Hi John,

I have tried many times to image NGC 2276 but because of it's high latitude the initial slew is off by quite a bit in RA. However CCDAP makes a correcting slew and it puts it on the chip. My problem is that after returning from the focus star CCDAP encounters the same pointing error but refuses to make the correcting slew. If I sync on the initial slew then it messes up my pointing model and focus stars are off the chip.

I don't really see why an excessive pointing error should negate a correcting slew, but if it is necessary then couldn't that error amount be selectable by the user? I'm attaching my log.

Thanks,
Ron Stanley

ccdap20080115_222632.log (6 KB, 60 downloads)

Hi Ron,

Your pointing is nearly 2 degrees off in RA. I put in a limit to the correcting slew to protect the equipment, figuring no mount should be off that much. The actual threshold is 2 degrees so there might be some internal rounding issue. I would have thought 2 degrees was more than enough for automated imaging systems but guess I could open the threshold up more.

You may want to look into the source of the pointing error. Some obvious things that you probably already know about:

1. Before connecting to your mount, set your PC clock to "internet time" using one of the many time setting programs.

2. After setting the PC, connect to the mount. Most mounts get their time setting at first connect. This is true of both AP and ME's at a minimum and probably more.

3. As an added measure, use an image link and sync before an automated run to insure the mount pointing is as good as it can be.

FWIW on a Time Keeper Program to make sure goto pointing is at its best...

I have sucessfully used "About Time" v4.8, careware (freeware) time mgmt. software, by Paul Lutus.

http://www.arachnoid.com/abouttime/index.html

Excellant program that can be run in memory and you can set the "time setting interval" to anything you wishon the fly. Less than a minute between time check/set can be achived by using a negative number in the options window.

Sweet and simple software. TY Paul.

BDK
Houston

John,

I don't understand why it would make a correcting slew when slewing to the target but not make a correcting slew when slewing back from a focus run. I've redone my pointing model and normally I'm not more than a couple arc minutes off, however NGC 2276 is less than 5 degrees from the pole so a pointing error that would be minimal at the equator will be magnified so close to the pole. I think this is why the tolerance should be variable depending on declination.

-Ron

PS I'm already running an internet time setting program.

Ron,

Try the attached version. I think it will work for you.

ccdap3421test4.zip (327 KB, 11 downloads) Increased slew error tolerance

Thanks John,

I'll give it a try next time out.

-Ron

Hi John,

I tried again tonight and the behavior was the same. It would make an initial correcting slew but it wouldn't make a correcting slew when coming back from the focus run.

-Ron

ccdap20080127_003040.log (7 KB, 70 downloads)

Hi Ron,

I guess I am a bit puzzled. In your first posting, the pointing error was reported as:

22:30:54 Pointing error (arcmin): RA -113.2; Dec 0.0
22:30:54 Excessive correcting slew not made

I doubled the allowable error from 2 degrees to 4 degrees. Now this run shows:

00:37:45 Pointing error (arcmin): RA 218.8; Dec -8.5
00:37:45 Excessive correcting slew not made

with the pointing error increasing further.

The first log was prior to culmination and the second log was after. I suspect there is some increasing pointing error with your mount around the pole. I doubt that it should be dec related from any spherical geometrical considerations and it may in fact be a mount firmware anomaly. Of course I can further increase the allowable error but I am reluctant to do that without further investigation and understanding. I will have to dig into this myself under the stars once I am up and running - probably later this week.

Hi John,

I think you are right, it seems like I can never get good pointing to NGC 2276 even if I have just finished a good model. I have had generally good luck with the Gemini model but I also have Maxpoint. Next time out I will build a model in Maxpoint and see if that makes a difference. I will post the results. Thanks for your help.

-Ron

Hi Ron,

I took a look at your logfile and saw you are having trouble plate solving. This would be one of the first things that I suggest correcting, as without a good plate solve, CCDAP3 doesn't have the data it needs to put the scope accurately on the target. Even when the plate solve seemed to work, the mount pointing was pretty far off the target. Seems like there may be something wrong with your model or something in your setup may be loose.

I setup CCDAP3 here tonight and did a short seq on NGC2276. I wanted to see if there might be a anomaly in CCDAP3, but everything worked as expected, so from what I can see, CCDAP3 is doing what it is told to do. I have attached my logfile for a reference. If you can figure out the reason for your plate solve failures and correct that, you might find that your model is OK. Good luck.

ccdap20080127_191040.log (8 KB, 65 downloads) NGC2276 CCDAP3 logfile

Hi Frank,

I believe the pointing error is something in the way the Gemini calculates the model. When I concentrate on modeling near the pole it throws off the model elsewhere. The model is very accurate up to about 80 degrees declination but it breaks down between there and the pole. The only problem I have with CCDAP is that it will make a correcting slew from the initial goto and it will put NGC 2276 right on the center of the chip, but then when it goes to focus it won't make a correcting slew coming back.

If I sync on the initial slew then it really screws up my model when going for focus stars. My FOV is only about 11 x 15 arc minutes, it's tiny, which is why sometimes the plate solves are difficult.

IF CCDAP would make the same correcting slew coming back from a focus star that it makes initially then I think it would all work.

-Ron

ccdap20080127_215431.log (6 KB, 45 downloads)