Need ome Help with my PMX/Camera

[PRejto]

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

[CDKPhil]

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.:lol:

Cheers
Phil

[PRejto]

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.

[CDKPhil]

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

[bmitchell82]

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! :)

[frolinmod]

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.

[PRejto]

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

[PRejto]

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

[CDKPhil]

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

[frolinmod]

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.

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.

Take the worm cover off and time the worm cycle?

Alas, I'm not an expert at this sort of thing, so I don't know what's causing the problem.

[PRejto]

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

[gregbradley]

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.

[Paul Haese]

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.

[frolinmod]

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.

[Paul Haese]

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.

[PRejto]

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

[frolinmod]

Well, it doesn't have much, if that's any consolation. I'd love to have that little.

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).

[PRejto]

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.

[CDKPhil]

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

[PRejto]

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

[CDKPhil]

Thats great Peter.
I am glad you are solving your problems.
I hope it is smooth sailing from here.

Cheers

[Paul Haese]

From the photo you provided I think the focusor is raked out a little too far and that might be causing the DAF adjustment in the model. I would also consider the connection with the camera itself.

The rest of the model is looking pretty good. I would lower the PA by the required amount. try doing 21 points at a time on the polar alignment and use a very small area of the sky, preferrably a small constellation out to the east. Do the adjustments each time and do this 3 times or until you are really happy with the polar alignment. Then do your full sky model. You should be able to get down to 15" at least for pointing with a 100-250 point model.

[PRejto]

Paul,

Thanks for your input! The picture of my camera actually doesn't represent focus. Focus is actually further out....around 95. The camera seems firm and I have no idea short of an entirely different mounting solution how I can improve this. Greg mentioned turning the focuser upside down so I might try that, and I have not tried locking the focuser with the screw. (I'm worried about doing that and trying to electronically focus, but maybe I'd better do that anyway!). Would it be better to have the focuser tube racked in further with a longer extension tube? I really like the Baader Click Lock, but the extension is quite short. How can I get the best of both worlds?

Re T-Point run of 21 points....I cannot image to the east except above 70-80 degrees. To the west is ok. How low to the west should I go? due west. NW or SW?

It also seems clear that I'm going to need to add a field flattener to the equation. The TEC140 flattener is rather expensive and it doesn't reduce. A flattener/reducer I'm told works on the TEC140 is the Borg 7887 (from Cloudy Nights). I'm wondering if I could use a Borg 2" nose piece from the Focuser to the 7887, then use a Borg Cannon EOS adapter and finally a Moravian EOS adapter which bolts to the camera. Is there any chance this would be firm enough? I suppose the EOS adapter is made to support a lens with the camera supported on a bar; this would be reversed with the adapter supporting the camera...

Thanks again,
Peter

[Paul Haese]

My Tpoint runs have a lowest elevation of 45 degrees. Going lower can give inconsistent results. So I think 45 degrees is the lowest you should go. Others may disagree.

With the camera, am I to understand that this camera has a SLR lens adapter permanently on it? If so this is going to be the source of the flexure. Screw mounting is the only way to go, SLR mounts always have some movement and it does not need to be much. Can the camera be used without this mount?

The usual way to go about things with reducers and flatteners is to have the field corrector after the focusor and then have a custom made adaptor between the field corrector and the camera / filter wheel. Precision parts makes these adapters.

Would you consider another camera? That might help your situation.

[PRejto]

Hi Paul,

Thanks for your comments.

Currently my camera has a 2" standard nosepiece which is bolted onto the camera body with 4 screws. That goes directly into the Baader Click Lock extension tube, which goes directly into the 2" FT Focuser (which has a twist locking compression ring. I was just asking about the possibility of using a Cannon EOS adapter on the camera as a way of nailing the distance to the potential field flattener (also using an EOS adapter). Seems from what you are saying that this would not be firm enough, so I will forget that future solution.

Last night proved frustrating to say the least. I not sure if I've made much progress but did 8 T-Point runs of 21 points, then after the 6th run I accidentally crashed pretty hard right into the counter weight and gave it a huge knock. Yikes. That was around 1 am. I ran T-point 2 more times and got the results in # 8.

The first time I tried to follow your advice exactly. I went due West (cannot go due east very much) to around 50-60 degrees elevation and collected 21 points in a small area. This proved useless as the PA dialog info said not enough points to refine model, collect more points.....so I collected another 15 or so in a pie shaped wedge towards directly overhead, keeping the scope on the same side of the mount. To make a long story shorter on subsequent runs I slightly enlarged the pie shaped wedge of stars to 21 and used this over and again. I got the following super model results, (minus run 4 because I forgot to write the results down):

1. MA = 56.7 Tighten E 1.3 tics
ME = 0.0 Raise 1.3 tics

2. MA = 43.3 Tighten E .9 tics
Raise 1.3 tics

3. MA = 25.7 Tighten E .5 tics
ME = 0 Raise 1.3 tics

4. no data

5. MA = 26.5 Tighten E .5 tics
ME = 0 Raise 1.3 tics

6. MA = 0.0 no adj indicated
ME = 0 Raise 1.3 tics

Walked into mount counter weight!!

7. MA = ??? Tighten E 2.3 tics
ME = ??? Lower 1.3 tics

8. MA = 0.0 no adj
ME = 0.0 Raise 1.3 tics

I'm a bit onfused about these numbers. It sems as if MA was improving a little with each of the first 6 runs, but every time I raised the mount ME wasn't changing. Until I walked into the mount I raised it 1.3 at least 5 times. Could that be correct? Also, I tend not to believe the final result of MA=0.0 even though confidence was listec as "high."

I've attached pictures of the area of the sky I collected the points in, and also photos of the terms and #8 PA recommendations.

Sorry this is so long, but appreciate further help!!

Peter

[Paul Haese]

That last run looks pretty good. The terms look normal and the alignment looks pretty good, some minor refining later might help, but for now try imaging and see what the results are like.

Using Tpoint can often make you oscillate over the pole if something has just a fraction of flexure. Your numbers overall look good now so doing some imaging will give you a better idea of what is going on. My suggestion is to do some images at 1 minutes, then some images at 5 minutes and some images at 10 minutes (all guided). Doing this will narrow down whether there is flexure in your system and will test your success on polar alignment.

[frolinmod]

I agree with you except that I'm able to get down to 30 degrees okay. But I mentioned this to Patrick Wallace and he disagreed! He thinks one should go as low as one's horizon permits. I hate to disagree with Patrick, but I'm not on a high mountain with perfect atmosphere, so...

[Paul Haese]

Yeah, that could well be right. I have a site with great seeing but consider that even down low the seeing can give inconsistent results when fine tuning.

[PRejto]

Thanks Paul!

I'm relieved to know I might finally be on the right track after too many false starts.

I've yet to try guiding so that will be the next obstacle. I have an Orion Star Shoot camera/phd kit so will try that out soon on my AT66EDQ. Any tips about setting up the PMX for that would be welcome.

Peter

[Paul Haese]

That should connect easily. I have been using the SSAG for autoguiding with the PME and it works a treat. Standard settings in PHD worked for me before I switched to Maxim. 2-3 seconds is about what you want with this mount.

[gregbradley]

I am not so sure about the Sky X. Yes it had a few more bells and whistles but it also seems less stable at least with a PMX. It will drop out on you if there is any problem. The Sky 6 never did that. Sky X does it regularly.

PEC software in the Sky X also seems bugged and not working reliably.

I agree with if you got your system working well don't change anything. Its hard to get it to that point.

Greg.

[gregbradley]

I am not sure who Patrick Wallace is but with amateur gear and amateur locations anything below about 45 degrees gets poor. You can see it in the subs if you image over several hours. The stars just get fatter and fatter in luminance as the scope goes lower. That's at long focal length. With short focal lengths you tend to get away with lots of things!

Greg.

[frolinmod]

Patrick Wallace is the author of Tpoint. We were discussing images taken for automated calibration rather than production images. He indicated that images taken at low elevations were important to include for best modeling.