A lens of diameter `5.0cm` and focal length `f = 25.0 cm` was cut along the diameter into two identical halves. In the process, the layer of the lens

A lens of diameter `5.0cm` and focal length `f = 25.0 cm` was cut along the diameter into two identical halves. In the process, the layer of the lens `alpha = 1.00 mm` in thieckness was lost. Then the halves were put together to form a composite lens. In this focal plane a narrow slit was placed, emitting monochromatic light with wavelength `lambda = 0.60 mu m`. Behind the lens a screen was located at a distance `b = 50 cm` from it. Find:
(a) the which of a fringe on the screen and the number of possible maxima,
(b) the maximum width of the slit `del_(max)` at which the fringes on the screen will be still observed sufficiently sharp.