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kljw
member


Reged: 01/24/13

Loc: Scotland
Image Shift
      #5775190 - 04/03/13 10:32 AM

Hi
i have recently (Feb 2013) took delivery of a LX200 12". last night was my first time out, due the need to get a buggy made to move the scope about.
when trying to focus, using the focus knob on the scope, i noticed that the image appeared to move across the eyepeace, so by the time it was in focus i had to centre the object again.
when i fine tuned the focus, with the meade electronic unit, the image stayed central.
can any one offer a reason for this please?

many thanks


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Spacetravelerx
Pooh-Bah


Reged: 12/23/12

Loc: New Mexico
Re: Image Shift new [Re: kljw]
      #5775295 - 04/03/13 11:14 AM

Keith,

You are experiencing the very famous "Focusing Shift". This happens when focusing you are mechanically moving the mirror and the mirror tilts very slightly as it is moving up and down the tube - hence the shift in your eyepiece.

The Meade Zero Image Electronic Micro focuser of course does not shift the mirror at all, hence no image shift.

Note, the new LX600 and LX850 have Internal Crayford-Style 7:1 focusers to eliminate focus shifting. The LX850 also includes the motor focus for good measure.


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kljw
member


Reged: 01/24/13

Loc: Scotland
Re: Image Shift new [Re: Spacetravelerx]
      #5775346 - 04/03/13 11:32 AM

Andrew
thats fine, as long as i have not broken things, i can live with it.....

many thanks.

Keith


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jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: Image Shift new [Re: kljw]
      #5775357 - 04/03/13 11:36 AM

Quote:

as long as i have not broken things, i can live with it.....




No, nothing is broken - and you can easily minimize the effect by always finishing your focusing in the direction that is lifting the mirror. I think I remember that on that model it is counterclockwise. That way the mirror will always return to very nearly the same position and thus so will the object. No need to recenter.


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kljw
member


Reged: 01/24/13

Loc: Scotland
Re: Image Shift new [Re: jrcrilly]
      #5776943 - 04/04/13 02:08 AM

John C
many thanks for the info, i will give that a try.


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thesubwaypusher
scholastic sledgehammer
*****

Reged: 07/08/04

Loc: New York City
Re: Image Shift new [Re: jrcrilly]
      #5814157 - 04/21/13 09:46 PM





counterclockwise.




Yes.

OP, welcome to the world of large mirrors!


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Qwickdraw
Pooh-Bah
*****

Reged: 03/03/12

Loc: Ann Arbor, MI
Re: Image Shift new [Re: thesubwaypusher]
      #6007102 - 08/05/13 06:27 AM

I just bought a used 12" LX200 and it appears to have very bad focus shift. Even in a low power EP the image travels most of the way across the FOV. I have to wonder if this also affects culmination?

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Kraus
Pooh-Bah


Reged: 03/10/12

Loc: Georgia.
Re: Image Shift new [Re: Qwickdraw]
      #6008376 - 08/05/13 09:23 PM


This may be why my declination circle has its error when the tube is tilted well north or south. My mirror might be rocking. Oh oh. I best go back to using the mirror lock.


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Rick Woods
Postmaster
*****

Reged: 01/27/05

Loc: Inner Solar System
Re: Image Shift new [Re: Kraus]
      #6008467 - 08/05/13 09:58 PM

Don't try to use the focuser when the mirror lock is engaged.

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redlinedb16a
super member


Reged: 10/17/10

Re: Image Shift new [Re: Rick Woods]
      #6013522 - 08/08/13 12:06 PM

I regressed my mirror slide and it cures the image shift for about a year

But I have no problems tearing my ota appart
Some do


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Qwickdraw
Pooh-Bah
*****

Reged: 03/03/12

Loc: Ann Arbor, MI
Re: Image Shift new [Re: redlinedb16a]
      #6015731 - 08/09/13 12:32 PM

Quote:

I regressed my mirror slide and it cures the image shift for about a year

But I have no problems tearing my ota appart
Some do




I need to try this, I just bought this Feathertouch focuser from Starlight hoping this would help. Although I love the focuser it did not help with the severe image shift. Does anybody know if the Peterson EZ Focus kit will also fit the feathertouch unit?


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Qwickdraw
Pooh-Bah
*****

Reged: 03/03/12

Loc: Ann Arbor, MI
Re: Image Shift new [Re: redlinedb16a]
      #6015732 - 08/09/13 12:33 PM

Quote:

I regressed my mirror slide and it cures the image shift for about a year

But I have no problems tearing my ota appart
Some do




Cured or lessened?


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redlinedb16a
super member


Reged: 10/17/10

Re: Image Shift new [Re: Qwickdraw]
      #6018202 - 08/10/13 08:19 PM

Not cured but thick film coat corrects it for a limited time

After it moves a lot it will need to be re applied

I'm working on a solution
Installing a brass shim strip between the two with grease
The brass will lessen the machined gap
Thus removing image shift


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faltered
professor emeritus


Reged: 04/01/05

Re: Image Shift new [Re: redlinedb16a]
      #6020956 - 08/12/13 02:41 PM

get yourself an SCT focuser. Something like this...

http://www.telescopes.com/telescope-accessories/focusers/zhumellsctdualspeedf...

Then once you have your telescope focused roughly, you can lock the mirror (then dont use the main focus knob when its locked) and this accessory will allow you to focus without any image shift.


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Qwickdraw
Pooh-Bah
*****

Reged: 03/03/12

Loc: Ann Arbor, MI
Re: Image Shift new [Re: faltered]
      #6021078 - 08/12/13 03:43 PM

The only issue with using the focuser is that I have a binoviewer. Binoviewers don't like focusers.

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faltered
professor emeritus


Reged: 04/01/05

Re: Image Shift new [Re: Qwickdraw]
      #6022976 - 08/13/13 01:42 PM

ah.. i have not tried binoviewer with a focuser - i assume it will not allow you to reach focus that way?

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Qwickdraw
Pooh-Bah
*****

Reged: 03/03/12

Loc: Ann Arbor, MI
Re: Image Shift new [Re: faltered]
      #6023431 - 08/13/13 04:42 PM

Quote:

ah.. i have not tried binoviewer with a focuser - i assume it will not allow you to reach focus that way?




That and the extra weight are a problem.


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