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LX200R secondary mirror

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#1 hargy

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Posted 16 February 2014 - 10:19 PM

I was wondering how I could make sure my secondary mirror is centered perfectly for collimation. I have used the Ho-Tech laser collimator however, on the mirror that I place where the eyepiece goes, the 3 dots are not centered. Is there some sort of adjustment I can do to correct this?

#2 hargy

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Posted 16 February 2014 - 10:49 PM

Here's another question. If i remove the front lens to look at the secondary mirror and I put it back in the same place (screw holes) will that alter the optics in any way?

#3 nitegeezer

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Posted 17 February 2014 - 01:21 AM

Before you remove the corrector plate and take a chance of doing some serious damage, are you sure you have a collimation problem? Have you done a star test?

Since the secondary mirror is not flat, I would not expect a clean reflection with a laser. The fact that you are getting any reflection at all tells me that it is not too bad, and probably better than you could achieve by taking the corrector off and making a manual adjustment.

#4 SteveRosenow

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Posted 17 February 2014 - 03:38 AM

I just went through this on my LX6. I'll add to what Nitegeezer said.

First, DO NOT remove the corrector under ANY circumstance unless you have it marked for position and rotation. You risk nearly irreparable damage to the optical train's alignment. Meade's design has the secondary, primary, and corrector plate assembly optically figured to match each other not just as a set, but also through rotational alignment.

You need to conduct a star test before doing ANY sort of work.

Best method is to select Polaris, or this can be done in the daylight using sunlight reflecting off of a distant object such as a car bumper or power line insulator. My method is a steel ball bearing positioned on a fence post about 50 feet away.

You need to de-focus the pinpoint of light to where you have a "donut" of light about 1/8th the field of view, and determine the collimation adjustments that way.

#5 Pcolon1

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Posted 17 February 2014 - 04:00 AM

I was wondering how I could make sure my secondary mirror is centered perfectly for collimation. I have used the Ho-Tech laser collimator however, on the mirror that I place where the eyepiece goes, the 3 dots are not centered. Is there some sort of adjustment I can do to correct this?

Edited by hargy (02/16/14 10:46 PM)

Because of the shape of the mirrors, there's pretty much a low chance of getting the laser to bounce in the way you are expecting. I made the same mistake on my lx90 last year when I had absolutely no idea what I was doing. Needless to say, I ended up separating the secondary mirror from the corrector plate and almost ruined the scope. Toss the laser and do a star test. Collimation on an sct last a good while so it's not needed to be done repeatedly enough to need a laser anyway.

Here's another question. If i remove the front lens to look at the secondary mirror and I put it back in the same place (screw holes) will that alter the optics in any way?


As long as the corrector plate (what you are calling the lens), secondary, and primary mirrors are in the original position, it won't matter. The corrector plate is mated to your mirrors to reduce imperfections from manufacturing.

#6 hargy

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Posted 17 February 2014 - 01:21 PM

I'll try it again... thanks for the responses.

#7 Christopher Erickson

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Posted 17 February 2014 - 04:49 PM

I was wondering how I could make sure my secondary mirror is centered perfectly for collimation. I have used the Ho-Tech laser collimator however, on the mirror that I place where the eyepiece goes, the 3 dots are not centered. Is there some sort of adjustment I can do to correct this?


WHICH Hotech laser collimator are you using?

#8 Markigno

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Posted 17 February 2014 - 05:26 PM

I was wondering how I could make sure my secondary mirror is centered perfectly for collimation. I have used the Ho-Tech laser collimator however, on the mirror that I place where the eyepiece goes, the 3 dots are not centered. Is there some sort of adjustment I can do to correct this?

Hi, when the three laser points (which at focus, they form a single point) does not fall to the center of the mirror target, then it means that the secondary mirror is not centered.
The problem of secondary mirror not centered is verifiable even with a star test. With a star out of focus if the shadow of the secondary is not centered in both intra-focal and extra-focal, then the secondary mirror is not centered.
If the secondary mirror is slightly off-center, then it is not worth correcting with removing the corrector
If the test with Hotech CT collimator with three points on the mirror target are to only 1 or 2mm away from the center target, then let it be so. Do not touch anything
Marco

#9 hargy

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Posted 17 February 2014 - 06:12 PM

I am using the advanced ho-tech ct laser.
Yes. it's with the laser and it's on the mirror target. This is good to know cause if you look close it looks like a circle with points or a rounded triangle and it isn't dead center.

#10 Markigno

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Posted 18 February 2014 - 07:57 AM

looks like a circle with points or a rounded triangle

This form, like a small triangle of the laser is quite normal, because they are 3 separate laser and will probably not match perfectly in a single point. the important thing is that the center of the image formed by the three laser (either a small circle or a small triangle , that's fine too) , coincides with the center of the target drawn on the back of the mirror target , or at least just 1 or 2mm out of center.
Always remember one thing: this is still a laser (although built very well ), but the result should be " interpreted " and never taken as absolute truth. The star test is the "real " way to collimate a telescope perfectly ( whatever the optical scheme ) .
I own Hotech advanced CT laser collimator and I use it for my LX200R 12". This laser is a very powerful tool (it is almost comparable to an optical bench) , but you have to know how to use it well.
The quality of the final result also depends greatly on the focuser (or visual back ) if it is orthogonal to the primary mirror (and this never happens with a telescope SCT) . There is a special procedure to align perfectly the optical axis to the mechanical axis , using this laser . The result is surprising , but to do this it is mandatory to remove the corrector plate . This is not hard to do, but it requires good manual dexterity and precision. It should also own a focuser or visual back with the screw adjustments orthogonal. Keep in mind that a telescope SCT is very tolerant to small misalignments (I mean axial, not collimation misalignments), and these do not create problems with a good collimation on a star. But if you intend to do this work for precise alignment optical/mechanical with the laser , I can explain all the steps to follow .
Marco

#11 hargy

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Posted 19 February 2014 - 09:51 PM

Thanks markigno; I would appreciate it. looking forward to seeing your info.

#12 Markigno

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Posted 20 February 2014 - 07:24 PM

Ok hargy, these are the basic steps to align the optical axis and the mechanical axis in an LX200 Classic, R, ACF with advanced Hotech CT laser collimator:

1) OTA pointing up, remove the screws of corrector plate and remove the great ring of plastic.
2) Mark with a pen the outer edge of the corrector plate and the telescope tube (this is the reference to reassemble the corrector plate with the right rotation). NOW you can remove the corrector plate.
3) Turn on the laser sight cross, do the procedure of co-alignment between OTA and the laser (as explained in the manual).
4) Mount the mirror target in the visual back or focuser with adjustable orthogonal
5) Check if the cross laser sight, reflected by the target mirror on the target collimator, coincides with the laser sight reflected from the primary mirror on the target collimator.
If the two reflections, are not aligned (forming a single cross), then act on the adjustment screws orthogonality of the focuser until the two reflections coincide.
Now the focuser is perfectly perpendicular to the optical axis of the primary mirror.
6) Remounting the corrector plate (matching the marks you made before removing it), put the plastic ring and the screws loosely.
7) Repeat the procedure of co-alignment between the laser and ota, center the secondary mirror (if needed) by moving the corrector plate in order to make the shadow of the secondary mirror concentric with the reflection of the primary mirror (on target collimator)
8) Tighten the screws of the corrector plate to lock it.
9) NOW you can make the whole process of collimation of the telescope with laser

In this video you can see the whole procedure explained very well. You are using a Celestron HD where you can only remove the secondary mirror. In Meade telescopes is necessary to remove all of the corrector plate, but the procedure is identical. Good luck,
Marco

#13 hargy

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Posted 21 February 2014 - 05:55 PM

I tried to work on it on my off days but ran out of time.. There is always next week.

#14 hargy

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Posted 29 March 2014 - 07:20 PM

What a project this has been. It turns out my Ho-tech laser was off. I sent it back for a new one but I think they sent me back the same one without fixing it. I cant complain about them not willing to take it back again since I let a lot of time lapse before I tried to collimate my scope due to moving and not having the time to do anything. when I had the time, one of the laser points was way off and I thought it was my scopes secondary mirror.
So after reading up on removing the corrector plate and collimating my scope. I built up enough courage to start this task. I was able to clean the inside of the corrector plate and check for slop in the primary mirror and. after cleaning the corrector plate ( I recommend not using lint free cotton pads due to the lint issue when dry) I let it air dry and it looked brand new again. I put it back together and was able to see the error I had prior. The corrector plate slipped down a bit over the years. I secured it in place and bolted it down. the cone was spot on dead center. I calculated the error from the laser and adjusted the error. When I took it out for a final star test, I was shocked at how much more detail I was able to see in Orion's Nebula. The star test was just a tad off and I started to fiddle with the knobs and knocked it out again. The good news is now I know my mistakes. When I have time, I will do a better job at collimating the scope. I do have a question for you pros. 2 out of the 3 screws are fairly snug but the 3rd feels loose. Is this normal or should all three be snug?

#15 nitegeezer

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Posted 29 March 2014 - 07:49 PM

Having one loose sounds kind of strange. When I adjust mine, I keep the screws fairly snug, to the point that I have to loosen screws before I can tighten one. When I get done, I try to tighten all just the same amount to hold the secondary firmly in place and it stays in place well unless I take it on a field trip down a bumpy road.

#16 Christopher Erickson

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Posted 29 March 2014 - 08:18 PM

What a project this has been. It turns out my Ho-tech laser was off. I sent it back for a new one but I think they sent me back the same one without fixing it. I cant complain about them not willing to take it back again since I let a lot of time lapse before I tried to collimate my scope due to moving and not having the time to do anything. when I had the time, one of the laser points was way off and I thought it was my scopes secondary mirror.
So after reading up on removing the corrector plate and collimating my scope. I built up enough courage to start this task. I was able to clean the inside of the corrector plate and check for slop in the primary mirror and. after cleaning the corrector plate ( I recommend not using lint free cotton pads due to the lint issue when dry) I let it air dry and it looked brand new again. I put it back together and was able to see the error I had prior. The corrector plate slipped down a bit over the years. I secured it in place and bolted it down. the cone was spot on dead center. I calculated the error from the laser and adjusted the error. When I took it out for a final star test, I was shocked at how much more detail I was able to see in Orion's Nebula. The star test was just a tad off and I started to fiddle with the knobs and knocked it out again. The good news is now I know my mistakes. When I have time, I will do a better job at collimating the scope. I do have a question for you pros. 2 out of the 3 screws are fairly snug but the 3rd feels loose. Is this normal or should all three be snug?


It is my understanding that David Ho is rather fanatical about his collimators working perfectly and that he personally checks out and collimates any unit sent back for any reason.

Is it possible that there is something else going on with your scope that might make it appear that the collimator is off?

As for the third collimation screw not being as tight as the others, That doesn't sound right and something else could be going on. Of course don't overtighten any of the three screws.

If you have a camera service center in your area, that might be a good place to find someone who can inspect your scope for subtle problems.

#17 hargy

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Posted 30 March 2014 - 04:34 PM

David Ho may be fanatical about his collimators but mine is off a couple of mm. I taped a piece of paper over my lens cap and marked where the three dots are. I rotated the paper and only 2 point of light match up. 1 point of light is off. I also checked with a ruler and the laser should point .5 mm of the right. Like I mentioned before, I let a lot of time lapse and I feel I can not call and complain about this issue. I will contact him and see if there is a way I can collimate the laser myself and resolve my own error.

#18 Christopher Erickson

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Posted 30 March 2014 - 04:50 PM

I'll bet that he will want to make it right for you more than he would worry about warranty status.

#19 hargy

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Posted 30 March 2014 - 09:33 PM

I sent him an email and asked how to adjust it. I did not ask to repair or place the unit. I will let you know what happens when it does. I will admit after watching his new video, it sure make more sense to do a complete collimation and easier to follow along.

#20 hargy

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Posted 31 March 2014 - 04:30 PM

I sent out an email last night and it was answered within a couple of hours. Now either David Ho is reading this or someone told him about it. He personally responded to the email and will take care of it for me without a second thought. Now that is how all customer service should be like. I am very impressed with fast response to fix this.
+1 for David Ho and Ho-tech company !!!

#21 Christopher Erickson

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Posted 31 March 2014 - 04:50 PM

I sent out an email last night and it was answered within a couple of hours. Now either David Ho is reading this or someone told him about it. He personally responded to the email and will take care of it for me without a second thought. Now that is how all customer service should be like. I am very impressed with fast response to fix this.

+1 for David Ho and Ho-tech company !!!


Actually I would speculate that David is just doing what he usually does.

Giving his customers his highest-priority.

If someone in this forum had tipped him off, he would have personally-contacted you before you had even sent your email.

I put Hotech right up there with Astro-Physics and Televue when it comes to customer service.

#22 nitegeezer

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Posted 31 March 2014 - 06:48 PM

This is slightly off topic, but we are kind of there already.

How does the laser collimation compare to a star test? I am just wondering if this is one of those really neat products that is nice to have but is not required, or does it actually make the view that much better that it is a must have. I sure wish I had an unlimited astronomy budget!!

#23 Christopher Erickson

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Posted 31 March 2014 - 07:27 PM

This is slightly off topic, but we are kind of there already.

How does the laser collimation compare to a star test? I am just wondering if this is one of those really neat products that is nice to have but is not required, or does it actually make the view that much better that it is a must have. I sure wish I had an unlimited astronomy budget!!


First, I am a big fan of star tests for checking collimation and evaluating for optical aberrations.

In my experience, the Hotech ACT allows you to go one step farther and check the collimation of various compound telescope optical axis "subsystems" as well as an overall collimation. A star test only allows you to do an overall collimation. So in theory, the ACT collimator can give you a sharper overall collimation because you can check and tweak various subsystems (focuser, diagonal, corrector plate concentricity, etc.) Of course not all compound telescopes allow you to adjust every subsystem (baffle tube orthogonality, etc.) so in those cases all you can do is confirm the accuracy of manufacturing and assembly and seek professional repair if any of them are way-out.

As for star tests, I always use a crosshair eyepiece to keep the out-of-focus star carefully-centered and on-axis in the eyepiece.

I hope this helps.

#24 nitegeezer

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Posted 31 March 2014 - 07:45 PM

I read an article in S&T a month or two ago that had an interesting method of collimation. I am not sure if it was just for reflectors or if it would also work for compound scopes. I really want to try it but the weather is not cooperating. According to the article, one should move the out of focus star around in the view until the sweet spot is found, and then with the collimation screws the sweet spot should be moved to the center. This means the scope does not need to be moved between each movement of the screws. It sounded real easy and neat, but like I said I don't have the sky to check it out.

#25 Christopher Erickson

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Posted 31 March 2014 - 08:20 PM

I read an article in S&T a month or two ago that had an interesting method of collimation. I am not sure if it was just for reflectors or if it would also work for compound scopes. I really want to try it but the weather is not cooperating. According to the article, one should move the out of focus star around in the view until the sweet spot is found, and then with the collimation screws the sweet spot should be moved to the center. This means the scope does not need to be moved between each movement of the screws. It sounded real easy and neat, but like I said I don't have the sky to check it out.


I am aware of that technique and I think the theory is sound. However eyepiece quality, focuser collimation, diagonal collimation, seeing, tube currents, sky gradients and atmospheric refraction can make it rather-challenging in actual practice and in the end, you still only get an average collimation of all of the optical sub-assemblies in whatever unknown-state of collimation they are individually-in.

Of course a summary star-test is perfectly-fine for most people, most of the time. Only the most critical visual observers and hard-core astrophotographers who want to get every last drop of performance out of their compound telescopes will invest in a Hotech ACT collimator.

Another class of user who would value the Hotech ACT might be those that get very-few good nights and don't want to waste one fiddling with collimation all-night when they could be observing or imaging instead.

I hope this helps.






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