Abstract: A focal length varying device for a camera comprises a photo taking optical system having a variable focal length; a discriminating device for discriminating whether or not adequate photographing is possible; and a system for automatically changing the focal length of the photo taking optical system on the basis of the result of discrimination made by the discriminating device.

Abstract: A magnification change-over device for a camera is provided with an incident optical path for the incidence of the light of an object to be photographed; a first optical path for guiding the object light incident on the incident optical path to a first aperture; a second optical path for guiding the object light incident on the incident optical path to a second aperture; changeover means for selection between the first and second optical paths; and optical means for differentiating the magnification of an image formed through the second aperture from that of an image formed through the first aperture.

Abstract: An optical system of changeable magnification comprising a master lens arranged normally in axial alignment to an image receptor to be switchable to another light path which includes a rear converter, and a reflection mirror arranged so that when the master lens is switched from the first to the second light path, the light emerging from the converter is directed to the image receptor, while blocking the first light path off the image receptor, thereby the image magnification is changed from one value to another.

Abstract: A radio communication system includes a transmitter unit, a transmission line and a receiver unit. The transmitter unit produces a vertically-polarized wave carrier or a horizontally-polarized wave carrier or both, in accordance with transmission data to be transmitted to the receiver unit. The receiver unit discriminates the levels of the thus transmitted vertically- and horizontally-polarized wave carriers to reproduce the original data.

Abstract: A data transmitting-receiving system including both a transmitter part and a receiver part. The transmitter part transmits a modulation signal on one of the vertically and horizontally polarized waves and, at the same time, transmits a carrier on the other of the waves. The modulation signal on one of the waves is received and demodulated by the receiver part with the carrier on the other of the waves also received by the receiver part.

Abstract: A method for preservation of an aqueous glucose isomerase solution is disclosed in which an aqueous glucose isomerase solution is mixed with a an alkaline material to adjust its pH value within a range of from 9 to 12 whereby the aqueous solution can be stored at room temperature for a period not less than three days without microbial contamination, putrefaction, denaturation and deactivation of the glucose isomerase.