More than one person has claimed that the Ultima 2X barlow is in fact 2.5x.


I get larger images with the Ultima than I do with a 2.5x Powermate.

I have seen this suggested other times.

One thing to consider is that the magnification of a barlow is not fixed,
rather it depends on some geometric factors. The fact that putting the barlow
in front of the diagonal (nice trick on a Newt) is said to give 3X
magnification is only an approximation.

I think Stephen Paul is on the right track here.

jon