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Plans for no-flop mirrors modification for C EdgeHD's?

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19 replies to this topic

#1 George P Dunham

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Posted 19 February 2019 - 06:52 PM

My understanding is that the Celestron RASA line has a no-flop focuser mechanism.  Is there any plan for Celestron or a third party to offer this as a modification for existing Celestron SCT's?  It would be a real treat to eliminate mirror flop in an otherwise decent telescope.



#2 pkrallis

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Posted 19 February 2019 - 08:17 PM

I wouldn't hold my breath.



#3 WadeH237

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Posted 19 February 2019 - 09:05 PM

That focuser was designed by a frequent contributor to these forums.  He has said in the past that it would not be feasible to retrofit it to existing scopes.


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#4 George P Dunham

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Posted 19 February 2019 - 11:27 PM

That was what I was hoping to dig up.  Thanks Soyuz.

 

Then is the nylon screw method a reasonable DIY fix?



#5 Michael Covington

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Posted 20 February 2019 - 12:21 AM

The EdgeHDs already have a mirror lockdown mechanism.  I have not tested it thoroughly, but it's definitely better than nothing.



#6 Rovert9988

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Posted 20 February 2019 - 12:25 AM

As Michael mentioned the Edge scopes have mirror locks. I've noticed that they do help reduce mirror flop. Overall they seem to work decently, but definitely allow for some mirror movement still.

#7 George P Dunham

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Posted 20 February 2019 - 09:30 AM

Locks don't help with remotely operated Hyperstar configured Edge scopes when on an imaging run.  My mirror flop is pretty minimal but it makes my t-point model and protrack modeled tracking less than optimal.



#8 rmollise

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Posted 20 February 2019 - 11:22 AM

My understanding is that the Celestron RASA line has a no-flop focuser mechanism.  Is there any plan for Celestron or a third party to offer this as a modification for existing Celestron SCT's?  It would be a real treat to eliminate mirror flop in an otherwise decent telescope.

That's already there in the form of the Edge's mirror locks, which do eliminate mirror flop. Or are you talking about focus shift?



#9 aruckle

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Posted 20 February 2019 - 01:41 PM

Last year we installed mirror locks on our C14 which I would think "parking brakes" would be a more descriptive term for what they do.

 

They work very well for an attended scope but would not be suitable for a remotely operated scope as build.  However with some added work and two electric solenoids, could be suitable for remote installations. 

 

The parts used to make them were not expensive at all however, we did do a bit of machining of the standard parts purchased of the hardware store and drill and tap two holes in the back of the C11.

 

 

aruckle

Attached Thumbnails

  • Mirror lock parts layout #3.jpg
  • C14 mirror locks installed.jpg


#10 WadeH237

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Posted 20 February 2019 - 02:32 PM

Guys,

 

I believe that this thread is about the new zero-shift focuser that Celestron is using on the RASA 8 and 14 scopes.  I do not believe that it's about mirror locks.

 

Different things.



#11 George P Dunham

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Posted 20 February 2019 - 03:27 PM

Guys,

 

I believe that this thread is about the new zero-shift focuser that Celestron is using on the RASA 8 and 14 scopes.  I do not believe that it's about mirror locks.

 

Different things.

Yes....not about locks.  Unless someone makes or wants to make computer actuated locks for remote imaging runs with autofocus on a hyperstar configured edge.



#12 George P Dunham

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Posted 20 February 2019 - 04:16 PM

That's already there in the form of the Edge's mirror locks, which do eliminate mirror flop. Or are you talking about focus shift?

No...I want to address the flop that occurs as the telescope changes position.  I use TSXpro and use a 300 point t-point model.  It builds a great model and pointing is within a few arc minutes and tracking allows for 4 minute unguided exposures with ProTrack running.  If I had not mirror flop I can get 20 minute unguided exposures.  I've done this by building the model with the mirror locked but at some point I need to focus and at that point I may or may not introduce error which throws my model off and tracking is reduced to 4 minute unguided.  I can autoguide with great results but twenty minutes unguided is more that enough for anything I do with hyperstar...I guess I'm spoiled.



#13 DuncanM

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Posted 20 February 2019 - 04:20 PM

Locks don't help with remotely operated Hyperstar configured Edge scopes when on an imaging run.  My mirror flop is pretty minimal but it makes my t-point model and protrack modeled tracking less than optimal.

 

 

What camera are you using? Could a thin OAG be inserted into the image train?


Edited by DuncanM, 20 February 2019 - 04:23 PM.


#14 lwool

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Posted 08 March 2019 - 08:18 AM

I bought a C8 Classic XLT in 1990, it has a bad case of mirror flop.  So bad that if it's collimated on one side of zenith the moved to the other side it is out of alignment.

 

 I have disassembled the complete OTA to determine the best way to fix it.

 

I have the tube on a surface plate now and was able to get a dial indicator on the front of the mirror mount to measure deflection between the baffle tube and mirror mount assembly.

 

It measured .005" so I removed the primary mirror, cleaned the grease off all components and measured the clearance both front and rear.  It measured .006" front and .008" rear of slop.

 

This is WAY more than can be fixed with grease!

 

I am making holders with elastomeric rings to fix this, these rings are 60 shore a durometer so they can be installed with no clearance and lubricated with Corning high vacuum grease.

 

If this doesn't fix the problem I sure don't know what would.

 

I have tested the mirror motion with these rings to be sure there would not be a problem with stiction, they seem to be very smooth.

 

I plan to place re-black the tube I.D. and place it in a 125f oven to cure the paint and then once again to off gas the lube before re-assembly.

 

Is there anything else I should do to this telescope before closing it up?

 

Thanks for any advice you can offer.


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#15 rmollise

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Posted 08 March 2019 - 11:42 AM

Guys,

 

I believe that this thread is about the new zero-shift focuser that Celestron is using on the RASA 8 and 14 scopes.  I do not believe that it's about mirror locks.

 

Different things.

Nevertheless, the title of the thread is "flop," NOT "focus shift." ;)


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#16 WadeH237

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Posted 08 March 2019 - 02:25 PM

Nevertheless, the title of the thread is "flop," NOT "focus shift." wink.gif

But the context in the very first post makes it clear what he's actually asking about :)



#17 George P Dunham

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Posted 08 March 2019 - 05:22 PM

Being the OP, I will refresh.  I was asking about mods or fixes for "flop" that occurs with changes in position of the OTA ... not focus shift (if they can be separated).  I was curious if Celestron or a 3rd party had a back compatible modification.  The answer was no...bummer.  I then asked if the "nylon screw" mod was a good alternative.  Still haven't heard.

 

My concern is about tracking accuracy with a TheSkyX pro/Protrack and a good t-point model.  Once "flop occurs which isn't model-able, the tracking accuracy is degraded.  With my C14 EdgeHD on a MX+ mount and a good model...I am able to track unguided for up to about 4 minutes which is quite good for what ever flop is occurring.   If my scope had no mirror flop, I could track for up to 20 minutes unguided.  I have done this with a t-point model inplace and the mirror locked.  As soon as I focus though, my accuracy degrades due to flop.

 

I am focusing periodically during remote imaging sessions with a hyperstar set up so the mirror must remain unlocked.



#18 WadeH237

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Posted 08 March 2019 - 06:40 PM

I stand corrected.

 

The new RASA focuser is a zero shift focuser.  As a side effect, I presume that it also addresses mirror flop while tracking.

 

There are aftermarket solutions (completely unlike the RASA focuser) to address mirror flop while tracking, but they preclude the possibility of focusing while the mirror is locked, which would effectively eliminate them as a possibility for Hyperstar.

 

In any event, the answer remains the same.



#19 rmollise

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Posted 09 March 2019 - 07:29 AM

But the context in the very first post makes it clear what he's actually asking about smile.gif

Clear? Hardly. :)


Edited by rmollise, 09 March 2019 - 07:30 AM.


#20 WadeH237

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Posted 09 March 2019 - 08:46 AM

Clear? Hardly. smile.gif

Agreed, as my post immediately above this says.

 

Clear skies :)




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