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  1. #81
    Greg Davis's Avatar
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    Here are some pictures of the sensitometer. The step wedge is suspended above the film, rather than the film pressed down onto the wedge. It seems to have been designed to have the wedge separated from the film by a piece of glass that measures .3mm thick. It also had two pieces of 1.0 ND filters taped to the underside of the glass creating even more space between wedge and film.

    I am waiting for a reply from a glass manufacturer about a sample piece that will let me replace the original and I ordered some new ND and color correction filters to get the color balance up to 5500K.

    It looks like I can place the filters above the wedge so it won't interfere with either the film/wedge spacing, nor the light sensor. This device is electronically controlled for exposure. I included a shot of the sensor. If the ND filters block the light to this sensor, ie., if I filter at the bulb, it responds by giving a longer exposure. The solution is to filter at the wedge itself.

    To eliminate the gap, I may attach the wedge to the underside of the glass so it is closer to the film. The wedge was also aligned so that the numbers read correctly when looking at the emulsion side of the test negative. I would have thought the numbers should be read from the base side. I need to send an email to Tobias Associates and see if they can tell me if my machine may have been tampered with or if all of this is correct.
    Attached Thumbnails Attached Thumbnails _DSC5715.jpg   _DSC5717.jpg   _DSC5716.jpg   _DSC5718.jpg   _DSC5720.jpg  

    _DSC5721.jpg   _DSC5722.jpg   _DSC5723.jpg   _DSC5724.jpg   _DSC5725.jpg  

    _DSC5726.jpg  
    www.gregorytdavis.com

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  2. #82
    ic-racer's Avatar
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    Ok, after seeing the unit I have changed my thinking a little.
    1) That thing is fantastic, I should have bought it ! The older Wejex is just a stepper motor driving a shutter, and a little light bulb.
    2) I can't see the crack from the pictures.
    3) I agree with trying to put it back to its original state. I was able to get spare parts for my older Tobias for my densitometers. I suspect they may have the replacement glass that you need. Service@tobiasinc.com

  3. #83
    Greg Davis's Avatar
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    Well, as I said in my PM, I emailed them, just waiting for a reply. The crack isn't there, because you are looking at a mylar replacement I put in to see if it would work. It bows too much so I need the rigidity of glass. The glass had to be removed regardless due to damage. It gouged the test film I tried inserting.
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    Did millions of people suddenly disappear? This may have an answer.

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  4. #84
    Greg Davis's Avatar
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    After reading the manual you sent me and Kodak's sensitometry manual, it sounds like I need to know the output of my machine in terms of lux. I am not sure how to measure that exactly. I know how to use my incident meter to get a general lux reading, but physically, I cannot get my meter in that thin little slot. It reflects the light off a mirror onto the tablet, so I assume that I am losing some intensity there. If not I can measure at the mirror plane. I cannot measure at the film plane.
    www.gregorytdavis.com

    Did millions of people suddenly disappear? This may have an answer.

    "No one knows that day or hour, not even the angels in heaven, nor the Son, but only the Father." -Matthew 24:36

  5. #85
    ic-racer's Avatar
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    Fresh Kodak and/or Ilford film. Process it to ISO standard (D76 with appropriate gamma), per instructions and work backward from the equations in the manual to find the lux.

    If you try to get a meter in there and calculate the lux that way, then when you test fresh Tri-X you will get some wonky result, so what do you do??

    I think it is best to calibrate your sensitometer to some standard like "Fresh Tri-X processed to ISO standards = 400" and test all other films from there. I actually tested fresh TMY, Delta 100 and Delta 400 and averaged the results to calibrate mine.

  6. #86
    Greg Davis's Avatar
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    Tobias got back to me this morning..."The assembly is part number A1170 $410.00 2 week wait."

    Quite unhelpful.
    www.gregorytdavis.com

    Did millions of people suddenly disappear? This may have an answer.

    "No one knows that day or hour, not even the angels in heaven, nor the Son, but only the Father." -Matthew 24:36

  7. #87
    ic-racer's Avatar
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    Quote Originally Posted by Greg Davis View Post
    Tobias got back to me this morning..."The assembly is part number A1170 $410.00 2 week wait."

    Quite unhelpful.
    OK.

    I have a question about it before making any suggestions. Is that assembly spring loaded to compress the film against the glass? I'm not totally understanding why the clear plastic you have on there is not working as well as the original glass.

  8. #88
    Greg Davis's Avatar
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    No, no springs. It is a set gap. It does not make good contact with the film, and even if it did, the glass still separates the film from the tablet. The gap is roughly .010 inches, the glass is .011 inches thick. If the film is .002 inches thick, the surface of the emulsion is still .019 inches from the tablet. That is more than 1/64 of an inch.
    www.gregorytdavis.com

    Did millions of people suddenly disappear? This may have an answer.

    "No one knows that day or hour, not even the angels in heaven, nor the Son, but only the Father." -Matthew 24:36

  9. #89
    Greg Davis's Avatar
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    Here is a detail of the spacer used and the recess for the glass/tablet combo. I remeasured with my calipers to double check what I had written last. The spacer is .5 mm, and the recess is another .5 mm, meaning the total gap between the sensitometer base and the tablet is 1 mm. If I place the tablet on the bottom of the glass I will reduce the gap, but I will not get pressure between the tablet and film.
    Attached Thumbnails Attached Thumbnails _DSC5730.JPG   _DSC5728.JPG  
    www.gregorytdavis.com

    Did millions of people suddenly disappear? This may have an answer.

    "No one knows that day or hour, not even the angels in heaven, nor the Son, but only the Father." -Matthew 24:36

  10. #90
    Bill Burk's Avatar
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    What if you make a smaller piece of glass, just to fit in the window (with some kind of tab to keep it from falling through), put the step wedge under glass, emulsion in contact with the film being tested. This could let the weight of the glass press the wedge against the film. And cost you nothing.

    Also, if you find your tests come out overexposed, looks like you could put ND filters over the sensor to get longer exposures.

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