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125 ETX Focusing Problem

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#1 REC

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Posted 11 April 2013 - 09:57 AM

My 125 ETX has real bad image drift to the point of the object moving out of the FOV and have to move the scope as I try to get it in focus. I have tried moving the focus knob all the way one way and back, but not much improvement/

Is there any step by step method for removing the back and tighten the focuser as something back there must be loose. I don't have any problems focusing my 90ETX.

Pictures of te steps or how to video would be great!

Thanks,

Bob

#2 tomatohead

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Posted 11 April 2013 - 05:44 PM

this may help:http://www.weasner.com/etx/techtips/2011/etx125_focus_mod.html

#3 redlinedb16a

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Posted 25 April 2013 - 12:04 PM

I ripped mine to pieces a few times
Nothing to it
Grab the purple tube and unscrew it carefully

It will give you a perfect view of the mirror and slide
I regreased my slide and that corrected it

There's no adjustment on the focus
It's just a threaded rod.
I have a step by step here
http://www.astronomy...mbly-my-ota-...
If you can't view the pics let me know

The etx is easy

#4 REC

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Posted 26 April 2013 - 10:14 AM

Well I was at the Meade booth at NEAF last week and the tech guy suggested the same thing, unscrew the barrel to get at the focuser. The only thing he cautioned is that once you open it up, you take the chance of messing up the collimation. So is this way better then opening up the back of the housing?

I'll try this link you listed, but looks like I have to subscribe or join?

Thanks for your help!

Bob

#5 redlinedb16a

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Posted 26 April 2013 - 10:28 AM

When I get home ill post pics
Yes if you unscrew the corrector plate or tube there is a chance you the alignment can be off
Mine has be apart several times and I have zero issues
Images are extremely crisp

Pay attention to how tight the tube was
Make alignment marks to ensure you don't over or under tighten it when putting it back together

Personally if you pull it apart I'd flock the tube,flocking made a world of diffrence in mine,I gather more light now

When you remove the mirror and grease the slide the grease will take up some slack which will help
I used gray Molly grease
On the focus rod also

#6 REC

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Posted 26 April 2013 - 10:33 AM

Ok, found your article and pictures. Where and what do I grease? Is there anything I have to tighten to help remove the image drift?

Bob

#7 redlinedb16a

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Posted 26 April 2013 - 12:39 PM

I removed the mirror and the mirror holder as one assembly
I applied a lite coat of grease onto the outside of the tube that the mirror/holder slide on
When you unscrew your tube and remove it,the mirror will be attached to the rear section
Work the focus knob and you will see what moves and what doesn't

That should show what needs to be greased

The only way to align the mirrors perfect again is too send it to meade or experiment which I wouldn't do unless I absolutely had to

On the back of the ota if you further dissassembly the scope there's are collimnation screws marked with red paint

I don't see unscrewing the tube having much mis alignment effects unless you screw it on way tighter or looser than when you pulled it off

Now with that said I'm in no way telling you to move foward
If you are not comfortable or mechanically inclined it may not be a good idea

On a 1-10 scale with 10 being the most difficult
To me it's a 2,easy and wear latex gloves in a clean environment

#8 redlinedb16a

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Posted 26 April 2013 - 12:46 PM

Look at the black tube in the center of the mirror

That's the tube that needs grease
There is a small metal ring that acts as a clip to hold the mirror on
That must be removed to be able to slide the mirror holder off the shaft
Posted Image

I don't quite remember what holds the focus shaft onto the mirror holder which I why I said unscrew the whole ota purple tube
That will allow you to see behind the mirror

#9 redlinedb16a

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Posted 26 April 2013 - 02:02 PM

After going thru my memory and photos
Here's the back of the ota behind the plastic
Pull off the focus knob unscrew the tube pull
If you choose to remove the mirror and mirror holder remove the clip on the small tube
Slide mirror/holder and focus shaft comes with it

Here's some pics
Posted Image
Notice the screws with red paint,I wouldn't touch those as they are for aligning the mirrors

And notice the clip on the tube that needs to be removed if you choose to remove the mirror
Posted Image

Now if your not sure about removing the mirror it can be grease in place but carefully not to get excess grease on the mirror
Bring the mirror all the way back like on my pick
Grease the front half of the tube.
Bring the mirror all the way to the front against the clip and grease the back half
Just a thin coat,nothing that drips or could fall off

What the grease does is lubricates of corse but grease will fill the gap between the tubes and will make it harder for image shift to occur

As I put my grease on I rotated my mirror around the tube as I pushed it down the slide to help evenly distribute the coat of grease.

I wiped off the lil extra that built up on the back side of the mirror holder

Honestly it's all easy to do
Just take your time and don't drop anything or touch the reflective mirror service

#10 REC

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Posted 26 April 2013 - 02:34 PM

Well thank you very much for these step by step instructions and pictures and yes they are worth a thousand words:)

For the grease, what do I use and where do I get it?

Then the other matter is how to remove the scope from the fork mount as I guess that has to be done first?

Bob

#11 redlinedb16a

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Posted 26 April 2013 - 03:15 PM

Leave the scope on the mount

Just grip the purple ota and turn it counter clockwise
Remove just the purple tube

The plastic back of the scope will remain on the forks

If you want to remove the mirror get a .50 mm Allen wrench remove the focus knob

Remove the lil metal circle clip on the small tube

Simply slide the mirror assembly off

Grease shaft and re install

#12 redlinedb16a

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Posted 26 April 2013 - 03:21 PM

I removed my whole assembly cause my scope got rained on and debris inside
The etx 125 is Not a sealed ota
Look under the tube where the 1/4" 20 tripod mount is.....that's an opening in that 1/4" gap that allows debris in

#13 redlinedb16a

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Posted 26 April 2013 - 07:25 PM

Sorry forgot about the grease
I bought some napa Molly lube
It's thin and gray
I used it on my lx200 gears
Great stuff

#14 REC

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Posted 27 April 2013 - 08:24 AM

Ok well I think I have enough information to tackle this project now. Need to find the grease in a local store if I can, otherwise I'll have to order a tube online. Any other type that you know of that is in a retail store?

Thanks so much for taking the time to help me with this solution :bow:

Bob

#15 rtanton

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Posted 27 April 2013 - 10:00 AM

Another alternative would be Dow Corning high vacuum grease. It is a good lube for applications other than metal to metal at high speed. It is silicone based with fumed silica filler and its viscosity will not change with temperature. Because it is silicone you need be careful where it is applied. Being stripped of light ends it will not migrate onto optics as a vapor. You can find small quantities on line e.g. http://www.amazon.co...p/B00B3O2YW4...

#16 redlinedb16a

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Posted 27 April 2013 - 12:38 PM

Lowes or homedepot will have grease
The thicker the grease the more resistance you will have which will allow less image shift
Some types of grease would act like glue
Stay away from red or blue grease
White,light brown will do also

#17 REC

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Posted 27 April 2013 - 02:33 PM

I forgot to ask from your last reply about flocking. In this picture it looks like you have lined the inner tube with some kind of felt or something? What do you suggest I use and how do you go about flocking it?

#18 redlinedb16a

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Posted 27 April 2013 - 03:22 PM

I got my flocking from scopestuff.com
Extremely fast shipping

However the flocking is not easy to do perfect
If you do mess up the glue is so strong it will rip the flocking off if you pull it apart then the glue has to be scrapped out

It's not to hard but a pain if you mess up
http://www.scopestuff.com/ss_flok.htm

Google telescope flocking,I think there's other stuff too

#19 Geo.

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Posted 27 April 2013 - 07:33 PM

The worst mirror flop I ever saw was in a 125. +1 for the dow grease. The small tub they sell on eBay will service several scopes.

The only way to screw up the collimation is to fool with those screws with the red thread lock on 'em.

#20 REC

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Posted 28 April 2013 - 09:07 AM

Thanks George, did you flock your tube too?

Bob

#21 rtanton

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Posted 28 April 2013 - 11:41 AM

Bob, a very important grease function is to minimize dreaded mirror shift...more so than lubricity. Too much lubricity can actually be a problem. While working at Meade, I had our guys try a silicone based lube containing PTFE. My thought was that a stable viscosity with temperature fluctuation combined with excellent lubricity would be a winning combination. I was wrong! Tests showed a very smooth focus: however, the lubricity was too much and the mirror refused to stay put when the scope was tilted upward...this was on a larger scope, but I would be concerned even on an LS.

Russ

#22 Geo.

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Posted 28 April 2013 - 04:10 PM

Yes, I usually flock my tubes. The ETX is a lot easier than say a C11. Just thread off the tube and go to work. I usually pull the optics on a SCT to avoid any sticky situations. :foreheadslap:

#23 redlinedb16a

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Posted 04 May 2013 - 11:35 AM

How did it go?

#24 REC

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Posted 04 May 2013 - 12:43 PM

I have not picked up the grease yet, have to order it. Will do that today. I did rack the focuser in and out a couple of times and it did help some, at least the target does not go out of the FOV!

Bob

#25 REC

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Posted 04 May 2013 - 12:45 PM

Redline, BTW I passed on your instructions to a guy at Meade I know and he said they were excellent directions! If he gets any questions from the field on this topic he will recommend your posts.






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