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1970s Orange Celestron C8

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#26 Tom Stock

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Posted 02 August 2020 - 04:39 AM

pick out the plastic and you will find they are standard socket head screws.

#27 Beeham

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Posted 02 August 2020 - 06:58 AM

UPDATE:

 

The T adaptor came and it's too small. Only threads on about 1.25 rotations, just as everyone else has explained.

 

It did thread on enough to attach my camera without falling off and achieve prime focus, which was pretty fun. Even with this half-on t adaptor I was able to see Jupiter and its jovian moons, Saturn (albeit no ring detail or definition, but an oblong shape to silhouette, if you will, the rings), and a nice close up of the moon.

 

Next step is to try the diagonal which is coming today. If that doesn't thread on properly either, then I'll do the grinding/lubrication process which I am utterly unfamiliar with. However, from what I've read, I am willing to take on the challenge.

 

Clear skies.

I've poked around the topic of the SCT threads on older Celestrons a bit myself, and as best as I can discern, the issue is not that they changed threads - all orange-tubes have the same 2" x 24tpi nominal threads.  (This exempts the really early non-orange versions.)  The issue is the tolerance spec on the threads; the early scopes had "tight tolerance" threads and the newer ones have "looser tolerance" threads.  This results in the male threads (on the scope) being slightly larger on older scopes than on newer.

 

As a result, old accessories (female threads) seem to fit on everything, new accessories seems to sometimes not fit old scopes, as you are experiencing.

 

Note that this is not a 100% phenomenon - I have a contemporary 2" diagonal that threaded on to my 1977 C8 like butter, but a contemporary focal reducer would bind.  It seems it depends on the specific tolerances of the accessory and the scope.

 

The thread-lapping route (which sounds like what you need) will knock down the threads a few thousandths of an inch and make them behave like contemporary threads.  The only other option I am aware of is doing the trial-and-error route to find accessories that happen to have the right fit to thread on easily, but that's time consuming.

 

I think you're doing the right thing just lapping the threads.

 

Just my $0.02. I hope this is helpful - good luck with your project!


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#28 Beeham

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Posted 02 August 2020 - 07:04 AM

 

 

Exactly which diagonal is this? Could you possibly provide a link?

The 2" diagonal I use on my 1977 C8 is the Apertura (house brand) from High Point Scientific.

 

https://www.highpoin...agonal-d2qcfsct

 

It threaded on to my C8 with no problem.  I have had binding with other contemporary SCT threads.  The Apertura just seems to have the right thread tolerance to match the old tight-tolerance threads; whether this is due to the spec in the Apertura machining (which I doubt) or just dumb luck with respect to tolerance is open to speculation.

 

That being said - I've had no problems with the Apertura, for a mid-grade diagonal it actually seems quite nice. 



#29 tim53

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Posted 02 August 2020 - 11:14 AM

His tripod looks to be a 1983 or later tripod. They were known to have leg locks that broke. I had one and loved it.

I have one of these that was NOS when Frank's Camera in Highland Park closed down.  I'd love to use it.  I've heard that the leg locks can be replaced with metal locks, but it's been so long I don't recall where they come from.



#30 davidmcgo

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Posted 02 August 2020 - 11:23 AM

Bicycle seat post clamps if I recall.

 

Dave


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#31 Kasmos

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Posted 02 August 2020 - 04:30 PM

About the VBs and threads. I've had my C90 since '79 and C8 since '80. Back then the visual back I bought for my C90's Large Accessory Ring would thread on fine, but it needed a gasket made to fully tighten against it. The VB that came with C8 had no problem going on it, so I suppose there's always a chance of some variables.



#32 Defenderslideguitar

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Posted 02 August 2020 - 06:53 PM

I think I have two of them ……………………. I'll check   but as I recall they fit on both my 1979 die cast C-8  and my just departed  73 sandcast



#33 Littlegreenman

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Posted 03 August 2020 - 04:19 PM

I've poked around the topic of the SCT threads on older Celestrons a bit myself, and as best as I can discern, the issue is not that they changed threads - all orange-tubes have the same 2" x 24tpi nominal threads.  (This exempts the really early non-orange versions.)  The issue is the tolerance spec on the threads; the early scopes had "tight tolerance" threads and the newer ones have "looser tolerance" threads.  This results in the male threads (on the scope) being slightly larger on older scopes than on newer.

 

As a result, old accessories (female threads) seem to fit on everything, new accessories seems to sometimes not fit old scopes, as you are experiencing.

 

Note that this is not a 100% phenomenon - I have a contemporary 2" diagonal that threaded on to my 1977 C8 like butter, but a contemporary focal reducer would bind.  It seems it depends on the specific tolerances of the accessory and the scope.

 

The thread-lapping route (which sounds like what you need) will knock down the threads a few thousandths of an inch and make them behave like contemporary threads.  The only other option I am aware of is doing the trial-and-error route to find accessories that happen to have the right fit to thread on easily, but that's time consuming.

 

I think you're doing the right thing just lapping the threads.

 

Just my $0.02. I hope this is helpful - good luck with your project!

I had an early C8; a Tele-Vue low profile VB would jam after 1 turn and a half on that. Then I bought a one -speed SCT Crayford focuser, early 2000's. I think it was branded William Optics but was sold another name as well.

 

More detail point #1: Tele Vue sells an SCT Rich View Kit, consisting of a 2" SCT visual back, a 2" diagonal, and a Panoptic 35mm eyepiece. Absolutely wonderful for looking at Scorpio, the Lagoon Nebula, etc.

Point #2: There was a time in our hobby before you could buy a 2 speed focuser. Now they seem to be an almost must-have or required.

 

Since that time I have read on various internet forums multiple explanations for the C8 SCT focuser problem. It's one of those things that if you ask 3 "experts" you will get 5 opinions.

But, ignoring explanations the result is the same: some accessories will fit, some won't, and thread lapping will fix it.

Please, if you have any 1970's era C8 with a visual back fits/works, keep the two together if you ever sell it!  Think of it as improving the universe.
 


Edited by Littlegreenman, 03 August 2020 - 04:21 PM.

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#34 trigger

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Posted 03 August 2020 - 05:06 PM

I agree with the socket head screws and new nylon washers. Doing that to my 90's Meade now.



#35 Cosmic_Lox

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Posted 04 August 2020 - 04:26 PM

The diagonal came today and it fits! If anyone is wondering, it's made by ProOptic and is 2" with the 1.25" adapter. 

 

Here are some pictures: 

 

 

 

 

 

 

 

Attached Thumbnails

  • IMG_7417 copy.jpg
  • IMG_7416 copy.jpg

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#36 bob midiri

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Posted 04 August 2020 - 06:48 PM

Awesome Eric, you are ready to observe now. Make sure you align the finder with main scope during daytime so you will be ready to observe tonite. Good luck, let us know how first light is ! Bob


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#37 Cosmic_Lox

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Posted 04 August 2020 - 09:44 PM

I have technically already witnessed first light a few days ago. The past few nights I have been viewing via my Nikon d3100 and (slightly too small) t adaptor screwed right onto the backplate. (I do not own a visual back for the telescope and I had no means of inserting an eyepiece until today.) The t adapter screwed on just enough for my camera to stay on with just a little bit of play. I was surprisingly able to achieve prime focus, but I'm pretty sure the Ota is in dire need of collimation. Although I can focus in on stars, etc, detail is no where near as sharp as it should be. I will collimate it in just over an hour when it's dark outside and see if this solves the problem.

 

Here is a single frame of Jupiter last night: 

 

DSC_0472 copy.jpg

 

Hard to tell with a single (and such a quick) frame, but I do think the collimation is off. I didn't know how to check collimation by defocusing on a star, so I will try that tonight. It should be much easier tonight anyway because I can use my eyepieces now. 

 

So, tonight will be first light with an eyepiece and properly fitted. Very exciting! 


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#38 Cosmic_Lox

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Posted 05 August 2020 - 07:31 PM

It got worse before it got better, but eventually I did get it (somewhat) better collimated. I will give it another go tonight.

 

I observed Saturn and the surface detail was vaguely apparent, Cassini division clearly visible. Light pollution is extremely heavy and seeing conditions were less than ideal, maybe 2 or 3 out of 5. It was pretty cool!

 

If anyone lives near CSUN and wants to help out, that would be great. If not, I will get this thing properly collimated or die trying. 


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#39 ANM

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Posted 07 August 2020 - 04:52 PM

Also, just wanted to mention, I wanted to post a picture of the serial number on my OTA, but it appears to literally be scratched off. 
 
 attachicon.gifimage1.jpeg
 
Weird, huh? Some rebel amateur astronomers stealing telescopes and trying to cover their tracks? lol.gif
 
Oh, and when messing with the wedge, trying to adjust the angle of the mount, the plastic 'wings' on the screws broke off. All of them. My needle nose pliers are not doing the job. I don't have many tools, any suggestions? Obviously, I'll try a standard adjustable wrench, but I doubt it will properly grip.

 

attachicon.gifimage1 2.jpeg

 

 

Thank to anyone who can help,

Eric

You need to replace them with these:

https://www.ebay.com...nIAAOSw4VpcFMAa

All the knobs on my C* wedge are these, just make sure you get the right size...


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#40 Cosmic_Lox

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Posted 07 August 2020 - 07:30 PM

Well, the telescope is definitely better collimated. The tracking is hit or miss, it will track fine for a few minutes, and then track incredibly poor for a few minutes, and so on. Maybe the gears need to be greased? Or, perhaps, it is the not-so-even ground that I am set up on. 

 

Anyway, here is Jupiter from last night: 

 

Jupiter.jpg

 

[nikon d3100 at prime focus, 2x Barlow. Preprocessed in PIPP and best 35% of around 4000 frames stacked in AS, no wavelet adjustments or sharpening.]

 

 


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#41 bob midiri

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Posted 07 August 2020 - 08:17 PM

very nice image!!


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#42 davidmcgo

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Posted 07 August 2020 - 08:28 PM

Unfortunately the erratic drive was pretty normal for these.

 

Dave



#43 Cosmic_Lox

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Posted 07 August 2020 - 08:58 PM

Dave,

 

I'm hoping there is a way to get the tracking decent enough to at least observe or image a planet for a few minutes without having it drift out of my field of view.

 

Is there anything that can be done to help with tracking (ie greasing gears etc.)? Or, if it is tracking to the best of its ability, how can I tell? If properly polar aligned and mount is level, about how long should Jupiter stay in the field of view? (I'm using an SCT 2" diagonal with 1.25" adapter, Nikon dslr with 1.25" t adapter (nose-piece) inserted into the diagonal, and a 2x Barlow.)

 

Thanks,

Eric



#44 Don W

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Posted 07 August 2020 - 09:27 PM

Are you 100% sure you have an accurate polar alignment?

 

Here's a link to the user manual for that scope:

 

http://www.company7....8manual1971.pdf

 

Polar alignment starts on page 12.


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#45 Kasmos

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Posted 07 August 2020 - 09:49 PM

Dave,

 

I'm hoping there is a way to get the tracking decent enough to at least observe or image a planet for a few minutes without having it drift out of my field of view.

 

Is there anything that can be done to help with tracking (ie greasing gears etc.)? Or, if it is tracking to the best of its ability, how can I tell? If properly polar aligned and mount is level, about how long should Jupiter stay in the field of view? (I'm using an SCT 2" diagonal with 1.25" adapter, Nikon dslr with 1.25" t adapter (nose-piece) inserted into the diagonal, and a 2x Barlow.)

 

Thanks,

Eric

It's probably the added weight of your camera depending on the scopes position. The scope really should be more or less balanced so not to put strain on the drive. Celestron sold thread on weights that went on the front cell to balance the tube when using cameras etc. Also, if you don't have a drive corrector it can drift especially at high powers. They usually have has a speed control with two buttons for quick fast and slow  correctins.

 

For more info check out this link and scroll down to the owners manual

https://www.astronom...lum.com/c8.html


Edited by Kasmos, 07 August 2020 - 09:53 PM.

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#46 Cosmic_Lox

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Posted 07 August 2020 - 10:40 PM

Don

 

Such a great manual. I was absolutely polar aligned. To what degree to accuracy? I don't know. Probably not incredibly accurate, but centered with a 12.5mm eyepiece. I think the problem might be leaving the RA clamp unengaged. I didn't know that clamp "'locks' the fork mount to the drive system" (manual page 15). Tonight, I'll make sure to have the RA clamp engaged while recording my videos and see how it does tracking.

 

 

Kasmos

 

I am very interested in looking for one of those drive correctors though. And I'll absolutely get some counterweights! 



#47 davidmcgo

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Posted 07 August 2020 - 11:20 PM

That would make a big difference!  But there is a lot of error in the two motor spur gear and when I try imaging I usually discard a lot of frames as it tends to jump back and forth.  A worm drive would have been a big improvement.

 

Dave



#48 bob midiri

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Posted 08 August 2020 - 07:33 AM

For drive corrector you might want to get a motor dec for this scope, so if you buy a used dual axis drive corrector you have both RA and dec control. I think you need some counterweights to balance camera. Bob



#49 ANM

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Posted 08 August 2020 - 08:58 AM

Well, the telescope is definitely better collimated. The tracking is hit or miss, it will track fine for a few minutes, and then track incredibly poor for a few minutes, and so on. Maybe the gears need to be greased? Or, perhaps, it is the not-so-even ground that I am set up on. 

 

Anyway, here is Jupiter from last night: 

 

attachicon.gifJupiter.jpg

 

[nikon d3100 at prime focus, 2x Barlow. Preprocessed in PIPP and best 35% of around 4000 frames stacked in AS, no wavelet adjustments or sharpening.]

I don't think you have much to complain about...


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#50 Cosmic_Lox

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Posted 09 August 2020 - 08:08 PM

Saturn from two nights ago with the orange C8 and a Nikon d3100: 

 

IMG_7439-1.JPEG

 

I just purchased an asi 120mc super speed, so the planetary hunt is on!


Edited by Cosmic_Lox, 09 August 2020 - 08:09 PM.

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