Problems with ca

[Zachariah]

Can anyone suggest how I might reduce ca on my 90mm refractor. I have heard some filters help.

Also do laser collimators need collimating? If so how?

[Merlin66]

There are filters you can add to reduce the CA (see FLO site) and there's a thread running on how to collimate your collimator - do a quick search you'll find it.

[steppenwolf]

The filter you are thinking of is called a 'fringe killer' but it is a bit of a kludge to be honest as it doesn't actually resolve the source of the problem - focusing several wavelengths of light at the same point - but I have heard of people getting good results from one.

This is a current laser collimation thread that may be of assistance.