A direct bubble size measurement technique which employs a device to collect and expose bubbles has been revived. Rising bubbles are collected into a vertical tube filled with water and directed to a flat viewing chamber at the top for imaging. The dimensions of the device were selected to make the unit writable for use in industrial mechanical flotation cells and columns. The bubble images, collected using a video camera, are manually processed off-line in the version described here. Operational details as well as practical limitations of the technique are illustrated though measurements completed in two banks of four pilot-scale Denver cells processing a sulphide ore.