The present invention provides a method of producing a DNA library comprising a plurality of DNA sequences of interest, where each DNA sequence of interest has at least two predetermined positions, with at each predetermined position a codon selected from a defined group for that position, the codons within a group coding for different amino acids. In particular the present invention discloses a modular projection lens assembly with enhanced structural integrity andor increased placement precision of its most downstream electrode. A shaped tower at, at least one end of the elongated slot having a pair of legs rotatably retains a latch for securing the daughter card to the connector. With the high frequency dithering probe having the improved scanning speed, a test sample can be observed within a short time and an object being changed can be also observed.