Blind plate solving a touch out - any suggestions?

[dannybgoode]

I’ve got APT, ASPS and Stellarium all just about talking to each other however whenever I blind solve or use Goto ++ the target is not quite central, or conversely the software says it is central but it’s a touch out  

So for example tonight I used Goto ++ to centre on M81 and whilst the software said it was bang centre it clearly wasn’t. 
 

Luckily I could see the core in live view so could centre naturally but now when I blind solve as a test Stellarium is saying the core is toward the upper of the frame.

 Doesn’t matter too much for galaxies but if I’m going to rely on it for Nebula etc then I need it to be a touch more accurate than it is otherwise I’m going to end up missing targets. 
 

Any ideas? 

[dannybgoode]

Here’s a screenshot of Stellarium. M81’s core is pretty much dead centre in the frame looking at actually images. 

[JamesF]

I'm only guessing, but is it possible that you need more star data files to get better accuracy?

James

[david_taurus83]

I find it sometimes doesnt Sync the last movement. So when it settles I press shoot, solve again and then sync. It should update the correct position.

[stash_old]

settings in apt platesolve - acceptable goto error 

[han59]

Solvers can fail but it is very very very rare. In all other cases the error is less then one pixel. If your telescope is not perfectly polar aligned, you could need two syncs rather then one. So check your number of tries, the acceptable error as indicated above and equinox setting(s) J2000 or Jnow.  

 A J2000 vs Jnow error is the most likely cause.

[dannybgoode]

Thanks all. I’ll have a fiddle. As I say when I solve an actual image it shows out in Stellarium and it thinks it’s centred doing a blind Goto and it’s actually out by the same amount. 
 

I’m nearly there so hopefully won’t take too much to resolve  

[stash_old]

if you are using eqmod then creating a triangle around you object helps - this does not have to a small triangle of solved images 

[han59]

Stash remind of an other problem, modeling of eqascom (eqmod). If you use eqascom, the eqascom model could be wrong. The number of  APT retries (goto++ attempts default two times) will indicate this. Reset the eqascom  align and sync data for the alignment.  It could have collected wrong alignment points from telescope sync command.  You can switch this add alignment points behaviour off:

Quote

 Start by clearing out any existing model and put EQASCOM into “dialog mode” (rather then “append on sync”) for alignment. A sync will be treated as standard ASCOM sync rather than as a trigger to add an alignment points.

 

[stash_old]

1 hour ago, han59 said:

Stash remind of an other problem, modeling of eqascom (eqmod). If you use eqascom, the eqascom model could be wrong. The number of  APT retries (goto++ attempts default two times) will indicate this. Reset the eqascom  align and sync data for the alignment.  It could have collected wrong alignment points from telescope sync command.  You can switch this add alignment points behaviour off:

 

Yes this is true and the fix is to clear out the saved model as you say,delete offending bad syncs (really your kidding) or just create a new smaller triangle of points which can work. The former,total reset, being the easiest.

I do get this problem very rarely and the advantages outweighs the problems - for me anyway. 

I get consistently,but not 100%, sub 4 sec platesolving using some horrible software called ASTAP LOL 🙂

Even with Platesolving (any product) you can see the image dead centre and the Platesolver doesn't solve and starts scanning around the sky. It occurs ,for me,with images of bright Clusters - guess its a case of  "can't see the stars for the cluster" LOL - sorry a pun . Changing parameters might work but thats not any use when you are doing a sequence ,especially unmanned! 

Of course an out of balance mount/scope will cause the same effect as no matter how the mount tries to move it cant and normally just produces the same RA/DEC - this causes  a looping effect until the number of tries,in platesolving, is reached.

Overall Platesolve still a "god send" .

 

[dannybgoode]

Thanks all for your replies. 
 

Is there a reason why an image doesn’t show quite correctly in Stellarium once solved? 
 

For example the screen shot I have posted of Stellarium shows where it thinks the scope is pointing when it is quite clear from the actual sub that the galaxy core is more or less dead centre. 
 

I blind solved the sub and hit ‘show’ in Pointcraft and this is what shows in Stellarium?

[stash_old]

Poss List -

1. JNOW instead of J2000 or visa versa - As I understand it (I do it just because) all the software you use should use the same Epoch - So APT,Stellarium/Stellarium Scope,EQMOD (even though I think I read (misread) somewhere it doesn't care !) etc.

2. Date and time including daylight saving same.

3. APT is showing a cropped image in its display where as Stellarium is showing the image as per full scale

4. Bug in Apt or Stellarium - check forums

5. Its correct and just not what you expected. 🙂

But I dont use Stellarium (I use Sky Chart) so maybe someone will come up with a correct reply for you 🙂

[spillage]

When using APT I always ran off a single frame from the home position and solved and synced this. Then moved on to my target. Could it be that the time on stellarium is out? have you tried to use CdC? I am sure I only used platesolve2 with APT.

[bottletopburly]

4 minutes ago, spillage said:

When using APT I always ran off a single frame from the home position and solved and synced this. Then moved on to my target. Could it be that the time on stellarium is out? have you tried to use CdC? I am sure I only used platesolve2 with APT.

Same here I usually shoot an image and solve and sync in home position using APT 

[han59]

I run a simulation in APT and got in the same problem. However there is a APT button "Jnow" near "connect /disconnect telescope" which fixed the problem.  Does this work for dannybgoode?

This test can be done in simulation. Just load an image in APT, solve it and sync the (real) mount. Then check the results.

Han

Before:

 

Activate the button Jnow

 

With the button Jnow activated:

[dannybgoode]

@han59 I have the JNow button pressed and it still does not make a difference - still shows out in Stellarium and CdS (tried this just to be sure.

May be I am missing something.  I am due to rebuild this laptop anyway so will be doing a complete reinstall of everything so will see if th problem persists after that and if it does I will have another fiddle with things.

Thanks everyone for their help so far.

 

[han59]

@dannybgoodewhat are the indications showing in your setup? You can see in my last screenshot what to expect. That will identify where the problem lies.  So specific the RA,DEC solution in APT, the RA, DEC position of the mount after sync and the RA, DEC position (J2000 or Jnow or both) of the frame in Stellarium.

[dannybgoode]

@han59 sorry only just seen your post. When I next set it up I’ll have a look at see if I can spot where the error is. 

[dannybgoode]

Thanks all to who responded on this one. Thought I’d post a quick update - bit embarrassing really but I was missing out a step. 

It turns out that just bind plate solving an image without putting a target in the first box of Pointcraft don’t quite work. To help others who may have a similar issue the workflow that seems to have best success is:

1/ Use APT’s Goto function to skew to a target and then take a frame. At this stage the targeting is likely to be out  

 2/ Then go into Pointcraft, look up the target again and do a normal plate solve (not a blind plate solve) on the image you have just taken. 
 

3/ Press Sync and Pointcraft will populate all the fields in the middle box. 
 

4/ Then use Goto++ to perform its auto routine and you then be about bob on