the appointed time, ACP initiated Acquire Star. IC443 was at altitude 62° at the time, well above the minimum 48° I've specified in FocusMax. I have specified mag 3 to mag 5 in FocusMax as the acceptable range of focus stars.

Instead of choosing a nearby star, FocusMax chose one far away, but didn't even point to that one.

The log file and a screen shot of TheSky, showing the location of IC443 and the star in Leo that FM chose, can be found here: <astronomy.mdodd.com/files/Mike_Dodd.zip> According to the log, FocusMax searched an area as large as 10° x 10° but then chose a star 54° away! How can it do this?? Here are the relevant log entries. The "current pointing" entry is correct for IC443.

20:21:16 Current pointing: RA 06:17:43.6 Dec 22° 30' 51.1"
20:21:16 ** Getting catalog stars between mag 3 & 5 **
[...smaller field searches...]
20:21:21 Field search = 10.0 x 10.0 (degrees)
20:21:23 3 potential target stars found
20:21:24 Target stars = 3
20:21:24 Identified target stars:
20:21:24 Star 1 mag 3.50 RA:10:07:55.6 Dec:16° 42' 34.7" Sep: 54.21 Alt:53.41
20:21:24 Star 2 mag 4.59 RA:10:08:29.0 Dec:09° 56' 39.2" Sep: 56.46 Alt:55.8
20:21:24 Star 3 mag 3.90 RA:10:33:23.2 Dec:09° 15' 01.5" Sep: 62.45 Alt:61.88
20:21:24
20:21:24 Using 3.50 mag star at RA 10:07:55.6 Dec 16° 42' 34.7" Alt: 53.41
20:21:24 Slewing 54.2089 degrees to target star

If FocusMax searched a field of 10°x 10°, why did it identify three target stars halfway across the sky, and not the 5-6 (at least) nearby mag 3-5 stars? This makes no sense to me.

The RA and Dec in the log indicate a target star in Leo -- but the OTA was not pointing anywhere close to that direction after the slew. Leo at the time was at Az 120°, but the OTA really was pointing about 60° east of north, where my horizon is 80°.

I think FocusMax somehow messed up my AP1200's pointing model.

Not only did it not point to the star in Leo, when it slewed back to IC443 after the failed Acquire Star, the OTA was way off there as well. Here's what happened:

FocusMax slewed the scope back to what it believed was the original target. But the OTA ended up pointing at the horizon, not at IC443. The RA shaft appeared to be in the correct angle, but the Dec axis was almost horizontal.

When this occurred, I shut down FocusMax and ACP, then went to the observatory to park the AP1200 using the hand box.

After the park, the counterweight shaft was horizontal as it should be for Park 1, but the OTA was pointing downward 50°-60° It should have been horizontal.

I readjusted the AP1200 using my machinist's level, then powered-up and resumed from Park 1, as is necessary after something like this happens.

This large slew to a focusing star and seriously-wrong pointing after returning to the target occurred on two different nights, with two different but close targets: first NGC2174, then IC443. The autofocus occurred at about the same time on both nights -- 8:20pm -- so both targets were in the same area of the sky.

Whatever is happening, it's screwing up my AP1200 -- slews are seriously wrong and a hand box park results in the Dec axis parking 50°-60° away from where it should.

I'm suspicious because the wrong-star slew to Leo was 54° last night, and 64° two nights before. Also, the OTA was pointing roughly 60° away from the target star in Leo both times.

60° seems to be a common factor in this mess.

Does anyone have any ideas what's going on, and how to fix it? Thank you.

---Mike