Re: [ATM] How would you mount a secondary in a LHN?

["Chris Dalla Piazza" <dalchri@hotmail.com>]

Bob,

Thank you for the advice.  I was thinking that I would have to make the core
in the negative lens bigger than the core in positive lens to make space for
the stop.  I was just assuming that there would not be enough air gap for
the thickness of the stop.

Last night I discovered that I can fit a nickel between the two lenses and
it can bounce around about 2" so that should be enough for a healthy stop.

Also, thank you for the previous advice on the trepanning cutter!  That
addresses perfectly my need to core a specific diameter.

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Bob May
Sent: Sunday, October 01, 2006 5:35 PM
To: atm@atmlist.net
Subject: Re: [ATM] How would you mount a secondary in a LHN?

When you make the secondary holder, you want to capture just the
first element in the clamping action.  There is a space between
the two elements and that will be enough to put a stop on the
holder.  Put a paper or plastic washer between the ring and the
glass and you will be fine.  Don't forget to put another washer
on the other side.  The end of the holder needs to be threaded so
that the nut can be used to tightened on the glass and then a cap
put over the end of the holder to hide the adjustments for the
secondary tilt.  The part of the holder through the second piece
of glass can be slightly smaller in diameter so that it doesn't
hit the second piece of glass.
All really easy to do after you think about it a while.
I had originally considered clamping to the right thickness at
the center but realized that the edge is where the lenses really
need to be clamped for thickness properly.  Also, don't forget to
grind a ring on the negative lens so that it doesn't touch the
other lens at the edge but rather just in from there.  You will
prevent a sudden breakage of the glass by doing this as edges
will have a large force that can't be supported and thus will
break while the two pieces hitting in the more center will
survive the forces.
Bob May
bobmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
Replace the obvious words with the proper character.

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