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Date: 13 Aug 2007 07:38:58
From: canopus56
Subject: Minimizing mirror flop in a 10 inch Newt
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As part of an ongoing project to minimize cone error in a GEM mount,
for my 10" Newt I have things isolated down to mirror flop. You
follow the flop rotating the scope from east to west RA and a Zhumell
laser collimator. Does anyone have any recommendations on how to
temporarily but safely suppress mirror flop in a 10" Orion Newt? I'm
assume that the cell simply needs to be removed and the clasps holding
the mirror in place tightened. On the otherhand, I understand that
the free-flop movement is there to prevent stresses from building up
in the mirror. - Canopus56
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Date: 13 Aug 2007 23:46:21
From: KLM
Subject: Re: Minimizing mirror flop in a 10 inch Newt
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nylon or teflon shims - simple. I actually have a place I can get nylon
button in many widths with adhesive back. But of course others
will have 10,000,000.9464537325 reasons why this cannot and
should not, work, and will be a disaster. but I do it.
canopus56 wrote:
> As part of an ongoing project to minimize cone error in a GEM mount,
> for my 10" Newt I have things isolated down to mirror flop. You
> follow the flop rotating the scope from east to west RA and a Zhumell
> laser collimator. Does anyone have any recommendations on how to
> temporarily but safely suppress mirror flop in a 10" Orion Newt? I'm
> assume that the cell simply needs to be removed and the clasps holding
> the mirror in place tightened. On the otherhand, I understand that
> the free-flop movement is there to prevent stresses from building up
> in the mirror. - Canopus56
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Date: 13 Aug 2007 17:27:16
From: canopus56
Subject: Re: Minimizing mirror flop in a 10 inch Newt
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On Aug 13, 4:15 pm, "William R. Mattil" <wrmat...@ix.netcom.com >
wrote:
<snip all >
Thanks to everyone for the tips. I now have a list of options to work
through. - Canopus56
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Date: 13 Aug 2007 17:15:20
From: William R. Mattil
Subject: Re: Minimizing mirror flop in a 10 inch Newt
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canopus56 wrote:
> As part of an ongoing project to minimize cone error in a GEM mount,
> for my 10" Newt I have things isolated down to mirror flop. You
> follow the flop rotating the scope from east to west RA and a Zhumell
> laser collimator. Does anyone have any recommendations on how to
> temporarily but safely suppress mirror flop in a 10" Orion Newt? I'm
> assume that the cell simply needs to be removed and the clasps holding
> the mirror in place tightened. On the otherhand, I understand that
> the free-flop movement is there to prevent stresses from building up
> in the mirror. - Canopus56
>
Chris has given you some good information on securing the mirror. But
what a lot of people don't realize is that movement can come a number of
sources and the Primary is only one of them. In larger Newts I think
that secondary, housing and spyder need to come under close scrutiny.
And then there is the tube itself which contributes as well. Then there
is the focuser which on inexpensive scopes can usually be improved.
Differential Movement in a Newtonian Design can never actually be
removed. At best only minimized.
Bill
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Date: 14 Aug 2007 14:18:15
From: jasso
Subject: Re: Minimizing mirror flop in a 10 inch Newt
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>As part of an ongoing project to minimize cone error in a GEM mount,
>for my 10" Newt I have things isolated down to mirror flop. You
>follow the flop rotating the scope from east to west RA and a Zhumell
>laser collimator. Does anyone have any recommendations on how to
>temporarily but safely suppress mirror flop in a 10" Orion Newt? I'm
>assume that the cell simply needs to be removed and the clasps holding
>the mirror in place tightened. On the otherhand, I understand that
>the free-flop movement is there to prevent stresses from building up
>in the mirror. - Canopus56
>
You could try placing rubber feet under the mirror so that you can tighten up the clamps and still have room to expand
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Date: 13 Aug 2007 12:29:22
From: LarryG
Subject: Re: Minimizing mirror flop in a 10 inch Newt
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On Aug 13, 9:38 am, canopus56 <canopu...@yahoo.com > wrote:
> As part of an ongoing project to minimize cone error in a GEM mount,
> for my 10" Newt I have things isolated down to mirror flop. You
> follow the flop rotating the scope from east to west RA and a Zhumell
> laser collimator. Does anyone have any recommendations on how to
> temporarily but safely suppress mirror flop in a 10" Orion Newt? I'm
> assume that the cell simply needs to be removed and the clasps holding
> the mirror in place tightened. On the otherhand, I understand that
> the free-flop movement is there to prevent stresses from building up
> in the mirror. - Canopus56
Tightening the mirror clips/claps may introduce strain that would
affect optical performance. You may want to look for a small rubber
shim(s) that can be glued onto the inside of the mirror cell which
will close the gap between it and the mirror at all points. Something
like a wide rubber band or part of a bicycle innertube or neoprene
surgical tubing comes to mind. Preferably, you should choose
something semi-soft, that won't degrade with time.
Cheers,
Larry G.
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Date: 13 Aug 2007 09:28:14
From: Chris L Peterson
Subject: Re: Minimizing mirror flop in a 10 inch Newt
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On Mon, 13 Aug 2007 07:38:58 -0700, canopus56 <canopus56@yahoo.com >
wrote:
>As part of an ongoing project to minimize cone error in a GEM mount,
>for my 10" Newt I have things isolated down to mirror flop. You
>follow the flop rotating the scope from east to west RA and a Zhumell
>laser collimator. Does anyone have any recommendations on how to
>temporarily but safely suppress mirror flop in a 10" Orion Newt? I'm
>assume that the cell simply needs to be removed and the clasps holding
>the mirror in place tightened. On the otherhand, I understand that
>the free-flop movement is there to prevent stresses from building up
>in the mirror. - Canopus56
What sort of mirror cell is this? It is not necessary to allow _any_
mirror movement in order to prevent stress. A mirror that isn't rigidly
supported in its cell is a sign of a poorly designed cell, or of a
broken one. Perpendicularity error (which is what I assume you are
calling cone) aside, if the mirror moves you'll never have good
collimation, either.
For small mirrors, I'm a big fan of gluing them down to their three rear
supports using silicone- I use a dime to set the glue thickness. The
front clips, if any, don't touch the mirror at all, but are simply there
for backup if the glue breaks (which I've never seen happen). Done
properly, the amount of mirror movement will be essentially
unmeasurable- it won't impact collimation or pointing accuracy.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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