Re: (IAAC) Obj: M34 - Inst: Orion Optics 250MM F4.8 Vixen GP/DX

    Your telescope is a refractor, am I correct?  I am not sure if the
mirror in a refractor is supposed to be tight, but I wouldn't think it
should be very tight.

    I own a 14.5" Starmaster truss mounted dobsonian reflector.  I do know
that my mirror is extremely loose.  Yes, I said loose.  It rests on a mount
that allows it to flex with temperature variations.  When I am transporting
the mirror in the mount, it will move around a lot.  When it is in the
telescope, it is resting on the mount and although you don't hear it moving
when the telescope is moved, it is free to move ever so slightly if it needs
to so it can flex with temperature variations.  If I tightened the mirror
down to keep it from moving, what I would cause is the inability of the
mirror to expand or contract with temperature variations and thus it may
actually bend slightly because it doesn't have room to stretch.  The bending
is probably what your manufacturer is concerned with because the bending
will result in astigmatism, if I'm not mistaken.  In short, mirrors need
room to move.

    If I were you, I would contact the company and have their technical
support get the thing correct and have them walk you through the steps to
get it collimated correctly.  I don't own a refractor, so I can't help you
on this one.

    Different subject.  I noticed in your observing reports that when the
report calls for magnification, you entered the focal length of your
eyepiece.  Actually, magnification is figured by dividing the focal length
of your telescope by the focal length of your eyepiece.  If, for instance,
the focal length of your telescope is 1200mm and you use a 25mm eyepiece,
your magnification is 48x.  I looked in the Orion catalog and could not find
your scope.  Is it a refractor?

Hope this helps.

----- Original Message -----
From: <barry.sharpe@btinternet.com>
To: <netastrocatalog-announce@atmob.org>
Sent: Monday, January 21, 2002 6:53 AM
Subject: Re: (IAAC) Obj: M34 - Inst: Orion Optics 250MM F4.8 Vixen GP/DX

Hi everyone,

Perhaps someone can help me, I took my telescope to a member of our local
astronomical society. Who just happens to be a Dr of physics works at our
university. After repeated attempts at collimating my scope he could not get
it right. so he stripped my scope removed primary and secondary mirrors. And
found the offending item to be a nylon screw that holds with 2 others the
side of the mirror to be lose.
he tightened it rebuilt the scope and collimated it no problems. because it
is a new scope he suggested i phone the makers and make a little complaint.
Whilst doing so the makers informed me that this was incorrect and that what
the gentlemen did may cause an astigmatism in my mirror. And would have
invalidated any warranty on my scope. Firstly thier was a lot of play in the
mirror so much so that if you moved the scope you could feel the mirror move
inside. The telescope makers claim that this would not have affected the
collimation. However i said surly it must do because in effect if the mirror
moves off center then the collimation is bound to be affected. He denied
this rather vermently and told me that what we had done was wrong. The
gentlemen that had helped me is a long standing astronomer who lectures
cosmology clases and looks after all the obervatories as well as radio
telescopes surly he must know. my telescope since the rebuild is performing
far better than it ever did. Am i to worry i don't believe he tightened it
solidily just enougth to stop it moving around. Any thoughts would be
greatly appeciated.

> ----
> Observation Poster: Barry Sharpe <barry.sharpe@btinternet.com>
> Observer: Barry Sharpe
> Your skills: Beginner (< one year)
> Date/time of observation: 19th January 2002 19:30 UT
> Location of site: Welwyn Garden City  (Lat 51:47:24 , Elev 0:10:45 )
> Site classification: Suburban
> Sky darkness: 7 <1-10 Scale (10 best)>
> Seeing: 4 <1-10 Seeing Scale (10 best)>
> Moon presence: Minor - crescent or far from object
> Instrument: Orion Optics 250MM F4.8 Vixen GP/DX
> Magnification: 25mm
> Filter(s): None
> Object(s): M34
> Category: Open cluster.
> Class:
> Constellation: Per
> Data: mag   size
> Position: RA :  DEC :
> Description:
> M34 found nice open cluster near zenith, spread out cluster in 25mm. Many
> white stars suggesting young cluster stars fill FOV. One double in centre
of FOV, 50 - 100 stars; quiet a few pairs of stars, nice pinpoints of light.
> nice open cluster. could not discern any particular pattern but view was
constantly interupteb by cloud.
> --
> Optional related URLs:
> ** This observing log automatically submitted via the Web from:
>   <a href="/bti/redirect.html?http://www.visualdeepsky.org/enter-log.html"
> To stop receiving all 'netastrocatalog' lists, use the Web forms at:
> <a href="/bti/redirect.html?http://www.visualdeepsky.org/subscribe.html"

To stop receiving all 'netastrocatalog' lists, use the Web form at:

To stop receiving all 'netastrocatalog' lists, use the Web form at: