A portable reader module, comprising: a housing (100, 101) comprising: an internal space; a first receptacle configured to removably receive a portable device comprising an imager and a light source, the first receptacle comprising a first optical entrance (420, 430, 431) comprising a first opening for the imager to the internal space of the housing (100, 101) and a second opening (430, 431) through which light from the light source can enter the internal space; and a second receptacle configured to removably receive a cartridge, the second receptacle comprising a second optical entrance to the internal space of the housing (100, 101) so that the cartridge is visible to and from the internal space; a light-deflecting optical element arranged within the internal space of the housing (100, 101) to define an optical path between the first opening of the first optical entrance (420, 430, 431) and the second optical entrance; and an illuminating path for illuminating the cartridge defined in the housing (100, 101), wherein the housing (100, 101) is configured to allow the internal space to be light-shielded, wherein the illuminating path comprises a reflector (472, 481) for reflecting light from the light source of the portable device to the cartridge, and wherein internal walls of the housing (100, 101) in proximity to the second receptacle are provided with a low-reflexion surface while internal walls of the housing (100, 101) in proximity to the second opening (430, 431) are provided with a diffuse reflecting surface providing the reflector and improving light distribution, or wherein the reflector is a separate reflector arranged in proximity to the second opening (430, 431). a housing (100, 101) comprising: an internal space; a first receptacle configured to removably receive a portable device comprising an imager and a light source, the first receptacle comprising a first optical entrance (420, 430, 431) comprising a first opening for the imager to the internal space of the housing (100, 101) and a second opening (430, 431) through which light from the light source can enter the internal space; and a second receptacle configured to removably receive a cartridge, the second receptacle comprising a second optical entrance to the internal space of the housing (100, 101) so that the cartridge is visible to and from the internal space; an internal space; a first receptacle configured to removably receive a portable device comprising an imager and a light source, the first receptacle comprising a first optical entrance (420, 430, 431) comprising a first opening for the imager to the internal space of the housing (100, 101) and a second opening (430, 431) through which light from the light source can enter the internal space; and a second receptacle configured to removably receive a cartridge, the second receptacle comprising a second optical entrance to the internal space of the housing (100, 101) so that the cartridge is visible to and from the internal space; a light-deflecting optical element arranged within the internal space of the housing (100, 101) to define an optical path between the first opening of the first optical entrance (420, 430, 431) and the second optical entrance; and an illuminating path for illuminating the cartridge defined in the housing (100, 101), wherein the housing (100, 101) is configured to allow the internal space to be light-shielded, wherein the illuminating path comprises a reflector (472, 481) for reflecting light from the light source of the portable device to the cartridge, and wherein internal walls of the housing (100, 101) in proximity to the second receptacle are provided with a low-reflexion surface while internal walls of the housing (100, 101) in proximity to the second opening (430, 431) are provided with a diffuse reflecting surface providing the reflector and improving light distribution, or wherein the reflector is a separate reflector arranged in proximity to the second opening (430, 431).