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Equipment Discussions >> Cats & Casses

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dr.who
professor emeritus
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Reged: 01/05/12

question on trails on stars with a C11
      #5473155 - 10/16/12 11:41 AM

Sorry to post but I now have a case of the worries. And thank you in advance for advice!

Ok. Was talking to my friend, who has been in the hobby going on 50 years, who got me into this hobby and was explaining to him what I was seeing in my C11 regarding stars.

They look like a wind is blowing from one side so there is a small trail on the other side like one would see from smoke out of a moving ship or the like.

He said he hoped it was just that the mirror wasn't cooled down enough (I had the CAT cooler on for 45 minutes and the OTA was in the unheated garage) but there was a possibility there was a problem with the mirror...

Could it be a mirror problem? And if so how do I tell?


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Patrick
Postmaster
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Reged: 05/16/03

Loc: Franklin, Ohio
Re: question on trails on stars with a C11 new [Re: dr.who]
      #5473255 - 10/16/12 12:43 PM

Quote:


They look like a wind is blowing from one side so there is a small trail on the other side like one would see from smoke out of a moving ship or the like.





I gather that these aberrations are moving? The only things I know of that would cause movement would be either an uncooled optic or bad seeing conditions. It sounds like you've ruled out the uncooled scope. Have you tried rotating the eyepiece and diagonal to see if the image moves? Are you viewing over a house or other building that's putting out heat? Do you have any problems with your eyes?

Patrick


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dr.who
professor emeritus
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Reged: 01/05/12

Re: question on trails on stars with a C11 new [Re: Patrick]
      #5473514 - 10/16/12 04:06 PM

Thank you Patrick. It looks like wind blowing on one side of the star with the other side having little trails like tails.

As to viewing over a house etc...

This was constant for all stars including Vega which was near zenith when I was looking. Though I was on a brick driveway with a asphalt street within a few meters.

I did not move the EP or diagonal but will try that.

My eyes are 20/20 and I have no other issues with them...


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Stelios
Carpal Tunnel
*****

Reged: 10/04/03

Loc: West Hills, CA
Re: question on trails on stars with a C11 new [Re: dr.who]
      #5473540 - 10/16/12 04:25 PM

Sounds like collimation is extremely off to me.

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MikeBOKC
Post Laureate
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Reged: 05/10/10

Loc: Oklahoma City, OK
Re: question on trails on stars with a C11 new [Re: dr.who]
      #5473569 - 10/16/12 04:43 PM

Suggest you center a fairly bright star and defocus on both directions to see iff the "donut" ring pattern is symmetrical. If not you have a collimation issue. There are lots of resources on the web to explain CST collimation, which should get yourt scope in the pink if that is indeed what is happening.

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wolfman_4_ever
Pooh-Bah


Reged: 07/15/11

Loc: El Segundo, Ca, So. Cal
Re: question on trails on stars with a C11 new [Re: Stelios]
      #5473638 - 10/16/12 05:16 PM

Quote:

Sounds like collimation is extremely off to me.




+1


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dscarpa
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Reged: 03/15/08

Loc: San Diego Ca.
Re: question on trails on stars with a C11 new [Re: dr.who]
      #5473809 - 10/16/12 06:53 PM

That's exactly what stars look like in my C-9.25 when it needs to be collimated. It's a bit of of pain though not hard to do. The problem is you need good seeing or a rather expensive cat collimating device to do a good job. I'm careful carrying my cats around that's for sure. Unless it gets a pretty hard wack my C-9.25 holds collimation really well. It's only needed it a few times in the 4 years I've had it. David

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Doc Bob
professor emeritus
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Reged: 02/27/09

Loc: Maryland, USA
Re: question on trails on stars with a C11 new [Re: dscarpa]
      #5473857 - 10/16/12 07:19 PM

Dr Who,
You're out of collimation! or perhaps the diagonal is out of sorts - or the eyepiece is off!

Regards,
Bob


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dr.who
professor emeritus
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Reged: 01/05/12

Re: question on trails on stars with a C11 new [Re: Doc Bob]
      #5474310 - 10/17/12 12:37 AM

Gentlemen,

Thank you!

I did defocus and there was a bit of a shift on one side but it wasn't outrageous... Is just say one or two lines of the many lines (air gaps? other word of it) between the bright parts of the image enough to cause this? As in it's out of collimation but not badly?

Sorry don't know the words to describe it and its frustrating...


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Jared
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Reged: 10/11/05

Loc: Piedmont, California, U.S.
Re: question on trails on stars with a C11 new [Re: dr.who]
      #5474349 - 10/17/12 01:17 AM

Draw a picture of what you are seeing (in focus as well as on Eire side of focus), then post a picture of your drawing.

It sounds like coma resulting from poor collimation.


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Starhawk
Space Ranger
*****

Reged: 09/16/08

Loc: Tucson, Arizona
Re: question on trails on stars with a C11 new [Re: Jared]
      #5474353 - 10/17/12 01:21 AM

SCTs reward collimation nazis. Get to really high power, such as with a 3mm eyepiece or a barlowed 6mm, and collimate to get a PERFECT concentric bullseye pattern in-focus.

When you back off to normal observing magnification, prepare to be amazed.

-Rich

Edited by Starhawk (10/17/12 01:21 AM)


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dr.who
professor emeritus
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Reged: 01/05/12

Re: question on trails on stars with a C11 new [Re: Starhawk]
      #5474375 - 10/17/12 01:48 AM Attachment (41 downloads)

Thank you again!

Based on what you are all telling me it looks like a collimation issue. Something for the next star party as I am not keen on doing this myself for the first time nor do I see investing in that $400+ Hotech SCT collimation tool.

I found a photo that captures it somewhat...


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Bob Griffiths
Getting Grouchy
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Reged: 10/10/05

Loc: Frederick Maryland
Re: question on trails on stars with a C11 new [Re: dr.who]
      #5474665 - 10/17/12 08:58 AM

Quote:

Thank you again!

Based on what you are all telling me it looks like a collimation issue. Something for the next star party as I am not keen on doing this myself for the first time nor do I see investing in that $400+ Hotech SCT collimation tool.

I found a photo that captures it somewhat...




From reading your posts here and also on the Astronomy Forum (the avatar on that forum makes me think its you..lol) I HONESTY can't figure out why you are hesitant to collimate the scope yourself..

IT IS NOT ROCKET SCIENCE ..

Bob G


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dscarpa
Post Laureate
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Reged: 03/15/08

Loc: San Diego Ca.
Re: question on trails on stars with a C11 new [Re: dr.who]
      #5474862 - 10/17/12 11:14 AM

Your scope doesn't look like it's out of collimation that all much. Someone posted a pictorial guide to collimation showing which secondary screw to turn and which way. I have it but can't post a picture. Mayby someone else can. David

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dr.who
professor emeritus
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Reged: 01/05/12

Re: question on trails on stars with a C11 new [Re: dscarpa]
      #5474883 - 10/17/12 11:26 AM

Hi Bob. That would be me on both sites.

It isn't so much that I am hesitant as it is not something I have done before and thus better to use the old medical school method of "see one, do one, teach one" in my mind. Plus it's an excuse to force myself to go to the Star Party1

Cheers dscarpa. I have a technical and theoretical understanding of how to do it I just have never done it so I am succumbing to a case of nerves I guess. But then again this weekend or next I will probably get a case of the "He who dares, Wins!" and just go out and try it...


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Kevdog
scholastic sledgehammer
*****

Reged: 07/11/12

Loc: Desert Hills, AZ
Re: question on trails on stars with a C11 new [Re: dr.who]
      #5546937 - 11/30/12 10:29 AM

That's exactly what my Meade LT8 did when I first got it. And just this week the C11 I picked up used.

Yes, SCT collimation is scary when you haven't done it. I was worried I'd screw something up. But it's not as hard as you think.

There are some very good links here with some great pictures that explain what to do.
http://www.cloudynights.com/ubbarchive/showflat.php/Cat/0/Number/1623446/page...

The best hint I found (which was mentioned above) was to place your finger on one of the screws of the secondary and look through the eyepiece. If the obstruction of your arm is on the same side that the shadow is leaning to, you've found the screw to adjust. Turn it a bit (small adjustments, especially given your picture) one way and see if it gets better or worse. If worse, turn it the other way.

Also just make sure the screws don't get loose. You want to prefer to tightnen (but not too tight) rather than loosen. If you need to tighten one and it's too tight, slightly loosen the other two.

My C11 was sooooo bad that the shadow of the secondary was way off to one side. I still need to do the fine tuning yet as the air wasn't still enough the other night. Just got the scope on Tuesday.


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dr.who
professor emeritus
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Reged: 01/05/12

Re: question on trails on stars with a C11 new [Re: Kevdog]
      #5580878 - 12/20/12 03:10 PM

Thank you Kevdog. If the weather holds tonight and tomorrow my project will be to setup the C11 on the CGEM, align, stick it on Polaris, and go to town. That is a great tip regarding what screw to focus on with the finger!

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Asbytec
Guy in a furry hat
*****

Reged: 08/08/07

Loc: La Union, PI
Re: question on trails on stars with a C11 new [Re: dr.who]
      #5581285 - 12/20/12 07:14 PM

Yea, go for it. It's easy. When a scope is out of collimation, it will flare the stars to one side. As others said, I'm sure mis-collimation is what you're seeing. You really gotta get collimation down sooner or later. Why wait?

After you get the hang of it, collimate closer to focus. Personally, I find it easier with just one or two rings showing - a very slight turn of the focuser. Then check the in-focus pattern. De-focus just a bit and repeat until in-focus looks perfect.


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dr.who
professor emeritus
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Reged: 01/05/12

Re: question on trails on stars with a C11 new [Re: Asbytec]
      #5587544 - 12/24/12 05:22 PM

Cheers Norme. So far though the nights (Thursday, Friday, and Saturday) I have open to do the collimation have ALL been cloudy! Must be because of that Binoviewer and ES 11mm 82* EP I bought to use in them! Hopefully tonight after Mass...

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Asbytec
Guy in a furry hat
*****

Reged: 08/08/07

Loc: La Union, PI
Re: question on trails on stars with a C11 new [Re: dr.who]
      #5587964 - 12/25/12 01:11 AM

Good luck, Dr Who, on the weather. Gotta check mine.

Merry Christmas. Nice presents.


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