A small (MASSIVE) problem

[Daniel-K]

ok on looking down my sw200 tube i noticed a black mark on my mirror after reading about mould and how damaging it can be (previous owner stored it in a garage unused for 18 months) i though i would take the primery mirror out for a closer inspection, i have no idea what it was but it wasnt dust.i managed to get it off with a micro fibre cloth.so far so good.put the mirror back in and now even when i collaminate the mirror doesnt look like it is centred in the tube i dont know what to do can some one please help

[Psychobilly]

Google for "Centering a Newtonian Primary" and see which of the many guides that are out there you fancy following... Some are filled with pages of maths...some are entirely practical...

Google

And Astrobaby comprehnsive pages on Collimating a Newtonian..

Astro Babys Guide to Collimation

Peter...

[Daniel-K]

i cant get the 3 mirror clips in veiw

[NickK]

Although I'm not a reflector owner - a small set of photos would probably help those to help you.

[Alkaid]

i cant get the 3 mirror clips in veiw

If you can't see the three clips when looking down the focuser, it means that the secondary mirror needs adjusting. Although I can't understand why if you only removed the primary Perhaps when you tightened the screws that hold the primary mirror assy to the tube, you tightened one all the way before tightening the others? The trick is to tighten each screw a little way, working from one screw to the next so that the mirror stays in the middle of the tube. Do this until all the screws are tightened (but not too tight).

When you look down the main tube from the front, does the primary look concentric with the tube, i.e in the middle?

[Daniel-K]

Ok I managed to sort collamination out but now when It focus's the focuser is nearly all the way out

[NGC 1502]

Ok I managed to sort collamination out but now when It focus's the focuser is nearly all the way out

If the focus position is now further from the tube than before, then

the primary mirror must be further up the tube than originally.

Did you replace the mirror cell correctly in the original holes ?

If you did, I can think of two reasons that focus is further out from

the tube.

Perhaps all the collimating screws are further in than before ? this

would shift the mirror up the tube. If you tighten all three by the

same amount, this would bring the mirror away from the secondary

and the focus position would be closer to the tube. You would need

to recollimate again if this is the problem.

Maybe the mirror is not sitting in the cell properly ? unlikely perhaps,

but this would also put the mirror in the wrong place.

HTH, Ed.

Edit - just a thought, are you focussing on a distant object ?

If you are trying the scope on a nearby target, then focus will

be further out from the tube than for a sky object.

[Daniel-K]

Hi ed I think you have solved my problem I think the secondary has gone further forward and inwas focusing on a corner on the top of a block of flats about a quarter mile away and it focused fine but I will try and move the secondary back tomorrow after work thanks ed