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#1 John

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Posted 09 June 2020 - 11:32 AM

Hello everyone,

 

I recently bought myself a Polaris 127mm reflector telescope and I am having a little trouble with collimation. Every night before I go out, I use a cheshire to collimate the telescope, but when I star test the collimation using the provided 9mm eyepeice the rings are never centered, resulting in a comet looking star when focused. When I use the cheshire I get the crosshairs centered on the secondary mirror. This is how I am supposed to use the cheshire, right?

 

I'm not bumping the telescope around when I take it outside, so I am a little confused as why the mirror alignment is off every time I star check it after collimating with a cheshire. 

 

Is there something that I am doing wrong, or is this a normal thing with reflectors?

 

I love using this telescope and I am amazed every night at what I can see through it once I have the mirrors aligned. Any help would be greatly appreciated. 

 

Thank you, 

 

John



#2 MistrBadgr

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Posted 09 June 2020 - 02:26 PM

Hi John!

 

I have one of the Polaris 127 scopes also.  Unfortunately, with the scope being what I call a boosted Newtonian, meaning the actual primary mirror has a very short focal length mirror and then a booster lens in the focuser, it is the most difficult scope I own to get a totally precise collimation on.  By concept, the scope is known as a catadioptric, meaning that both a mirror and a lens is necessary to get a viewable image, like a Smidt Cassegrain, Maksutov Cassegrain,  It is actually a very close cousin to a Maksutov Newtonian.  Both a Maksutov Newtonian and our scopes have s short focal length spherical mirror and have a lens that makes all the corrections for spherical error, and a short focal length spherical mirror has a lot of that.  The difference is that a Mak Newt has the correcting lens in front of the primary mirror, while our scopes have it after the secondary mirror, at the true focal point of the primary mirror.  At that point, any slight error in positioning or in the angle the image cone deviates from exactly straight on, messes up the spherical correction.

 

The over-all scope roughly has a focal ratio of 8.0.  The primary mirror on mine has a truly reflective diameter of 128mm by actual measurement and, to the best of my ability to tell, the focal length of the primary mirror is 450mm.  That gives in a focal ratio of 3.52.  The negative effects from collimation error, from information I have researched, goes up inversely to the square of the focal ratio. So the primary mirror is a little over five times more sensitive to collimation error than a true f/8 mirror.  Then, the booster lens enters the picture with its own sensitivities to collimation error, which I have no idea how to calculate, even if I did now what the focal ratio of it is.

 

Getting rid of all the coma that you are seeing takes a lot of work and even more patience.  At one point, when I first started working on mine....maybe three days into it, I was ready to throw the thing across the room, then stomp on it.  The most likely problem is that the secondary mirror is not lined up exactly as it should be with the booster lens.  I found several potential sources:

 

1.  The position of the secondary mirror along the primary mirror's optical axis.  You can move this back and forth using the center screw and the normal three collimation screws.  The center screw works opposite the other three, allowing you to move the whole secondary mirror at a tedious pace.  Once you make a move, you then get to redo the rest of the collimation of both the secondary mirror and the primary.

 

2.  On mine, I found a base piece that has the screws for the finder (located on the inside of the main tube) has a smaller radius of curvature than the metal tube of the mirror.  With the finder mounted tight enough not to move around, it tends to warp the optical tube.  With the scope in its rings, mounted on the tripod, the error can be collimated out.  However, do not loosen or rotate the optical tube in its rings or the collimation will be adversely affected.  On mine, I took that piece out and shaved out some of the plastic to change the radius of curvature to more closely match that of the scope.  I suspect that plastic piece is built for a 114mm scope, but is being used in the 127.

 

Another way of approaching this problem is to leave that part alone, and shim between the focuser base and the main tube.  This is a trial and error process.  I used pieces of cardboard from the back of a note pad for my experimentation.

 

3.  The last item will probably not affect you when using the light weight eyepieces that come with the scope, but will if you use much heavier ones.  This issue has to do with the way the draw tube (the tube the eyepiece actually fits in) is supported in the focuser body.  There is a strip of slick material in the base of the focuser opposite the rack and pinion.  This strip and the rack and pinion are the only contacts the draw tube makes with the focuser base.  It is adequate for light eyepieces, but with heavier ones that I use, there is no support in a direction running perpendicular to a line from the existing support strip and the pinion.  This situation is true in all entry level mass produced reflector scopes currently made by any company that you will find being sold in the world today.

 

What I did was to make some strips out of a file folder that had wax impregnated thin cardboard for its material.  These were slightly wider than standard double sided tape.  I alternated double sided tape and strips of the folder material, a couple layers of each to start with, down the length of the focuser base tube.  There are three different places where I put the strips:  One across from the rack and pinion "ditch" in the tube, and the other two on either side of that ditch such that they formed an equilateral triangle.  There is a supporting strip every 120 degrees around the circumference of the tube.  At first, I had a strip of double sided tape, then a strip of folder material, then double sided tape, then another layer of folder material.  This worked for a while, until the materials compressed and the draw tube started wiggling (sideways) again.  I opened up the focuser, pulled the draw tube out, and the lower level of folder material, being slick and being curved in a way it was not made, popped loose.  This happened with all three of the combined strips, leaving one layer of double sided tape stuck to the focuser base material, and the rest of the material loose as three cardboard and tape sandwiches.  I put an extra layer of double sided tape inside the focuser body, on top of the existing pieces, stuck the cardboard sandwiches back on top, and hurriedly put the draw tube back in place.  During the draw tube insertion, I had some trouble holding the cardboard in place, as it wanted to slide some with the draw tube.  Later, I had to do this whole thing again.  Now there are three pieces of tape under the cardboard strips.  There seems to be enough material in there now that the whole thing seems to be permanent.  It is able to support my 82 degree Meade eyepieces well.

 

With some experimentation, I found that the light energy in the coma I was seeing was coming from light that was being reflected off of tube walls and other surfaces inside the scope that were not supposed to be reflecting surfaces.  The intensity of the coma was also affected by the amount of haze in the sky that was reflecting light pollution back downward.  I ended up buying some material normally called "flocking" or "light trap", which absorbs over 99% of the light that hits it.  I ended up covering every surface except for a few screw heads that would require very small pieces.  The flocking has a sticky back, but I did not want small pieces coming loose and falling on the primary mirror, so the screws were painted with flat black paint instead of shiny black.  I also used a black sharpie pen (cone tipped and not the fine point) to blacken the bevels of the primary and secondary mirrors.  I made the equivalent of a lens hood out of a gallon paint can, sprayed it flat black, then lined it with flocking on the inside.

 

By the time I was done, contrast was approaching that of a good refractor.  The scope is now good to 225 or 250X on the Moon with my high end eyepieces and no Barlow lens. (4 to 5 mm eyepieces).  The scope especially likes an old 4.7mm Meade 82 degree eyepiece...they don't make that any more.

 

The focal position for the booster lens in the focuser seems to be just right when observing the Moon.  When looking at deep sky, the focuser has to be adjusted inward with just the lenses, which take it away from its best position.  I found a 2X Barlow, a Meade No 140 (can only be obtained second hand) that requires about 5mm out focus, which seems to be just about right.  With that particular Barlow, the scope is capable of splitting two six magnitude double stars with a separation of 1.1 arc seconds, which is about as good as a good refractor that size gets.  On double stars and minimal haze, I do not see any coma on double stars at all.  If the sky is really hazy, I will start seeing bits of it in some cases of really bright stars, but not the big stuff that makes a star look like a comet.

 

For deep space objects, resolution is not quite as good as I would like without the Barlow, but they don't call those "dim fuzzies" for nothing.  I am keeping my eye out for eyepieces that have more back focus than most to sharpen the image a bit for deep space, but I am fairly content with things as they are.

 

Well, you probably do not need all of this, but once I opened the closet door, everything came spilling out.  Just pick through the items and take what you want.  If you have any questions, Holler!

 

Best Regards,

 

Bill Steen


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#3 John

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Posted 09 June 2020 - 03:50 PM

Thanks for all the information Bill. 

 

What would moving the secondary mirror up or down do? Should I move it up or down, or is that just trial and error until I get it right? And what am I looking for when I move it?

 

And what your saying about not moving the telescope through the rings; does that mean that I should stick to one area of viewing without having to re-collimate?

 

About the finder bracket; if I were to remove that and re-shape it would I be able to put it back in place?

 

Would it be worth it to by light trap material or are the differences negligible?

 

Thanks for the help,

John



#4 MistrBadgr

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Posted 09 June 2020 - 08:58 PM

Hi John,

 

I looked at the board one last time before going to bed and it is almost midnight.  I will answer your questions tomorrow, when I am thinking better. :)

 

Bill


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#5 MistrBadgr

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Posted 11 June 2020 - 10:28 AM

Hi John,

 

Sorry I am a day late.  I had things come up, distracting me, and I forgot to do this yesterday.

 

I am going to do these one question at a time, just to keep from making some stupid mistake and having a whole bunch of effort go "zip" and disappear forever.

 

Question 1:  What would moving the secondary mirror up or down do? Should I move it up or down, or is that just trial and error until I get it right? And what am I looking for when I move it?

 

The signs may be subtle.  When you look through your cheshire, assuming that you can see the whole secondary mirror, if the mirror looks eliptical with the major axis either along the main tube's axis or perpendicular to it, then it is out of place along the main tube axis.  if the secondary mirror looks long along the main tube axis, then it should be too close to the primary mirror.  If it looks short along the main tube axis, then the secondary mirror is too far away from the primary mirror. 

 

If the secondary mirror seems oriented askew of the primary mirror, like its axis are significantly off of the main tube axis, then the secondary mirror is probably rotated some as well.  In that case, look at the "tip" of the secondary mirror or housing, where the black metal clip is, and make sure it is centered.  Be sure to use the tip of the mirror or housing as a reference and not the clip.  The clip was misplaced some on mine and threw me off for a while.  Incidentally, that clip was put on there to hold the secondary mirror (on my scope) while the glue set at the factory.  I found it unnecessary for holding the secondary mirror in place for me.  In face, the secondary mirror does not come out of its housing even if I wanted it to.  On mine, I took the clip off, just to keep it from covering up mirror surface.  The only draw back with the clip off, it made it harder to see the secondary mirror roll orientation.  If you take yours off (quite an effort, requiring taking the whole mirror out of the scope, them putting it back in), consider filing a little notch in the end tip of the plastic housing that you can see when looking down through the focuser.

 

Once the mirror roll is correct, look down the focuser tube and see if the mirror housing looks cocked to one side, which it may be.  In that case, you need to adjust the collimation screws to get the housing look like it is aimed straight at the primary mirror and not cocked off to one side.

 

After that, use your cheshire eyepiece to recenter the primary mirror.  I used the three black stops that go around the primary mirror as references when looking though the my cheshire.  I happen to have a short cheshire that allows me to see thee whole secondary mirror and not just all of the primary, so it is a bit easier than with a really long cheshire.  Once you get the three black stops lined up so that they look like you are seening them evenly sticking into the view, then you can adjust the primary mirror's screws to get the reflection of the focuser centered in the middle of the view, behind the crosshairs of your cheshire.

 

If this is confusing, let me know and I will try again.  I am going by memory and may need to actually go out and stick a chechire into my scope.

 

Hope this helps,

 

Bill


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#6 MistrBadgr

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Posted 11 June 2020 - 10:55 AM

Question 2:  And what your saying about not moving the telescope through the rings; does that mean that I should stick to one area of viewing without having to re-collimate?

 

Some times, especially with longer scope tubes, you can end up with the scope in a positon that is difficult to look though the eyepiece.  What some people do in that circumstance is to loosen the rings and roll the scope inside the rings to put the eyepiece in a more comfortable position.  I found that doing this definitely decreases viewing difficulties and awkwardness, especially as I get older.  The only problem with that on this scope is that the pressures and tensions on that main tube change enough to cause the metal to deflect differently enough to make small changes to the collimation.  Namely, the orientation of the focuser compared to the secondary mirror.  With long focus primary mirrors, there is more tolerance for something like this by their very nature.  Plus, they do not have a booster lens in the way, which is extremely sensitive to collimation errors.  A third factor is that the distance between the rings and the focuser is greater on long tubes, therefore any defiations are smaller to start with.

 

What I do is I rotate the tube in its rings, while on the mount such that the focuser is exactly on the opposite side of the primary tube as the mount or the dovetail that attaches to the mount.  With the tube in this position, with the rings tightened they way I will use them during observations, I collimate the scope and use it exactly that way during observations, no mater where I point the scope in the sky.  I just have to move myself around and put up with awkward positions, or simply wait until an object is in a better part of the sky for me.

 

Bill


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#7 MistrBadgr

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Posted 11 June 2020 - 11:09 AM

Question 3:  About the finder bracket; if I were to remove that and re-shape it would I be able to put it back in place?

 

Yes, it goes back in place.  What you do is remove material between the two screws to keep it from pushing up against the primary tube metal and warping its shape.  I think sanding the material out is probably the safest, but very tedious.  I ended up using a Dremmel (sp?) tool.  The final result was a bit on the rough and crude side, so I put down some of the light trap material I was using as a buffer.  I small piece of black felt might be better.  Just cut a reasonably sized strip and poke holes through it for the two screws to fit through.  Put a couple layers if you want.

 

The plastic outside of the two screws falls away at a faster rate than the main tube curves, but I could not think of anything much to do about that.  I laid down some extra layers of light trap in those spots to help fill in the gap and hopefully help reduce any pressure to bend the tube metal.  In your case, some black felt might be glued to the plastic piece if you wanted to.  Possibly you may not need to do anything there.


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#8 MistrBadgr

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Posted 11 June 2020 - 11:44 AM

Question 4:  Would it be worth it to by light trap material or are the differences negligible?

 

This question is a lot more subjective.  I deliberately went overboard with flocking on this scope to prove to myself where the energy for various forms of interference was coming from.  Most people would not put that much flocking in their scope or at least on all the items I put it on.  How much benefit it provides depends a lot on the nature of the scope and how much light pollution there is at the observing site.

 

My Polaris 130 is not a good light pollution fighter, with its f/5 primary mirror.  The Polaris 127 does a better job, even though it has a shorter focal length primary mirror.  The booster lens, which creates problems we have discussed, works as a baffle and blocks some of the light pollution that affects image contrast. 

 

I have the Polaris 114 also.  Though not quite as good of a light pollution fighter as a long tube refractor, it works well enough that I have not made any modifications to it at all, even though I have somewhat high levels of suburban light pollution.  Looking at the dark sky chart from the Clear Sky Chart website, I am in a zone that is shaded dark red, with only bright red and white being higher light pollution levels.  I know that contrast would be improved if I did do the work on the 114, but I am not bothered enough by contrast issues to warrant doing the work.  The Polaris 114 is a really tolerant scope with its f/8 focal ratio.  If I did anything, I would probably build a hood of some sort to stick out in front and shade the secondary mirror area from light pollution coming in from the side.  If you wanted to cut down on light pollution in your Polaris 127, that might be the place for you to try first.

 

I guess, to sum things up, it all boils down to what interferes with what you are seeing and keeps you from enjoying your scope.  If you are enjoying what you are seeing and nothing is getting in the way of that, then don't do anything.  You don't want to try to fix a good situation until it breaks!  For now, just mastering collimation on your scope will be a significant task.  If you get collimation down well, for that type of scope, you are well ahead of most astronomers.  Other improvements can come along as your observational skills develop, putting more demands on what your scope can show you.  You can explore a lot of things with that scope, with a good collimation on it.

 

Let me know if you have any more questions, or if I need to explain one of these differently or simply better.

 

Best Regards,

 

Bill


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#9 John

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Posted 11 June 2020 - 01:41 PM

Thank you very much Bill.

 

I just need a little specification on your first response about the secondary mirror. 

 

You said,  "The signs may be subtle.  When you look through your cheshire, assuming that you can see the whole secondary mirror, if the mirror looks eliptical with the major axis either along the main tube's axis or perpendicular to it, then it is out of place along the main tube axis.  if the secondary mirror looks long along the main tube axis, then it should be too close to the primary mirror.  If it looks short along the main tube axis, then the secondary mirror is too far away from the primary mirror."

What do you mean by this? I also have a short cheshire and I can see the whole secondary mirror through it. 

 

And when you say that the mirror may be rolled, do you mean that the mirror surface isn't facing the focus entirely?



#10 John

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Posted 11 June 2020 - 02:32 PM

I have noticed that the secondary mirror is not centered in the focuser. Do I have to move the secondary mirror so that it is centered when looking through the focuser?

 

If the answer is yes, then you don't have to answer my above question.

 

John



#11 MistrBadgr

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Posted 11 June 2020 - 03:02 PM

Hi John,

 

The secondary mirror should look centered in the focuser.  It should look like a perfect circle also.  If it looks like it is veering off in some direction, I am thinking you are being lead in that direction because the mirror is rolled around the main tube axis some, causing you to veer off of that line in order to get the primary mirror centered in the view of your Cheshire eyepiece.  I have been there before with mine.  If I remember correctly the mirror tip was rolled in the same direction that the whole thing seems to be pointing.  However, I am not 100% sure of that.

 

Hope this helps!

 

Bill


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#12 John

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Posted 11 June 2020 - 03:12 PM

Hi Bill, 

 

That makes a lot more sense. I think I have gotten the secondary mirror centered as best as I can. 

Now I will have to re-collimate the mirrors; will that mess up the secondary mirror being centered?

 

Also, will the movement of the secondary mirror help keep collimation better?

 

Thanks for clarifying for me, 

 

John



#13 John

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Posted 11 June 2020 - 05:08 PM

Hello again, 

 

When I use the cheshire to align the primary mirror I get it aligned like I am supposed too. But when I remove the cheshire, the spider is not centered in the focuser.  The only way for me to fix that so that the cheshire agrees with the spider being centered is to mess with the secondary mirror again, but I already have that were I need it. What needs to be done about this if anything?

 

You can disregard the previous post as I have figured out the answer. 

Thank you for all of your help, 

 

John



#14 MistrBadgr

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Posted 11 June 2020 - 09:52 PM

Hi John,

 

It may take a few iterations to get everything lined up and working together.

 

When you set up your secondary mirror, try looking for the three rubber stops of the primary mirror in the view and adjust the secondary mirror to get them showing equally in the secondary mirror as viewed through the Cheshire.  If you cannot see the stops, try racking the focuser outward some to take in a bigger view.  Hopefully, you can get them to show up...at least the very inside edges.  Do not use the position of the spider in the view at this point.  The position of the stops on the primary mirror are pretty much fixed as far as the secondary mirror is concerned and can make a good reference for centering the primary mirror in the view from the secondary.  Then, go to the adjustment screws on the primary mirror and adjust those to get the spider showing properly in the view of the secondary mirror.  The primary mirror's stops should remain in view.

 

Another way I use to check the position of the primary mirror is to stand in front of the telescope and look down past the spider to the primary mirror.  Use one eye and adjust your position until the spider vanes line up exactly with their image in the primary mirror.  Then, look at the open space between the center circle of the spider and secondary mirror and the outer edge of the primary mirror.  If that space seems the same all the way around, you are very close to dead on, if not exactly there.  You can move toward or away from the scope to make that space change, keeping the spider legs and their reflections lined up, until that bright space is very small, to give you a better idea how much difference there is from side to side.

 

There are other techniques with other equipment that can be used as part of the collimation process, but I think the work can be done with what you have.  I am trying to stay away from what you do not have, specifically a laser collimator and putting a black dot in the center of your mirror for some guidance.  I normally use all the tools I have to cross-check one method with another, but I have collimated my scope without that specific equipment successfully.

 

Something else you can try is to look at the reflection of the secondary mirror in the primary.  Look from a position on either side of the spider leg between the center and the focuser and see if you can see if the light coming through the focuser shows up and looks centered.  Then go to one of the legs perpendicular to that first one and see if that same light looks centered from that direction.  I am not sure if you can see it or if what you do see will be misleading, but it is worth a try.  It might give you an idea of which way something is off.

 

Hope this helps and not just confuse.  I am leaving out some things related to the focuser actually aiming directly across the primary tube perpendicular, which has to do with that tube warping and having to shim the focuser to get it aimed right.  I am trying to NOT flood you with too much, when it might not be necessary.  As I have said earlier, this type of scope is the hardest one to get properly collimated that I have owned.  However, when I get mine done right, it always seems worth the effort when I use the scope.

 

You are most welcome for the advice.  I hope it does end up helping you get that good collimation.

 

Best Regards,

 

Bill


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#15 John

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Posted 12 June 2020 - 11:41 AM

Hi Bill, 

 

Lining up the spider with the reflections definitely helps, along with seeing if the focuser is centered with the secondary mirror. 

I cant get the light from the focuser to be centered in the secondary mirror while also having the three primary mirror clips visible. When the light from the focuser is not centered I can't collimate because the primary mirror adjustment screws wont turn far enough. Also, this results in a spider that is very off center when looking at the primary mirror from the front of the telescope. Any ideas on what to do?

 

At this point, would it be easier to by a laser collimater and mark the center of the primary mirror?

Thank you for sticking with me through all of my confusion, 

 

John



#16 John

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Posted 12 June 2020 - 04:12 PM

Hello again, 

 

After several hours of trial and error I was able to get the secondary mirror aligned perfectly. I then aligned the primary mirror without the cheshire and everything is concentric. But when I put my cheshire in, it is wanting me to veer way off in order to get the primary aligned with the cheshire. Any thoughts on what is going on? Is this something that needs to be fixed by adjusting the secondary mirror? I have it visually aligned properly so I'd rather not mess with the secondary mirror any more unless I have to.  

 

I think that now my telescope is in a lot better shape then it was before.

 

Thank you,

 

John



#17 MistrBadgr

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Posted 12 June 2020 - 04:12 PM

Hi John,

 

As thoughts about this have been rolling around my head, little bits of information are slowly coming to the surface.  Those bits come back to me slower at age 69 than they did when I was younger. (smile)

 

I think your secondary mirror is still out of position in some way.  It may need to tip downward a little bit.  I am remembering now that the angle of my housing was a little less than 45 degrees (pointier on the tip). I speculated at the time that they may have designed things to put the reflection a little bit high on the mirror to avoid having the clip on the nose of the secondary get in the way.

 

If your mirror housing seems to point to the side one way or another, then it is still rolled a tiny bit.  It is definitely touch and go with this thing.

 

I remember at times starting out using the reflection of the primary mirror at the start to get it set up as good as I could before working on the secondary mirror, knowing I would be coming back to the primary later.  That kept me from using a Cheshire or laser collimator in the focuser for that initial function.  I would also peek around one of the spider legs from one side and then the other and look at the reflection of the leg on the opposite side.  If the reflection looks the same distance away from the leg you are peeking around, then the mirror is centered in that direction.  I would then go to a leg perpendicular to the first one and do the same thing.  Adjusting with screws on the back of the primary mirror, I would go back and forth between the two legs until both looked as completely centered as I could tell.  That is about as good as can be done, I think, for getting the primary set looking straight at the spider and out of the scope.

 

I would then look down the focuser and see if the secondary mirror in its housing looked to be pointing straight at the primary mirror, which is kind of a crude observation, but it works as an attempt to look at the whole forest and not at individual trees.  At that point, if need be, I would adjust secondary collimation screws to get the whole housing and mirror looking like it was pointed as straight at the primary mirror as I could get it.  I might compare back and forth between using the Cheshire and just using naked eye and getting back some from the focuser and moving my position around so that the outer ring of the focuser draw tube and the circle made by the inside of the booster lens.  Then compare the positioning and shape of the secondary mirror to those circles.  They should all be concentric.  If not absolutely so, you might need to live with it for a bit.

 

Then, I used the Cheshire to get the three stops evenly showing in the view, adjusting secondary collimation screws.  At this point, the cross-hairs in your Cheshire (assuming what you have has those) should cross in the middle of the image of the primary mirror.  If not, then there is something wrong with the relationship of the secondary mirror and the draw tube in the focuser.  If all of this much looks well, then the last step should be to make any adjustments on the primary mirror to center the reflections of the spider legs with the cross-hairs of the Cheshire.

 

If you have followed something like this and some things do not quite line up, then there may be something still going on with the relationship between where the focuser is pointing, compared to the secondary mirror.  That may have to do with irregularities in the main tube metal.  One reason can be what we talked about with the finder attachment piece, the tube metal itself might be bent a very tiny bit, or the draw tube might not be completely straight in the base of the focuser.  I have done several different things to correct the situation at different times and sometimes more than one.  1. Reshaping that attachment piece for the finder.  2. Shimming under the focuser to point the draw tube in a slightly different direction.  3.  Holding onto the end of the draw tube with my fingers and placing the heal of my hand on the focuser base and giving it a quick flex to bend the tube metal in the direction I think it needed to go.  4.  Rebuilding the inside of the focuser, as described before, to give the draw tube more support and keep it straight.

 

You asked about a laser collimator.  That can be another way to work on collimation which can be effective. You can use that, once you think things are fairly straight, to move the red dot on the primary mirror with the secondary collimation screws.  Then, if you have a version that has a frosted screen on the collimator, you can then adjust the primary screws to put the reflecting red dot into the middle of the screen.  If you can get it centered well enough that the whole dot disappears into the hole in the middle of of the screen, then you are pretty much as dead on as you can get.

 

However, there are all kinds of combinations that can give that result in terms of the laser pointing to the right locations, with all the components  not being in the exactly correct positions.  With these solutions, the image as a whole is not good.  The laser is looking at specific points and you are assuming all the rest is correct.  A laser can solve some of the problems, but can miss others.  I use a laser one tool for this scope, but I definitely use all the others I can think of.

 

A couple of other points to consider (and I am not trying to discourage you from getting one at all):

 

A laser collimator is relatively heavy, compared to the eyepieces you have, more like the higher end eyepieces that I use.  It may be enough weight to flex the draw tube position inside the focuser body, requiring modification of the focuser to support that additional weight.  It may not, but keep that in mind.

 

When you get your laser, compare the diameter of the part that fits down into your focuser with the diameter of your eyepiece barrels.  I found one of my lasers with a narrower barrel than the eyepieces I use and ended up putting strips of cellophane-like tape that would not compress around the barrel of the laser to make it match my eyepieces.

 

When you first get your laser, put it in the draw tube and tighten down the thumb screw(s) just enough to hold it in place, but not enough to keep you from rotating it.  Look at the red dot as it hits the primary mirror and rotate the laser in the draw tube carefully and as gently as you can.  If the laser is aligned correctly, the red dot will stay in exactly the same position.  If it draws a little circle as you rotate the laser, then the alignment is off.  There should be three set screws, probably allen screws on the laser's housing that hold one end of the laser's tube inside of the larger housing.  There is normally an "O" ring holding the other end.  That inside laser tube is normally made of thin aluminum, be careful and do not over tighten the screws or you will put dents into the aluminum exactly where you do not want them.  I recommend loosening up the other screws just a touch and then tightening up the one you want to tighten.

 

Well, that is about as big of a data dump as I can do at one time.  Let me know if anything is unclear and I will try again.  Also, let me know if I left anything out that you asked about, or if you have other questions.  I want to stick with you until you get this solved to your satisfaction.

 

Best Regards,

 

Bill


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#18 John

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Posted 12 June 2020 - 04:24 PM

Hi Bill, 

 

That seems pretty straight forward. Thanks. 

 

So what I need to do now then is to look at the front of the telescope and look at the primary mirror to make the adjustments needed that will move the secondary mirror so that the light coming from the focuser is centered no matter where I look from?

 

If that didn't make sense, let me know and I can re word it. 

 

Thanks, 

 

John



#19 MistrBadgr

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Posted 12 June 2020 - 09:14 PM

I think what you said is correct.  It is a bit of a judgement call, when looking from one side of a spider leg and then the other.  Neither will look like that little spot of light is in the center, but the average of the two should amount to it being in the center. 

 

The whole exercise can be a bit of a mind bender, figuring out what things mean in relation to what to move, which direction, and how much.  Even if you do not get it all the way, keep using the scope and look at things with it.  How objects look to you in the field is the final judgement, especially double stars.

 

Keep communicating as you need to.  Helping people like you is what I am here for. :)

 

Bill


Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#20 John

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Posted 13 June 2020 - 07:26 AM

Hi Bill,

 

I think then what I will do is reinforce the focuser so that it doesn't wobble and then star test the collimation. I have reshaped the finder bracket and it seems to fit a lot better now. 

 

I'm still confused though on the cheshire. It wants me to move the primary mirror way out in order to achieve the "correct collimation". Is this because the secondary mirror is not exact? If that is the case, do I need to move the secondary mirror or does it not matter as long as I can see the entire primary in the secondary mirror, along with the three mirror clips?

 

Thanks for the help, 

 

John






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