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

[Jim McMillan]

Hi Mike,

If pointing is going way wrong where it's been fine before, I still suggest checking the set screws on the spur gears in your mount. What happens when you slew around the sky with the handbox? Is pointing ok, or is it also way off? If you revert to using ACP's focus routine, what happens? It seems to me there's some more troubleshooting required before we know it's a FocusMax issue.

Jim

[Mike Dodd]

Hi Mike,

If pointing is going way wrong where it's been fine before, I still suggest checking the set screws on the spur gears in your mount. What happens when you slew around the sky with the handbox? Is pointing ok, or is it also way off? If you revert to using ACP's focus routine, what happens? It seems to me there's some more troubleshooting required before we know it's a FocusMax issue.

Jim

I'll check the gears, but I don't believe that they're loose.

The AP1200 points perfectly. After one of these way-off slews, I can loosen the clutches and move the axes to the Park 1 position using a machinist's level, then tighten the clutches and power-up, resuming from Park 1. A GOTO any bright star puts that star near the center of my finder scope. A little tweaking with the hand box direction keys at 12X speed centers the star on my ST-8 chip. I then use the AP1200 hand box to synchronize the pointing model.

Subsequent GOTOs in ACP or TheSky put the target star within a few arcsec of the center of the chip.

Furthermore, I can start a plan, and ACP successfully slews to the target, plate-solves with a pointing error of 3-7 arcsec, starts the autoguider, and takes 15 or 20 good images.

It's hard for me to believe that this could occur if the gears are loose.

I'm not familiar with ACP's focus routine, but I'll read up on that and give it a try.

---Mike

[Bill Mattil]

Mike,

This should be pretty easy to duplicate since you have all the pieces.
Don't use ACP to actually run a plan. And from the console after the
scope slews to IC443, you can if you like, execute an "update pointing"
to confirm that IC443 is really in the FOV. Then just use the "Acquire
Star" Feature manually. This reduces the problem to the simplest
possible configuration. And the results of this test would be extremely
interesting.

I have *never* seen this behavior and from the lack of traffic on this
thread I suspect that it's an anomaly. So running this simple test
removes ACP from the equation.

Bill

[Mike Dodd]

Mike,

This should be pretty easy to duplicate since you have all the pieces.
Don't use ACP to actually run a plan. And from the console after the
scope slews to IC443, you can if you like, execute an "update pointing"
to confirm that IC443 is really in the FOV. Then just use the "Acquire
Star" Feature manually. This reduces the problem to the simplest
possible configuration. And the results of this test would be extremely
interesting.
Bill

Yes, I saw your post in the FocusMax Yahoo group, and I'll give this a try.
-----
Mike

Mike Dodd
Montpelier, VA USA
http://astronomy.mdodd.com
http://NotWhatIVotedFor.com

[Mike Dodd]

Hi Mike,

If you revert to using ACP's focus routine, what happens?
Jim

I must be missing something, Jim. What exactly is "ACP's focus routine" and how do I revert to using it?

I read through the ACP documentation, and the only thing I can find about autofocusing talks about using FocusMax's Acquire Star.

Is there something else that ACP does autonomously?

Mike

[Dick Berg]

Hi Mike,

The AutoFocus() routine in AcquireSupport.wsc has two separate paths through the code - one hands over the focusing entirely to FocusMax, using its Acquire Star functionality to select stars, slew, focus, ...; in the other path ACP selects stars, adjusts exposures, slews, ... does everything but only hands over the actual focusing operation to FocusMax.

To change the mode of operation, uncheck or check the "Use FocusMax AcquireStar feature" checkbox on the ACP/Preferences/AutoFocus tab.

However, you should note that ACP is set up to look for a focusing star (and only one, not three) in a 5x5 degree box around your target star, in the mag 6-9 range, not the mag 2-4 (3-5?) that you've been using. (Why are you focusing on such bright stars?) You should definitely not move too far from the target by using ACP's focusing. It would be really strange if you did.

It is possible to change the magnitude limits (it's in "FindBrightStar" in AcquireSupport), but doing that will have all sorts of unintended consequences for other operations, like perhaps guiding. For testing, you could make the change, but I'm not sure you should leave those changes in place for operations.

Hope this helps. Jim would have made the same comments, I'm sure!

[Bill Mattil]

(Why are you focusing on such bright stars?) You should definitely not move too far from the target by using ACP's focusing.

For what it's worth I agree with Dick 100% here. Focusing on such bright stars is probably not a good idea. And this topic still has not been addressed.


I am sure that there is a lot of smoke and mirrors surrounding this problem. And I suspect that at the bottom of it lies the simplest possible explanation. And that is that the AP Driver is in la la land with respect to where the scope is really pointing. It doesn't seem to be ACP unless somehow custom horizons are creating it. But that's an incredible long shot. If I were Mike, and I'm not - I'd not be using the newest AP driver from Ray. Those people choosing to walk the cutting edge of technology had best lay in a supply of bandages. <lol>

I am using the older Ajai driver and I have *never* seen this. In a number of years. And that should be a useful data point. In fact, I've only rarely, if at all, seen FM flip the scope to find a focus candidate star

Bill

[Mike Dodd]

Hi Mike,

[...]the mag 2-4 (3-5?) that you've been using. (Why are you focusing on such bright stars?) [...]

Maybe I misunderstood what FocusMax needs. I followed Neil Fleming's tutorial
http://www.flemingastrophotography.com/focusmax.html to create my V curves. It calls for using a mag 4 star, and I assumed that FocusMax also wanted mag 4 stars For normal focusing.

Are you saying I can and should use dimmer stars? If so, that certainly would increase the number of suitable target stars Close to almost any target I image.

What magnitude range do you recommend, and what exposure range (ST-8 camera) works for those stars?

Thanks for any clarification. Maybe I've been causing my own problems here.

Mike

[Eric Dose]

Two ways I know of to select a starting FocusMax mag limit. (1) try to get maybe 100-200K counts flux in 1-3 seconds through your focusing filter. Alternatively, (2) target the brightest star that just barely fails to saturate your detector in 1-3 seconds, at perfect focus & in good seeing.

For my C-11 and ST-8XME, that's much more like mag 7 than mag 4.