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  1. #1

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    Philips B&W Analyser PDT2020 - Connection of Safelight

    Up to now I have used the above analyser with my safelight permanently on and it appear to be producing OK prints. I have assumed that once a satisfactory test print has been produced and the probe calibrated to it then the calibration allows for the extra illumination provided by the safelight.

    Switching the safelight off means the probe gives a higher exposure reading of course. As the probe is calibrated to the safelight being on, I presume that the higher exposure reading would simply give too dark a print. Therefore using a probe without the safelight would simply mean re-calbrating the probe dial so that the previous "correct" exposure reading would be repeated.

    Is there a flaw in this "logic" and if so what advantage is obtained by using the probe with only the enlarger light on?

    Should there be any advantage in obtaining exposure readings without the safelight influencing the reading, then does anyone know what I need to do to connect the safelight to the analyser so that when the enlarger light is on the safelight is off. I could simply manually switch the safelight on and off as required for exposre determination but automatic switching would be preferable.

    The analyser has two power wires from the back of the unit: One runs to a three pin plug which connects to the mains: the other runs to a female connector into which the enlarger's transformer is plugged so when the analyser is switched on for analysis or exposure the power then runs to the enlarger.

    I have noted that analysers such as the RH Designs need to have the safelight off to work properly so presumably there is a means( some kind of a switch?) which ensures that as power runs to the enlarger it is disconnected to the safelight. Presumably a kind of a two way switch which either sends power to the enlarger via the analyser or power to the safelight but not both together?

    Any help will be gratefully received.

    PS You are dealing with someone whose electrical knowledge is very limited but who is able to follow instructions hopefully in terms of connect A to B etc.

    Thanks all

    pentaxuser

  2. #2

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    If it's for colour the safelight can skew the filters.

    Some colour analyzers can be blinded by not much light. Causing more problems

    OTOH I leave my safelight on for B&W and the few times I use the analyzer it works fine. But my safelight is pointed away from the easel and no light falls on it.

    I just flick the safelight switch on/off.

  3. #3

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    Nick Thanks for very prompt reply. I was waiting to see what other replies I got before thanking those replying but so far yours is the only one. I may yet get other replies. In the UK my thread came late in the evening so others have only had tonight to see it.

    It may be that wiring in a switch which turns the safelight off as it turns the enlarger on is more complicated than I had thought. Maybe with my particular analyser it is impossible as no one has come up with anything.

    I take your point on colour analysers. My Colourstar 3000 is affected by my DUKA 10 Sodium safelight even at very low levels. It seems to be the magenta readings that are affected the most.

    Placing the lid of a 10x8 paper box over it seems to virtually eliminate all its light, although up to now I have been printing blissfully without bothering to do this.

    I have been giving this more thought and it poses me the same question as for B&W. Namely if the analyser has been calibrated to get an acceptable colour print with the safelight on in terms of both exposure and colour balance then even if the Y,M and C lights on the star now behave differently compared to what they would read if the safelight was off, shouldn't this get me to the same correct filtration as it has been calibrated with the safelight on.

    In other words if we assume that a perfect colour print is 60Y and 40M and this is what the star says with the safelight on becasue it has been calibrated with it on, then presumably with the safelight off I'd get different readings but these would now not produce a perfect print as the colour star would need recalibrating for the safelight being off.

    I hope what I am driving at makes sense to you although my logic may be flawed. I have a strong feeling it may be flawed but I cannot get my head around why this might be.

    Frances Schultz makes exactly your point in her excellent article on the Colourstar 3000 but of course her article was a practical one on its use and was not on the theory aspects. So it hasn't helped me discover the error in my argument above.

    So I'd appreciate help in being guided through what my flaws are.

    I am way off my original thread here but I may as well raise the issue here rather than start another thread.

    I have a normal Ilford B&W safelight for B&W of course. The DUKA is reserved soley for colour and anyway switching the DUKA on and off as I understand it may render it unsafe for both colour anbd B&W due to it being at a different wavelength until it has warmed up

    Thanks

    pentaxuser

  4. #4
    Bob F.'s Avatar
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    Many timers allow you to plug your safelight in and will switch the safelight off when it switches the enlarger light on and vice-versa. An external adaptor to use the timer's enlarger lamp output to switch between the enlarger and a safelight could be made but you are dealing with mains voltages, at least on the safelight side, and would need to know what you are doing (though the circuit could be simply a relay, depending on the enlarger lamp voltage and whether it is DC or AC). Simpler to just put an inline switch used for table lamps from a DIY store in the safelight power lead and do it manually.

    You are correct about the Duka: according to the instructions, it takes several minutes to reach it's correct working colour after switching on.

    Cheers, Bob.



 

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