Go Back   IceInSpace > Equipment > Astrophotography and Imaging Equipment and Discussions

Reply
 
Thread Tools Rate Thread
  #1  
Old 17-05-2012, 08:50 AM
PRejto's Avatar
PRejto (Peter)
Registered User

PRejto is offline
 
Join Date: Jan 2011
Location: Rylstone, NSW, Australia
Posts: 1,397
Need ome Help with my PMX/Camera

I'm too new at this to totally understand what to do next, or if there really is anything wrong. I've been through many many T-Point routines with my PMX and I attach he latest effort from last night....a run of nearly 200 points. This is prime focus on my TEC140 and a Moravian 2-8300 CCD.

I'm noticing that during the T-Point run I am getting noticable trailing on even 5 sec images. It doesn't always happen and seems random. I guess it might have something to do with the mount having just stopped slewing and immediately taking a photo; perhaps the tracking has not settled down. But, this behavior seems new and I don't recall seeing this a few weeks ago.

In any case, after the T-Point run I turned on ProTrack and slewed over to Omega Centauri. I attach two 2x2 binned/strectched single frames. What I see I don't really understand. The 20 sec exposure shows a bit of trailing, or is it optical distortion towards the edges? The 45 sec exposure sure looks like trailing, but then I don't understand why some stars appear not to trail...especially towards the right side of the image.

The camera is very ridgedly mounted using a Baader Click Lock extension, and the Feather Touch Focuser has a very sturdy locking ring. Yet, could it be that the CCD is not truly perpendicular to the optical plane? I'm just guessing; there is probably a much simpler explanation, hopefully! I know focus isn't perfect, but shouldn't focusing be symetrical over the field?

I'm not sure why I cannot even get 45 sec exposures not to trail with this mount and these adjustments. Any tips greatly appreciated!!

Peter
Attached Thumbnails
Click for full-size image (T-Point.jpg)
175.7 KB45 views
Click for full-size image (omega cent 20 sec 2x2 bin no dark protrack on.jpg)
158.0 KB51 views
Click for full-size image (omega cent 45 sec 2x2 bin no dark protrack on.jpg)
141.6 KB57 views
Click for full-size image (Terms-2.jpg)
155.5 KB27 views

Last edited by PRejto; 18-05-2012 at 06:16 AM.
Reply With Quote
  #2  
Old 17-05-2012, 10:38 AM
CDKPhil's Avatar
CDKPhil
Phil Liebelt

CDKPhil is offline
 
Join Date: Mar 2011
Location: Australia
Posts: 279
Hi Peter

Have you programmed your PEC?
Are you mounted on a pier or a tripod?

Are you using the latest daily build for Sky X?
I read on the SB forum that there was a fix for Pro Track with the latest build.
Someone said they need to have the Pro Track tab open for it to work.

I was out last night with my MX and did a short Tpoint run of 50 stars, I activated Pro Track for a test. The star I centred drifted about 50 arc seconds in RA over 40 minutes. I have not programmed PEC yet. And my polar alignment was slightly out in azimuth. And I think you need a pointing sample of over 250 for Pro Track to work effectively.

If your camera is not orthogonal wouldn't you get the same result regardless of the length of exposure? If its blurry or out of focus that is of no consequence to tracking.

Is the trailing in RA or DEC?

If you get really stuck go from the ground up. make sure all your mounting surfaces are tight, pier to ground, pier to mount, mount to OTA, OTA to camera.

If that doesn't work contact Bisque.

I am probably telling you to suck eggs but you asked for it.

Cheers
Phil
Reply With Quote
  #3  
Old 17-05-2012, 11:32 AM
PRejto's Avatar
PRejto (Peter)
Registered User

PRejto is offline
 
Join Date: Jan 2011
Location: Rylstone, NSW, Australia
Posts: 1,397
Hi Phil,

No problem sucking eggs....I just feel like I suck at this!

1. I am using the latest daily build of TSX
2. I am firmly mounted on a pier
3. I have not beeen able to do any PEC yet because CCDSoft will not run with my camera, even with ASCOM, and I've tried 3 different drivers. I will need to look at PemPro soon.
4. Pretty sure trailing is in RA
5. I've checked the pier, mount attachment, scope to dovetail, and focuser to camera for tightness. All seem excellent.
6. If I had a problem with slop I highly doubt I could get the T-Point results posted.
7. I will try ProTrack with the tab "open."

Your results speak loudly; I cannot get close to that and I think my alighnment is superior to yours. I keep thinking that there might be something wrong with my basic sidereal tracking. But, I still don't get why stars look like they are trailing on the left side as opposed to the right side of the image.
Attached Thumbnails
Click for full-size image (TEC140-PMX.jpg)
179.2 KB47 views
Reply With Quote
  #4  
Old 17-05-2012, 12:36 PM
CDKPhil's Avatar
CDKPhil
Phil Liebelt

CDKPhil is offline
 
Join Date: Mar 2011
Location: Australia
Posts: 279
You Look like you have a great set up there.

This might be really obvious but when you connect to the MX from the Sky X do you turn sidereal tracking on. I am not sure if it comes on when you connect. I make it a habit to click on it anyway.

If you have not set up your PEC maybe this is causing the trailing?
I would do some longer exposures of 2 minutes or so and see how long the trails get. You might be able to see the error in the worm.

Here is a shot of my alignment from last night.


Cheers
Phil
Attached Thumbnails
Click for full-size image (Screen Shot 2012-05-17 at 1.32.07 PM.png)
145.3 KB34 views
Reply With Quote
  #5  
Old 17-05-2012, 12:42 PM
bmitchell82's Avatar
bmitchell82 (Brendan)
Newtonian power! Love it!

bmitchell82 is offline
 
Join Date: Jul 2008
Location: Mandurah
Posts: 2,597
there are two easy way to see if your camera has tilt.

1. Rotate your camera if the direction of the stars changes. Chip is tilted

or

2. Focus on a star in the center of the FOV, if your stars are pin point along a diagonal but smudged along the same angle but away from the central clear band. try where the stars where smeared perpendicular to the main clear focused stars at its farthest point awayr. focus on that star and then do another exposure, if you have tilt then the opposite corner should be really egged...

Otherwise from that I cant help you!
Reply With Quote
  #6  
Old 17-05-2012, 05:40 PM
frolinmod's Avatar
frolinmod
Registered User

frolinmod is offline
 
Join Date: Dec 2010
Posts: 573
Quote:
Originally Posted by CDKPhil View Post
The star I centred drifted about 50 arc seconds in RA over 40 minutes.
Don't want to sidetrack Peter's thread, but...

Phil, if you have a large scope like I do then that's probably flexure. With an EdgeHD 14 on an ME I was getting about one arc second per minute of time drift in RA. It was flexure. Turning on ProTrack made it (appear to) stop. Quite impressive. Sounds like ProTrack is NOT working for you. That's not good.

It's not the number of pointing samples, it's the model. The pointing samples are the raw data that is used to compute the model. Once a model is in place, the pointing samples are not used. It's the model that is used. The better the model, the better ProTrack will work. Sometimes you can get good models without having to collect a large number of pointing samples. Sometimes you can't and just plain have to collect a bunch of pointing samples.

One of my favorite ways to graphically see what's going on with tracking is to set the Declination track rate in Telescope->Tools->Bisque TCS->Parameters so as to intentionally cause significant star trailing.

Last edited by frolinmod; 17-05-2012 at 05:58 PM.
Reply With Quote
  #7  
Old 17-05-2012, 06:51 PM
PRejto's Avatar
PRejto (Peter)
Registered User

PRejto is offline
 
Join Date: Jan 2011
Location: Rylstone, NSW, Australia
Posts: 1,397
Thanks Brendan and Phil,

I will try rotating the camera!

Phil, tracking was certainly "on!" I'm also totally surprised to see that your polar alignment is at least as good if not better than mine, and that you got there so quickly. I've been chasing this down for many nights so experience counts for a lot!

I'm really curious now to figure out if my CCD might have some tilt. A few weeeks ago I was using a 2" extension on the feather touch focuser to reach focus. It was just an inexpensive York Optics one with a single set screw. After nearly having the camera fall off (yikes) I looked into a more secure way to couple the camera and came up with the Baader. But, the Baader is much shorter requiring the focser to use nearly the full travel to get to focus. I wonder if the draw tube might be sagging? I know the FT focuser is highly regarded so that would be a surprising result perhaps. I looked at some older images taken with the 2" extension tube and I don't see the distortion over the field. I hope this isn't the cause because the Baader was really expensive and I had to source it in Germany. If I get rid of it I'm back to square one.

Peter
Reply With Quote
  #8  
Old 17-05-2012, 07:04 PM
PRejto's Avatar
PRejto (Peter)
Registered User

PRejto is offline
 
Join Date: Jan 2011
Location: Rylstone, NSW, Australia
Posts: 1,397
Ernie,

Would you kindly elaborate on your statement about changing the DEC rate intentionally to diagnose tracking issues. How much do you change the rate, and what is it you look for in the resulting image? How long of an exposure would you take to see what it is you are uncovering?

Is there a way that I can find out if my PMX is tracking at the correct rate? If you look at the T-Point run I posted, and look at the polar alignment, is there any other reason why I should see so much trailing? If PE (which I have not measured yet due to my CCDSoft frustrations) is the cause would not my error be huge to do this in such a short interval (45 sec)?

I'm sorry for so many elementary questions!

Peter
Reply With Quote
  #9  
Old 18-05-2012, 08:28 AM
CDKPhil's Avatar
CDKPhil
Phil Liebelt

CDKPhil is offline
 
Join Date: Mar 2011
Location: Australia
Posts: 279
Quote:
Originally Posted by frolinmod View Post
Don't want to sidetrack Peter's thread, but...

Phil, if you have a large scope like I do then that's probably flexure. With an EdgeHD 14 on an ME I was getting about one arc second per minute of time drift in RA. It was flexure. Turning on ProTrack made it (appear to) stop. Quite impressive. Sounds like ProTrack is NOT working for you. That's not good.
Thanks for the feedback. I will be doing some more testing with a larger T Point run. It will be interesting to see if that makes some difference. This run didn't cover much of the sky, it was only 20 or so points on each side of the meridian also it was very Southerly. I am using a Plane Wave CDK 12.5. I wouldn't have thought there would have been a lot of flexure in this OTA with its carbon fibre tube.


Peter

I hope you do not need to replace your Baader tube.

Did you have a chance to do any more testing last night?




Phil
Reply With Quote
  #10  
Old 18-05-2012, 11:21 AM
frolinmod's Avatar
frolinmod
Registered User

frolinmod is offline
 
Join Date: Dec 2010
Posts: 573
Quote:
Originally Posted by PRejto View Post
Would you kindly elaborate on your statement about changing the DEC rate intentionally to diagnose tracking issues.
The DEC tracking rate is normally zero. Setting it to a non-zero value simulates offsetting your polar alignment in Azimuth without actually disturbing your real polar alignment. You'll then get diagonally trailed stars that will make it easier to see what sort of tracking errors you're getting.

Quote:
How much do you change the rate, and what is it you look for in the resulting image?
The rate you want to change is Telescope->Tools->Bisque TCS->Parameters->Advanced->User defined->Track Rate (% Sidereal)->DEC. You can set it to from 1 to 100. Set it back to 0 to undo the change. If I remember correctly, I had to save to flash and reboot the mount for the change to take effect. My memory could be bad. YMMV. How high you set it depends on how long your exposure is going to be. Setting it to 100 will cause long very diagonal star trails, probably right off the chip in no time flat. So start with 50 and take a few shots with different values and different exposures.

Quote:
Is there a way that I can find out if my PMX is tracking at the correct rate?
Take the worm cover off and time the worm cycle?

Quote:
If you look at the T-Point run I posted, and look at the polar alignment, is there any other reason why I should see so much trailing? If PE (which I have not measured yet due to my CCDSoft frustrations) is the cause would not my error be huge to do this in such a short interval (45 sec)?
Alas, I'm not an expert at this sort of thing, so I don't know what's causing the problem.

Last edited by frolinmod; 21-05-2012 at 05:55 AM.
Reply With Quote
  #11  
Old 18-05-2012, 11:10 PM
PRejto's Avatar
PRejto (Peter)
Registered User

PRejto is offline
 
Join Date: Jan 2011
Location: Rylstone, NSW, Australia
Posts: 1,397
Thanks everyone for all this help. I couldn't test anything last night due to weather, but did go out tonight. My star distortions seem not to be due to the extensions....both distort. I took some rotated pictures but don't have time to study them until after the weekend.

Peter
Reply With Quote
  #12  
Old 20-05-2012, 07:39 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 17,877
You're on the wrong track. That is tilt not tracking error.

Tracking errors affect all stars in the shot. Your stars on the right are quite round (a tad elongated). But on the left they quite long.

Your camera is not square to the telescope. If you are using adapters to connect the camera look for where it is not seated properly or the camera is sagging in the focuser or the focuser is sagging under the weight.

TEC Feathertouch focusers flex least when they are upside down (they don't flex much though).

Sure you can do PEC and get rounder stars but if your polar alignment is relatively close and your balance is relatively close and your autoguider is working then you should get round stars pretty easily with a PMX. You should not have to work at it too hard.

Greg.
Reply With Quote
  #13  
Old 20-05-2012, 11:00 PM
Paul Haese's Avatar
Paul Haese
Registered User

Paul Haese is offline
 
Join Date: Jan 2009
Location: Adelaide
Posts: 9,937
I agree to some extent with Greg's assessment. This looks like a combination of differential flexure and some tilt. I am assuming these images are guided? If guided then the following is my assessment.

If the elongation gets longer over a period of 2 minutes, then longer again over 5 minutes you know this is flexure.

The tilt is evident because elongation on the 45 second shot is not consistent over the entire image. That indicates tilt.

If no guiding is applied, try guiding for a couple of images. Check your balance too. These mounts require near perfect balance in both axis, having counter weight heavy or scope heavy does not apply with these mounts.

I would also work a little more on you PA. While ok it should be better and will help to improve your pointing accuracy.

Also why have you got tube flexure ticked in your model? Your scope would not need this correction in the model.
Reply With Quote
  #14  
Old 21-05-2012, 06:02 AM
frolinmod's Avatar
frolinmod
Registered User

frolinmod is offline
 
Join Date: Dec 2010
Posts: 573
Quote:
Originally Posted by Paul Haese View Post
Also why have you got tube flexure ticked in your model? Your scope would not need this correction in the model.
Paul, you need to upgrade from TheSky6 to TheSkyX. You just have to. Please take my word for it.

He didn't tick the tube flexure term, Tpoint did. He just clicked on the SuperModel button, then a new model was computed by Tpoint. He accepted the new Tpoint computed model. In other words, it was Tpoint that determined he has tube flexure, how much tube flexure he has and ticked that term in the model. He may not actually have tube flexure, but if not, then he does have something that looks and acts exactly like tube flexure. Doesn't really matter what we call it.
Reply With Quote
  #15  
Old 21-05-2012, 01:54 PM
Paul Haese's Avatar
Paul Haese
Registered User

Paul Haese is offline
 
Join Date: Jan 2009
Location: Adelaide
Posts: 9,937
Quote:
Originally Posted by frolinmod View Post
Paul, you need to upgrade from TheSky6 to TheSkyX. You just have to. Please take my word for it.

He didn't tick the tube flexure term, Tpoint did. He just clicked on the SuperModel button, then a new model was computed by Tpoint. He accepted the new Tpoint computed model. In other words, it was Tpoint that determined he has tube flexure, how much tube flexure he has and ticked that term in the model. He may not actually have tube flexure, but if not, then he does have something that looks and acts exactly like tube flexure. Doesn't really matter what we call it.
Ah I see, but that would seem odd for such a scope??? Surely that scope would not have flexure?

Not sure about upgrade, if it ain't broke... well you know. Besides I have to pay for another Tpoint then too. If TPoint was included in the upgrade package I would consider it.
Reply With Quote
  #16  
Old 21-05-2012, 08:40 PM
PRejto's Avatar
PRejto (Peter)
Registered User

PRejto is offline
 
Join Date: Jan 2011
Location: Rylstone, NSW, Australia
Posts: 1,397
Hello,

Firstly, thanks to all for helping me out with these issues! As I have said earlier I am extremely new to all of this. I've done a bit of planetary photography, but never tried this aspect of the hobby. Thus, it is the first time I'm using any sort of mount with these abilities, and I never have used a CCD Camera before. Clearly, I am at times overwhelmed by the large number of factors to juggle!

A few things are becoming clear however, and ambiguities in the PMX/T-Point manuals don't help.

1. My Polar Alignment is probably way more inaccurate than indicated. I think I possibly have a highly polluted model because I collected points all over the sky instead of restricting myself to a more confined area and developing a refined PA. The manual says to get the first 6 points in a confined area and then to get additional points from a larger area of the sky. To me that is fairly ambiguous and I basically accepted points quite far away, and probably too low. I think that, + camera flexture, has led to erroneous data. Also, my pier is not entirely level. SB says this doesn't matter, but I think it might to some extent in that it just adds a further correction factor. I intend to level the pier and start over.

2. I had a brief window to experiment with some very short photos on Friday night. I also have downloaded a trial copy of CCDInspector. The photos are unguided (I have yet to even try this yet!) and 10 seconds in duration. I took two photos with the camera rotated 180 degrees for the 2nd. I don't see the degree of distrortion in the previous photos I posted at the top of this thread, but I would appreciate some input re the curve maps that I am attaching. I took the images before reading about acceptable single frame images, but I hope something useful might be seen anyway. The images are unprocessed, no darks, just stretched in CS5. Binning was 1x1 but I reduced the image size by 50% to post here.

I think the fall off in sharpness is possibly the result of using no field flattener and the KAF8300 chip is slightly larger than the acceptable flat field of view from the TEC140. There is also the possibility that the inbuilt filter wheel (with 31mm filters) in the Moravian G2-8300 camera is vignetting the field slightly though Pavel Cagas (of Moravian) says this isn't the case. Anyway, what I am most concerned about is whether what CCDInspector is reporting is a minor or serious problem. Any and all help is greatly appreciated!!

Peter

PS I have another question about binning. Should binning cause the object being imaged to shift in the field of view and reduce the field of view? From what I've read, I don't think so but stand to be corrected. I'm also attaching 2 additional images captured by the camera plugin in TSX.

photo 5: binning 2x2
photo 6: binning 3x3
Attached Thumbnails
Click for full-size image (New test 10 sec position 1 1x1 bin reduced 50%.jpg)
116.4 KB28 views
Click for full-size image (Curve Position 1 .jpg)
110.2 KB22 views
Click for full-size image (New test 10 sec position 180 1x1 bin-reduced 50%.jpg)
112.4 KB31 views
Click for full-size image (Curve Position 1 rotated 180.jpg)
106.7 KB22 views
Click for full-size image (New test 10 sec position 180 2x2 bin.jpg)
89.0 KB25 views
Click for full-size image (New test 10 sec position 180 3x3 bin.jpg)
70.8 KB20 views
Reply With Quote
  #17  
Old 22-05-2012, 12:50 AM
frolinmod's Avatar
frolinmod
Registered User

frolinmod is offline
 
Join Date: Dec 2010
Posts: 573
Quote:
Originally Posted by Paul Haese View Post
Surely that scope would not have flexure?
Well, it doesn't have much, if that's any consolation. I'd love to have that little.

Quote:
Originally Posted by Paul Haese View Post
I have to pay for another Tpoint then too.
You need TheSkyX Professional, Camera Add On to TheSkyX and Tpoint Add On to TheSkyX. Because you're a very special person, you are entitled to upgrade pricing. The add-ons listed here have no subscription fee. You can also run TheSky6 and TheSkyX at the same time (though only one or the other can be connected to your ME at a time).
Reply With Quote
  #18  
Old 22-05-2012, 12:59 PM
PRejto's Avatar
PRejto (Peter)
Registered User

PRejto is offline
 
Join Date: Jan 2011
Location: Rylstone, NSW, Australia
Posts: 1,397
Offline I was asked to post a photo of my camera and attachment to the focuser. The Feather Touch compression ring + the Baader Click Lock seem very sturdy. I cannot detect any free play when these are tightened down strongly.

The binning photos I posted earlier show that there is clearly something wrong either with my camera, or more likely with the ASCOM drivers I need to use with the camera to use the camera plugin in TSX. I did not realize I was having this problem; clearly using 2x2 binning for T-Point runs has given me invalid pointing data. The centre of the 2x2 binned images is not here the scope is pointing.
Attached Thumbnails
Click for full-size image (camera with Baader Click Lock.jpg)
89.0 KB30 views
Reply With Quote
  #19  
Old 22-05-2012, 04:49 PM
CDKPhil's Avatar
CDKPhil
Phil Liebelt

CDKPhil is offline
 
Join Date: Mar 2011
Location: Australia
Posts: 279
Hi Peter
I was just having a look at your T Point model. If you look at the
Term ( CH non perpendicularity of HA & OTA) you will see your OTA is miss aligned. you have over 1000 arc second of error. T point has almost corrected this but there is still error.

I have included a pic of mine so you can compare the difference.

Cheers
Phil
Attached Thumbnails
Click for full-size image (Screen Shot 2012-05-22 at 5.42.33 PM.png)
153.3 KB26 views

Last edited by CDKPhil; 22-05-2012 at 05:40 PM.
Reply With Quote
  #20  
Old 23-05-2012, 06:28 AM
PRejto's Avatar
PRejto (Peter)
Registered User

PRejto is offline
 
Join Date: Jan 2011
Location: Rylstone, NSW, Australia
Posts: 1,397
Hi Phil,

Yes, that term CH was very worrying, but I think the problem has been resolved without making any changes whatsoever to my OTA.

Here is what I think has gone wrong for me. I found a statement in the T-Point manual that indicated that the software must distinguish between the terms HA and CH, and that these terms can become confused as they are both east west shifts.

Firstly, I made a stupid error in using my camera and automated T-Point. I basically synched and then took a large run that initially collected points fairly low to the west. I was also unaware that the Ascom driver for my camera has a serious bug in that it does not bin 2x2 properly. It provides just the upper left quadrant of a 1x1 binned image, so in my theory, this introduced an error that looks like the OTA is not perpendicular to the DEC axis.

In any case, whether my theory is right or wrong, I have redone the PA last night and thus far my results are very promising! I had to give up before totally finishing because it was late and I was freezing, but my results so far without super model are MA= 22.3 arcsec, ME = 135.6 (lower axis .8 tics). With the super model MA = 0, ME= 135.9 (lower .8 tics). Best of all in both models the term CH = 0!!!

Peter
Attached Thumbnails
Click for full-size image (May22 T-Point super model terms.jpg)
188.7 KB23 views
Click for full-size image (May22 T-Point PA before super model.jpg)
182.6 KB20 views
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 10:00 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Bintel
Advertisement
Testar
Advertisement