I have a RB67. Also have a Panasonic PE 201 C flashgun, which I have used with 35 mm cameras. I attached it to the 67 and connected it to the camera with the synch cord. No film in the camera as I was wanting to see if the flashgun would fire. The flash fires at all speeds. The flashgun has a GN of 20 at ISO 100. It can be set to Auto, or Manual. Instructions with the gun state Aperture F2.8 covers 1.5m-7.0m; and with aperture of F4, covers 1.0m - 5.0m., when the gun is used in the Auto mode. Manual mode is fairly simple as there is a table on the reverse of the gun - select distance, then read down and select aperture corresponding to the ISO film being used. I want advice re fill in flash when using the above gun. I have read pages in a couple of photo books but have not grasped the formula completely. I believe it to be along the lines of take a meter reading as normal, then close down the lens to stop the flashlight burning out the subject. Anyone here who can explain the principle in a clear manner ? I suppose once I grasp the ins and outs, and have done it a few times, then it will be straight forward for me. Initially I will be using colour neg. film to master the technique (hopefully) and then use colour slide film. Looking forward to helpful answers.