Path difference is the difference in path traversed by the two waves , measured in terms of wavelength of the associated wave. It has a direct relation with phase difference. Phase difference decides the nature of interference pattern but phase difference is found out by path difference. Let's assume that, two stones are thrown at two points which are very near, then you will see the following pattern as shown in the figure below: Eg: let's mark the first point of disturbance as S1S1 and the other as S2S2, then waves will be emanated as shown above. By having a cross-sectional view, you will see the same waves as shown in the figure below (in the below explanation wavelengths of waves emanated from two different disturbances is assumed to be the same). The waves emanating from S1S1 has arrived exactly one cycle earlier than the waves from S2S2. Thus, we say that, there is a path difference between the two waves of about λλ (wavelength). If the di...
One way to minimize this aberration is to use glasses of different dispersion in a doublet or other combination. Another approach uses spaced doublets.
