Last updated: 16 May 2002

Collimating an ETX Mak

From: Tony Costanzo (

Finally got back ETX, and like many of the others, the scope was again out of collimation. I have a idea why this is happening as I will explain latter. The optics, drive and cleanliness tested out very good so I decided to collimate the unit myself, It is not difficult. ( Please note! this may Void your warranty) If you notice when you get you etx back that the secondary obstruction shadow is at 5:00, try this. (In daylight) Flip the mirror down and look strait through the back, you should see the secondary mirror offset at around seven o'clock. Remove the focus knob and 3 screws that hold the OTA to the plastic housing, carefully pull the ota out of the housing and place on a table face the ota with the focus the same way it came out of the housing (right side). There are six screws on the back all take an allen wrench to adjust. Three of those screws have a large flat head, these hold the mirror assembly in the ota, do not touch these. You will notice 3 other set screws with lock tight painted on them. Mark their current position with a pencil making sure to keep the orientation the same. With a allen wrench loosen the two set screws on the left, (you have to break the seal of the lock tight so it takes a little force) and just back off all pressure on these two screws, Its about an eight of a turn. Now look through the OTA you should notice that the secondary now seems centered or closer than it was, tip the scope back up and put a little pressure on these screws, check the ota again. Finally put the unit back into the housing and check the collimation on a Christmas ornament. Fine adjust those two screws until the collimation is perfect. (It should be nearly perfect by just backing off the pressure on two set screws.

I tested the unit against a 6 inch Quantum, and felt the the image was just as good, even better on some of the darker planetary detail. Please DO NOT attempt to do this unless you a sure your optics are good and you have had some experience collimating telescopes.

Why so many units out of collimation?? I've had three. Either their collimating device is not calibrated correctly, or the lock tight is causing the problem.

Have fun! and clear skies to all
Tony Costanzo,

From:	Jacques Michaud (

I collimated my ETX some weeks ago.Well it is not so easy! After reading
the collimating method by Tony Costanzo-hello Tony- I believe necessary
to give some further advices:

First,MAKE SURE that your mak is actually misaligned.Unfortunately, it
is not uncommon that the secondary baffle is uncorrectly centered (isn't
it Mike?). In such a situation,when looking backwards through the
meniscus lens, the scope is apparently out of collimation though it can
be perfect!The secondary baffle just need (!) to be moved back to th
exact center. So, before starting anything, make a "Christmas tree
ornament" test which will tell you all the truth about your need for

Second, though I read somewhere on Mike's site that the baffle could be
moved back by yourself, I STRONGLY RECOMMAND not to try to do so.Indeed
i tried.. and never succeeded because the glue between glass and
baffle,though being a kind of "goo" is elastic;after a while the baffle
comes back to its previous (and wrong) location.Trying too many times,
(unsuccessfully in my case) gives good chances to reach some disaster at
the end.Better follow the excellent Mike's advice: If the baffle has
moved,send your ETX back to MEADE. Remember also that a slight
misalignment of the secondary baffle ras not big consequences during
night observing, except in case of important light pollution. Third,the
SIX screws which Tony Costanzo refers to are indispensable for tilting
the primary mirror, NOT THREE ONLY.The three protruding ones allow to
push the mirror plate, the three others pull it. As one screw of each
pair is loosened its partner must always be tightened and vice-versa.

Fourth,the only reliable method I used, without recourse to special
sophisticated tools is as follows:

Perform a Christmas tree test

Remove the plastic housing,adjust the pair of screws in (or close to)
the direction of the distorsion of the diffraction pattern.(Look for 
Legault site "imagerie CCD  haute rsolution").One eight of a turn will
probably be enough.

Put back the OTA in its plastic housing and perform a new test.

Resume the process until the diffraction pattern is perfectly circular.

This may be a long and delicate trial-and-error process. But I don't
know any other really efficient one.Of course this requires much care
(clean and "safe" working area,marking precisely the positions of the
screws before moving them etc.).

No need to say that doing so will probably void you warranty.

Well;bon courage!

By the way ,Mike,though you are tired to read so many congratulations,
thanks for your wonderful web site!

Jacques Michaud  

Subj: 	ETX-125EC collimation
I'd like to let you and your readers know that with insight from the
Tips posting by Tony Costanzo on your site, and additional insights he
has shared I have successfully collimated my ETX-125 to where it
produces the find textbook airy disk - symetric ring pattern star images
that my 90 does. Recall that my scope initially came well out of
collimation, that I returned it to Meade and they sent it back a month
later - better but still not properly collimated as it should be. Meade
does seem to have a quality control problem with respect to ETX-125

I do want to warn your readers who have a 125 they believe is not
properly collimated and want to tackle the task themselves that it is
not as simple as implied by the initial posing in the Tips area. It took
me multiple times of disassembling, adjusting, reassembling and testing
in order to get it right. And I had to adjust all three set screws and
two of the three flathead screws on the back of the OTA to get it right.
Each pair of screws (Flathead & set) appear to work in a pull/push
relationship and pivot the primary mirror. But each set seems to work in
concert with the others and adjusting just one set won't affect
adjustment. Let's just say the task should only be attempted by someone
familiar with collimation techniques, be a patient person, and have
access to a tempurature stable location in which to conduct consistent
(Christmas tree ornament type or equivalent) collimation tests over
extended time (i.e. perhaps hours). And there is also the potential
warranty impact of doing such an unsupported procedure. But I am very
pleased with my results.

Subject:	"Bullseye"collimation for ETX
Sent:	Saturday, August 4, 2001 20:32:08
From: (Douglas G Canard)
I collimated my Etx using a "100 yard rifle precision sight-in" target
by Outers puchased at Wal-mart for about 3 dollars.

I first removed my scope from the mount. Remove the flip mirror housing
and focus knob. Hang up the target on a wall, be sure you have adaquate
lighting on the target. I strapped the OTA to my tripod wedge {while
down and in the terrestrial mode} and aimed it at one of the smaller
bulleye patterns near the corner of the target. While looking through
the rear of the OTA i could see the bullseye pattern and then centered
the bullseye in my field of view. I then took a collimation tool
{plastic piece with a hole poked in the center that came with my
reflector} and held it up to the back of the OTA MAKING SURE IT WAS
CENTERED. This is to line up your eye properly while looking at the
bullseye. The outer scoring ring of the bullseye should barely touch the
edge of your field of view with a small gap between them. If not then
move OTA and tripod either towards or away from the target.Look at the
silhouette of your secondary mirror, is it covering the small red
bullseye and perfectly centered inside the innermost {8 points} black
scoring ring? If not mark the primary adjustment screws with a pencil.
Before you do anything make sure your baffles arent off-center as this
seems to be a common problem. My secondary was slightly off in the 7
o-clock position. I loosened the bottom adjustment screw  on the
lefthand side of the OTA a little less than an 1/8 of a turn in a
counterclockwise direction which put my secondary dead center. A well
calibrated eyeball is a plus for this procedure. This will definitely
put you in the ballpark, it did for me. I reassembled scope and did a
star test on Vega while it was directly overhead. Good diffraction rings
and airy disc while looking through a 10 mm ep. However I had to move
the star towards the top of the field of view about a quarter of the way
for perfection which actually turned out to be caused by my flip mirror
being slightly out of whack. My secondary baffle is ever so slightly out
of center on my secondary mirror yet didn't seem to effect evaluation
too much.

I was able to do this in under 30 minutes but results may vary depending
on your scope and experience with collimating. This procedure worked
quite well on my reflectors also.

Doug Canard-Coal Hill,AR.

Subject:	Re: ETX collmination
Sent:	Monday, August 6, 2001 18:00:23
From: (Clay Sherrod)
They may not, indeed, be out of collimation. All Maksutovs can exhibit
what I call "lateral axial astigmatism" which results in star images
appearing slightly askew from center when out of focus, when indeed they
are precisely collimated exactly at the point of focus.  Questar and
Meade Maks both will show this often.

When Maksutovs are collimated, particularly with computerized optical
benches, they are typically done so exactly at the precise focal plane;
the nature of the primary shifting as it achieves focus or either way
inside or out, will result many times in the fact that ONLY at the exact
focal plane is the scope in precise collimation!

Thus, you may have extremely good collimation and yet your out of focus
star image suggests that it is not.  To test, merely aim the scope at a
2nd magnitude (not brighter) star nearly directly overhead and not test with it even slightly to one side of dead center.

Look at the image in as good a focus as you can provide, and do only
when the seeing is near perfectly steady.  Increase the magnification
until you reach the limit (judge by an out of focus image and see if you
detect motion of the large "donut"...if so then you are so high in
magnification that you are resolving air currents, not images).  If very
good, and at high power, examine the star closely in sharp focus.  The
central "disk" or Airy Disk should be uniformly round throughout its
perimeter, with no extrusions nor bulges.  Around that image you should
see TWO (perhaps more) Airy Rings.....examine to make sure that they are
precisely symmetrical in relation to the bright Airy Disk.  If the rings
do NOT touch nor decrease their spacing throughout the entire 360
degrees then your optics are very well collimated, no matter what the
out of focus star image tells you.

This question/concern comes up quite often, both to me and to the folks
at Questar.  But likely that is what it truly is.....there are
exceptions, of course, but do the in-focus test and let me know how you

Good luck and bright skies!

P. Clay Sherrod
    -----Original Message-----
    I read a warning on Electric Focuser installations you have on the
    Mighty Weasner Web page. I purchased a used ETX90EC this past winter
    and I now realize it is out of collmination. The star images out of
    focus are definitly skewed in one direction. Can you tell me what
    are my options or direct me further?

Subject:	Re: Collimating an Etx105 (or any Cass-Mak (read from the bottom up)
Sent:	Thursday, March 7, 2002 13:16:10
From: (Clay Sherrod)
Samuel -
You will see that ONE screw of each pair actually does the adjusting;
the other one "locks" the alignment in place ONCE ALL THREE ARE DONE.

The ones that lock can be backed of gently and you will feel them all
suddenly come free and turn freely with no resistance....the ones that
collimate will not...they are spring loaded so to speak.

The locking screws are in the same location relative in every pair, so
go an loosen each of these three screws (one from each pair that has no
resistance once loose....).  You have unlocked your mirror for
collimation at that point.

Now go back and start the collimating process with ONE SCREW AT A TIME
using the OTHER three screws.  Do one and then put the assembly back to
where you can test it....if that is the wrong one or the wrong
direction, do another.

Once collimation is achieved, merely go back and GENTLY tighten the
original THREE locking screws one at a time finger tight.....go back and
tighten in succession just a tiny bit at a time until all are tight
enough to firm up against the mirror and hold it tightly!  That will do

Best of luck!

Clay Sherrod

  ----- Original Message ----- 
  From: sam 
  Dear Clay,

  Do not misunderstand me. When I had my ETX90, never did I opened the
  optical set (I am a cowerd cow when it comes to costly staff). I
  modified the mechanical part, but I never once did I screwed off the
  corrector lens.

  Imagine you live in the open wilderness, far away from a source of
  water. How would you manage when problems arise (and they will surely

  Thanks again for your time.

  Ok, I am trying to join in as much information (and reilable
  information, not just "information" to attempt this when the day
  comes) as possible.

  For example, I have learned from you that one screw from the pair is
  to adjust the thing, and the other one is up to hold "something" in
  place. That means that JUST one screw is to be modified? Please,
  expand this information, I just let you know the information I have in
  hand now.

  Do I have to touch ONLY the screw in the pair set that is not sealed,
  or BOTH of them? (I read that, as they go in pairs, you have to touch

  I am really very interested in knowing this, becouse the difference
  between a collimated and des-collimated optical set in just the BIG
  difference in astronomy (providing the opticals are good, of course).

  Thanks, doc.
  Yours faithfully,


    ----- Original Message ----- 
    From: Clay Sherrod 
    To: sam 
    Sent: Thursday, March 07, 2002 7:50 PM
    Subject: Re: Collimating an Etx105

    Hello Samuel -
    By all means if you think you have the concept down (sounds like you
    do....) go ahead and attempt the collimation.  You are correct on
    the pairs of is to adjust and the other is to hold
    firm.  Just go slowly.  Not sure what you mean by "modify" the
    screws, but you should not do this...they work great as they are. 
    Just get in there and tweak....then reassemble, then tweak again. 
    Until you get it all correct!

    It is a very tedious and long process, but if you take your time you
    will definitely be able to do it!

    Best of luck!!  (by the way, there really is NO cheap optical bench
    components......using a point of light and the eye is still my
    preferred method anyway!)

      ----- Original Message ----- 
      From: sam 

      Dear Clay,

      Thanks for your prompt news.

      I am concerned about it. I know that there is no way to do this in
      real time star-test. I have to disassemble the OTA rear part,
      modify the screws, assemble it back again, and do a star test.

      But according to your experience with ETXs... How should I modify
      these screws? I know they go in pairs, and the best thing to do I
      have read about, is to push a screw and pull the other in the set,
      and then to push both.

      You have to understand that I prefer to do the collimation myself
      rather than getting it back to the USA (I live in Spain) each time
      the thing goes uncollimated. The costs would raise up to $200!! I
      bought my 105 from USA (a friend went there and bought it for me.)

      My old ETX90 EC went fine until itself got uncollimated (I don't
      know how, becouse it never got bumped and I didn't use it much).
      So it is not TRUE that a Mak is always collimated.

      Nevertheless, I couldn't renounce to the excellent optical quality
      Maks deliver compared with the classical cassegrain option (the
      overall resolution is much better on the Mak).

      Thanks for your invested time with me,

      Samuel de Roa

      PD: by the way, Do you know of a cheap laser optical bench?

        ----- Original Message ----- 
        From: Clay Sherrod 
        To: samuel 
        Sent: Tuesday, March 05, 2002 4:24 AM
        Subject: Re: Collimating an Etx105

        Samuel -
        I strongly recommend never attempting to collimate a Maksutov
        without a complete laser optical bench.  They are not simple at
        all to collimate and attempts will just lead to trouble. 
        Frankly, unless the scope is bumped or damaged, there is no
        reason to ever have to is an optically locked

        I urge you to not be tempted to improve collimation....for one
        thing you cannot check collimation on a Maksutov via an out of
        focus star like you can with other scope types.  They are
        collimated precisely at the focal plane....not on either side of
        it, and verifying via an unfocused star is NOT reliable in a

        Dr. P. Clay Sherrod
        Arkansas Sky Observatory

          ----- Original Message ----- 
          From: samuel 
              Dear sherrod,

              I am waiting for an ETX105, and I previously owned an

              I am VERY concerned about the collimation, becouse my
              ETX90 went from PERFECT collimation to BAD collimation
              WITH TIME.

              Please, could you tell me a safe and not much complicated
              method to achieve collimation in an ETX105 telescope?

              Yours and clear skies my friend,


Subject:	Re: ETX-90 RA Collimation
Sent:	Thursday, March 14, 2002 7:10:21
From: (Clay Sherrod) can easily tell which is which.  However, Meade will only
charge you $75 for a complete optical overhaul...collimation on a MAK is
NOT something you do yourself without an optical bench.

For one thing, an out-of-focus star image in any MAK will NOT have the
pretty concentric ring pattern you are looking for.  They are collimated
precisely AT focus, not beyond it because the primary it the only
collimating tool there is and it must be at the focal plane to set. 
Thus, out of focus star images are the WORST way to judge if your scope
is out of collimation, unlike the SCT or Newtonian scopes.

Anyway, the one that sticks out is the LOCKING screw....the other one of
each pair is the adjusting screw.  Back off all three locking screws
first, then adjust the others until final collimation is achieved (you
are going to be surprise at how difficult this is the with ETX) and then
you gently tweak the three locking screws firmly against the back of the
mirror (NOT tight); you then gradually increase the torque on each once
in succession, checking the alignment each time to assure you have not
pushed the mirror BACK out (which you will from time to time); never
tighten one all the way....they must be firmed up in succession!

Good are most definitely going to need it!!

Dr. P. Clay Sherrod
Arkansas Sky Observatory

  ----- Original Message ----- 
  Subject: ETX-90 RA Collimation

  Clay, I found you through Mike Weasner's site. I hope you don't mind
  the direct e-mail contact.

  I have questions about collimating a Mak....the ETX in particular. I
  have collimated both a newtonian and a sct in the past, so I'm familar
  with the procedures for those types. In my ETX, the in focus picture
  shows the rings to be brighter at the 4-5 o'clock position. I tried to
  adjust the position of the secondary following the fix on Doc's page,
  however, that didn't fix anything. Also, if I use the 45 degree prism
  I have, I get a similar result. So my scope needs collimation.

  The six screws on the back of the mirror cell are all the same. All
  have locktite painted on them. The only difference between them is one
  screw of each pair is screwed all the way down to the cell, the other
  has about 3/16 or 1/4 inch between the bottom of the screw head and
  the mirror cell. Which screw is the one I use to adjust and which is
  the one that holds the mirror in position once I have it adjusted? Or
  can you tell?

  Also, with the airy disk picture described, airy disk slightly offset
  at the 4-5 o'clock position, which screw(s) should I start on? The set
  nearest to the offset?

  Again, I hope you don't mind the contact, and I'll try not to bother
  you in the future, too much. Thanks in advance....

Subject:	Collimating an ETX 90, in-depth.
Sent:	Thursday, May 16, 2002 5:13:00
From: (martyn)
Quite some time ago I reported to you on an uneven illuminated
startest I observed with my ETX 90.
Below, for the benefit of all I will describe what I found and how I
dealt with it.
I have also included a small jpeg image which depicts my actual
startest that worried me...I hope you can include it.

star test
I got my etx last July(2001) and soon I noticed a couple of things from the beginning: these issues were noticable from 48x to 195X. 1)Bright Mars showed some "spurious" light outside the limb at the 8 o'clock position of the image. I attributed this to the seeing that evening which wasn't all that good. 2)Bright Jupiter also showed some "spurious" light outside the 8 o'clock position of the limb. I attributed this to the seeing also at first, but during excellent seeing this was visible also. Apart from the SEB, NEB and some polar darkening the etx did not show Jupiter any better than a 60mm f11.7 refractor I once owned. Also, the oblong shape of Jupiter (elongated at the equator) never showed to clearly...except once when viewing Jupiter in early morning daylight when the disc's orientation with respect to the optical system was different. 3)The lunar limb of a full moon would look A BIT mushy all around the 8 o'clock position of the limb. 4)While viewing sunspots (filtered ofcourse), I had the distinct impression that I had to shift my head sideways to "get the image right in my eye". This also counts for viewing the lunar surface, but to a lesser degree. 5)Saturn did not show any "spurious" light, once -during excellent seeing- I actually had an great view of the ringsystem and cassini division(as a gap) at 328X. BUT....the planet's disc had the wrong shape: a bit elongated in vertical direction - southpole to northpole (astigmatism). Under normal seeing conditions the cassini division would consistently show poorer on the western side of the planet than on the eastern side. 6)Bright stars consistently showed "spurious" light on the 8 o'clock position at any magnification. At higher magnifications -195X and 266X- my startest showed a very unevenly illuminated diffractionpattern, as shown in the accompanying image. Clearly light was directed away from the optical axis towards the 8 o'clock position in the eyepiece. Untill a while ago I sort of learned to live with it and "see through" it. When I compared my etx star-image with the star-image of a properly aligned 100mm f10 refractor I felt enough is enough. I was going to align my etx myself. Here's how I collimated my ETX. The only optical component that is adjustable by the user is the primary mirror, i.e. the main (9.6cm)mirror that collects the light. (The mirror that you can see in the back of the telescope, when looking into the tube from the front). These instructions deal with adjusting THAT mirror. I did have help from H.R. Suiter in the form of his book: "Startesting Astronomical Telescopes". This book provides rocksolid support for any collimation endeavor. First of all: removal and refitting instructions, then the mechanics of adjusting the mirror followed by collimation and determining the tilt adjustment-direction. Collimating an etx is not difficult. You can really do it yourself, It's just "a bit" tedious. You can not collimate under the stars, as the optical tube needs to be removed from the mounting for adjusting the primairy mirror and refitted for testing. This will most likely have to be done several times (tedious, remember?), so I will first explain these two steps. Removing: This is done by first loosening the setscrew on the focusknob and then slide the focusknob off the focusrod. Next, use a #2 allen wrench(not included with the set of wrenches supplied with the scope) to completely loosen the three recessed allen bolts on the back of the ETX. The optical tube cannot fall out as it is held snugly by the mount, still, while removing the tube keep it pointed slightly up or horizontal(to prevent any surprises). To remove the tube, grab it with BOTH hands and slide it out straight, gently without wild jerking movements. Lay the tube on a soft surface. I use a slab of foam with two pieces of foam on top of it in between which the etx tube can be securely laid down. When the tube is thus out of the mount during adjusting of the mirror, you may or may not want to cover the hole in the backplate with some tape. This may depend on how long the tube is outside the mount or how dusty your working area is. For prolonged periods out of the mount I used to cover the hole with some tape. Leave a piece unattached to the backplate to be able to easily remove the tape when refitting the tube. Do not stick anything into the opening to cover it!!! Also, during handling of the tube, keep the lid on! Perhaps, for this purpose use a plastic cover that fits/slides over the tube front. This will be easier to remove and refit, remember you will most likely have to do this several times. When the mount was "uninhabited" for prolonged periods I would cover it with a plastic bag, to prevent the mirrorbox from getting full of dust. Refitting: Obviously, this is done in opposite order from removing. When refitting, you will have to make sure that the focus rod goes into it's designated hole. For the purpose of proper tube-orientation you may want to identify the top of the tube by sticking a white sticker onto the top of the corrector-lens cell. Also, remove any cover you placed over the hole in the backplate of the tube. When you slide the tube in, be carefull, don't force it. Gently let the focusrod go through it's hole and move the tube gently(always gently) into the mount until it stops. Refit the allenbolts so that the focusrod is not positioned against the edge of it's hole, but is centred in the that you may have smooth focusing. Centering the focusrod in it's hole can also be done while the allen bolts are screwed in but not tight, just by rotating the tube a tiny amount in the correct direction. Then tighten the three allen bolts (do not use excessive force). Re-attach the focusknob. Mirror adjusting mechanics: Collimating the primary mirror of the etx is done by changing the tilt of the primary mirror. The primary mirror is attached to a plate which in turn is attached to the telescopetube-flange in the back of the tube by means of screws. When you look at the back of the removed etx-tube, you will see three sets of two screws on the telescope flange. These srews hold/fix the mirror assembly plate that you can see in the centre of the back of the etx-tube, it is the plate with the small opening in it. Each set of two screws consist of a push-, and a pull-screw. The pull-screws actually screw INTO the mirror-assembly plate and thus hold the mirror-assembly. The push screws do not screw into the mirror-assembly plate but push against it. The push-screws set/define the tilt of the primary mirror. You should base any tilt adjustments on the push-screws and tighten the mirror-assembly plate against them by tightening the pull-screws. This makes for more predictable adjustments. If you need to "push" the mirror at one screwpair-position when the pull-scew is tight, just loosen that pull-screw a bit so that you will be able to screw IN the push screw a bit and then tighten the pull-screw again. Clockwise turning a pushscrew (screwing it in), will tilt the mirror forward in that location. Counterclockwise turning a push-screw enables you to tighten it's partner pull-screw so as to tilt the mirror backwards in that location. When one screw of a push-pull pair is adjusted, it's partner must always be counter-adjusted. Adjusting one pair in one direction, is equivilent to adjusting the opposite two pairs of push-pull screws in the opposite direction. In other words, "pulling" on one side of the primary mirror is equivilent to "pushing" on the opposite side of the primary mirror. Collimation will possibly last longest with a properly collimated mirror assembly as close as possible to the telescope-flange. Never overtighten the push-pull screws. Fingertight, than just a tiny bit more. NEVER EVER completly undo the pull-screws!!!! If one would have come out completely by accident, you will be able to get it back in I'm sure, as the position of the mirrorassembly plate will still be held by the two remaining pull-screws. But if you had removed two pull-screws, chances are that the mirror-assembly plate will shift, and the holes for the pull-screw are no longer lined heed the above advise. If a push-screw would come undone completely, no problem. Just find the thingy and screw in again. There are no side effects. And remember, define the tilt of the primary with the push-screws, and lock in place with the pull-screws. Now you know this, you will still need to determine the tilting axis and angle. Actually that's easy...really! Testing and Collimating: Under the stars, aim the etx at a brightish (magnitude 2 or 3) star. Use a higher power eyepiece. Focus the star, and then turn the focusknob counterclockwise until you see a nice fat defocused annulus. You are now viewing the star outside of focus, i.e. the scope is "focused on an object" closer than infinity, (where miscollimation is seen better than inside focus). If your etx is miscollimated the annulus will not be round, but will be bulged on one side. Determining tilt-direction: Now, put your finger in front of the lens against the lenscell...but not onto the lens. You will see a diffraction image of your finger intruding in the defocused star-annulus. Put your finger in a position where it intrudes in the middle of the bulge of the defocused star-annulus. Transfer this point back to the rear of the telescope and thus the primary mirror. That is the point where the primary mirror must be PULLED. The farther the eyepiece is outside of focus, the easier the finger diffraction image shows up. If there is no push/pull pair of screws in that point or at the opposite side of the primary mirror, you can adjust(pull) the nearest push/pull pair of screws. Adjust small amounts, 1/8 of a full turn for instance, or maybe even less if your miscollimation is not severe. Remember, small adjustments have big effects!!! If you have adjusted too far, simply adjust back again. If you are lucky, there is a push/pull pair of screws exactly at the position where you had to "pull" the mirror - or at the opposite side where you then would "push" the mirror. If you are not this lucky, you may have to adjust a nearest pair of push/pull screws every time and thus eventually nudge the mirror in the correct tilt. I say every time, because after every adjustment made, you will need to test collimation and determine in which direction to tilt the mirror - if at all. This involves removal and refitting of the OTA every single time. If this nudging does not appeal to you, you may try to get the mirror in such a tilt that the collimation error coincides exactly with the position of a push/pull pair of screws. Then you only need to adjust in one direction. Once your collimation gets close, it will become a bit more difficult to establish in which direction the mirror should be adjusted. Studying the diffraction pattern takes more care when you get this close. Eventually, you will hit the bullseye so to speak, and your ETX is properly collimated. It may take a bit of time but I feel it was worth the effort. Your images will show that you did a VERY good thing. Collimation preparations, misfortunes, luck and learning: The collimation of my etx was severely off. You can check for serious miscollimation simply inside, by looking -with one eye, positioned at the OTA axis- into the front of the OTA from about 5 feet distance. You should be able to see the secondary mirror concentric inside its own reflection in the primary mirror. The secondary and its reflection should also be concentric with the edge of the primary mirror. If you can not get these three "rings" perfectly concentric, you etx WILL need to be collimated. If your etx is not collimated, this means that also the primary-baffle is tilted. As the front of this baffle is far in front of the tilting point it will present you with a ominous reflection of itself in the primary mirror. When I started collimating my etx, I knew from the startest what the tilt-axis would be. Light was thrown away from the optical axis towards the 8 o'clock position. I thought I was able to deduce the correct adjustment direction and started by making an adjustment, resulting in a worse primary-tilt. Then I applied the same "knowledge" to correct my misadjustment. By the way, I thought I had to combine 2 tilts to move the mirror in a certain direction, as that direction did not coincide with the position of a push/pull pair of screws. Anyway, it became a mess. I decided to start anew from scratch. I "pulled" the mirror assembly right against the back of the telescopeflange and see what kind of image that would give...practically no image. There was no intelligeble focus at all - startest was almost unreadable. Then I "pushed"(all three push/pull screws adjusted) the mirror just an extremely tiny bit forward so that it was away from the telescope flange so that I would be able to adjust the mirror in any direction I wanted. Next, looked into the scope from the front and determined whether the secondary mirror, it's reflection in the primary mirror and the edge of the primary mirror where concentric. Not surprisingly, they were not. I was now going to get a crude alignment by centering these three rings. I first "pushed" and "pulled" the mirror in several directions, just to see what the effects would be of what I was doing. With what I learned this way, I made adjustments and still made mistakes. Deducing any adjustment directions based on the reflections in all those curved mirrors can be quite confusing. You also have to place your eye EXACTLY at the OTA axis. The reflection of the long baffle may seem handy for crude aligning by simply making the reflection as small as possible, but depending on how accurate you work this may also be a very frustrating me. Using this shadow easily results in over-adjusting. Eventually I had the reflection of the secondary mirror and the edge of the primary mirror quite concentric with the edge of the secondary mirror. It was not 100% perfect, but it looked better than it had in the months past. These adjustments were made with the telescope out of the mount for a "prolonged" time, and this is where I covered the back of the OTA and had the mount in a plastic bag. (((By the way, doing something like this removes any notion of mistical optics that Meade may have given us through their advertising, to prevent us from daring to tinker with this optical gem born of higher magical spheres....if you know what I mean. The ETX is a man-made piece of hardware that CAN be adjusted, no lightning will strike you if you do....))) At this point I aimed the etx at Jupiter, it showed a much cleaner disc. Defocusing slightly showed that the defocused disc was not quite "concentric" with the actual disc of Jupiter. Startesting revealed a diffraction pattern visible on ALL sides of the airydisc, but not perfectly evenly lit. Turning the focusknob counterclockwise away from focus revealed the unfocused star-annulus to be somewhat/slightly bulging on one side still. It was from this point on that I started making the adjustments as I described above under "Testing and Collimation" and "Determining the tilt adjustment-direction". Now I am able to believe Meade's advertising for this little gem. I am even happier with the scope now then ever before. An added bonus is that viewing just past bright streetlights no longer produces so much contrast-reducing glare. I would be happy to answer any questions anyone may have with regards to this issue. regards, martyn

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