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I had a problem similar, so I took the mirror out completely and placed it on a piece of clean white paper and traced the outline of the mirror. After cutting out the shape, I then folded the paper in half horizontally and vertically, so I could find dead centre of the shape. I marked the centre of the paper with a black dot and attached it to the face of the mirror with very soft tape on the edges and put the mirror back in the scope. Then using a laser, I adjusted the rotation and tilt until the laser hit the mark on the paper. After gently removing the paper, I took a photo and measured how central the mirror was, and it was pretty close. After that, Astrobabies guide did the rest ...

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As an after thought, I did have to adjust the mirror by adjusting the spider vanes as it was off to one side. The photo of your secondary clearly visible in the tube looks like it is in need of centering via the vanes too??

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6 hours ago, Ledge1962 said:

As an after thought, I did have to adjust the mirror by adjusting the spider vanes as it was off to one side. The photo of your secondary clearly visible in the tube looks like it is in need of centering via the vanes too??

Update looks like some guy from the swansea astronomy centre will pop down within 2 weeks to look at it, hes owned a newtonian he thinks he can do it.. he said it should take 10 minutes.

I rather not touch this secondary anymore i feel im making it worse 

Not sure about the vanes nervous to tamper with it now 

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7 hours ago, Ledge1962 said:

As an after thought, I did have to adjust the mirror by adjusting the spider vanes as it was off to one side. The photo of your secondary clearly visible in the tube looks like it is in need of centering via the vanes too??

Cant turn the screws to adjust spider vain screws are far to tight

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I've an Orion optics UK 12inch f4 Newtonian and it has an off set secondary. Spent month's trying to centre then came across the article about fast newtonians being offset. I'd bought the telescope second hand and thought there was something wrong with it but produces good star images with a coma corrector which is a must too for these scopes. 

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Posted (edited)
25 minutes ago, Nigella Bryant said:

I've an Orion optics UK 12inch f4 Newtonian and it has an off set secondary. Spent month's trying to centre then came across the article about fast newtonians being offset. I'd bought the telescope second hand and thought there was something wrong with it but produces good star images with a coma corrector which is a must too for these scopes. 

The secondary is also offset away from the focuser and down the tube, not sure if you knew, from Lockwood

" The offset of the secondary mirror away from the focuser (and downward in the tube) is given below.

          Offset = (primary diameter - fully illuminated field diameter) * secondary diameter / focal length / 4    =    (D - FIF) * Sd / FL / 4"

 

more..

" If you do not wish to offset your secondary (if you don't care like me or the spider holes are already drilled) and you care about fully illuminating a portion of the field, then calculate its offset, look up the size of the secondary for a 0.00" illuminated field, and add twice the amount of the offset to that secondary size.  That is a good approximation of the minimum size of the secondary (centered in the optical tube, not offset) that will fully illuminate the very center spot of the field.  We are simply making the secondary larger rather than offsetting it.  The rest of the field will be unevenly illuminated.  If you want a 0.5" fully illuminated field, then look up that secondary size and add twice the offset."

 

My thoughts:
 

Centering the secondary with a sight tube automatically offsets the secondary down the tube- a laser does not do this unless special (more difficult IMHO) procedures are used.

Edited by jetstream
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I used the telescope last night and i saw m13 fine the difference between an 8inch and a 6 inch aptiture is huge.. far better than my celesteon 150 for detail :)

I think il just leave it the way it is seems to work fine all this is to complicated for me tbh 😂 

Thanks everyone 

 

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As I pointed out if you check the Astrobaby guide it IS quite acceptable for the mirrors to appear to be a tad off centre and for it to look like the guy from the astronomy centre left it.  In fact I think you had reach a similar level of success with your own experiments when you look at your own photos.  Mine looks the same when I am done.

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