# Unusual shape of maxima in one slit experiment?

I'm experimenting with the one slit (and eventually two slit) light diffraction phenomenon.

The set up is simple (excuse the clutter):

The laser is a $532\ \mathrm{nm}, 1\ \mathrm{mW}$ device, placed about $10\ \ \mathrm{cm}$ from the vertical double slit, which is made from safety razors. The latter is about $166\ \mathrm{cm}$ from a wall and the slit is estimated to be $0.1 - 0.2\ \mathrm{mm}$ wide.

Here a good photo from a single slit run:

The $10^{th}$ minimum is about $6.5\ \mathrm{cm}$ from the centre maximum.

I'm fairly pleased with that result but rather puzzled as to the unusual shape of the maxima, which the literature invariably shows as oblong ovals.

I've since tightened things up by making the slit more vertical and the laser beam more horizontal, as well as some other minor modification but to no avail. Another, this one red, laser gives the same result/problem.

Has anybody encountered this or have a possible explanation for these strangely formed maxima?