Offset secondary

[Ally8446]

Calling all Skywatcher Skyliner 200mm dob owners. Does your scope have an offset secondary similar to the attached photo?

If not, then how do I correct it ?

The collimation is near as makes no difference to perfect for visual observing.

Incidentally the larger dark area of the offset is towards the primary.

Clear skies.

Ally

[Moonshane]

this sort of offset is perfectly normal and to be expected in a relatively fast newt. it's fixed when the secondary is glued to the stalk.

[bingevader]

What he said.

It's what mine looked like straight out of the box and everytime I've collimated it since!

Cheers

[ramstar]

I've spent 2 hours this afternoon fiddling with mine and in frustration ended up with it like the photo, thinking I'll never get the hang of this collimation lark. I feel a lot better now - thank you all

[Ally8446]

This is just what I wanted to hear folks, great news, thank you. Now I can concentrate on just looking.....IF ONLY THE CHUFFIN CLOUDS WOULD CLEAR..

[Moonshane]

absolutely! (although your primary needs a tweak) :0)

[Ally8446]

absolutely! (although your primary needs a tweak) :0)

Cheers Moonshane. I've tweaked it ready for tonight (fingers crossed).

[Jason D]

I would like to clarify that the secondary mirror silhouette will appear shifted for a properly collimated scope regardless of whether the secondary mirror was mounted on its stalk centrally or with an offset. Attached is a view from my scope with a centrally mounted secondary mirror.

Jason

[Moonshane]

interesting Jason. didn't realise that.

[Ally8446]

I would like to clarify that the secondary mirror silhouette will appear shifted for a properly collimated scope regardless of whether the secondary mirror was mounted on its stalk centrally or with an offset. Attached is a view from my scope with a centrally mounted secondary mirror.

Jason

Excellent news, thanks Jason. Very useful tip.

[Jason D]

interesting Jason. didn't realise that.

Refer to attachments. Whether the secondary mirror mounted centrally or with an offset away from the focuser, upon the completion of proper collimation the optical axis of the primary mirror will strike the secondary mirror above its geometric center -- that is what shifts the secondary mirror silhouette. The distance between the optical axis intersection point and the geometric center is about the same in both cases -- that is why the amount of the secondary mirror silhouette shift will appear about the same in both cases.

Jason

[Moonshane]

excellent Jason, thanks - I can see how it works now :0)

[stargazerslivingroom]

Great diagrams, Jason.

Thanks so much.

Steve