Multi Purpose Coma Corrector - info required

[spacezebra]

Hi there

I would be interested in learning more about coma correctors and seeing some pics as to how they are actually attached to scope - for use with eyepiece and use with web camera.

Cheers Petra

[janoskiss]

You use them basically just like you would a barlow. Stick in focuser, and then stick your EP/camera inside it.

[spacezebra]

Oh, okay

I thought that you may need an adapter of some kind for 1.25's - looking at the pics on various websites.

Does the CC enhance image?

Cheers Petra

[Don Pensack]

The brands on the market are all 2", as they were first designed with photography in mind. Coma is a particular problem in photographs taken through short f/ratio scopes.
Visually, since not every eyepiece has the focal plane in exactly the same place, and because 2" eyepieces are usually a lot taller than 1-1/4", TeleVue developed a coma corrector, called the Paracorr (Paraboloid Corrector), which allows an adjustment for different eyepieces.
The TeleVue Paracorr also extends the focal length 15%, which applies a slight field flattening to the telescope's focal plane. Between the coma correction and mild field flattening, star images are tightened up all the way to the edge of nearly every 2" eyepiece out there.
A coma corrector cannot change astigmatism and lateral chromatic aberration or pincushion distortion. If the eyepiece has these, whether due to deficient design or the inability to handle the wide light cone in a short focal ratio, the Paracorr will not correct it.

Are the star images at the edge of the field in your photos smeared out radially from the center of the field? Are the star images at the edge of the field in your eyepieces soft and large? Is your scope f/5 or shorter?

Yes to all of these? Then you're a good candidate for one. They're not available in 1-1/4" though (except used), so my comments would only apply to a scope equipped with a 2" focuser.
Don