repair to sn8 - optics.

[MikeMS]

All.

after the success of fixing the LX90 I have offered to look at a new but very poorly sn8 tube.

It is still in its plastic wrapper but the secondary mirror has become loose and been smashing into the glass lense and the primary mirror. When you use the focuser you can hear glass being grounded!!

I think the optics are beyond repair and the sn8 is out of production now. Do you think I could source a F4 8" mirror and turn it into a newtonian? The tube and rings seem very well made and it would be a cheapish option to bring it back to life.

Any advice greatfully received.

And do you want to see a picture of it? It is not pretty.

Kind regards,

Mike.

[NGC 1502]

Hi Mike, if the optics are a write off then it would need to be very cheap. I suppose you could use the tube/cell/focuser and some Newtonian mirrors. But I don't know who does 8" F4 other than a custom set from Orion Optics UK.

Regards, Ed.

[Pablito]

I bought damaged optics from SN8" recently.

The first important thing - the corrector has to be in one piece, without chips etc.

It's easy to get primary and secondary. But you have to note that primary is spherical not parabolical.

From my set I gave primary and secondary for repolishing and recoating. And the secondary will be smaller because 80mm is oversized I think.

I will have the optics ready the next week.

I have carbon fiber tube prepared

[Peter Drew]

A picture please, it would help a great deal.

[MikeMS]

okay, hopefully pictures attached, and it is worse than I thought. Yes it is a crack in the corrector plate and the bolts on the secondary mirror holder have snapped, not come loose.

I have no idea how this could have happened.

Regards,

Mike MS

[tomo]

I too have a cracked corrector plate, on an Orion Optics XLX200 8" Schmidt Newtonian. See picture. To be honest I just don't know what to do with it . It would be a shame to consign it to the recycling bin. May be I should just put it on AstroBuySell and see if anyone makes an offer. I sold the mount to part fund the replacemnent (10" Meade Lightbridge).

Tom

[MikeMS]

Tomo.

Have you thought of just masking the broken part off? Unlike the damage the scope I have has, you could cut some black cardboard to cover the crack. I would suggest you cut a disc the same size as the corrector plate diameter and slide it over to the crack is covered, it will be like when the moon moves infront of the sun!!

I would think you would not see it in the resulting image. You would need to cover the inside to stop the glass chipping and falling on the mirror. Not ideal but a free repair.

Regards,

Mike.

[Pablito]

Tom,

There two ways:

- remove the corrector and make spider - telescope will work,

- ask Orion Opt. for new corrector.

[MikeMS]

When you say make a spider and the scope will work, is that true? Or are you saying it will work but not as well? The corrector plate is not a piece of flat glass, I am sure it does perform some function, or the manufacturers would not go to all the effort to make one.

I hope you are right and I wrong, but I fear not.

Kind regards,

Mike MS.

PS I will lash up this setup and try.

[Pablito]

Sure it will work but not as well as with the corrector due to focal lenght. Schmidt's corrector corrects spherical aberration of spherical primary mirror and that's it. It works on rule "+" and "-" compensation.

People made Newtonians with spherical primaries but usually for planetary observation with long focal lenght (F/10 or slower).

The crack is not so big but I think you will see some distortion. Secondary has to be replaced because the chips deformed flatness. Even if refigured, looks like dimentions are too small now.

[fwm891]

The corrector is there to 'correct' spherical aberation from the primary mirror which is figured to a sphere or ellipsoidal shape. The corrector has a complex curve on one face to do this. Depending on the figure of the primary removing the corrector and using a spider to hold the secondary would produce mediocre or poor images at the eyepiece. New corrector best option.

[Revs]

Oldham Optical should be a good alternative to OO. David Lukehurst gets his from them.. Oldham Optical Web Site

HTH

[Pablito]

New corrector best option.

Or refiguring primary to parabola.

[tomo]

Thanks for all the ideas guys. You have certainly given me plenty to think about. I rather like the refiguring idea. Something to discuss with Oldham Optical. I could cannibalise the remaining parts and have a new telescope reborn from the old.

Thanks Tom