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  1. #21

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    Richard, thanks for the input, but could you expand on how photocell interacts with the timer and making it "see" less light expands timer's range?

  2. #22
    Ken Nadvornick's Avatar
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    I would also be interested to hear any insights, given my issues with the available timing duration range in the VCL4500 head using an original sensor.

    Ken
    "They are the proof that something was there and no longer is. Like a stain. And the stillness of them is boggling. You can turn away but when you come back they’ll still be there looking at you."

    — Diane Arbus, March 15, 1971, in response to a request for a brief statement about photographs

  3. #23

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    I have always disliked mounting sensors inside CL heads, and the Aristo VCL4500 is both quite hot and very bright. So I mounted the sensor inside a piece of 0.5inch standard aluminium square tubing in the side of which there is a 0.375inch hole which corresponds to a similar hole in the side of the Aristo unit. The piece of tubing is screwed to the outside of the unit and enough light gets to the sensor. The sensor is held parallel to the mounting surface by a long thin rectangle of glass slipped into the tube. This also acts as a heat protector although it is probably not necessary. I finished the unit in a hurry so that I could use it, and it's not very pretty. I have attached a photo.

    The setup is excellent. The VCL4500 unit that I have is the basic one, in which the green tube is on all the time without being able to be varied (except off) and the blue is variable from zero to bright enough to swamp the green almost entirely. The sensor with the Vario unit gives a "first order" adjustment to time if the contrast is altered, so calibration is not as important as I first thought. I am using up lots of random old papers at the moment and when I settle on one or two papers that are readily available here at the end of the Earth I will do a full calibration. At present it's trial and error but not nearly as much error as I expected.

    An advantage of having the sensor outside is that it reduces the very powerful light to get values that fit conveniently with the timer (although that is adjustable if necessary)
    Attached Thumbnails Attached Thumbnails IMG_4917.jpg  
    Last edited by john_s; 04-06-2013 at 05:24 PM. Click to view previous post history. Reason: add

  4. #24
    RH Designs's Avatar
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    This is the part in question, Farnell updated the product code:

    http://uk.farnell.com/jsp/search/pro...0&Ntt=118-2340

    As it's a diode the polarity is important; the lead not next to the one marked with a dot goes to the tip on the 3.5mm jack plug we use and the centre pin of the 3-pin DIN plug used on the Zone VI. You can just see the dot at the bottom right of the illustration on the Farnell web page.
    Regards,
    Richard.

    RH Designs - My Photography

  5. #25

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    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.

  6. #26

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    Quote Originally Posted by Richard T Ritter View Post
    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?

  7. #27

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    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.

  8. #28

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    Thanks John, this now makes more sense.

  9. #29
    Rafal Lukawiecki's Avatar
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    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: http://www.apug.org/forums/forum379/...used-220v.html
    Rafal Lukawiecki
    See rafal.net | Read rafal.net/articles

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