After the scheduled class time was over, some of us went over to another lab to take a look at a Michelson interferometer. This is an iPhone photo taken looking upstream at the fringes formed by this interferometer. Everyone was able to safely put their eye at this location and see the fringes for themselves. Safe because the source was an incandescent light with a narrowband filter and a diffusor screen - never look upstream at a laser. We had a lively discussion on how it is that "which-way" ambiguity having to do with the 2 arms of the interferometer and small tilts in the end-of-arm mirrors give rise to these fringes. For example, the presence of 7 fringes means that the two mirrors are misaligned by 7/2 wavelengths from ideal - each half wave gives one fringe - or by (7/2)*500nm = 3.5 microns.
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