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Intes Micro MN66 mak newt collimation help!

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#1 Tyson M

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Posted 08 December 2018 - 12:41 AM

Good day!

 

I need some assistance.  I have collimated a newt before many times but this mak newt is a bit more challenging. I have tried for two nights, with a collimation cap, and a hotech laser collimator, but I simply cannot get perfect round stars out of focus on either side of the periphery. 

 

On axis, the perfectly concentric Fresnel rings appear, then the out of focus diffraction rings morph to look like a bite is taking out of the bottom right side, as it drifts up and to the northwest in my field of view (looking at Aldeberan in Taurus)

 

The star focusing down to a sharp point more or less with a 10mm eyepiece (I know, not high enough), but I know something is wrong and I cannot fix it with the two tools I have.

 

I presumethe shipping of the scope possibly knocked the entire secondary mirror so it is not centered square with the focuser, and I might have to adjust the middle secondary screw but I dont want to damage the secondary mirror or primary mirror by playing with the center one.

 

I am wearing out these old secondary screws and figured I should stop while I am ahead.  I broke one of 3 of the secondary collimation screws already.

 

Any suggestions? Thanks in advance! 

 

I have attached a picture of the broken secondary screw, and the center screw I am thinking about playing with now. 

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#2 agmoonsolns

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Posted 08 December 2018 - 01:33 AM

Possibly make sure the focuser is square with the tube assembly and light path?


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#3 PETER DREW

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Posted 08 December 2018 - 04:28 AM

I had a similar problem, whilst using the adjusters the secondary turned slightly so it wasn't facing the focuser squarely. I finally had to remove the complete corrector cell to reposition it.

#4 Cotts

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Posted 08 December 2018 - 10:01 AM

Nice scope, Tyson.  Wherever did you find it?

 

It sounds as if the secondary is off a bit in rotation...That's the centre screw but be extremely delicate when turning it...  

 

You'll need a proper sight tube (a collimation cap isn't accurate enough).   It's a few inches long, has a teeny hole at one end and cross hairs at the other.....  Check for perfectly circular secondary mirror image through the sight tube.... and centered in the image of the primary mirror...

 

 Or the focuser may have gone off level....The difficulty here is that you can't see where the laser hits the secondary without removing the primary mirror assembly and looking up the tube... (downside of a solid tube....)

 

If it does come to a dis-assembly of the corrector/secondary you can probably go ahead and replace those evil 'slot' screws with metric screws with socket/hex heads which don't strip...   

 

When i received the scope from russia the secondary was loose and flopping...  I had to take the corrector/secondary off completely (mark the rotation orientation with tape) in order to tighten everything up..   Be sure to  watch for tiny little shims which need to go back where they came from precisely.. I would photograph each step to be sure.  It's a persnickety job but, I found, once everything is snugged up and collimated it stays collimated pretty much permanently..

 

Dave  



#5 PETER DREW

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Posted 08 December 2018 - 10:15 AM

You should be able to remove the whole cell unit without disturbing or removing the optics separately. Just mark the cell orientation. y
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#6 Jeff B

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Posted 08 December 2018 - 11:10 AM

Mike, I assume your MN has the ability to slide the focuser forward and back along the tube axis.  Also, the secondary offset is small but already there and you should be able to see it, so don't fuss over that.  Now you will have to flood the interior under the focuser with a lot of light as that baffling under the focuser is very effective at its job.  This will help aligning the focuser and secondary.

 

First, and I mean FIRST, loosen up the secondary assembly using, I believe that center screw enough to pull the secondary holder flush up against the back of the meniscus.  Then tighten it enough to hold it in place.  This effectively squares up the secondary holder and secondary relative to axis of the meniscus.

 

Second, slide the focuser forward, or back to center the secondary axially under the focuser as best you can., then rotate the secondary holder assembly to center it rotationally with the image of the primary as best you can.  Tighten up the nut to hold it firmly in place but allow for some rotatonal adjustment later.

 

Now, align the focuser with the secondary as best you can using the sight tube and any push/pull adjustment screws, shims or what ever as well as tweaking the focuser's axial position if needed.

 

Re-check the secondary rotational alignment and adjust if necessary.

 

Once you are satisfied that the focuser is well aligned with the secondary and the secondary is properly positioned under the focuser, tighten up the secondary against the meniscus as best you can with that external nut.  If the secondary holder system was firm but adjustable when you made the adjustments above, your alignments should stay put. 

 

You can now proceed to use your laser, just like in a newtonian:

 

Adjust the secondary tilt using the little screws until the laser hits the center dot in the primary.

 

Then adjust the primary so that the return beam enters the laser aperture, and, of course, it's best to barlow the laser when doing that.

 

And you should be done.

 

I've found the key is the very first step of pulling the secondary holder flush with the meniscus, otherwise I can chase my tail around.

 

Jeff


Edited by Jeff B, 08 December 2018 - 11:18 AM.

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#7 Jeff B

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Posted 08 December 2018 - 11:14 AM

BTW, you can replace those three screws.  I went to Ace Hardware an got allen head metric replacements.  Of course, do them one at a time.

 

Jeff


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#8 Tyson M

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Posted 08 December 2018 - 12:00 PM

Thank you all for posting!

 

BTW, you can replace those three screws.  I went to Ace Hardware an got allen head metric replacements.  Of course, do them one at a time.

 

Jeff

I live in Canada, we do not have an Ace Hardware, but we have a Lowes which I think might work. Do you know the pitch of the threads or the length off hand? If not I will just take out the broken screw and go down.  If they have no inventory I will look at internationally ordering from ACE.

 

 

Mike, I assume your MN has the ability to slide the focuser forward and back along the tube axis.  Also, the secondary offset is small but already there and you should be able to see it, so don't fuss over that.  Now you will have to flood the interior under the focuser with a lot of light as that baffling under the focuser is very effective at its job.  This will help aligning the focuser and secondary.

 

First, and I mean FIRST, loosen up the secondary assembly using, I believe that center screw enough to pull the secondary holder flush up against the back of the meniscus.  Then tighten it enough to hold it in place.  This effectively squares up the secondary holder and secondary relative to axis of the meniscus.

 

Second, slide the focuser forward, or back to center the secondary axially under the focuser as best you can., then rotate the secondary holder assembly to center it rotationally with the image of the primary as best you can.  Tighten up the nut to hold it firmly in place but allow for some rotatonal adjustment later.

 

Now, align the focuser with the secondary as best you can using the sight tube and any push/pull adjustment screws, shims or what ever as well as tweaking the focuser's axial position if needed.

 

Re-check the secondary rotational alignment and adjust if necessary.

 

Once you are satisfied that the focuser is well aligned with the secondary and the secondary is properly positioned under the focuser, tighten up the secondary against the meniscus as best you can with that external nut.  If the secondary holder system was firm but adjustable when you made the adjustments above, your alignments should stay put. 

 

You can now proceed to use your laser, just like in a newtonian:

 

Adjust the secondary tilt using the little screws until the laser hits the center dot in the primary.

 

Then adjust the primary so that the return beam enters the laser aperture, and, of course, it's best to barlow the laser when doing that.

 

And you should be done.

 

I've found the key is the very first step of pulling the secondary holder flush with the meniscus, otherwise I can chase my tail around.

 

Jeff

The focuser is an adjustable base feathertouch focuser, and the whole unit was collimated perfectly by Markarian Fine Optics prior to shipping. I saw the green masking tape with marking they used to keep the correct orientation of the corrector with the primary. 

 

After reading your detailed post (which I very much appreciate), I think the only issue is the secondary being square with the focuser, that crucial first step.  



#9 Tyson M

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Posted 08 December 2018 - 12:02 PM

You should be able to remove the whole cell unit without disturbing or removing the optics separately. Just mark the cell orientation. y

I will certainly mark the orientation if I have to take off the corrector.  After Jeff's post, I may not have to, which would be nice. 



#10 Tyson M

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Posted 08 December 2018 - 12:06 PM

Nice scope, Tyson.  Wherever did you find it?

 

It sounds as if the secondary is off a bit in rotation...That's the centre screw but be extremely delicate when turning it...  

 

You'll need a proper sight tube (a collimation cap isn't accurate enough).   It's a few inches long, has a teeny hole at one end and cross hairs at the other.....  Check for perfectly circular secondary mirror image through the sight tube.... and centered in the image of the primary mirror...

 

 Or the focuser may have gone off level....The difficulty here is that you can't see where the laser hits the secondary without removing the primary mirror assembly and looking up the tube... (downside of a solid tube....)

 

If it does come to a dis-assembly of the corrector/secondary you can probably go ahead and replace those evil 'slot' screws with metric screws with socket/hex heads which don't strip...   

 

When i received the scope from russia the secondary was loose and flopping...  I had to take the corrector/secondary off completely (mark the rotation orientation with tape) in order to tighten everything up..   Be sure to  watch for tiny little shims which need to go back where they came from precisely.. I would photograph each step to be sure.  It's a persnickety job but, I found, once everything is snugged up and collimated it stays collimated pretty much permanently..

 

Dave  

Hello Dave,

 

It is a very nice scope, I was lucky to find it preowned at Markarian Fine Optics.  It has a feathertouch focuser.  I use it on a heavy duty alt az mount but it really need a dob mount for it.  The OTA has some interesting fading marks, so it will need a paint job some day but the corrector and primary are perfect condition.

 

This is my 6" apo that I can afford lol, and I love it because it has a unique feel.

 

I just need to replace the secondary screws, make a dew shield, and some day give it a paint job.



#11 Jeff B

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Posted 08 December 2018 - 12:16 PM

Sorry Mike, no I don't the screw information.  Your plan sounds like a good one.  I do wish that big external "nut" was a bit shorter so that I can grab hold of that big center "bolt" and keep the secondary assembly from rotating while tightening that big nut up.  A bit annoying but, for my samples, once I got everything firmed up, it all tended to stay in place.

 

Very nice scopes.  I've at least six or seven of them from 5" to 8"  and not an optical lemon in the bunch.

 

Jeff



#12 hoof

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Posted 08 December 2018 - 12:17 PM

Yeah the secondary rotation is likely the orientation.  My MN66 has had that issue for a while, I could never figure out how to rotate it when it was fully loose after loosening the three hex wrench screws.  I'd get the rotation right (via the middle screw), then it'd misalign again when tightening everything up.

 

I recently found a solution (though I have yet to check it under the stars, the downside of my new night vision device distracting me with pretty nebula!).  If you loosen two of the screws, the central screw can turn easily, but the whole configuration remains tight enough to not shift when retightening things down.  With that, I was finally able to get everything aligned up with my collimation tools.

 

All that said, I've had fantastic views with my MN66 even with the rotation misalignment of the secondary.  High power views, up past 250x are sharp (when the seeing allows for it).  My MN66 has become my primary visual scope ever since I wrapped it with reflectix and no longer have to wait for cool-down.  Optical quality of this optic is astounding, even with a mis-rotated secondary!  

 

Good to hear the screws are easily replaceable as I've almost stripped mine in various attempts to align it! :)


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#13 Tyson M

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Posted 08 December 2018 - 12:24 PM

Yeah the secondary rotation is likely the orientation.  My MN66 has had that issue for a while, I could never figure out how to rotate it when it was fully loose after loosening the three hex wrench screws.  I'd get the rotation right (via the middle screw), then it'd misalign again when tightening everything up.

 

I recently found a solution (though I have yet to check it under the stars, the downside of my new night vision device distracting me with pretty nebula!).  If you loosen two of the screws, the central screw can turn easily, but the whole configuration remains tight enough to not shift when retightening things down.  With that, I was finally able to get everything aligned up with my collimation tools.

 

All that said, I've had fantastic views with my MN66 even with the rotation misalignment of the secondary.  High power views, up past 250x are sharp (when the seeing allows for it).  My MN66 has become my primary visual scope ever since I wrapped it with reflectix and no longer have to wait for cool-down.  Optical quality of this optic is astounding, even with a mis-rotated secondary!  

 

Good to hear the screws are easily replaceable as I've almost stripped mine in various attempts to align it! smile.gif

Yes, you're absolutely right.  Even with my misalignment, sweeping up M45 and Hyades (barely fit in the FOV, probably lost a star member or two) with a 40mm Pentax XL and 27mm panoptic were amazing.

 

I could get it so I could use a 6Delos one night! At the center, it focuses to a tight point. This scope is worth the tinkering.

 

I just ordered an Astrosystems Chestire and Sight tube from Don here, as he had a very good price on the two. 



#14 TG

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Posted 08 December 2018 - 02:09 PM

Good day!

I need some assistance. I have collimated a newt before many times but this mak newt is a bit more challenging. I have tried for two nights, with a collimation cap, and a hotech laser collimator, but I simply cannot get perfect round stars out of focus on either side of the periphery.

On axis, the perfectly concentric Fresnel rings appear, then the out of focus diffraction rings morph to look like a bite is taking out of the bottom right side, as it drifts up and to the northwest in my field of view (looking at Aldeberan in Taurus)

The star focusing down to a sharp point more or less with a 10mm eyepiece (I know, not high enough), but I know something is wrong and I cannot fix it with the two tools I have.

I presumethe shipping of the scope possibly knocked the entire secondary mirror so it is not centered square with the focuser, and I might have to adjust the middle secondary screw but I dont want to damage the secondary mirror or primary mirror by playing with the center one.

I am wearing out these old secondary screws and figured I should stop while I am ahead. I broke one of 3 of the secondary collimation screws already.

Any suggestions? Thanks in advance!

I have attached a picture of the broken secondary screw, and the center screw I am thinking about playing with now.

Tyson, I have collimated about three of these scopes. The first thing to know is that the secondary is minimally sized for keeping the CO small. What results from this is that there is vignetting at field periphery. This will show as out of round fresnel patterns toward field edge. With my MN-66's this started almost the moment the star was off center. So bear this in mind when collimating.

Secondly, the M-N is different from a plain Newtonian in that, in the Newt, the aperture stop is at the primary mirror while in the M-N, it is at the corrector. Consequently, focuser tilt is not tolerated as it's not possible to tilt the corrector. The primary-secondary-focuser optical axis has to coincide with the corrector axis as well.

I would start collimation with first making the secondary as parallel to its holder (screwed into the corrector) as possible. Then adjust the focuser up/down (the better M-N's have this adjustment) till the secondary is centered (but may present as oval). Next rotate the secondary by first loosening its retaining ring. There is a tiny set-screw in the retaining ring which has to be loosened first. Once you have a circular looking secondary in the focuser, you can proceed with the usual Newt collimation steps, iterating if necessary. My primaries had all a plug in the center so I could never use auto-collimation, but using a cheshire, I could successfully collimate them to perfection.

Since these are fairly short focal length scopes, using an artificial star, with extension tubes for the eyepiece (I used barlows with optics screwed off), will be a good idea to check the final primary collimation.

Finally remember that I-M offsets the secondary a bit so it may not look centered after final collimation.

Good luck,
Tanveer.

EDIT: fixed typos
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#15 agmoonsolns

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Posted 08 December 2018 - 04:02 PM

For a dew shield, I just ordered a roll of very stiff, dense, and thin black foam off of ebay for $10 shipped. BTW, there's enough here for several large dew shields. I then measured and cut enough for my MN66, sewed on (but one could just use super glue or something similar) six velcro patches (three on each side) and poof, I was done. It was already round from being rolled up and so I just wrap part of one end around the top of my scope, attach the velcro, and hold it tightly in place with a strip of 2" elastic (like what people use in sewing/making their own clothes - about $10 on Amazon for a huge roll of it). I sewed the ends of the elastic together so it's like a giant, thick rubber band. Absolutely brilliant at holding things in place, even when it's super windy. Best part, none of this can scratch or harm the tube assembly and can be stored in very small places, just roll it back up.


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#16 Cotts

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Posted 08 December 2018 - 10:08 PM

Tyson, a Canadian source for every possible kind of screw.....https://brafasco.com...ons/?store_id=5 Vancouver or https://brafasco.com...ons/?store_id=3 Calgary....

 

Dave


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#17 Tyson M

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Posted 09 December 2018 - 12:10 AM

Tyson, I have collimated about three of these scopes. The first thing to know is that the secondary is minimally sized for keeping the CO small. What results from this is that there is vignetting at field periphery. This will show as out of round fresnel patterns toward field edge. With my MN-66's this started almost the moment the star was off center. So bear this in mind when collimating.

 

Secondly, the M-N is different from a plain Newtonian in that, in the Newt, the aperture stop is at the primary mirror while in the M-N, it is at the corrector. Consequently, focuser tilt is not tolerated it's not possible to tilt the corrector. The primary-secondary-focuser optical axis has to coincide with the focuser axis as well.

 

I would start collimation with first making the secondary as parallel to its holder (screwed into the corrector) as possible. Then adjust the focuser up/down (the better M-N's have this adjustment) till the secondary is centered (but may present as oval). Next rotate the secondary by first loosening its retaining ring. There is a tiny set-screw in the retaining ring which has to be loosened first. Once you have a circular looking secondary in the focuser, you can proceed with the usual Newt collimation steps, iterating if necessary. My primaries had all a plug in the center so I could never use auto-collimation, but using a cheshire, I could successfully collimate them to perfection.

 

Since these are fairly short focal length scopes, using an artificial star, with extension tubes for the eyepiece (I used barlows with optics screwed off), will be a good idea to check the final primary collimation.

 

Finally remember that I-M offsets the secondary a bit so it may not look centered after final collimation. 

 

Good luck,

Tanveer.

So is that the oval fresnel rings I am seeing at the periphery? And if it is offset, that would make sense about not lining up. Still, I am not sure I have a fully illuminated field with just the laser and sight cap.

 

I am hoping the combination astrosystems chestire and sight tube will eliminate my uncertainty.



#18 TG

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Posted 09 December 2018 - 02:38 AM

So is that the oval fresnel rings I am seeing at the periphery? And if it is offset, that would make sense about not lining up. Still, I am not sure I have a fully illuminated field with just the laser and sight cap.

I am hoping the combination astrosystems chestire and sight tube will eliminate my uncertainty.


Vignetted fresnel rings tend to be circular on one side and ovalish/cutoff circles on the other. If you are seeing ovals that change orientation 90° on either side of focus, this is plain astigmatism which comes from a misaligned optical train, in particular the corrector.
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#19 Tyson M

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Posted 09 December 2018 - 11:29 AM

Vignetted fresnel rings tend to be circular on one side and ovalish/cutoff circles on the other. If you are seeing ovals that change orientation 90° on either side of focus, this is plain astigmatism which comes from a misaligned optical train, in particular the corrector.

It doesnt happen when I focus, it happens when the star drifts to the edge of the FOV.  Which I am guessing is vignetting, which could be the result from my alignment (with the laser and sight cap).



#20 Cotts

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Posted 09 December 2018 - 11:48 AM

It doesnt happen when I focus, it happens when the star drifts to the edge of the FOV.  Which I am guessing is vignetting, which could be the result from my alignment (with the laser and sight cap).

If this happens with stars at all edges of the field equally then it is vignetting caused by the small secondary mirror.  This will happen more with a low power eyepiece, too.  Additionally if you can determine that the amount of vignetting is the same all around the edge then your collimation is actually very good!

 

The MN66 purposely has a tiny secondary mirror , around 25mm diameter or about 16%, so that its diffraction effects make the scope indistinguishable from a refractor of the same aperture...  The downside is that the MN is not a wide-field sweeping scope at all.  But planets, lunar, solar and double stars - a champion.. a poor-man's APO refractor!

 

Dave


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#21 JeffreyAK

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Posted 09 December 2018 - 11:49 AM

By chance does the "Bite" location correlate with the focuser tube?  In my old MN76, the focuser tube was a bit too long, so at high magnification it intruded into the light path.  Maddening until I figured out what was happening, my solution was to shorten the focuser tube a bit.  It was more noticeable on one side of the field and less noticeable on the other opposite side, and the orientation correlated with the focuser tube.


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#22 Tyson M

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Posted 09 December 2018 - 11:53 AM

If this happens with stars at all edges of the field equally then it is vignetting caused by the small secondary mirror.  This will happen more with a low power eyepiece, too.  Additionally if you can determine that the amount of vignetting is the same all around the edge then your collimation is actually very good!

 

The MN66 purposely has a tiny secondary mirror , around 25mm diameter or about 16%, so that its diffraction effects make the scope indistinguishable from a refractor of the same aperture...  The downside is that the MN is not a wide-field sweeping scope at all.  But planets, lunar, solar and double stars - a champion.. a poor-man's APO refractor!

 

Dave

It was with a 10mm pentax XW. So not the widest eyepiece. 



#23 Tyson M

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Posted 09 December 2018 - 11:56 AM

By chance does the "Bite" location correlate with the focuser tube?  In my old MN76, the focuser tube was a bit too long, so at high magnification it intruded into the light path.  Maddening until I figured out what was happening, my solution was to shorten the focuser tube a bit.  It was more noticeable on one side of the field and less noticeable on the other opposite side, and the orientation correlated with the focuser tube.

All options are on the table atm.  I think the first step is to do a complete system collimation, mark the orientation of the corrector and start from the beginning, with the steps outline up above by others. I assume the focuser is position is fine.

 

Then I will use my new astrosystem chestire and sight tube and hotech laser, and get it perfect and check the views on the periphery then. 

 

Is the feathertouch is too long? I doubt this but worth checking into if the problem persists after all of this. 



#24 agmoonsolns

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Posted 09 December 2018 - 04:24 PM

Does this have anything attached to the tube with screws? I once saw a 6" Newtonian that would have two tiny "bite marks" in the out of focus star images similar to what you described. Turns out it was the long screws holding the finderscope bracket onto the tube were too long and entered the light path and could be seen in the out of focus star images. Kind of like what the above poster was describing with the focuser tube, but with screws.



#25 agmoonsolns

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Posted 09 December 2018 - 04:24 PM

At least things getting into the light path are easy to check for. :-)




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