A real contrast control is more sophisticated than that Len. I see it as follows:
For real contrast control, the light output of the two flaskguns must be controlled independently. The easiest way to do this, is to trigger them on a different moment in time. The trigger pulse of my Z-1 has the leading edge of the flash trigger pulse synchronised with the first curtain and the trailing edge synchronised with the second curtain. Normally a flash will fire on the leading edge. In "contrast control mode" one flash is triggered at the first curtain and the second flash is able to ignore the leading edge and is triggered on the second curtain. The shutter speed has to be a bit slow to allow the electronics of the camera and the flashes to recover after the first flash. I guess in your example of AF500FTZ plus RTF the camera selects automaticly 1/30 second. The contrast control can be achieved if the camera knows that one flash must give "normal"exposure and the other flash one or two steps less (for 1:2 or 1:4 lighting ratio)I do not realy know the FTZ500, but I guess the contrast ratio is adjusted on the gun, who informs the Z-1 contoller. I made once an experimental electronic circuit to extract two trigger pulses from the Z-1 pulse: one corresponding with the first curtain and one corresponding with the second curtain. In this way I could have contrast control with two automatic flashguns, controlling their light output independently (without TTL). Jos from Holland. Len Paris wrote: >>If one of the flash units had an ND filter on it, the TTL system >>would still quench both flashes when enough light has reached >>the film but the flash with no ND filter would contribute more >>light than the flash with an ND filter, giving you one brighter >>source of light on one side of the picture and a dimmer source >>of light acting as fill, to reduce contrast from the other side. >>Feel free to correct the error of my thinking but I believe that >>this is how it happens with my PZ-1p when I use the RTF and the >>AF500FTZ together. >>Len - - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
