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

Thanks Jerry and everyone else.

The scope in question is an orion optics Uk model and is a newtonian reflector at 250mm, The gentlemen who helped me i believe new not to overtighten the mirror, but felt that the nylon screws will indeed give a little in themselves. But he was adamant that the mirror should not move in its mounting certainly as much as it was. He had tried to collimate the scope pre the adjustments and could not get it correct. the tube was rolled along the workbench carefully and he had noticed the mirror moving, It was at this point that he had decided to take the scope apart. retightend the screws then collimated the scope. Now it is in collimation no problems in fact my views are visibly better stars are dots not streakes of lights. However the company concerened is a telescope maker a small comapny but they make thier own mirrors and tubes etc. the gentlemen i talk to owns this small company. If it had been a salesman i would have not listened to him because of the stature of the gentlmen helping me i mean a Dr of physics and a practising lecturer on astronomy and cosmology.  but because of whom i talked to i feel very confused.  

> Barry,
>     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.
> Jerry.
> ----- 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.
> Barry
> > ----
> >
> > 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
> are
> > 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.
> Very
> > nice open cluster. could not discern any particular pattern but view was
> constantly interupteb by cloud.
> > --
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