Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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Yes its quite sad isn't it, but no I am not joking. 
Ever since i figured out how to play with the little dot in the center of a defocused star at 400x, nothing is the same. I sat out there last night for almost 6 hours on and off, waiting for the clouds to disperse. I had the same factory old collimation for a while so i tweaked it and it seemed to make a perfect start test at 400x, but then i got greedy and started tweaking a bit too much.
It made the telescope totally out of whack 
I couldn't even focus on dim stars anymore. So being frustrated a little i worked for a few long hours to get back to acceptable central doughnut status. But still, my current collimation is not anywhere near the close-perfection i attained during my first collimation screw turns at the beginning of the night.
Right now, one of the screws (screw A) is tightened to its end, so that even if i loosen the other 2 screws, (screws b and c), it still cannot move clockwise anymore.
I suspect that i should unscrew that particular screw A, but it throws my collimation way out of whack when i do.
Is it okay for one screw to be at its end, while the other two are not? or will this be a worse form of collimation compared to having all 3 screws same distance to their ends. Again, only screw A is screwed in till its end, B and C are not.
I have pictures on the way! approximate ETA is 20 minutes...
I am just charging up my sony cybershot zeiss 1080 full hd still image digital camera. Here is the camera ill be using for this purpose:
http://www.provantage.com/sony-dsct200~7SNYG019.htm
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 1723
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I have encountered this condition before.
I THINK that the cause is that if you loosen all of the screws, the secondary might shift a tiny by. Because it is a Negative 5x mirror, even if it *BLEEP* a mm or two, it can have some consequence.
It the thing was in perfect collimation before you touched it, then we know that is CAN collimated successfully, so I would guess that something has changed.
Unfortunatly, I can't advise you as to how to correct it.. While I have encountered the condition, it was never to the point that I couldn't quite get the collimation back in.
I would try this though.. I would stand the the OTA on the visual back end. Then, I would loosen all three screws enough so that the secondary could "Hang" by the screws.. We are talking a turn here.. Just enough that the pivot at the back of the secondary can move freely so that it if is slightly off center, by hanging from the screws, gravity should re-center it. Then EVENLY draw up the screws.
Basically, I think the screws my be in at a slight angle now, and doing this should make them all "Straight" again.
Again, I never tried this, but I have always suspected that a screw that bottoms is a symptom of this condition.
Again, only turn each screw about one turn so that you are taking all of the pressure off of the fulcrum on the back of the Secondary.
There is one other condition KNOWN to cause this condition. If you badly overthighten the screws, the fulcrum on the back of the secondary can actually dent inverted metal cup (the dew shield) that the assembly sits in. Bad news, because you can't fix that without taking the secondary mirror assy out and flattening the housing.
But you would have to tighten them pretty stinking tight to do this. Unless you were really torquing down the screws, this should have not happened....
Let me know if you attempt. I think everyone on the board would be curious to see it this works.
If you
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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no no, i never tried to tighten the screws too hard.
I use a tiny little allen wrench 5/64 size and i use the long end of it to turn the knob, not the short end which gives you more torque in the turn.
Also i only use enough force to barely turn it, if i see its not moving as screw A is, i dont force it too much.
I dont understand something, every time i tighten or untighten say screw B, does that mean i have to loosen or tighten screw A? Can one of the collimation screws be tightened or loosened without touching the other 2 screws? or does an adjustment always need to be made to the opposite screw?
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
Edited by Brooklyn (08/13/08 06:30 PM)
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Mike D
scholastic sledgehammer
Reged: 08/15/07
Posts: 854
Loc: South GA
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Your only solution is going to be to loosen screw A, but to loosen screw A you're also going to want to loosen screws B and C. So loosen all three screws 1/2 a turn and start your collimation over from scratch.
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Vixen SXD
Vixen ED80Sf
Hutech 350D
STI Stiletto
Meade 2080
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davidpitre
Pooh-Bah
Reged: 05/10/05
Posts: 1408
Loc: Central Texas
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If you are unable to collimate on a star, try this in daylight:
Set the scope horizontal so that you can see into the OTA and get concentric rings where the mirrors reflect each other.
Stand back an appropriate distance (somewhere around 10') to the point where the widths of the concentric rings are about even.
Now start the collimation process to the point where the rings' edges are concentric much like they would appear in the eyepiece. This will get you in the ball park to where you can touch it up on a star image when you get the chance.
I've found that if this is done carefully, I can approach decent collimation with this method.
If the screw that has bottomed out prevents this process, then I would back all 3 screws out equally 1/2 to 3/4 turn, and then do it. Make sure the scope is pointed slightly down before you back them out in case you lose the secondary.
I'd wager that you won't have to do this though when you collimate looking into the OTA. I'd guess the bottomed out screw will need to go the opposite direction.
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David
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 1723
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In general, yes. If a screw is tight and you need to go further, then yes, you will have to loosen one or both opposite screws depending on whose method you are using.
I wrote a guide to collimation on the other Astro website. It has step by step directions.
If you did not over-tighten, then I suggest you loosen all screws as indicated in my previous note and try again.
Regards.
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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Here come the pictures...
notice on this first one it looks like the glass is actually cracked!! i have not been able to reproduce this phenomenon with any of my bright flashlights nor reusing this camera over and over in the same spot.
I cant make it show this glass crack again. Anyone have any idea what it is? i joke when i say glass crack, as its probably just some small imperfection.
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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if anyone knows how i can attach more than 1 photo per post, please let me know. These photos are originally over 1.5 megs each, and i resize them to 90,000 bites each using irfanview (freeware).
Let me explain which screw is which. The screw that is screwed in to its end is the one of the right looking at the picture. This is the left screw if seen from the eyepiece side. This is Screw A that i referred to before. Screw B is the left most screw in the picture, but it is the right control screw seen from the eyepiece. And Screw C is the bottom screw which serves as my 12 ocklock or 6 ocklock screw. A moves it left, B moves it right, C should move it up and down. Problem is, A is at its end.
I did not screw it in deeper than it already was from the factory. It only took me maybe 1/2 a turn to get it to the end of the screw.
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
Edited by Brooklyn (08/13/08 07:10 PM)
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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another
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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So it seems to me that this little cracked glass that is showing up ONLY on the pictures and not in real life, is because of the flash given off by the sony camera. We all know what happens when we put a flash light to our telescope optics....but funny thing is my large telescope which reveals dust and finger prints and even waves in the glass, would never reveal this crack in the south west corner. I tried, and couldnt see it.
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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Last pic:
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
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hudson_yak
sage
Reged: 11/15/07
Posts: 446
Loc: Hyde Park, NY, USA
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I have a couple pictures of the guts involved a few messages down in here that may give you some useful insight.
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/2493839/page/9/view/collapsed/sb/5/o/all/fpart/1
Mike
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Meade 8" LX10
Orion ED100 + SVP
Meade 12" LightBridge
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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Does it matter which screw you chose to be the 12 oclock or 6 oclock screw?
In my case, i chose the bottom most screw to be SCREW C, which is my middle (up and down movement) screw.
Screw A is on the right as seen in the pictures, but is on the left seen from the eyepiece side. Tightening this screw pulls the central light dot left, while loosening pushes it right.
Screw B is on the left as seen in the pictures, but is on the right seen from the eyepiece side. Tightening this screw pulls the central light dot right, while loosening it pushes it left.
I place my diagonal and eyepiece on an angle to correspond with an imaginary line formed through the telescope by Screw C.
I used this guide:
http://www.astromart.com/articles/article.asp?article_id=548
If you notice in the guide the person used a top screw as his middle screw, instead of a bottom one like i did. Any issues here?
There is a chance my diagonal was not perfectly lined up with the Screw C imaginary line. Does having these two objects not fully aligned cause problems during collimation? I would expect it does since up and down would really be diagonal in this case, but i am not sure.
Otherwise the only thing as i mentioned before is that Screw A is screwed in all the way. Im going to try to loosen it maybe half a turn and see if i can balance screw b and screw c to correspond with it. I will try the suggestions you guys posted and ill let you know.
Otherwise, anyone have any answers to my previous two questions?
I am downright fanatical in this regard, as i mentioned before, I almost had the optics at perfect collimation. The star test at 400x revealed a 360 degree diffraction pattern, but i got greedy. Tweaked and tweaked until i didn't know how to tweak back to where i came from.
Its pretty easy to get general good collimation with the doughnut hole, but what I'm trying to do here is to get perfect flawless alignment. This is the reason Screw A being screwed in all the way is bothering me, since it seems that this setup with uneven screw-ins might not hold collimation as well as all 3 screws being evenly screwed inward.
Here is the screw naming as seen in the pictures:
------------------A
B
---------------C
Here it is as seen from the eyepiece:
A
------------------B
---C
Ignore the dashes (----), only focus on the position of the screws relative to one another. Screw C is the vertical 12 ocklock 6 ocklock screw. A and B are the horizontal.
The imaginary line which splits the FOV in half goes from the C screw and equally divides the area between A and B, or B and A same thing.
Only thing i wanted to stress is WHICH screw is the one that is fully screwed in.
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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check out...
http://www.asterism.org/tutorials/tut14-1.htm
It shows how even though the central dot might be skewed to the left, the right screw isnt the only option.
This picture also shows how the left and right screws control the shadow in a diagonal motion, and not in a true horizontal motion as some other guides say it is.
http://www.astromart.com/articles/article.asp?article_id=548
Ed's guide for example states that the left and right screws should only be used for tuning the central shadow left or right, and that the middle screw is only used for up and down motion.
But as Ive come to experience, the former chart was correct.
If the central shadow is to the left and down, the B screw should be loosened counter clockwise. However if the shadow is to the left and up, the A screw should be Tightened clockwise. This little fact about the horizontal screws is never mentioned by ed or any of the other collimation guide i have read thus far.
So the 2 horizontal motion screws, are actually diagonal screws...
Nice little piece of info to come across, or rather to figure out...i kind of wish all the other guides would have thought to mention it.
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
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hudson_yak
sage
Reged: 11/15/07
Posts: 446
Loc: Hyde Park, NY, USA
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The main thing to grasp is, the screws are 120 degrees apart, and all do the same thing, causing the mirror to pivot about an imaginary line drawn between the other two. There are no 90-degree angles in the relative movement.
But, since people find it easier to work in left-right and up-down, some pages try to break it down that way. You can either do what they say, or think in terms of motion 120 degrees relative for each screw. But which screw you start with doesn't matter.
What I do is sort of undisciplined. Tweak each one in turn as long as it is making things better, and reverse direction once it starts making things worse so it's left at the best spot. Then do the same with another one.
You do not want any of the screws bottomed out, as I tried to explain in that other topic.
Mike
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Meade 8" LX10
Orion ED100 + SVP
Meade 12" LightBridge
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hudson_yak
sage
Reged: 11/15/07
Posts: 446
Loc: Hyde Park, NY, USA
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Ed's guide does not say the motion is only left or right when adjusting those screws, rather he says to ignore the up-down component to the movement during that step since that's taken care of in the following step with the last screw adjustment.
Mike
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Meade 8" LX10
Orion ED100 + SVP
Meade 12" LightBridge
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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Thanks so much hudson, you made that part of his guide everso clearer.
He does not say the motion is only left or right, but neither does he mention that the motion is diagonal. This is where the confusion arises. 
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 1723
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I tried to simplify the instructions.
The problem is that when collimating with a diagonal, the screws don't behave the same way. If you follow the instructions and have a "Right" and "Left" screw, then these screws behave oppisite of the screw in the 12 O'clock position. This is because the diagonal on the back of the telescope causes the image to be reversed left to right (Mirror image).
If you tighten the left or right screw when using a diagonal, it will appear to pull the shadow towards the screw being tighetned.
If you tighten the 12" O'clock screw, it will appear to PUSH the shadow away.
I recommend that people ignore the shadow being high or low until they get it corrected left to right. This means working with ONLY the left and rigth screws.
After they center it left to right, they can then use the 12" O'clock screw working against the left and right scews to move the spot up or down.
There are many different approaches one can take. The reason I recommend this one particular method is that anyone that does it once successfully forever understands EXACTLY which screws need to be moved and can very quickly touch up their collimation. Many people have written me over the last year to say that my instructions worked perfectly for them and for the first time, they felt that collimation was easy (it is).
Sorry my instructions were not clear for you.
Because of the crack in the corrector, I suspect that perhaps your scope does have a deformed mirror housing.
Ouch...
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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Brooklyn
scholastic sledgehammer
Reged: 07/24/08
Posts: 870
Loc: Central New Jersey
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Oh no no, ed your instructions were the best Ive seen period. No need to alter them i think. Its pretty hard to explain how the screws work technically, and at the same time explaining it in a simple way so everyone can understand.
I guess my brain works a bit more technically than others, perhaps this is why the simplified instructions didn't register. I took your concept of only using the left and right screws, and it worked for the most part. The only issue i had was that the left and right screws actually moved the shadow diagonally. I tried to get it centered but it wasn't quite that simple.
I suspect my problem was the bottomed out, all the way screwed in, Screw A (left control screw). I never did this, it was the way it came to me from the meade factory.
The only thing i got confused on was what hudson explained up above.
I was trying to think of the screws working in a left and right, and up and down pattern, but it didnt really work out that way.
"The main thing to grasp is, the screws are 120 degrees apart, and all do the same thing, causing the mirror to pivot about an imaginary line drawn between the other two. There are no 90-degree angles in the relative movement."
"think in terms of motion 120 degrees relative for each screw. But which screw you start with doesn't matter."
I guess everyone's brain works just a little bit different.
For me, the imaginary lines work better than thinking about the push and pull mechanism.
But otherwise Ed i wouldn't suggest changing your guide on account of me, especially when so many other people found it beneficial.
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Meade 8.25"(209.55mm) LX-90 EMC (SCT)
Albert Einstein =>
“Intellectual growth should commence at birth and cease only at death.”
“If you can't explain it simply, you don't understand it well enough.”
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 1723
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Thanks for the kind feedback.
Sadly, it seems like there is still something wrong with your scope.
I would still recommend that you back the screws off and let the secondary hang, then retry.
It is also possible that your corrector plate has moved. This condition amay also cause you to run out of travel on the collimation screws.
If the corrector really is cracked though,and the scope is under warentee, I would return it. It may have happened during shipping. Perhaps the box was dropped and the sideways torque on the secondary caused the corrector to crack.
Cracks NEVER get better on their own. It will spread in time. You can drill a hole in the glass to stop it if it is not under warentee.
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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