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I stumbled into a Celestron 8" SCT

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#26 Brent Campbell

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Posted 29 May 2016 - 10:20 PM

Me again.....can't stop thinking about your scope.     I would give Don from Astro Parts Outlet a call.  He has allot of stuff listed on his website and may have the parts you need.  To turn a wedge scope into one with polar alignment you would need a new tripod/wedge assembly.  Lots of those around if you look. 


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#27 Geo31

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Posted 30 May 2016 - 09:50 AM

This is my first SCT.   My son has the 9.25" on a rail (Orion's Ultima clone) on a GEM, and it's a horse to set up.  But, it is a heavier OTA, who knew another 1.25" of aperture could make such a difference.

 

The wedge/pod seems to function, it's just cosmetically challenged.  Also, I don't currently have another ride for this OTA.  While I will keep my eye open for a suitable GEM, I want to at least experience the fork mount (I've never used one before).  Part of the reason I was drawn to this system was the sudden realization that operating it would be a different experience to the Dobsonians and GEM-mounted refractors I already have.  Last year, the refractors were an eye-opening change on familiar targets, maybe this will be, too.    :waytogo:

 

Was there a kit to upgrade the wedge/pod to a unit with adjustable azimuth?

 

I'd 86 the wedge pod.  If you want to try to enjoy the C8 on a fork mount, I think the wedge pod will only lead to frustration.  Best solution (although not the cheapest) is a Meade Field Tripod (very similar to the Criterion Golden Triangle and very stout) and a proper wedge.  Clean everything up carefully (although skip any restoration at this stage).  If you find you like it, then restore it.  If you find you don't, sell the tripod and wedge (probably for what you paid) and move on.

 

I like the fork mount except when near the pole.  Then it becomes a pain.  Otherwise it's easy and convenient to use IMHO.


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#28 orion61

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Posted 30 May 2016 - 10:31 AM

The Wedgepods are not worth messing with The leg height is fixed and they are not stable.


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#29 terraclarke

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Posted 30 May 2016 - 03:25 PM

I think they are perfect for the little classic OT C5.
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#30 Joe Bergeron

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Posted 02 June 2016 - 10:16 PM

The person who allowed that scope to deteriorate to that degree is a savage animal.


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#31 Tenacious

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Posted 03 June 2016 - 09:20 AM

Actually, he is a non-astronomer.  I get that he "stored" the Celestar for years in a garage, perhaps without a garage door.  Thank God they left the tube cover in place.  I doubt he ever looked through it, even though an EP was left in the diagonal.   I'm grateful for the find and the chance to rescue it. 

 

I'm getting the bug to test it and get started with my program.  ;)  

 

I never imagined this was waiting just a mile away.


Edited by Tenacious, 03 June 2016 - 09:31 AM.

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#32 Tenacious

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Posted 06 June 2016 - 12:06 AM

The sky cleared for tonight and the Seeing was 3/5 due to breeze and turbulence.  So I pulled out the Celestar along with a 6" f/8 Newt and Frankenscope (60mm f/15).

 

The Dec control is smooth as is the focuser with little image shift.  The RA lock knob doesn't seem connected and that slow motion is hard to turn and very jerky.  I suspect these issues will be simple to fix,

 

While waiting for the optics to acclimate for over an hour, I actually spent more time with the other scopes.  After this, the Celestar's star image was the same on each side of focus.  Despite the collimation being just a tad off, the view of Saturn was good for those brief moments of good seeing.  Cassini's division would pop into view as would cloud banding on the planet with a 9mm Ortho.  The 6 x 30mm finder, while functioning, is not pleasant to use (it is stopped down internally).  It was also frequently in the way while trying to get my eye to the EP.  There is not much room around the EP.  The Celestar has a long focal length.  My usual medium power Ultimas (18mm and 12 mm) produced larger images.

 

I now understand why this is not a popular mount with some of you.  Even at low power, the image would almost continually oscillate, set in motion by the breeze (the other scopes did not do this).  Like other mounts before bracing, the oscillation always seemed to be in one plane.  I'll have to look into this more.  Tonight, I pressed my eye against the EP's eye-cup to steady the scope.  It worked fairly well.  I did not even attempt to power up the RA drive.

 

In truth, the 6" Newt showed more contrast and the view was simply more crisp and defined.  This scope has always been a pleasure to use because anything in the sky is comfortably visible from a sitting position.  The optics are among the best I have.  OTOH, the Celestar's corrector plate still has evidence of being wiped off and the collimation needs tweaking.

 

Frankenscope did a great job on the planets and e Lyra.  However, M13 was a glowing smudge, no individuals were resolved.

 

Overall, the Celestar has a different 'feel' from my other scopes.  Everything is tight, compact, and crowded.  I might prefer a Telrad, GLP, or a larger right-angle finder, or some combination of these.  The RA was frustrating, but probably repairable.  The instability (high freq. oscillation) was alarming.  I hope there is a cure for this.


Edited by Tenacious, 06 June 2016 - 12:13 AM.

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#33 Joe Cepleur

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Posted 06 June 2016 - 04:55 PM

 

I now understand why this is not a popular mount with some of you.  Even at low power, the image would almost continually oscillate, set in motion by the breeze (the other scopes did not do this).  Like other mounts before bracing, the oscillation always seemed to be in one plane. 

 

Consider yourself lucky! or, in grave danger… your call. Joe Cepleur, King of the Reading Nerds with Minimal Refurbishing Experience, offers a thought on your oscillation: 

 

I read a thread about a year ago, in which Tom Stock, the owner of a classic Orange Tube C8, solved the problem of oscillation. I've been searching for the thread and can't find it, but I'll post it if and when I do. From what I have seen of your work, you could re-create his solution, given the idea. 

 

All of these Celestron fork mounts on wedges appear to have some of this trouble, although the mount you have is said to be the worst of the worst. I suspect it could be improved, or perhaps even fixed, with Tom's solution. The mounting plate attaches to the wedge in four places (two each side). It is hinged such that it can be adjusted to any latitude. This requires for the two screws on each side to be too close together. Tom made a new plate out of aluminum, and then another from oak, with the screws much farther apart. This arrangement would not allow the wedge to be used anywhere in the world, but he designed it to be just fine for his latitude and those nearby (in case he travelled). He reported that this stopped the oscillation cold. The scope became rock steady. Aluminum and oak worked equally well, but oak was easier to fabricate (at least for him; this may depend upon one's skills and tools). You could become the envy of your friends, with an optically fine, vintage C8 that may have its own take on beauty, but is steadier than any stock C8 ever sold! 


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#34 Tenacious

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Posted 06 June 2016 - 05:40 PM

Thanks Joe.  I'm very interested,

 

I had a feeling someone might have put some brain-sweat into this mount.   I've seen posts by Tom Stock, maybe he will jump in if he gets a chance.  I'd love to see his ideas.

 

Last night, I carried the whole system in one trip to set it up and to put it away.  Next time, I'll separate it into more manageable chunks. I'm also thinking of replacing some of the fasteners with knobs.   On the plus side, it appears that all of the hardware is SAE thread sizes rather than some of the uncommon metric pitches.

 

   "..You could become the envy of your friends, with an optically fine, vintage C8 that may have its own take on beauty, but is steadier than any stock C8 ever sold! "         I don't know about envy, but, embracing this mount does seem like the road less traveled and maybe trying to get there will be more fun.   :grin:


Edited by Tenacious, 06 June 2016 - 07:34 PM.


#35 jgraham

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Posted 06 June 2016 - 06:05 PM

If the mount turns out to be problematic you might consider deforking it and moving to another mount via a Vixen dovetail. Before finally reforking my 8" LX50 I fitted it with an ADM Vixen rail and a nice 50mm RACI finder and used it on a Twilight I altaz mount. This made a fantastic star-hopping scope and was a joy to use.

 

LX50 TW1-1j.jpg


Edited by jgraham, 06 June 2016 - 06:06 PM.

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#36 Geo31

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Posted 06 June 2016 - 09:12 PM

Scroll to the bottom.....

 

 

http://www.ngc1514.c...estron/tips.htm



#37 Tenacious

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Posted 06 June 2016 - 09:52 PM

 

 

I now understand why this is not a popular mount with some of you.  Even at low power, the image would almost continually oscillate, set in motion by the breeze (the other scopes did not do this).  Like other mounts before bracing, the oscillation always seemed to be in one plane. 

 

Consider yourself lucky! or, in grave danger… your call. Joe Cepleur, King of the Reading Nerds with Minimal Refurbishing Experience, offers a thought on your oscillation: 

 

I read a thread about a year ago, in which Tom Stock, the owner of a classic Orange Tube C8, solved the problem of oscillation. I've been searching for the thread and can't find it, but I'll post it if and when I do. From what I have seen of your work, you could re-create his solution, given the idea. 

 

All of these Celestron fork mounts on wedges appear to have some of this trouble, although the mount you have is said to be the worst of the worst. I suspect it could be improved, or perhaps even fixed, with Tom's solution. The mounting plate attaches to the wedge in four places (two each side). It is hinged such that it can be adjusted to any latitude. This requires for the two screws on each side to be too close together. Tom made a new plate out of aluminum, and then another from oak, with the screws much farther apart. This arrangement would not allow the wedge to be used anywhere in the world, but he designed it to be just fine for his latitude and those nearby (in case he travelled). He reported that this stopped the oscillation cold. The scope became rock steady. Aluminum and oak worked equally well, but oak was easier to fabricate (at least for him; this may depend upon one's skills and tools). You could become the envy of your friends, with an optically fine, vintage C8 that may have its own take on beauty, but is steadier than any stock C8 ever sold! 

 

I think this might be Tom Stock's thread:    http://www.cloudynig...nge-c8-ringing/

 

@ jgraham   That's a nice looking setup.  I'm not ready to throw in the towel yet, but it looks good.

 

@Geo31  Thanks for the link.  



#38 ETXer

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Posted 06 June 2016 - 10:20 PM

"It worked fairly well.  I did not even attempt to power up the RA drive."

 

If you do try power it up, let us know what happens.  I'm curious if it still works and if so, how well after all that exposure.


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#39 Joe Cepleur

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Posted 07 June 2016 - 07:28 PM

Yes; that is Tom Stock's thread:

 

Orange C8 Ringing
Started by Tom Stock, Mar 06 2015 12:10 AM

http://www.cloudynig...nge-c8-ringing/

 

I remembered it not quite correctly. He did not (could not!) widen the spacing of the bolts, but he changed the center of mass to be between the bolts, rather than far outside of them, with the result that the oscillation was radically curtailed. Although he notes that his solution would not work near the equator, offhand, it seems the idea could be modified to work there, with some kind of angled or extended plate. 


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#40 Tenacious

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Posted 07 June 2016 - 09:23 PM

After reading Tom's thread, I went down to my Celestar, turned the fork perpendicular to the diving board motion of the cantilevered base, and confirmed that the base flexes as he described.  It is easy to see that the fork flexes, but, the base is not nearly as obvious.  Great insight Tom!  

 

I wonder if there is some resonance of the natural frequencies of the 2 parts (the fork and the base). The combined oscillation may be more than additive, depending on the latitude setting and the angle of declination.  Who knows?

 

I'm excited about the possibility of making some new slotted parts that would allow latitude adjustment of +/- 10 degrees of my home (I'll probably never travel farther than that with this scope.) and a fixed hole for alt/az operation.   It would also be cool to include an adjustable azimuth.   I can dream!  :lol:

 

If the settle time could be reduced, perceptions of this mount might change.


Edited by Tenacious, 07 June 2016 - 09:36 PM.


#41 Geo31

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Posted 07 June 2016 - 10:02 PM

IMHO the issue with the classic C8 mounting is not the forks per se.  It's the fact it's designed with 3 moment arms that are too long and not supported enough (at least in 2 of the 3).

 

1.  The center of mass of the wedge with scope mounted is well off-center of the mounting plate on the tripod.

 

2.  The mounting plate on the wedge is far too high (something Tom corrected) which is exacerbated by the long forks.

 

3.  The forks themselves are a long moment arm, although I think they are the least of the problem.

 

I'll bet if you mounted a C8 base on a rock steady pier, the forks would not create enough "jiggle" in the image to say so.  In fact, I'd wager it would be less than the "jiggle" of the average GEM.

 

IMHO the forks get the blame, but unjustly so.  Interestingly enough my C5 is rock solid on the wedge, but there is SO much less mass.


Edited by Geo31, 08 June 2016 - 09:43 AM.

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#42 terraclarke

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Posted 08 June 2016 - 07:52 AM

Yes, my classic C5 is rock steady as well in its fork mount, of course, the base is the same dimensions as the C8. For anything larger, I much prefer mounting on a GEM.

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#43 Tenacious

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Posted 23 June 2016 - 08:40 PM

UPDATE:     I just got home with this.

 

DSC02061.JPG   1095   DSC02062.JPG

 

I haven't researched it yet, but this one is probably a later design than the original Celestar fork.  The Celestar's Dec motor seems to be a simple DC type while this one is probably a stepper.  There was also no hand controller included with this new fork, was it also optional?  The drive runs from two 9VDC batteries.  There are encoders included with both axes, but so far, I've found nowhere to plug them in.  Are they add-ons?

 

The new fork came with what I think Celestron called the Heavy Duty Field Tripod.   I need to do more research.   The beauty is the new items are in much better cosmetic and functional shape, saving me a lot of time.


Edited by Tenacious, 23 June 2016 - 08:44 PM.

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#44 Tenacious

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Posted 24 June 2016 - 10:05 AM

It looks like the encoders are for use with Celestron's Advanced Astromaster, one of the early digital setting circle computers with a database of 10,000 objects.  I will probably wait to pursue this.

 

This new mount uses the same cantilevered base plate for the fork module as my first Celestar (Most Celestrons?  Even Meade's design looks to be cantilevered.).   I really want to see if a different design can get the same stability improvement as what Tom Stock achieved.

1123



#45 Brent Campbell

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Posted 25 June 2016 - 11:01 PM

UPDATE:     I just got home with this.

 

attachicon.gifDSC02061.JPG   1095   attachicon.gifDSC02062.JPG

 

I haven't researched it yet, but this one is probably a later design than the original Celestar fork.  The Celestar's Dec motor seems to be a simple DC type while this one is probably a stepper.  There was also no hand controller included with this new fork, was it also optional?  The drive runs from two 9VDC batteries.  There are encoders included with both axes, but so far, I've found nowhere to plug them in.  Are they add-ons?

 

The new fork came with what I think Celestron called the Heavy Duty Field Tripod.   I need to do more research.   The beauty is the new items are in much better cosmetic and functional shape, saving me a lot of time.

Loops identical to my ultima fork.  Same vintage but the much more delux model.


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#46 walter a

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Posted 26 June 2016 - 05:15 AM

What a great deal, those here know how I love to keep scopes original but on these situations you could get REALLY Creative!

You guys see a YUUK too bad situation, I see a remarkable opportunity to be creative and create a scope known World Wide!

I wonder how a C8 Tube would look like as a Barber Pole?

Glow in the Dark Paint! Fluorescent paint with small Black lights hidden cleverly! Oh MY I could have a GREAT Time. I might even be tempted to get my Air Brush out and do a Questar/ETX Premier paint job. I say go for it, Make it yours. 

One good thing is that scope was made in about 1990-93 and is off of the fresh Celestron Master Blocks! I have seen those Celestars hit 97 Strehl! The secondary housing is more than likely loose, so be careful with it.

Think about the Fork Mount sanded and polished, left bright and shiny! The tube painted a Candy Apple Red! Or an Ultra Clean Bright Yellow

Tube with smooth bright front and rear cells...

I had a deluxe c/8 that was a bit of a beater and although not as brave as orion61 i did go with a more conservative black and silver

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#47 Tenacious

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Posted 26 June 2016 - 10:13 AM

I'm guessing that's a dew heater controller on the left fork and a silver cooling fan on the back of the OTA.  Did you add the fan and did it improve acclimation time?

 

I'd love to see a pic of the hand controller.  Celestron seems to have made 2 versions: a 4 button model AND a 5 button model.  It seems holding the 5th button allows the motors to move at a faster rate.  Which did your Deluxe use?



#48 orion61

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Posted 26 June 2016 - 10:59 AM

That is a Celestron Deluxe drive. If you push a direction on the handset then push the button opposite it the slew speed goes faster but you have to hold both buttons, first speed is for guiding, 2nd is 16X or 32X I cant remember.

I have a spare MiniMax Computer that would fit right on it. Making it Push-To.


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#49 Tenacious

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Posted 26 June 2016 - 11:11 AM

I have a spare MiniMax Computer that would fit right on it. Making it Push-To.

 

Oh.  I wondered about this.  Did the computer plug into the hand controller jack and drive the scope to target (probably very slowly)  or  did the user first loosen the axes locks and push to a ballpark position?  Later closed-loop models with GoTo ability must have had a faster slew rate.


Edited by Tenacious, 26 June 2016 - 11:41 AM.


#50 walter a

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Posted 26 June 2016 - 11:31 AM

Pic of hand contoller

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