SIr Isaac's Astigmatism...

[ollypenrice]

... is no more!

Sir Isaac is our 20 inch F4.1 Truss Dob, amateur built with Beacon Hill mirrors. He's always been astigmatic, a defect traced to his secondary mirror. Our friend and guest, Ralf, optical engineer by profession, has made a new secondary to his usual standard and this we have installed and collimated.

What a difference! Outside focus we get a very nice concentric diffraction pattern. Inside focus we get a circular pattern though not so good, meaning that some spherical aberration remains from the primary. However, at focus things are pretty crisp. You don't buy a 20 inch F4 to look at the planets but, none the less, Saturn was good and M13 excellent, even when low cloud made the Keystone itself invisible. The moon was outstanding at powers high enough to avoid being blinded!

Also very noticeable is the improved brightness. The old secondary was perceptibly tarnished but the new one gleams.

A successful operation. Maybe some work on the primary is now in order, but even without it Sir Isaac is a new man.

Olly

[Merlin66]

Glad to hear the news!

Long live Sir Isaac!

[swamp thing]

Nice to hear the big fellas got his eyesight on the mend.

[Moonshane]

great result Olly. even with such a great scope, there's always stuff to tinker with when you have a dob!

[Helen]

Now there's another reason to come again Olly! The view he gave me of the Veil Nebula will stay with me forever!!

Helen

[ollypenrice]

Now there's another reason to come again Olly! The view he gave me of the Veil Nebula will stay with me forever!!

Helen

Yes, it is one of his party pieces!!

Olly

[vdb]

I had A look at the veil at my first stay ... it was for the first time a hesitated to do visual work ... so clear ...

Yves.