Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Nothing is clear

  • Please log in to reply
39 replies to this topic

#1 Bobtownbuck

Bobtownbuck

    Sputnik

  • -----
  • topic starter
  • Posts: 28
  • Joined: 30 Jul 2019

Posted 08 August 2020 - 09:04 PM

Hi,  I have an Celestron 11 sct.  Every time I have used it, nothing is clear.  No matter how I try to focus, calibrate, use Bobs knobs, nothing seems to work.  I tried imaging with it, and Jupiter looked horrid.   It feels like it is an expensive paper weight.  Any help, suggestions, please, would be appreciated. Thnx...



#2 gnowellsct

gnowellsct

    Hubble

  • *****
  • Posts: 17,913
  • Joined: 24 Jun 2009

Posted 08 August 2020 - 09:09 PM

1.  What does it look like when you focus on a distant tree.  Do you get a clear sharp focus?

 

2.  What does it look like when you focus on a star.  Is it flared, or a "dancing point" (the dancing being the atmosphere)

 

3.  When you look at a star and go about 1 1/2 turns out of focus, do you see a dark spot in concentric rings?  Or an oval with the dark spot to one side, or a comet like flare.

 

4.  Post a pic of what you see from the front with the cover removed.

 

5.  Post a pic of how you put the eyepiece in the rear diagonal and how that attaches to the tube.

 

Greg N


Edited by gnowellsct, 08 August 2020 - 09:10 PM.


#3 Jim Waters

Jim Waters

    Skylab

  • *****
  • Posts: 4,444
  • Joined: 21 Oct 2007
  • Loc: Phoenix, AZ USA

Posted 08 August 2020 - 09:49 PM

Is it collimated correctly?  Is there a local astronomy club near you?  You should be able to get help there.



#4 Redbetter

Redbetter

    Cosmos

  • *****
  • Posts: 9,536
  • Joined: 16 Feb 2016
  • Loc: Central Valley, CA

Posted 08 August 2020 - 10:12 PM

Was this a new scope?  Or used?  Short on details of magnification used, etc.  

 

It would be interesting to hear how it star tested.



#5 ShaulaB

ShaulaB

    Vanguard

  • *****
  • Posts: 2,280
  • Joined: 11 Oct 2012
  • Loc: Missouri

Posted 08 August 2020 - 10:25 PM

Are you seeing thermal plumes, due to the scope's internal temperature not matching outside temperature? Dew? Is Jupiter below 30 degrees elevation above the horizon?

#6 Bobtownbuck

Bobtownbuck

    Sputnik

  • -----
  • topic starter
  • Posts: 28
  • Joined: 30 Jul 2019

Posted 09 August 2020 - 05:50 AM

Thnx for responding. The scope is new. The scope is collimated properly. I use Bob's knobs. No dew, the ota was outside to be acclimated. Jupiter is below 30 degrees, however, I used my 8se sct the night before and it was fine. My eyepiece is 19 mm Luminous from Celestron. And when I focus it seems like it doesn't quite get into focus. And there is a club nearby. Thnx

#7 Bobtownbuck

Bobtownbuck

    Sputnik

  • -----
  • topic starter
  • Posts: 28
  • Joined: 30 Jul 2019

Posted 09 August 2020 - 05:52 AM

And Greg N., I don't have the answers to your questions. But will try getting them tonight. Thnx

#8 Bobtownbuck

Bobtownbuck

    Sputnik

  • -----
  • topic starter
  • Posts: 28
  • Joined: 30 Jul 2019

Posted 09 August 2020 - 06:13 AM

Oh and Greg, the diagonal is a Celestron dielectric 2 inch/ 1.25 converter. Attached correctly to the ota. And the front looks perfectly fine.

#9 luxo II

luxo II

    Vanguard

  • -----
  • Posts: 2,353
  • Joined: 13 Jan 2017
  • Loc: Sydney, Australia

Posted 09 August 2020 - 06:28 AM

I'll suggest you should get in touch with a local club and ask for someone knowledgeable to pay a visit one evening possibly BYO eyepiece, an oldie that can be sanitised with isopropyl alcohol - it doesn't have to be your best one.


Edited by luxo II, 09 August 2020 - 06:30 AM.

  • jimandlaura26 likes this

#10 bobhen

bobhen

    Skylab

  • *****
  • Posts: 4,458
  • Joined: 25 Jun 2005

Posted 09 August 2020 - 06:51 AM

Don’t worry about Jupiter for now.

 

First: Remove Bob’s Knobs and use the standard screws and re-collimate.

 

C11s can take some time (hours) to acclimate. Where do you live? How long was the scope outside? What were the temperature differences between inside and out?

 

If you feel all is collimated and acclimated then point the scope near the zenith. How do the stars look in-focus at 100x? How do they look at 300x? How do they compare to your C8?

 

Now defocus until you see about 6-8 rings. What does the out-of-focus pattern look like? Is it oval or round? You want round. Are there heat plumes (wave like disturbances) rising from the center to the top? If you see these, the scope is not acclimated.

 

Compare the out-of-focus star pattern to your C8. Are there differences? Now move through focus until you get back to 6-10 rings on the other side of focus. What does that pattern look like? Is it close to the other out-of-focus pattern? You want them to be close.  Does the outside ring have the same brightness on either side of focus?  You want that ring to be close in brightness.

 

Now point the scope lower to the east. How do the stars look in-focus and out-of-focus? They should be the same as at zenith. How do they compare to your C8?

 

Now point the scope lower to the west. How do the stars look in-focus and out-of-focus? They should be the same as in the east and at zenith. How do they compare to your C8?

 

If the in and out-of-focus star pattern changes and the in-focus stars are flared and the scope requires re-collimation when you move from east to west then your primary mirror is loose and you need to send the scope back to Celestron.

 

ALSO…

 

Try another eyepiece.

 

Try observing without a diagonal - are the stars sharper? Then it could be the diagonal.

 

Change diagonals if you can.

 

Hope some of these things help diagnose the issue.

 

Bob


  • jimandlaura26 likes this

#11 Tapio

Tapio

    Gemini

  • -----
  • Posts: 3,117
  • Joined: 24 Sep 2006
  • Loc: Tampere, Finland

Posted 09 August 2020 - 07:06 AM

Sorry but I don't understand how removing Bob’s Knobs and using the standard screws would help.
  • gnowellsct and Andrew Brown like this

#12 Bobtownbuck

Bobtownbuck

    Sputnik

  • -----
  • topic starter
  • Posts: 28
  • Joined: 30 Jul 2019

Posted 09 August 2020 - 07:12 AM

Thnx for the information.

#13 Nippon

Nippon

    Soyuz

  • *****
  • Posts: 3,702
  • Joined: 22 Oct 2009
  • Loc: Central Florida

Posted 09 August 2020 - 07:51 AM

Seems on the Bob's Knobs there are people that swear by them and people that hate them. I used them on My Celestron Edge 8 and liked them because the Philips head screws that it came with did not seem to fit a #1 or #2 Phillips head screwdriver and would slip out a lot. The main argument from the anti Bob's Knobs camp is you can't tighten them enough to hold collimation. I found with My Edge 8 I needed to fine tune collimation at pretty high power like x300 or x400 with the star only a few rings out of focus. I also discovered that I got better collimation as evidenced by my scope's in focus performance if I collimated straight through without the diagonal. My gut instinct is that your C11 is not as well collimated as you think it is. 


  • jimandlaura26, Jim Davenport, Live_Steam_Mad and 1 other like this

#14 Bobtownbuck

Bobtownbuck

    Sputnik

  • -----
  • topic starter
  • Posts: 28
  • Joined: 30 Jul 2019

Posted 09 August 2020 - 08:02 AM

Thnx Nippon. Will give it a look tonight if weather permits.. I do live in a Bortles 7 area if that could be a contributing factor...

#15 Bobtownbuck

Bobtownbuck

    Sputnik

  • -----
  • topic starter
  • Posts: 28
  • Joined: 30 Jul 2019

Posted 09 August 2020 - 08:03 AM

And thnx Bobhen. Will need to write down what you wrote... lots of info

#16 Eddgie

Eddgie

    ISS

  • *****
  • Posts: 27,010
  • Joined: 01 Feb 2006

Posted 09 August 2020 - 08:46 AM

Hi,  I have an Celestron 11 sct.  Every time I have used it, nothing is clear.  No matter how I try to focus, calibrate, use Bobs knobs, nothing seems to work.  I tried imaging with it, and Jupiter looked horrid.   It feels like it is an expensive paper weight.  Any help, suggestions, please, would be appreciated. Thnx...

Seeing, thermals, or a combination of both are your likely issues. 

 

I don't know how much experience you have imaging planets, but to get a good result usually takes thousands of exposures and selecting maybe the best 200 to 300, stacking them, and processing them.

 

If you have a camera though, you can take a picture of a star defocused about 4mm.  Just get the star in as perfect focus as possible, then pull the camera out about 4mm, and take some pictures (stack them if you can).  Now, without moving camera, refocus on the star, then push the camera back in 4mm and take another picture (stack them if you can).

 

If you post the pictures of the defocused stars here, people can tell you if there is a problem with the telescope and my bet is that what they will tell you is that your seeing is poor and that you have thermals. 

 

Jupiter is low and daytime heat radiating off of distant rooftops, parking lots, and highways make a mess of the sky. 

 

Does this make the scope a paperweight?  Well, if you have not done a lot of planetary imaging I would say that it is too early to tell. Planetary imaging takes a fairly high level of skill (to get a good result) and in poor seeing, even a lot of skill will not always produce a good result.  If you don't have the skill (and I don't know if you do or don't) and don't have good seeing, then yeah, maybe it is a paperweight if you don't want to invest in improving your skill level and don't have the patience to wait for nights of better seeing. 

 

If you get some pictures of some bright stars using the method I gave above and post them here, we can tell you if there is any problem with your telescope or not. My guess is that it is probably OK, and that the low position of Jupiter and seeing conditions are preventing you from getting high resolution views.  It is rare for a C11 to work at its full resoulution visually, but with a few thousand exposures, you can often get images that show detail down to the scopes resolving power if you know how to do it.


Edited by Eddgie, 09 August 2020 - 08:47 AM.

  • jimandlaura26 and eblanken like this

#17 bobhen

bobhen

    Skylab

  • *****
  • Posts: 4,458
  • Joined: 25 Jun 2005

Posted 09 August 2020 - 10:01 AM

Sorry but I don't understand how removing Bob’s Knobs and using the standard screws would help.

You are trying to diagnose a problem. Why not use what Celestron specs and at least eliminate Bob’s knobs as one possible issue. After you find the issue and if it’s not the Knobs, then put them back if you like. 

 

Bob



#18 Bobtownbuck

Bobtownbuck

    Sputnik

  • -----
  • topic starter
  • Posts: 28
  • Joined: 30 Jul 2019

Posted 09 August 2020 - 10:12 AM

Eddgie, my skill set is still very green. And some of the things asked to do is not in my wheelhouse... yet. And living in Ohio doesn't give a lot of opportunities for imaging... thnx for your input.

#19 Reid W

Reid W

    Viking 1

  • *****
  • Posts: 999
  • Joined: 06 Oct 2010
  • Loc: Shreveport, LA

Posted 09 August 2020 - 10:44 AM

Here in Louisiana, we have two humidities..

90% (low)

95% (high).
  • Jim Davenport, Live_Steam_Mad and CeeKay like this

#20 Steve C.

Steve C.

    Viking 1

  • -----
  • Posts: 765
  • Joined: 24 Jan 2008
  • Loc: Sugar Land, TX

Posted 09 August 2020 - 11:54 AM

A 19mm eyepiece with a C11 would give you a magnification of approx. 150x. I would try the scope with a 40mm eyepiece.  Bad seeing gets magnified with higher powers.



#21 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 86,738
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 09 August 2020 - 12:05 PM

You are trying to diagnose a problem. Why not use what Celestron specs and at least eliminate Bob’s knobs as one possible issue. After you find the issue and if it’s not the Knobs, then put them back if you like. 

 

Bob

 

How likely is it the problem is the knobs?  I don't know but it seems unlikely.

 

On the other hand, I do read of problems swapping the screws so sometimes it's better not to change something unless it's a likely suspect.

 

Jon



#22 bobhen

bobhen

    Skylab

  • *****
  • Posts: 4,458
  • Joined: 25 Jun 2005

Posted 09 August 2020 - 01:45 PM

How likely is it the problem is the knobs?  I don't know but it seems unlikely.

 

On the other hand, I do read of problems swapping the screws so sometimes it's better not to change something unless it's a likely suspect.

 

Jon

I have no idea if the poster installed the Knobs correctly or not (if installed incorrectly, that can cause collimation issues) or if he has collimated correctly or if the knobs are even tightened correctly.

 

There are many threads about installation and collimation issues with Bob’s Knobs; some like, some don’t, some have serious issues. HERE is a link to a typical (of many) threads.

 

The thing is, if you collimate correctly, with normal setup and take down and storage etc., collimation should hold for months and years. So there is no real need for the knobs. If one is adjusting knobs every week or every time they setup or during a session something else is wrong.

 

For example: if one has to re-collimate after moving the scope from east to west, Bob’s knobs is not the answer. I purchased a brand new C11 back in 2000 that had primary mirror flop and had to go back to Celestron because collimation would not hold and that, of course, impacted image quality. Bobs knobs might, in that case, make collimation easier but they will not solve a collimation problem caused by mirror flop because the problem is with the primary.

 

Bob


Edited by bobhen, 09 August 2020 - 01:46 PM.

  • Live_Steam_Mad, Redbetter and eblanken like this

#23 Bobtownbuck

Bobtownbuck

    Sputnik

  • -----
  • topic starter
  • Posts: 28
  • Joined: 30 Jul 2019

Posted 09 August 2020 - 02:46 PM

Thnx everyone. I will try the lower power eyepiece and re collimate my ota. I do believe I correctly installed the knobs and adjusted it correctly, too. But nothing wrong with re doing the collimation. Clear skies for everyone

#24 Redbetter

Redbetter

    Cosmos

  • *****
  • Posts: 9,536
  • Joined: 16 Feb 2016
  • Loc: Central Valley, CA

Posted 09 August 2020 - 03:11 PM

I never have seen any good reason for Bob's Knobs on a Celestron SCT.  The screws work fine and should barely need any use.  They are tight and they stay put leaving collimation intact for a decade or more...well unless you ship them to Hawaii and they abuse your scope in the original packaging, to the point of cracking a fork.  Short of that, with thousands of miles of travel, some over mountain ranch roads in west Texas, the collimation held.  

 

One of the most common new SCT user mistakes seems to be to install Bob's Knobs immediately rather than doing any initial check and collimation with the original screws.  



#25 carolinaskies

carolinaskies

    Vanguard

  • *****
  • Posts: 2,262
  • Joined: 12 Dec 2014
  • Loc: Greenville SC

Posted 09 August 2020 - 07:11 PM

Did you check views before installing the BKs or just rush to put them on?

My guess is the latter since you just notice the poor performance. 

Now you're finding out why BKs are hated by more people than loving them.   BKs really aren't necessary for anyone who doesn't need to tweak for camera changes and Hyperstar changes for OTA's that have that feature.  

I wouldn't expect to have ANY other drastic issues with a brand new 1100 than cool-down and even that can be mitigated with covering with an insulated reflex blanket. Even low horizon planets will fluctuate views as the skies steady during the night.  They won't be regularly 'good' (unless you're at the coast and get laminar air flow) until you get beyond about 50 degrees.  



 




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics