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8" LX200 Way out of collimation - where to start

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#1 tommax

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Posted 09 March 2013 - 01:29 PM

Hi,

I have an 8" LX200 that I recently purchased, the owner claimed he installed Bob's knobs and the scope would no longer collimate... upon arriving I was able to roughly collimate the scope, even took some decent images of Jupiter with it.

Last night I tried to fine tune the collimation, without much luck, there was also some astigmatism which I had not seen before so the scope now sits in a way off collimation state, I am wondering what the experts here would do as a starting point with an SCT that way off collimation as a starting point.

I purchased a new set of Bobs knobs in anticipation of replacing but I am not sure if I need to. My plan was to get the scope as close as I could, then replace the current Bob's knobs in the scope anyways simply because I have them. If any of you are in WI near Milwaukee and know this stuff I would be happy to pay you to come and collimate the scope... short if that I would like to hear those who know more than I do suggestions on where to start.

I really appreciate any information...

:bow:

#2 tommax

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Posted 09 March 2013 - 03:55 PM

I want to clarify a bit, I want to know suggestions on where to start... I do not know how far in or out any of the current bobs knobs are and would like to get them as close to evenly screwed in at close collimation as possible and I just have no idea where to start with that.

#3 RogueGazer

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Posted 09 March 2013 - 04:21 PM

I am no expert but I know what I would do. I would tighten the knobs all the way down then loosen all 3 equally 1 turn. Find yourself a a bright star. Defocus enough to see the secondary mirror shadow clearly. You of course will want to center it as best as possible. Only adjust the same 2 knobs as needed leaving the 3rd alone. This will ensure you dont loosen things so much the secondary drops loose. If the 3rd knob needs tightened you will loosen the other 2 instead. If it needs loosened you will tighten the other 2 instead. Don't make large adjustments at one time.Tiny turns. After each turn you will have to realign your target star.
Remember this is not expert advise. My thinking is if the secondary is too loose it may not be properly centered where it needs to be. You also have to consider that the seller may have removed the corrector at some point and did not put it back on properly. This could present a very challenging situation to rectify.

#4 tommax

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Posted 09 March 2013 - 04:38 PM

Thanks Rougue,

That's what I was thinking only difference would be after getting them all tight and backing off a bit I would replace the bobs knobs he put in with my new ones (perhaps he purchased the wrong knobs?) and perform the rest as you state. According to the seller he never removed the corrector plate, he just thought he did something wrong and or stripped the bob's knobs... when I got the scope I am pretty sure they are not stripped at I have installed these on a couple LX200's and collimation screws never really feel "tight" from what I can tell and I think he mistook this as something being wrong.

Also do you (or anyone know) if the the mirror lock should be completely dis-engaged when collimating or should there be some pressure?

Thanks

#5 RogueGazer

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Posted 09 March 2013 - 05:02 PM

My Lx200 Classic has no mirror lock so I would think it is not necessary to get the job done but it probably wont hurt anything to use it.I would recommend if you do go with the Bobs knobs that are already in there you should tighten very slowly and gently in case they are the wrong ones. If they are too long it may cause damage to the mirror. Just guessing here. I have never seen the inside of the scope to figure out how it works.Might be best to swap them out with the new ones. Maybe just remove 1 and compare to the new ones and put it back in if all is ok.

#6 nitegeezer

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Posted 09 March 2013 - 05:53 PM

I am not an expert but I will offer my opinion. First I would snug up all the knobs, but not tight. Since you are worried whether the correct knobs were installed, I would now remove one and compare it with the set you just got that are supposed to be the right ones. At this point you can decide whether to use the current ones or the replacements. I would now take notes on the number of turns the first one needs to go snug. I would now repeat this procedure for the other two knobs. Now you know how many turns each knob is turned in. I would carefully loosen the one with the most turns and re-snug the ones with the fewest turns until the three are approximately equal. At this point you are now ready for the dark so you can do normal collimation with a star knowing the secondary should be at least close.

I hope this helps.

#7 Cliff Hipsher

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Posted 10 March 2013 - 10:13 AM

I'd start during the day so you can see what you are doing. Try to find something shiny. I use the chrome on my Harley. Start with a LONG fl eyepiece, get some sun glint centered and then defocus in both directions. Adjust the secondary as necessary. Move to your next shorter EP and repeat. You can also use a Barlow to get the power up....

The real benefit here is you do not need to power up the mount and chase stars....

Now you can fine tune after dark...

#8 tommax

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Posted 12 March 2013 - 12:20 AM

Thanks all... I did what was suggested and switched out the knobs, the ones looked fine to me for the most part and all new ones went in and snugged up fine with approx. 12 - 1/4 turns each... now I am just waiting for a night I can actually point it at a star to attempt to collimate.

#9 tommax

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Posted 14 March 2013 - 12:26 PM

I think I got it pretty close...

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#10 thesubwaypusher

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Posted 16 March 2013 - 10:48 PM

You got it! Now don't touch it and it should last for years.

#11 REC

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Posted 18 March 2013 - 12:43 PM

What power EP did you use when you took the image? Was this an afocal shot through the EP?

It looks pretty even now.

Bob

#12 tommax

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Posted 18 March 2013 - 03:14 PM

Bob,

That was a webcam in the back of a Meade flip mirror I believe.

#13 orion61

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Posted 29 March 2013 - 09:09 PM

if it is dead center on one side of focus but a little out on the other side of focus, the secondary, OR corrector is slightly off center.






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