Jump to content


Photo

About to trash my whole setup.

  • Please log in to reply
34 replies to this topic

#1 powerstroke01

powerstroke01

    Viking 1

  • -----
  • Posts: 531
  • Joined: 19 Jun 2007
  • Loc: Western Sierra Nevada Foothills

Posted 18 September 2012 - 10:31 AM

Im so frustrated, i just dont know what to do.
Im getting oblong stars. They all are oblong in the RA direction.
Im using a Losmandy G11, with an 10"lx200. Permanently mounted in my obs.. Even with autoguiding i can not get round stars.
Ive polar aligned and realigned. Ive collimated over and over again. Ive checked that the gears are meshed correctly. I even have the ovision worm. I have cleaned the main gear and worm and relubed.. And my pe is somewhere in the 7 range consistantly.
Ive used mirror lockup in the dslr. Ive reset the mount. Ive done everything i can think of and im sure im missing some things that i havent listed here.

This is soo frustrating because just 1year ago i could get round stars in a 10minute unguided exposure.

#2 Peter in Reno

Peter in Reno

    Fly Me to the Moon

  • *****
  • Posts: 6177
  • Joined: 15 Jul 2008
  • Loc: Reno, NV

Posted 18 September 2012 - 10:37 AM

If you are using guide scope, have you considered OAG? You'll be surprised of the results. I was getting exactly the same thing with a guide scope guiding an SCT until I threw away the guide scope and replaced it with OAG and Lodestar.

Peter

#3 powerstroke01

powerstroke01

    Viking 1

  • -----
  • Posts: 531
  • Joined: 19 Jun 2007
  • Loc: Western Sierra Nevada Foothills

Posted 18 September 2012 - 10:39 AM

No, not really. Ill have to do some reading.

#4 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2564
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 18 September 2012 - 10:39 AM

What have you done to start eliminating the possible sources of the problem?

Do you have a smaller scope that you could try out, like maybe a refractor, so see if the problem is in the scope, dovetail, etc.?

Narrowing things down to the mount or the scope/imaging train will probably help.

#5 D_talley

D_talley

    Vanguard

  • *****
  • Posts: 2130
  • Joined: 07 Jul 2005
  • Loc: Richmond VA

Posted 18 September 2012 - 10:39 AM

Have you locked the mirror on the scope, if that is possible?

Also, what happened in the past year that could affect the mount's performance. When did the O-worm get installed?

The fact that images are showing oblong stars even when guiding points me to the main scope mirror shifting or the guider mount shifting.

#6 powerstroke01

powerstroke01

    Viking 1

  • -----
  • Posts: 531
  • Joined: 19 Jun 2007
  • Loc: Western Sierra Nevada Foothills

Posted 18 September 2012 - 10:50 AM

What have you done to start eliminating the possible sources of the problem?

Do you have a smaller scope that you could try out, like maybe a refractor, so see if the problem is in the scope, dovetail, etc.?

Narrowing things down to the mount or the scope/imaging train will probably help.

I dont have any other scopes to try. How else can i narrow it down?

#7 powerstroke01

powerstroke01

    Viking 1

  • -----
  • Posts: 531
  • Joined: 19 Jun 2007
  • Loc: Western Sierra Nevada Foothills

Posted 18 September 2012 - 10:55 AM

Have you locked the mirror on the scope, if that is possible?

Also, what happened in the past year that could affect the mount's performance. When did the O-worm get installed?

The fact that images are showing oblong stars even when guiding points me to the main scope mirror shifting or the guider mount shifting.

I have not tried locking the mirror. Not sure its possible now that i think about it though.

The o-worm has been on the mount since i bought it.

I wonder if youre right about the mirror shifting. But the stars are oblong even in short exposures. Say of about a minute or so. And whats strange is that they dont seem to really get worse in longer exposures.. Maybe something in the camera????

#8 Stew57

Stew57

    Mercury-Atlas

  • *****
  • Posts: 2560
  • Joined: 03 May 2009
  • Loc: Silsbee Texas

Posted 18 September 2012 - 11:00 AM

Try rotating the camera 90 degrees. See if the direction of star elongation moves with the camera or is in the same orientation you have now.

#9 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2564
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 18 September 2012 - 11:03 AM

What have you done to start eliminating the possible sources of the problem?

Do you have a smaller scope that you could try out, like maybe a refractor, so see if the problem is in the scope, dovetail, etc.?

Narrowing things down to the mount or the scope/imaging train will probably help.

I dont have any other scopes to try. How else can i narrow it down?


That is going to make things tough. I suspect the problem is in the scope/imaging train and is most likely due to flexture. However, the new worm could be the issue as well.

If you upgraded to the new worm yourself, then you could put the old one back in and see what that does so that you can eliminate or verify that the new worm is the problem.

#10 powerstroke01

powerstroke01

    Viking 1

  • -----
  • Posts: 531
  • Joined: 19 Jun 2007
  • Loc: Western Sierra Nevada Foothills

Posted 18 September 2012 - 11:03 AM

Why didnt i think of that. haha I must try that tonight.

Thanks!

#11 powerstroke01

powerstroke01

    Viking 1

  • -----
  • Posts: 531
  • Joined: 19 Jun 2007
  • Loc: Western Sierra Nevada Foothills

Posted 18 September 2012 - 11:08 AM

What have you done to start eliminating the possible sources of the problem?

Do you have a smaller scope that you could try out, like maybe a refractor, so see if the problem is in the scope, dovetail, etc.?

Narrowing things down to the mount or the scope/imaging train will probably help.

I dont have any other scopes to try. How else can i narrow it down?


That is going to make things tough. I suspect the problem is in the scope/imaging train and is most likely due to flexture. However, the new worm could be the issue as well.

If you upgraded to the new worm yourself, then you could put the old one back in and see what that does so that you can eliminate or verify that the new worm is the problem.

I doubt the worm is the issue. Ive had very good success with it in the past. So had the previous owner.. So i could try the old worm...

Should i take the scope and everything off the mount, reasemble everything so make sure everything is tight?
I just dont get how i used to get good images and now i get movement...

#12 powerstroke01

powerstroke01

    Viking 1

  • -----
  • Posts: 531
  • Joined: 19 Jun 2007
  • Loc: Western Sierra Nevada Foothills

Posted 18 September 2012 - 11:10 AM

Actually i think you guys are right about flexure. Due to the fact i have a hard time getting good GOTO's..

#13 tjugo

tjugo

    Apollo

  • -----
  • Posts: 1013
  • Joined: 06 Nov 2007

Posted 18 September 2012 - 11:25 AM

Hi,

I was debugging a similar issue with my setup, Atlas + Epsilon 160 + short guidescope. The guide graph looked very flat but I was getting elongated stars mostly in the RA axis.

I tried everything, change guiding params, switch back and forth from maxim to PHD, change guide scope, drift alignment, PEC etc etc....

Long story short, the problem was some small amount mirror shift, usually mirror shift produces double stars but in my case it was producing elongated stars. I put together my old OAG and the stars are round and small again.

Some people suggested that the issue was focuser flex , probably, but the OAG took care of the problem.

Cheers,

Jose

#14 freestar8n

freestar8n

    Skylab

  • *****
  • Posts: 4048
  • Joined: 12 Oct 2007

Posted 18 September 2012 - 12:43 PM

Im so frustrated, i just dont know what to do.



OAG

Frank

#15 Jared

Jared

    Fly Me to the Moon

  • *****
  • Posts: 5077
  • Joined: 11 Oct 2005
  • Loc: Piedmont, California, U.S.

Posted 18 September 2012 - 02:31 PM

If you look at your guide results are they good? Based on the log, what is the RMS guide error? Do the RA and DEC numbers look similar?

If the guider is reporting good results, but you still have elongation in your stars you are likely looking at differential flexure and/or mirror flop. Frankly, that's to be expected using a guide scope with an SCT--especially one with no mirror locks. The only thing that makes me at all suspicious is the fact that your error was in RA. With differential flexure, the direction of the elongation will vary with the object.

Basically, with a 10" SCT used at Cassegrain focus (even with a reducer) you are likely to get better results with an OAG. The only downside is that it can be hard finding a guide star. That and the fact that you'd have to buy a guider.

#16 powerstroke01

powerstroke01

    Viking 1

  • -----
  • Posts: 531
  • Joined: 19 Jun 2007
  • Loc: Western Sierra Nevada Foothills

Posted 18 September 2012 - 02:39 PM

Thanks all! Im going to try a few new things tonight. Also ordered an OAG.. We will see how it works tomorow night.

#17 Peter in Reno

Peter in Reno

    Fly Me to the Moon

  • *****
  • Posts: 6177
  • Joined: 15 Jul 2008
  • Loc: Reno, NV

Posted 18 September 2012 - 02:52 PM

Which brand OAG did you get? What brand autoguider are you using?

Peter

#18 brokenwave

brokenwave

    Ranger 4

  • -----
  • Posts: 345
  • Joined: 10 May 2011
  • Loc: Scottsdale, AZ

Posted 18 September 2012 - 02:57 PM

Are you using a remote cable or program to trip shutter? and if you don't have a 5-10 delay after mirror flips up you are probably getting bounce somewhere. Try this:
If your exposures are short say 10 sec. or less. You might be getting bounce from the camera shutter. Try increasing your exposures by 5 seconds or so and use a dark piece of cardboard to block the front of the tube for that 5 seconds,
without touching the tube with it.
That will let what ever is bouncing settle down without the camera being exposed to what you are photographing. It will take that out of the problem solving if it isn't tracking error. Since you longer exposures are the same as short ones it sounds like something isn't totally locked.

#19 Alterf

Alterf

    Viking 1

  • *****
  • Posts: 629
  • Joined: 07 Apr 2006

Posted 18 September 2012 - 05:36 PM

A friend had a similar problem and found that there was play in the RA. Adjusting the RA backlash and tightening things down cured it. I hope you can find the source of the problem. Nothing is more frustrating.

Val

#20 powerstroke01

powerstroke01

    Viking 1

  • -----
  • Posts: 531
  • Joined: 19 Jun 2007
  • Loc: Western Sierra Nevada Foothills

Posted 18 September 2012 - 11:27 PM

Im bummed. Im out in the obs right now and im seeing huge jumps in the RA...
Its def in the mount and not the camera.
Today i took everything off the pier and started over.
I even left off the spotting scope and the guide setup to save a bit of weight.

#21 powerstroke01

powerstroke01

    Viking 1

  • -----
  • Posts: 531
  • Joined: 19 Jun 2007
  • Loc: Western Sierra Nevada Foothills

Posted 18 September 2012 - 11:29 PM

AHHHHH!!!!!! What the #(*(*&@$ changed in the last year?????

#22 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2564
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 18 September 2012 - 11:38 PM

Have you ever completely stripped the mount down and cleaned everything out? It's hard to think of what might be wrong with the mount if your PE is down at 7 (is that +/-7 or +/-3.5?). How is the total error, random and periodic? It is possible that you have a bad bearing in either the worm or, less likely, the axis that is causing the problem. There might also be debris of some king in the axis roller bearings.

#23 powerstroke01

powerstroke01

    Viking 1

  • -----
  • Posts: 531
  • Joined: 19 Jun 2007
  • Loc: Western Sierra Nevada Foothills

Posted 18 September 2012 - 11:55 PM

Its +-7.. pempro didn't do a good job correcting it. There is some periodic error that I can see but also alot of random error. Error that pec won't correct out.
I know that 7 doesn't seem too bad but keep in mind that I have the ovision worm. And I used to get round stars at 10mins at 1600mm focal length. Seems impossible now.
Whatever I do its the same result.
Should I tear the mount down? Thats really uncharted waters for me. But it seems like that's where all this is heading.

#24 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2564
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 19 September 2012 - 12:27 AM

Actually, +/-7 isn't all that great for that mount. However, it is the random error that may be the greater problem depending on how steep the PE error is. If you can really eliminate the OTA/image train as the source of the problem, then the mount's change over time is probably a good indication of the need for a strip down and tuneup. When you are out in an observatory, it is easy to get everything from dirt to bugs inside a mount that will cause problems that will degrade the mount's performance over time. The G-11 is pretty tough and I've seen some that were really abused but cleaned up just fine, but and occasional tuneup can do them good. It's not the most difficult mount in the world to work on except for the axis roller bearings which are a real pain to remove.

#25 Tori

Tori

    Ranger 4

  • -----
  • Posts: 377
  • Joined: 10 Jan 2012
  • Loc: Somerville, MA/Warren, NH

Posted 19 September 2012 - 05:26 AM

How permanent is your pier? Is it isolated from your footsteps? Any chance that YOUR movement is causing the problem?






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics