A method for optimizing signal to noise ratio in an optical sensor comprising: a. directing a beam of light onto a surface of a sample such that at least one characteristic of the sample is encoded in the beam of light as it interacts with the surface of the sample, the beam of light being at least partially reflected from the surface of the sample; b. directing the reflected beam of light onto an optical sensor having at least two discrete light sensitive surfaces (34, 36; 243, 236, 249); c. modifying , by translationally moving at least one mirror positioned between the sample and the optical sensor , a ratio of radiant power of the reflected beam of light between the at least two discrete light sensitive surfaces, wherein substantially all of the radiant power directed onto the optical sensor is apportioned onto the at least two discrete light sensitive surfaces; whereby the at least two discrete light sensitive surfaces and the mirror are arranged such that the mirror is translationally movable between at least a first position in which substantially all of the radiant power directed onto the optical sensor is apportioned onto the at least one light sensitive cell positioned along a first optical path and a second position in which substantially all of the radiant power directed onto the optical sensor is apportioned onto the at least one other light sensitive cell positioned along a second optical path; d. obtaining information from the optical sensor that is at least partially based on the ratio of radiant power between the at least two discrete light sensitive surfaces and at least partially based on at least one of the characteristics of the sample encoded in the reflected beam of light; and, e. determining based at least in part on the information the at least one characteristic of the sample. a. directing a beam of light onto a surface of a sample such that at least one characteristic of the sample is encoded in the beam of light as it interacts with the surface of the sample, the beam of light being at least partially reflected from the surface of the sample; b. directing the reflected beam of light onto an optical sensor having at least two discrete light sensitive surfaces (34, 36; 243, 236, 249); c. modifying , by translationally moving at least one mirror positioned between the sample and the optical sensor , a ratio of radiant power of the reflected beam of light between the at least two discrete light sensitive surfaces, wherein substantially all of the radiant power directed onto the optical sensor is apportioned onto the at least two discrete light sensitive surfaces; whereby the at least two discrete light sensitive surfaces and the mirror are arranged such that the mirror is translationally movable between at least a first position in which substantially all of the radiant power directed onto the optical sensor is apportioned onto the at least one light sensitive cell positioned along a first optical path and a second position in which substantially all of the radiant power directed onto the optical sensor is apportioned onto the at least one other light sensitive cell positioned along a second optical path; d. obtaining information from the optical sensor that is at least partially based on the ratio of radiant power between the at least two discrete light sensitive surfaces and at least partially based on at least one of the characteristics of the sample encoded in the reflected beam of light; and, e. determining based at least in part on the information the at least one characteristic of the sample. <EOS>