filters and focus

[piprees]

Just a quick one.

Do filters really knock focus out that much, and if they do, which, if any, are the worst culprits?

It does seem such a faff having to refocus everytime a filter is changed.

P.

[Shelster1973]

Most do claim to be par focal so should not need to adjust focus, but unless you are paying several hundred pounds for the filter then it will have a slight offset between each.

I thought it was a faff, but have decided that I will stick with one filter per night, so will only need the check focus to see if anything has changed with temp and seeing.