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Okay, I'm baffled...CG5 tracking issue

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#1 Tom Andrews

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Posted 16 October 2012 - 11:02 PM

I've had my C11-SGT setup for over 3 years now. No problems with tracking ever.

I just bought a used Meade LX200 EMC 8" OTA which was deforked. I put a dovetail bar on it for use on my CG5.

I'm using my Mallincam Xtreme exclusively these days. When using it with the C11 the mount tracks beautifully as evidenced by the first snapshot below taken last night (80 second integration).

However, on all 3 nights I've tried to use the Meade, I can only get integrations of 30 seconds or less. The mount acts like it's not tracking at all, I have to keep readjusting the image to stay centered in the FOV (see second snapshot below, 56 second integration, taken tonight).

I have checked the balance over and over and it's excellent. Leveling is perfect. I do everything exactly the same every night whether using the 8" or 11", including my alignment procedure. One night I use the 11" and everything works perfectly, the next night I use the 8" and it has the same tracking issue.

I'm hoping this is something obvious to someone...any suggestions?

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#2 Tom Andrews

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Posted 16 October 2012 - 11:03 PM

Second snapshot: Meade 8" OTA, 56 second integration.

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#3 wolfman_4_ever

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Posted 16 October 2012 - 11:47 PM

Have you checked your collimation or mirror flop?

#4 Dwight J

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Posted 17 October 2012 - 12:04 AM

Check to see if the dovetail has any slop when putting the 8 inch on. Otherwise weird effect. Do you have another OTA to try and recreate the effect with another scope? That would tell you if it was limited to something with the Meade.

#5 EFT

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Posted 17 October 2012 - 10:25 AM

All other things being equal, I would have to look to a problem with the scope/dovetail in this case. As suggested, you could have a mirror flop issue or something else related to the mechanics of the Meade scope.

#6 Tom Andrews

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Posted 17 October 2012 - 10:52 AM

Have you checked your collimation or mirror flop?


Dave,

Thanks for suggestions. I check collimation on all my scopes everytime out, it's a regular part of my alignment process. Collimation is good.

Mirror flop in this scope is the worst of the 4 SCT's and 1 Mak I have/had. I thought the C11 was bad but it's nothing like this Meade. However, three things tend to make me think it isn't flop in this case.

1.) Each night that I use this scope I can get up to 30 second integrations with no elongation.
2.) At the end of each integration the whole image on the computer screen moves and if I don't adjust it, it will move off the screen. It moves in the same direction constantly, one way when viewing East and the opposite way when viewing West.
3.) M27 is almost straight up (or close enough) that I don't think the mirror would be moving in 56 seconds.

Here's a picture from 10/08, 14 second integration:

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#7 Tom Andrews

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Posted 17 October 2012 - 11:23 AM

Check to see if the dovetail has any slop when putting the 8 inch on. Otherwise weird effect. Do you have another OTA to try and recreate the effect with another scope? That would tell you if it was limited to something with the Meade.


This is exactly where my brain has landed and here's why. I do have a 5" Mak that I've used on the CG5 and there's no problems. And here's the kicker that has been on my mind from the beginning; my Mak and C11 which came from the manufacturer with dovetails installed both have 2 screws on each end. The Meade was fork-mounted so there weren't 2 holes on each end to use, only one. What I was concerned about was vibration when I touched it, not this effect. And I can't picture in my mind how the dovetail would create such a consistent effect of the image moving on the screen in one direction as if the mount wasn't tracking, especially when it's pointed almost straight up. But then again, I don't pretend to understand engineering concepts.

I think we have nailed down the issue but would greatly appreciate if someone that understands these things could explain to me in layman terms how this is happening.

#8 A. Viegas

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Posted 17 October 2012 - 11:26 AM

Tom-

It could be your balance. I know you check that, but the C11 is much heavier so if you are balancing that setup without the MCX, wires,dew shield etc... the weight difference once you start imaging is not that big a deal. Meanwhile if you balance the 8" OTA sans all the equipment attached, once you put everything on the proportional increase in weight is enough to blow your balance.

Just my 2c

Al

#9 Tom Andrews

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Posted 17 October 2012 - 11:30 AM

All other things being equal, I would have to look to a problem with the scope/dovetail in this case. As suggested, you could have a mirror flop issue or something else related to the mechanics of the Meade scope.


Thanks Ed. Agreed, I think the dovetail is the culprit. Do you understand how it would create these effects and beable to explain it in less-than-engineering terms to me?

#10 rmollise

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Posted 17 October 2012 - 11:50 AM

Two possibilities in my experience:

1. Dovetail. Make sure the main screw and safety screw are cranked down good, and that there is no play in the saddle and that the dovetail is not loose/flexing on the scope.

2. Balance. Balance is extremely important to good tracking on the CG5, but this seems to be worse than any balance issue I've seen.

I would also check to make sure the tripod/GEM head attachment is not loose somewhere, but why this would not show up with the 11 is beyond me, unless the greater weight is helping keep things together.

As for the dovetail? Only one screw can be OK--most Celestron dovetails only have one screw up forward, but there are "outriggers" to keep the dovetail stable.




#11 Tom Andrews

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Posted 17 October 2012 - 12:54 PM

Tom-

It could be your balance. I know you check that, but the C11 is much heavier so if you are balancing that setup without the MCX, wires,dew shield etc... the weight difference once you start imaging is not that big a deal. Meanwhile if you balance the 8" OTA sans all the equipment attached, once you put everything on the proportional increase in weight is enough to blow your balance.

Just my 2c

Al


Al,

The next thing after the dovetail that made sense to me as a problem was balance. In fact it was the only thing that made sense because the dovetail didn't make sense in my mind. When I do my balancing I have everything on the scope including camera/cables, light shield, finderscope, and Telrad. And it works for the C11 with all that weight. Actually I can't believe I'm getting 80 second integrations with the C11! And I think it would have gone longer but there were light wind gusts that would come up for a few seconds then die off.

#12 A. Viegas

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Posted 17 October 2012 - 12:58 PM

Tom-

When you balance the C11 you are using 2 11 pound counterweights right? When you use the 8" do you keep the same 2 11 pounders and just slide them up the shaft? Try an experiment with just 1 counterweight with the 8" balanced. I know it sounds weird, but i can get better tracking with my C8 on CG5-AGST with just one 11 lb counterweight than with two...

Al

#13 wolfman_4_ever

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Posted 17 October 2012 - 02:12 PM

Thinking outside the box here but I have had the wiring of the MCX pull my mount oh so slightly just at a certain angle for the OTA. This would be from the backlash/slop in the mount and my lack of proper wire mounting. It would only happen with my HD8, when I had it, but would not happen with my HD11.

Just a thought.. You should see it in the live view though. It might take a few minutes.

#14 Tom Andrews

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Posted 17 October 2012 - 02:46 PM

Two possibilities in my experience:

1. Dovetail. Make sure the main screw and safety screw are cranked down good, and that there is no play in the saddle and that the dovetail is not loose/flexing on the scope.

2. Balance. Balance is extremely important to good tracking on the CG5, but this seems to be worse than any balance issue I've seen.

I would also check to make sure the tripod/GEM head attachment is not loose somewhere, but why this would not show up with the 11 is beyond me, unless the greater weight is helping keep things together.

As for the dovetail? Only one screw can be OK--most Celestron dovetails only have one screw up forward, but there are "outriggers" to keep the dovetail stable.



Rod,

So glad you jumped in here, I appreciate your experience/knowledge as I'm sure everyone else around here does.

The mount on the tripod is as tight as I can turn the hand knob. Checking that is part of my alignment process everytime out.

Well you threw a kink in things as far as the dovetail goes. I had a C5 and C8 but they were the SE models and the screws were covered with a label plate. My C11 is the only Celestron GEM mount OTA I've had and it has 2 screws at each end. So maybe the dovetail isn't the culprit.

I also told a lie and maybe another one. The 5" Mak only has 1 screw at each end. And after looking back on my pictures taken with it, all but one 56 second integration had the same problem and my notes say it was calm so it wasn't wind. But I do have one that was fine so I'm assuming that there's not an issue with the Mak and the bad pics were lack of knowing how to use the camera (that was back when I first got the camera). I am going to take the Mak out again next time to make sure it does work.

Here's a picture of the dovetail on the Meade (just for the heck of it):

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#15 rmollise

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Posted 17 October 2012 - 02:51 PM

The dovetail looks secure...but...isn't it a little narrow...or is that just my failing eyes?

I would also make sure that the camera is secure when it is on the M8. It isn't flexing for some reason, is it?

Dave's question about your cables is a good one...I've been bitten by that gremlin more than once...

#16 Tom Andrews

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Posted 17 October 2012 - 02:54 PM

Tom-

When you balance the C11 you are using 2 11 pound counterweights right? When you use the 8" do you keep the same 2 11 pounders and just slide them up the shaft? Try an experiment with just 1 counterweight with the 8" balanced. I know it sounds weird, but i can get better tracking with my C8 on CG5-AGST with just one 11 lb counterweight than with two...

Al


Actually there are three 11 lb. counterweights for the C11. And I only use one for the 8". I've done this from the beginning because the Celestron site shows one CW for the C8-SGT, two for the C9.25 and three for the C11. Plus my stepbrother recently bought a new C8-SGT and it came with one CW.

But good thinking and please keep at it, one of us is going to figure this out.

#17 EFT

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Posted 17 October 2012 - 03:16 PM

Tom,

It sounds like perhaps all things aren't equal. I think you have a variety of possibilities to check out here. I agree with Rod that the dovetail looks a bit narrow which could mean a less solid hold than the standard Celestron dovetail on the C11 (if that is what you are using).

#18 Tom Andrews

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Posted 17 October 2012 - 03:23 PM

Thinking outside the box here but I have had the wiring of the MCX pull my mount oh so slightly just at a certain angle for the OTA. This would be from the backlash/slop in the mount and my lack of proper wire mounting. It would only happen with my HD8, when I had it, but would not happen with my HD11.

Just a thought.. You should see it in the live view though. It might take a few minutes.


Hummmmm, now that's something I hadn't thought of at all...

I've been tying the cables at the top of the south-facing leg of the tripod allowing the cables to hang free from the back of the camera (see picture). It's plain ugly which is not up to my compulsive standards at all but I haven't obsessed over it because I have to set up and tear down every night. And why would it happen only with the 8 and not the 11? That is so weird but since it happened to you, it could be the problem. I'll have to experiment with that. Thanks!

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#19 Tom Andrews

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Posted 17 October 2012 - 03:34 PM

The dovetail looks secure...but...isn't it a little narrow...or is that just my failing eyes?

I would also make sure that the camera is secure when it is on the M8. It isn't flexing for some reason, is it?

Dave's question about your cables is a good one...I've been bitten by that gremlin more than once...


Tom,

It sounds like perhaps all things aren't equal. I think you have a variety of possibilities to check out here. I agree with Rod that the dovetail looks a bit narrow which could mean a less solid hold than the standard Celestron dovetail on the C11 (if that is what you are using).


Rod and Ed,

Both rails (C11 & Meade) measure 1-3/4" wide. I got the rail from Jim at ScopeStuff.

I bet all of you are going to jump on my lack of cable ties as my most likely problem so I will let my OCD take over and clean that mess up! :rainbow:

#20 Dwight J

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Posted 17 October 2012 - 03:44 PM

In addition to the actual mounting points of the dovetail flexing ( your image reminded me of what differential flecked looks like), the dovetail may not be snugged up or has a slight tilt. When I mount my OTA the dovetail is horizontal. More than a few times it has not been tight all the way or crooked. I now rotate the tube around the dec axis 180 deg after attaching it to check for this slack. Another scope I use has the Losmandy style dovetail and mounts solidly but is a pain to slide on.

#21 wolfman_4_ever

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Posted 17 October 2012 - 07:41 PM

It looks like you are using the stock CG5 saddle and a Vixen style dovetail..

I kinda had my cables ran the same way except I tied them off on the OTA handle. Only while pointing in the east and at about 45-75 degrees. I would be dead center then over a period of about 15sec I could watch the mount shift and the picture shift in the live view. If I grabbed the wires and lifted them up to reduce gravities effect, the issue would stop. As soon as I let go, it would start again until the slop was tight again.

#22 Tom Andrews

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Posted 17 October 2012 - 09:07 PM

In addition to the actual mounting points of the dovetail flexing ( your image reminded me of what differential flecked looks like), the dovetail may not be snugged up or has a slight tilt. When I mount my OTA the dovetail is horizontal. More than a few times it has not been tight all the way or crooked. I now rotate the tube around the dec axis 180 deg after attaching it to check for this slack. Another scope I use has the Losmandy style dovetail and mounts solidly but is a pain to slide on.


Dwight,

More good points. I am very careful when mounting my OTA's because I have read here about others' sliding off the mount. So I double and triple check that the dovetail bar is sitting in saddle correct.

Now if the dovetail is flexing, hummmm...

#23 Tom Andrews

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Posted 17 October 2012 - 09:23 PM

It looks like you are using the stock CG5 saddle and a Vixen style dovetail..



Correct.

I kinda had my cables ran the same way except I tied them off on the OTA handle. Only while pointing in the east and at about 45-75 degrees. I would be dead center then over a period of about 15sec I could watch the mount shift and the picture shift in the live view. If I grabbed the wires and lifted them up to reduce gravities effect, the issue would stop. As soon as I let go, it would start again until the slop was tight again.


I was tying my cables to the OTA handle too until I used the 5" Mak which doesn't have a handle. I used the Mak enough that I got out of the routine.

Next time out I will set up my normal way then try lifting the cables up to see if it makes the difference. Thanks again for offering this info, I might never have thought about it because the 5" and 11" work with the cables as is.

#24 Tom Andrews

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Posted 19 October 2012 - 04:35 PM

Okay, I took the screws loose on the dovetail bar and retightened them to the point of stripping the sockets.

I rechecked my balance again.

I rerouted my cabling slightly to take any weight off the camera, let me know if I should be doing something different.

Last night I tested both the Meade 8" and the Mak 5"; both had the same problem. I tried holding the cables during integrations and moving them to different positions. There was no difference no matter what I did. I also tried different points in the sky to see if horizontal was better than vertical or if the motion was different. There was no difference for altitude. The motion goes from right to left across the screen when pointed West and bottom to top when pointed East; that should indicate something or at least rule something out.

I recorded video from both scopes to show what's happening. I'm adding links to them on YouTube. I paused the recording for the bulk of the 56 second integrations so I could get the motion of 4-5 integrations in a short video. I also did one at 28 seconds to show the same problem. On the one of C14 I forgot to change the notes on the screen and it shows M27 so ignore that.

I realize that in any hobby user error accounts for probably 99% of the issues and it would seem logical that my problem is just that. If the 11" scope had the same problem then it would be concrete but it works to the limit of CG5 tracking. And it has worked consistently everytime where the other 2 scopes have consistently NOT worked everytime. Apparently no one else is having this problem and there are who knows how many CG5's out there with every size of scope possible. So any other suggestions would be much appreciated.

M27-Mak 5"-Integration 56 seconds
C14-Mak 5"-Integration 56 seconds
C55-Mak 5"-Integration 56 seconds
M27-Meade 8"-Integration 56 seconds
M27-Meade 8"-Integration 28 seconds

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#25 rmollise

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Posted 19 October 2012 - 05:29 PM

Look to the GEM head tripod connection next.






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