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I stumbled into a Celestron 8" SCT

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#51 walter a

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Posted 26 June 2016 - 11:38 AM

Sorry, but thats the best pic i have of the hand contoller.


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#52 Tenacious

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Posted 26 June 2016 - 11:57 AM

That's what I needed.  Besides, there is a lot of other detail there.  Thank you. 



#53 Tenacious

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Posted 02 July 2016 - 11:40 AM

I took the Celestar out last night.  The seeing was probably 4/5, there were high altitude breezes.  I gave it a lot of cool-down time.  I attempted to clean the corrector, it looked a though it had previously been wiped with a dirty dish cloth.  :lol:  Looking at the moons of Jupiter at 164x, they were not any kind of disk.  It was time to dial in the collimation.  Afterward, the appearance was improved, though still not the clean disks that I've learned to appreciate in the other scopes.  Maybe I can refine this further in the future.    1424

 

My second impression of the focusing was that it is a little stiff,  I still did not, however, notice much image shift.   After midnight, Saturn put on a pretty good show.  Several moons were there, and Cassini's division, along with banding in the clouds, would come in and out of view as the atmosphere had moments of steady seeing.  For grins, I swung onto E-Lyra.  Both pairs had black in between at 228x but the stars were not clean airy disks.  The ring nebula looked noticeably brighter at 114x than in my smaller apertures, as expected. 

 

Once again, I was continually impressed with the image scale available in my medium power EPs.  In fact, it occurred to me that the Celestron Ultima line of EPs (I have the 18mm and 12.5mm) were probably designed for this scope.  It felt that way.  The two 9mm EPs (a UO volcano orthoscopic, and Orion's 66 degree Expanse) also did well.  The surprise was trying a Burgess bino viewer at 102x.  Saturn took on a mesmerizing 3D appearance.  I think I like the binos on this scope better than any other that I've tried them with (both Dobsonians).  Maybe the tracking  made it that much better.

 

Speaking of tracking, installing two fresh 9 volts was all that was required.  I put no effort into an accurate polar alignment and it was still wonderful and refreshing.  Without a hand controller, I was unable to try out the DEC motor. 

 

The 6 x 30 finder is missing the o-ring at one end and was not usable.  At some point, I want to install a 50mm RACI finder and a Telrad.  Last night, I was able to find familiar targets by laying GLP along the sides of the OTA.  it was not convenient, but it worked.

 

I have not yet made anything to replace the springy base mount.  I did buy parts, including a 5/16-18 threaded rod.  Last night, I ran this against the top end of the factory base just lower than the top screw.  The shorter, factory rod is typically used as a fine adjustment against the bottom of the base plate.  I haven't done extensive comparisons, but, the high-frequency oscillations were far more manageable this time.

 

This Celestar is different set of compromises from my Newtonains and refractors.  I'm hoping cleaning and accurate alignment/collimation will improve it further.


Edited by Tenacious, 02 July 2016 - 11:41 AM.

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#54 terraclarke

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Posted 05 July 2016 - 10:46 AM

"The 6 x 30 finder is missing the o-ring at one end and was not usable."

Small fabric covered elastic hair ties work as a substitute. Try the Kroger, Target, or Bed Bath and Beyond hair care section- brand: Sc√ľnci, size: small, color: black.
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#55 walter a

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Posted 07 July 2016 - 07:57 AM

I found the focus a little stiff on mine as well but before putting it back together after the fan install i degreased  then relubed it with mobil 1 synthetic which has a good low temperature viscosity. There is a Petro Can, grease that i prefer but the name escapes me at the moment. After that the focus was very smooth


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#56 walter a

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Posted 07 July 2016 - 10:57 AM

I think the name of the Petro Can grease Is XL3 Artic operating range is like -40 to + 100 C


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#57 kansas skies

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Posted 07 July 2016 - 12:23 PM

I've been using the Mobil 1 grease on just about everything since seeing it recommended on Celestron's website. It seems to work very well year round. Our temperatures here vary from sub-zero to over one hundred degrees Fahrenheit throughout the year and the grease handles it just fine. I like the feel that it imparts to the moving parts - not so thick as to impede fine adjustments, but thick enough to smooth out the rough spots.

 

Bill


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#58 RussL

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Posted 07 July 2016 - 11:01 PM

That is a Celestar 8 Standard. I have one just like it from 1999. There was also another version (called Ultima or Deluxe, I forget) that included a declination drive and a different looking wedge and tripod, and also included periodic error correction. The wedge/tripod you have is known as a "wedge pod." The legs aren't adjustable so you'll need to set up on level ground, unless you use shims. The OTA is basically a C8, only with better coatings. It's a very good scope. The 9v battery will give you about 50 hours of drive time. There is a good write up on Company 7 about it (sorry I don't know how to do a link).

Edited by RussL, 07 July 2016 - 11:07 PM.

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#59 Tom Stock

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Posted 09 July 2016 - 12:02 PM

I used the mobile one grease on my C8, absolutely perfect.


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#60 10100111001

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Posted 18 July 2016 - 03:09 PM

attachicon.gifDSC02055.JPG  attachicon.gifDSC02054.JPG

 

 

I seem to be becoming one of you.   :lol:

 

I just brought this home 20 minutes ago from an estate sale.  There are no prominent labels or model numbers.  Of the items unique to this system, it appears that only the hand controller is missing.  The optics appear to be in decent shape.

 

So I'm curious what became of this scope! Also, the optics look really nice from the photo.



#61 Tenacious

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Posted 24 July 2016 - 01:23 PM


So I'm curious what became of this scope! Also, the optics look really nice from the photo.

 

It's alive and well.  Aside from collimation, I've done little to the OTA so far.  I intend to disassemble it, clean the optics, renew the lubrication, repaint the cast aluminum parts, and I'm considering installing active cooling.

 

I have been focused on Tom Stock's findings about the springy, cantilevered base.  I still haven't made a replacement base yet, but, I took some photos of the experiments outlined in post #53.

 

DSC02073.JPG

 

This, I believe, is the intended configuration of the stock Deluxe wedge.  The threaded rod drives against the bottom of the cantilevered base and acts as a fine adjustment and safety for setting the latitude.  It is a 5/16-18NC threaded rod with a fancy T-handle that matches the others.

 

 

 

 

DSC02074.JPG

 

I bought a longer rod and tensioned it against the top of the cantilevered base.  This reduced the settle times, after touching the focuser, to a couple of seconds when I was careful.  Now, I want to refine and clean-up this approach with a new base, probably braced and made of wood.

 

While the fork itself still flexes, I'm now more convinced that the stock cantilevered base shared a resonant harmonic with the fork and compounded the problem.

1961


Edited by Tenacious, 24 July 2016 - 01:28 PM.

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#62 Tenacious

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Posted 26 September 2016 - 10:34 AM

I finally made a replacement base for the fork mount.  I took photos before painting it black so it would show up better.  I haven't had a chance to compare it, vibration-wise, to the stock base yet.  It's raining.

 

DSC02078.JPG   DSC02079.JPG

2315

 

DSC02080.JPG


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#63 Geo31

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Posted 26 September 2016 - 11:25 AM

A few things here...

 

1.  How have you determined that the forks are flexing?  I hardly thing it's impossible, but I suspect they get blamed a lot when the problem is elsewhere.

 

2.  I think you may find, as Tom did, that making a new mounting plate that lowers the base in the wedge will provide better vibration reduction

 

I've long suspected the culprit is not the forks, but the wedge mounting set-up.  It would be interesting to hear from someone who has mounted a C8 base on a permanent pier with no wedge, but a permanently mounted, polar aligned mounting base.  There are some long lever arms in the stock set-up.  First the mounting point of the scope to the wedge is extended a good deal out from the center of the tripod.  Then, the base is mounted somewhat high in the wedge.  So again, I'm curious how a C8, mounted to a permanent mount would perform.  I'll guess the forks do not vibrate as much as people think.


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#64 terraclarke

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Posted 26 September 2016 - 12:12 PM

That is s lovely new wedge you have made!


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#65 Tenacious

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Posted 03 October 2016 - 12:10 PM

I mounted the new wedge plate.

 

DSC02083.JPG

2516

 

 

Stability:

I got a break last night to test the settle times of the new base plate.  Any normal activity (focusing, advancing the RA, bumping the EP with my eye, ect.) would dampen out in 3 seconds or less.  A purposeful 'ting' with my knuckle was still just over the 3 seconds.  I suppose, to be really scientific about it, I should have a standard, repeatable disturbance, maybe a rubber ball on a 6" string that is always released from 30 degrees.  :grin:   The focuser is not buttery smooth yet (future project), it sort of 'jumps' or 'cogs' when trying to zero-in.  Still, when trying to focus very gently, the system would dampen in 2 seconds.

 

DSC02084.JPG

It is my belief that most of what remains of the instability is in the long arms of the fork.  Both of the forks I have (this new one and the original one from the wedge/pod) are open on the side facing the scope tube.  See the last photo.  There are screw standoffs molded into the arms.  It suggests that Celestron left an option there to include a stiffening plate on each arm.  So, could a plate and maybe some kind of filler enclosed in the arm improve the settle time of the system even more?

 

Of course, now I need to take it back apart, glue the wood pieces together, and paint them all with satin black.

 

Collimation

This is my first SCT and I am learning new things about collimation.  Adjusting the secondary is an exercise in minutia.  OTOH, the design wont give it's best view without very near perfect collimation.  I started off de-focusing out to several rings and adjusting them to be concentric (This works pretty well for long Newtonians).  Then, I brought it back to sharp focus.  I repeated the process for just 1 ring out of focus.  And finally, just a touch off from sharp focus, on either side, the star image 'flares' out to one direction.  I spent much time and very small tweaks of the collimating screws trying to make this light pattern equal around all sides of the star.  I was alone and still don't have it perfectly adjusted, but the view is much improved. I will go farther with this after the focuser has been serviced and re-lubed.     

 I will be bringing this technique back to my Newtonians.  :grin:  

 

DSC02085.JPG

 


Edited by Tenacious, 03 October 2016 - 12:15 PM.

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#66 Tom Stock

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Posted 17 October 2016 - 06:41 AM

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.

I found the flex to be in this order (most significant first):

 

1) The wedge plate (diving board)

2) The RA base .. the RA bearing hub flexing at the base. My old LX90 had this problem really bad.

3) The forks themselves (minor compared to the rest)


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#67 Tom Stock

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Posted 17 October 2016 - 06:50 AM

 

It is my belief that most of what remains of the instability is in the long arms of the fork.  Both of the forks I have (this new one and the original one from the wedge/pod) are open on the side facing the scope tube.  See the last photo.  There are screw standoffs molded into the arms.  It suggests that Celestron left an option there to include a stiffening plate on each arm.  So, could a plate and maybe some kind of filler enclosed in the arm improve the settle time of the system even more?

 

I found it was actually the RA bearing hub.. ie: the base of the fork mount which flexed the most.  Unfortunately there is no fix other than re-designing the base.   My LX90 suffered from this as well, REALLY badly, (only) when on a wedge.  Loved the scope but that was it's Achilles heel... no addition of super wedges and heavy tripods could fix that. 


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#68 Tom Stock

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Posted 17 October 2016 - 06:54 AM

There is one work around I saw here once but I can't remember who did it.

 

It involved a 2x4 attached to the wedge plate, with a heavy weight which rested on the ground.  The idea was to kill the spring action of the plate.

 

I read that it worked really well although I have never tried it.

 

I've used tie down straps from the corners of the wedge to the legs pulled tightly.  This is how I discovered it was actually the plate, not the wedge, which was flexing.


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#69 Geo31

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Posted 17 October 2016 - 04:50 PM

There is one work around I saw here once but I can't remember who did it.

 

It involved a 2x4 attached to the wedge plate, with a heavy weight which rested on the ground.  The idea was to kill the spring action of the plate.

 

I read that it worked really well although I have never tried it.

 

I've used tie down straps from the corners of the wedge to the legs pulled tightly.  This is how I discovered it was actually the plate, not the wedge, which was flexing.

I have the link on my home computer.  I'll try to remember to post it when I get home tonight.  I may forget.  Lots of LONG days lately and tonight is no exception.  Long day at work followed to traipsing up to the new house and doing a few things and then back to the old house.  Don't expect to be home before 10:00.

 

I had planned on making a new wedge plate and making the fixture described above, but I think once the RVC-6N is done I'm going to part with my C8.


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#70 Tenacious

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Posted 18 October 2016 - 10:22 AM

I glued the stiffeners to the new wedge plate and painted with satin black.  If a casual observer is not looking for a modification, they might not notice that it's been modified.

 

DSC02092.JPG    DSC02091.JPG

2764

 

Terminology:  Someone please correct me if I'm wrong.  I've been calling the new part a wedge plate.  The slotted cast bracket on either side that bolts to the top of the tripod looks like the wedge.

 

"..I've used tie down straps from the corners of the wedge to the legs pulled tightly.  This is how I discovered it was actually the plate, not the wedge, which was flexing."  

 

I wondered how you came to this insight.  The fork arms are the more obvious suspect in my mind.  Given a modest tap with a knuckle, my fork arms can be set in motion.

 

 

"..I found it was actually the RA bearing hub.. ie: the base of the fork mount which flexed the most.  Unfortunately there is no fix other than re-designing the base.   My LX90 suffered from this as well, REALLY badly, (only) when on a wedge.  Loved the scope but that was it's Achilles heel... no addition of super wedges and heavy tripods could fix that."  

 

I haven't noticed this. but, I haven't been trying to isolate the hub yet, either.  There is a noticeable difference in the base castings of the old wedge/pod and this newer deluxe model.  The old has a simple bolt (1/2" diameter?) coming up from the bottom.  The new has an axle cast into the base with stiffening gussets, probably 2-1/2" in diameter.   I haven't been in there yet, but I'll bet the bearing is much larger.  Maybe that's why this drive requires two 9 VDC batteries instead of one.  :lol:


Edited by Tenacious, 18 October 2016 - 10:48 AM.

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#71 Tenacious

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Posted 18 October 2016 - 10:41 AM

 

There is one work around I saw here once but I can't remember who did it.

 

It involved a 2x4 attached to the wedge plate, with a heavy weight which rested on the ground.  The idea was to kill the spring action of the plate.

 

I read that it worked really well although I have never tried it.

 

I've used tie down straps from the corners of the wedge to the legs pulled tightly.  This is how I discovered it was actually the plate, not the wedge, which was flexing.

I have the link on my home computer.  I'll try to remember to post it when I get home tonight.  I may forget.  Lots of LONG days lately and tonight is no exception.  Long day at work followed to traipsing up to the new house and doing a few things and then back to the old house.  Don't expect to be home before 10:00.

 

I had planned on making a new wedge plate and making the fixture described above, but I think once the RVC-6N is done I'm going to part with my C8.

Did you have any luck finding the link?  I'd be interested to see it.



#72 Geo31

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Posted 18 October 2016 - 11:04 AM

I never made it back to the "old" house last night.  By the time I got to the new house last night I was done driving.

 

I was able to conger up a good search and hit on the first try.  Here you go.  Bottom of the page:

 

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

 

Regarding the fork arms, I still think they are the least of the problem.  As I stated before, the C8 on a standard wedge with tripod has 3 long lever-arms that are not well supported.  From an engineering standpoint, it's a bit of a nightmare. The forks, being the last link in the chain, are going to feel the effects of the wedge and mounting plate.

 

Tom remade the mounting plate so it sits lower in the wedge.  This is something I've been wanting to do.  With the Super C8 it may take flipping the base to get it low enough.  If I were to build a new wedge from a clean sheet of paper, I'd probably not have the wedge extend so far from the center of the tripod.  I can see why Celestron (and later Meade) did this.  The CG of the entire system ends up more or less centered over the tripod, but I'd rather sacrifice this a bit for a little more stability from a shorter lever-arm.

 

Again, I'll bet a C8 mounted on a solid permanent pier (angled - no wedge) would be far more vibration resistant.  I've never had the opportunity to test this though.



#73 Geo31

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Posted 18 October 2016 - 11:13 AM

Oh, and another compromise in the standard wedge is the need to support a wide range of latitudes.  Very low latitudes could potentially cause the forks to contact the wedge as you rotate in RA.

 

So in short (pun intended) if I were building a new wedge (especially for a very limited latitude adjustment for local viewing) I'd try to make the following changes:

 

1.  Shorten the overhang of the wedge from the tripod

2.  Extend the sides all the way back to the furthest mounting bolt on the wedge

3.  Lower the mounting plate in the wedge

4.  Stiffen the connection between the mounting plate and the wedge by using a side piece on the mounting plate that utilized two mounting screws to secure the angle of the mounting plate.

 

Again, it is my belief the wedge is the culprit, not the fork arms (or perhaps to a much lesser extent).



#74 Spacefreak1974

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Posted 18 October 2016 - 11:54 AM

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.

 

attachicon.gifLX50 TW1-1j.jpg

I'm thinking of getting the AR102/Twilight 1 Combo as a Grab and Go scope. Its nice to see the Twilight 1 will support an 8" SCT if I choose to do that as well. Is it pretty stable?



#75 Spacefreak1974

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Posted 18 October 2016 - 12:04 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.

I had a Meade LX10 8" SCT from a similar era. I tested the RA drive by sitting the scope on the floor with the scope perpendicular (not on the wedge), locking it and adding a piece of tape on the inside and outside (lined up) along the marks on the axis. If it moves then likely it will track fine. I turned it on and checked after a half hr. By sitting it flat this has the least amount of resistance on the motor and gears. If it works like this then try it on the wedge.Polar aligning a wedge is not that difficult. Some think it is but I was able to get good polar alignments with my LX10 that would track objects for over an hr at times. Lots of videos on Youtube!

 

Jon


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