Crayford focuser for SCT

Could someone explain how a Crayford focuser for a SCT works? What are the advantages and disadvantages? Is it worth the expense, i.e., does it significantly improve fine focus?

Thanks.

David,

Send me your email and I will forward a copy of the review that I wrote for Cloudy Nights re: the Feather Touch Focuser and SCT's.

Paul Atkinson