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Subject: [M]: RE: JMI focuser helps for shift?
From: Mark de Regt
Reply To: mapug@shore.net
Date: Tue Oct 02 09:45:17 2001
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Stefano--
I am afraid that the responses to date will confuse (they confuse me).
I have a 10" LX200 f/10. I use the JMI NGF-S fine focuser, so I have a bit
of experience in this department.
The main focuser for the LX200, as you may know, moves the main mirror along
a path inside the tube. This changes the distance to the eyepiece or
camera, thereby changing the focus. There are two types of problems with
the LX200 focusing. One is mirror flop, caused by unintended motion in the
mirror, particularly when the scope crosses the meridian. This can be
reduced with a mirror lock, as described in the MAPUG archives. The second
problem is mirror shift, caused by a slight (or not-so-slight) shift in the
angle of the mirror when the focuser changes direction. The best use for
the NGF-S, or any external Crayford-type focuser, is for fine focus, once
rough focus has been attained with the main focuser. Even better, you can
lock down the mirror after attaining focus with the main focuser, thereby
minimizing any future mirror flop, and use the NGF-S for fine focusing.
There is essentially no mirror shift with a Crayford-style focuser.
I hope this helps.
--Mark de Regt
> -----Original Message-----
> Stefano Padovan
> Sent: Monday, October 01, 2001 11:22 PM
> Subject: [M]: JMI focuser helps for shift?
>
>
> One simple question:I am considering to buy an electric focuser
> (the JMI or
> the Meade) for my LX200 12",this to focus in an easyer way.Does
> it work also
> to reduce the shift of the mirror?
> thank you everybody
>
> Stefano Padovan Photographer
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> www.padovan.net
> fashion portfolio on-line
> _/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
> www.Geocities.com/CapeCanaveral/Lab/7444
> my astronomy page
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>
>
>
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