Photocell for Zone VI compensating enlarging timer

[Deleted member 88956]

The photo cell watches the light and if it changes it tells the timer and the time will lengthen or shorten depending on the out put of the light. this way print number one matches print number 20. I live in an area where the power would change while I'M printing and this causes the out put of the light to change. Once I started testing the timer my prints were consistence. I also did the Fine Prints for Zone VI and would print a hundred prints at a time. The Cold light would change the out put as it heat up and cool down. Before the timer the prints would vary. After the timer the print were all alike.

Thanks again, but you were alluding to blacking out part of the cell window in order to improve timer's range, how is that related?

 

[john_s]

The timer uses units of time that can be considered "seconds" but are actual exposure units which vary in time length. With the Zone VI Compensating Timer and RH Designs StopClock Vario, each "second" is marked by an audible tick. As the cold light tube increases its output, the ticks become shorter. With the old single tube Zone VI head, the increase in speed was dramatic. If the light to the cell is is too bright by virtue of its being very close to the light source, the timer ticks will be very close together making the numbers inconvenient. The Zone VI Compensating Timer (IIRC) had some adjustment to reduce the effect of strong light, and the RH unit has also. See my post above in which I describe my sensor being outside the head and just looking through a hole at the very bright VCL4500 tubes (pointing more directly at the blue tube to ensure that it isn't swamped by the green tube which is on all the time.

Richard's suggestion to black out part of the sensor achieves something similar.

 

[Deleted member 88956]

Thanks John, this now makes more sense.

 

[Rafal Lukawiecki]

For what it may be worth, I've just posted a for sale for the 220V Zone VI Compensating Enlarging Timer with the photocell, unused. It's here: (there was a url link here which no longer exists)