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Thread: SEI Photometer help needed

  1. #11

    Join Date
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    Re: SEI Photometer help needed

    Quite the mystery. It's a shame that one of the meters does not provide the high brightness range, since that's the range most daylight luminances fall. But at least you have the white medium range that would provide readings for indoor subjects. But since you do have a meter with all three ranges working, and if you're feeling brave enough to attempt to find out why the high range filter setting is malfunctioning, you might try carefully loosening the two tiny screws - at 180 degrees apart - just above the housing separation near the setting thumbwheels. If it comes apart, probably holding the meter vertically, you may be able to see what's wrong (I'd suspect a mechanical issue rather than electrical). If there are three separate filters involved to produce the three ranges, the high range filter would be equivalent to ND 2.0. Why? Look at p. 22 of the link provided by my first post in this thread. Notice how the bright range covers from 32 candles/sq. ft. all the way to 3200 candles/sq. ft. (6-2/3 stops). However, from the Figure 1 illustration of the filter drive mechanism in that link, it's implied (to me) that graduated filters are used rather than separate filters. But Figure 1 may just be a concept sketch, so who knows what you'll actually find in there.
    Last edited by Jerry Bodine; 11-Aug-2020 at 10:46.

  2. #12
    MFWV
    Join Date
    Feb 2008
    Location
    West Sussex
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    6

    Re: SEI Photometer help needed

    Have you a multi meter? You need to check that a variable resistance exists between the battery contact button. I have two of these and am converting one to use a AA lithium ion battery. In the process my son and I have thought a lot. One important thing is that save for through the variable resistor, the negative end must NOT contact the brass tube which holds the bulb.

  3. #13

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    Re: SEI Photometer help needed

    Quote Originally Posted by almostpilot View Post
    Hello again.
    Well, curiouser and curiouser...
    Now both bases are working! I cannot for the life of me understand how, but yes, the base that has not worked for about 2 weeks suddenly started to work yesterday afternoon. And I also found that the cheap SEI can indeed be used, albeit with only two of the ND filters (the ones used for dark and medium brightness), as the ND filter for the brightest conditions does not slot in properly.
    I have not done anything special, other than keep pressing the microswitch button. All I can think of is that by trying it again and again some gunge inside freed up. I did spray some Servisol S10 switch cleaning lubricant in there 2 weeks ago, when I first tried to get the SEI to work, but as I said it looked like it had not done the trick. Oh well, now I have 2 SEI meters, (and 3 spare bulbs!).
    PS
    As a test I switched bases again from one unit to the other, and yes they now both work, on both units.

    Go figure!
    I also wonder if storage has something to do with it. The first unit had been stored horizontally for months (maybe years) but in the last 2 weeks I kept it upright. Whon knows...
    I discovered something worth knowing this week. The fact that the bulb lights up does not mean that all is well. My SEI developed a very “jittery” rheostat and very difficult to get the ammeter to hold still on the red calibration mark. The bulb was still lighting up. I re-read the instructions at the very end of the manual that pertained to installing a new bulb and calibrating it, and it all came clear to me. I sprayed some Radio Shack “Precision Electronics Cleaner” that I’ve had for years into the rheostat base, then worked the rheostat control vigorously back and forth and let it dry. That solved the jitters, but the ammeter was not reaching the red mark. I still had a spare bulb that came with the meter when bought new, so I installed it and found that it went right to the red mark without further work needed. So now I understand more about how this system works:
    The bulb degrades and puts out less light gradually over time. The function of the rheostat is to counter this degradation by adjusting the supply voltage from the battery sufficiently to enable the bulb output to return to its original output (thereby calibrating it). But eventually the bulb output diminishes to the point where the rheostat can’t cope sufficiently and the red mark can’t be reached. That’s when the bulb MUST be replaced.

    The rest of the story:
    I recently had my Gossen meter (not a spotmeter) recalibrated by George Milton at Quality Light Metrics in Hollywood, so I was confident it was usable as a standard for comparing other meters to. Then I was fortunate in finding a NEW Pentax Digital Spotmeter from a dealer in California. To check all three meters for accuracy, I set up a whiteboard outdoors in full sunlight on a day with clear blue sky at my home in the Seattle area (a miracle in itself), I made readings over a range of about 6 stops – EV 16.33 to 11 - using ND filters. All three meters agreed within 1/3-stop over this luminance range, with the largest difference being that the Pentax read ˝-stop high only at the very lowest luminance (EV 11). I can live with that.

  4. #14

    Join Date
    Dec 2009
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    Re: SEI Photometer help needed

    Glad to hear this all worked out for you!
    You could always put a ND filter in front of the telescope to replace the missing one if you don’t want to take the top off. It can be tricky to get the whole thing back together again if you open it up.

  5. #15

    Re: SEI Photometer help needed

    Quote Originally Posted by Bill Burk View Post
    Glad to hear this all worked out for you!
    You could always put a ND filter in front of the telescope to replace the missing one if you don’t want to take the top off. It can be tricky to get the whole thing back together again if you open it up.
    Thanks to all for the useful comments. I will not open it up, also because the darker filter does move into position, not fully (about 90% of the aera is covered) but the calibration spot is well covered by the filter, I have done a few tests and it looks like it is reading ok.

    I do not have my Pentax spotmeter (which I know is correct, ar to put it differently, gives readings that make my negs look the way I want them to... which is the name of the game IMHO) with me but in a few days time I will be able to compare the two SEI with it and see where I am.
    I will report later then.
    thanks

  6. #16

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    Dec 2009
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    Re: SEI Photometer help needed

    I would calibrate the SEI to a trusted meter when you have it. For example set both SEI and your Pentax meter to agree... then put some Scotch tape on the SEI ammeter glass and draw a new “calibration” line where it happens to be. The selenium cell is probably weaker than original, so with both meters in agreement the ammeter needle should be close to where it “needs to be”.

  7. #17

    Re: SEI Photometer help needed

    Quote Originally Posted by Bill Burk View Post
    I would calibrate the SEI to a trusted meter when you have it. For example set both SEI and your Pentax meter to agree... then put some Scotch tape on the SEI ammeter glass and draw a new “calibration” line where it happens to be. The selenium cell is probably weaker than original, so with both meters in agreement the ammeter needle should be close to where it “needs to be”.
    Yes, thank you
    that is what I am planning to do.
    thanks for all the advice, I will let you know how it goes.

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