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Celestron Powerseeker 127EQ Rebuild

Celestron collimation equipment reflector
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#1 ajfranke

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Posted 08 June 2015 - 05:22 PM

The Celestron Powerseeker 127EQ is a telescope that the internet loves to hate. It is an example of the controversial Jones-Bird (or Bird-Jones) design, and is 5" of aperture for less than $175. Both of these facts have associated pros and cons. I received this scope as a gift this past Christmas. I would like to document the modifications that I have made to the scope to improve its performance and usability, as examples to others. This thread is not intended as a stage for yet another debate of this scope's merits.

Faster/Easier Collimation

As shipped from the factory, the primary mirror lacks a center spot, and collimation is adjusted Phillips-head adjustment and lock screws on the back of the mirror cell. Neither of these features are conducive to collimation in the field. Additionally, the mirror cell's angle is stabilized during collimation by sets of compressed rubber o-rings instead of metal springs, resulting in a limited range of primary mirror angle and unsteady adjustment behavior.

First step: add a black center spot and ring reinforcer to the primary mirror. There are numerous tutorials elsewhere for how to do this, so I won't re-write one here.

6f3gHjk.jpg?1

Note that the rubber o-rings have already been removed from the mirror cell in this photo. They were carefully peeled/cut off with a pen knife.

Second step: replace collimation adjustment and lock screws, and replace rubber o-rings with springs. The inspiration for this step was niuno15's how-to on Astronomy Forum. The springs were sourced from a Home Depot spring assortment.

pwSTE7S.jpg?1

The replacement adjustment screws are 1" long 10-32 wing screws, and the replacement lock screws are 1/2" long 10-32 thumb screws. The difference in head design lets me easily feel which screws are which without taking my eye away from the eyepiece while collimating on a star.

q5AIbum.jpg?1

Improve Focuser Performance

Even with the improvements above, the scope was having trouble maintaining collimation. Collimation would qualitatively change with different eyepieces, and different collimation methods (laser vs. reference star) wouldn't agree in their results. The culprit was angular slop in the focuser tube. Heavier eyepieces would pull it to the side and skew collimation, and the heavy laser collimator would skew the tube while inserted. Inspiration and guidance for this fix came from here.

First, we remove the focuser assembly from the OTA, and disassemble it fully. Notable pieces include: the shiny silvered plastic draw tube, the stipple-painted plastic focuser base, the metal focuser pinion and adjustment knobs, and the Bird-Jones corrector doublet.  (One note: when re-assembling the focuser, I advise others to only screw in the corrector lens finger tight. This way, one can (very) carefully reach into the tube and unscrew the corrector by hand for collimation purposes)

 

qMjEhFk.jpg?1

Materials and tools:

  • Goo Gone, to remove sticky grease from focuser tube, focuser base, and pinion.
  • White Lithium Grease to re-grease focuser tube rack and pinion
  • Plastic collar stays from men's dress shirts, to be used as shims
  • Krazy glue, or other cyanocrylate-based glue
  • 200-grit sandpaper (not shown)
  • Teflon Tape (which would prove unnecessary)

YnUc0qJ.jpg?2

The focuser base contained a single ribbed plastic shim that did little to hold the focuser draw tube steady. It was removed, and both the focuser rube and base were de-greased with the Goo Gone. Below you can see exactly how much of a gap there is between the outer diameter of the draw tube and the inner diameter of the focuser base.

 

7LIYZXA.jpg?1

To fix this, we add the plastic collar stays as shims around the inside of the focuser base. Here they are being test-fit:

zyLlcmn.jpg?1

After being trimmed to length and glued into place:

MzM4dM6.jpg?1

The fit with the shims as-is was extremely snug, to the point of nearly getting stuck. Since the focuser draw tube's gear rack is plastic, and the pinion is metal, a fit that is too tight will lead to broken rack teeth. Thus, it was necessary to sand down the shims with the sandpaper until the draw tube moved more easily. Once a snug-but-movable fit was achieved, white lithium grease was applied to the focuser rack teeth, and the focuser reassembled. Here is the draw tube in place, with the focuser reassembled, after sanding:

GISiTzo.jpg?1

While some similar rebuilds use Teflon tape for additional shimming and friction reduction inside the focuser base, I did not notice a significant improvement in smoothness.

The focuser was re-attached to the OTA, and the scope collimated. Now the collimation is much more reliable, star and laser methods agree, and the focuser more reliably holds a constant focus with the increased resistance from the shims. There is no longer any noticeable slop of the focuser tube inside the base.


 


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#2 Jon Isaacs

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Posted 09 June 2015 - 01:08 AM

Hi:

 

Nice write up.  Have you had a chance to get it out under the night sky? Have you tried in on double stars?

 

One thing I did see, you suggest screwing the corrector finger tight.  If the scope is being transported in a car, it is possible the corrector could come loose and bounce around inside the scope, potentially damaging the mirrors.

 

Jon



#3 macdonjh

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Posted 09 June 2015 - 08:18 AM

Perhaps important to some: the construction of the 1-1/4" focuser supplied with Orion XT-6 and XT-6i Dobs is the same as what AJFranke found on his Powerseeker 127.  I used plastic sheet (something like 10 and 20 mil) purchased from a local hobby shop to shim my focuser.  Using plastic collar stays is a good idea.  There's a full article about my XT6i on Astromart if you're curious.


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#4 ajfranke

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Posted 09 June 2015 - 11:42 AM

Nice write up.  Have you had a chance to get it out under the night sky? Have you tried in on double stars?

 

One thing I did see, you suggest screwing the corrector finger tight.  If the scope is being transported in a car, it is possible the corrector could come loose and bounce around inside the scope, potentially damaging the mirrors.

 

Thanks!  I've only had it out for planetary and solar viewing so far since the rebuild.  

 

I think it would be rare that the corrector would loosen itself that far, but that's a good suggestion.  Storing and travelling with the corrector in a separate case (spare lens case?) would be safest.  It would also fit logically into a setup-scope-and-check-collimation procedure where the corrector has to be removed to use a laser, anyway.  



#5 Jon Isaacs

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Posted 10 June 2015 - 01:37 AM

 

Nice write up.  Have you had a chance to get it out under the night sky? Have you tried in on double stars?

 

One thing I did see, you suggest screwing the corrector finger tight.  If the scope is being transported in a car, it is possible the corrector could come loose and bounce around inside the scope, potentially damaging the mirrors.

 

Thanks!  I've only had it out for planetary and solar viewing so far since the rebuild.  

 

I think it would be rare that the corrector would loosen itself that far, but that's a good suggestion.  Storing and travelling with the corrector in a separate case (spare lens case?) would be safest.  It would also fit logically into a setup-scope-and-check-collimation procedure where the corrector has to be removed to use a laser, anyway.  

 

 

The reason for my concern is that sometimes eyepieces that are in a foam carrying case loosen.  

 

Have you had it out under the stars yet?

 

Jon



#6 ajfranke

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Posted 11 June 2015 - 10:03 AM

Last night I was able to take the scope out and put it through its paces.  This was in NYC, so Bortle 9 and very white, with some haze making for average seeing for the site (i.e. poor anywhere else).  

 

The scope held collimation very well with a heavy XCel-LX 7mm lens and 2x Barlow, and again with the 7mm and attached mobile phone in eyepiece attachment.  It was steady through multiple eyepiece changes, going back and forth between Jupiter and Venus, giving the sharpest view of Jupiter's cloud bands that I've had all year despite the seeing conditions.  The only hiccup came when I flipped the GEM and scope past the meridian to look at Saturn, and had to rotate the scope within its rings to put the eyepiece at a useful angle.  This action somehow threw off the collimation: either gravity shifted the focuser when the tube was inverted (so it still isn't perfect), or the OTA deformed slightly.  But recollimation took < 2 minutes.  

 

While I tried my best, I couldn't get my scope pointed squarely at Epsilon Bootis to try to split the double.  Call it bright skies, or a limitation of the non-angled finder scope and/or my leg strength to crouch and peer up through it.  


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#7 zogh

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Posted 13 June 2017 - 12:50 PM

After seeing the steps you took to tighten the wobble of the focuser, it gave me an idea.  I had noticed the excess play right off the bat & have just dealt with it until now. The shirt tabs are an awesome idea for shimming it up! But seeing that, and the whole sanding to fit seemed a hassle. So, why not something slimmer?

I cut Post It notes down to the sticky strip [approx 1/4" width] and fitted them layer by layer. For me it was two sets of two to get it tight, but still workable. I then trimmed back the excess from the end of the tube with an Exacto blade, and VOILA! a nice firm focus with no wobble.

Quick, easy, no glue, and no tricky sanding/shaping!

 

I am going out this afternoon to fit out the collimation screws with knobs thanks again for the tips!

 

The Celestron Powerseeker 127EQ is a telescope that the internet loves to hate. It is an example of the controversial Jones-Bird (or Bird-Jones) design, and is 5" of aperture for less than $175. Both of these facts have associated pros and cons. I received this scope as a gift this past Christmas. I would like to document the modifications that I have made to the scope to improve its performance and usability, as examples to others. This thread is not intended as a stage for yet another debate of this scope's merits.

Faster/Easier Collimation

As shipped from the factory, the primary mirror lacks a center spot, and collimation is adjusted Phillips-head adjustment and lock screws on the back of the mirror cell. Neither of these features are conducive to collimation in the field. Additionally, the mirror cell's angle is stabilized during collimation by sets of compressed rubber o-rings instead of metal springs, resulting in a limited range of primary mirror angle and unsteady adjustment behavior.

First step: add a black center spot and ring reinforcer to the primary mirror. There are numerous tutorials elsewhere for how to do this, so I won't re-write one here.

6f3gHjk.jpg?1

Note that the rubber o-rings have already been removed from the mirror cell in this photo. They were carefully peeled/cut off with a pen knife.

Second step: replace collimation adjustment and lock screws, and replace rubber o-rings with springs. The inspiration for this step was niuno15's how-to on Astronomy Forum. The springs were sourced from a Home Depot spring assortment.

pwSTE7S.jpg?1

The replacement adjustment screws are 1" long 10-32 wing screws, and the replacement lock screws are 1/2" long 10-32 thumb screws. The difference in head design lets me easily feel which screws are which without taking my eye away from the eyepiece while collimating on a star.

q5AIbum.jpg?1

Improve Focuser Performance

Even with the improvements above, the scope was having trouble maintaining collimation. Collimation would qualitatively change with different eyepieces, and different collimation methods (laser vs. reference star) wouldn't agree in their results. The culprit was angular slop in the focuser tube. Heavier eyepieces would pull it to the side and skew collimation, and the heavy laser collimator would skew the tube while inserted. Inspiration and guidance for this fix came from here.

First, we remove the focuser assembly from the OTA, and disassemble it fully. Notable pieces include: the shiny silvered plastic draw tube, the stipple-painted plastic focuser base, the metal focuser pinion and adjustment knobs, and the Bird-Jones corrector doublet.  (One note: when re-assembling the focuser, I advise others to only screw in the corrector lens finger tight. This way, one can (very) carefully reach into the tube and unscrew the corrector by hand for collimation purposes)

 

qMjEhFk.jpg?1

Materials and tools:

  • Goo Gone, to remove sticky grease from focuser tube, focuser base, and pinion.
  • White Lithium Grease to re-grease focuser tube rack and pinion
  • Plastic collar stays from men's dress shirts, to be used as shims
  • Krazy glue, or other cyanocrylate-based glue
  • 200-grit sandpaper (not shown)
  • Teflon Tape (which would prove unnecessary)

YnUc0qJ.jpg?2

The focuser base contained a single ribbed plastic shim that did little to hold the focuser draw tube steady. It was removed, and both the focuser rube and base were de-greased with the Goo Gone. Below you can see exactly how much of a gap there is between the outer diameter of the draw tube and the inner diameter of the focuser base.

 

7LIYZXA.jpg?1

To fix this, we add the plastic collar stays as shims around the inside of the focuser base. Here they are being test-fit:

zyLlcmn.jpg?1

After being trimmed to length and glued into place:

MzM4dM6.jpg?1

The fit with the shims as-is was extremely snug, to the point of nearly getting stuck. Since the focuser draw tube's gear rack is plastic, and the pinion is metal, a fit that is too tight will lead to broken rack teeth. Thus, it was necessary to sand down the shims with the sandpaper until the draw tube moved more easily. Once a snug-but-movable fit was achieved, white lithium grease was applied to the focuser rack teeth, and the focuser reassembled. Here is the draw tube in place, with the focuser reassembled, after sanding:

GISiTzo.jpg?1

While some similar rebuilds use Teflon tape for additional shimming and friction reduction inside the focuser base, I did not notice a significant improvement in smoothness.

The focuser was re-attached to the OTA, and the scope collimated. Now the collimation is much more reliable, star and laser methods agree, and the focuser more reliably holds a constant focus with the increased resistance from the shims. There is no longer any noticeable slop of the focuser tube inside the base.


 


Edited by zogh, 13 June 2017 - 12:56 PM.

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#8 Kaikul

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Posted 30 April 2018 - 02:17 AM

This was my very first scope. As with many other first time users, it gave me an entry-level scope that go me hooked to the hobby. Eventually I got me an SCT and a refractor, which - in combination with the collimation difficulty and that trouble-some focuser - caused me to put it aside. After finding this thread here, I think it's time to put some elbow grease and "hyper-tune" this tube. Who knows, it might turn out to be a good fit for EAA.

 

Now anybody got a good suggestion for replacing that crappy finderscope?


Edited by Kaikul, 30 April 2018 - 02:19 AM.


#9 vincentv

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Posted 30 April 2018 - 10:18 AM

Kaikul,

I used a finder base from orion. It bolted right in without mods, simply measure before buying. I tried a 6x30 raci but it had trouble in my light polluted backyard. 9x50 works nicely but I never used it on the 127 so I can't tell you about its balance.

A rigel quickfinder should work nicely as well. The stock finder is worse than useless.

 

To lock the corrector in place a small dab of black rtv might work. I've seen from the factory in a couple of other model scopes.

 

Regards


Edited by vincentv, 30 April 2018 - 10:23 AM.

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#10 Kaikul

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Posted 01 May 2018 - 11:50 AM

Kaikul,

I used a finder base from orion. It bolted right in without mods, simply measure before buying. I tried a 6x30 raci but it had trouble in my light polluted backyard. 9x50 works nicely but I never used it on the 127 so I can't tell you about its balance.

A rigel quickfinder should work nicely as well. The stock finder is worse than useless.

 

To lock the corrector in place a small dab of black rtv might work. I've seen from the factory in a couple of other model scopes.

 

Regards

 

vincentv, can you provide a link to that Orion base you have? I'm plotting my course on doing this rebuild. No sense in letting this much-maligned telescope not get time under the stars as much as my other two. Even with all its faults, I can only imagine what Galileo, Copernicus, and other astronomy luminaries of centuries ago might have discovered with it.



#11 vincentv

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Posted 01 May 2018 - 12:26 PM

I believe it was an orion 07214. It's been a long time since I sold the scope so measure before you buy. There's a lot of base options and many include slots to accommodate different screw spacings.

In the case of rigel it can be mounted with a single screw or simply glued with double sided tape.


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