Using wide lens adaptors
Supplementary lens adaptors are designed to supplement the existing optical range of the built-in zoom. They widen the field of view through out the entire zoom range. I is not technically easy for a zoom lens to perform brilliantly at the telephoto-end of the zoom at any time.
Adding a piece of glass designed to widen the field of view makes this task even harder as you extend the zoom to try an magnify the image. Without the wide angle adaptor on the front, you do not have to stretch the zoom so far. This is why you had a disappointing result.
© 2013 Pieter de Vries ACS