Densitometer Reflection Calibration

Discussion in 'Miscellaneous Equipment' started by Silverpixels5, Apr 18, 2005.

  1. Silverpixels5

    Silverpixels5 Member

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    I just recieved at Macbeth TR-927, and need to calibrate the reflection part. This would usually be done with an included plate that had known density targets on it....unfortunately I don't have it. Any idea where one could be found? Thanks!
     
  2. Eric Jones

    Eric Jones Member

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    X-Rite still manufactures Densitometers and Calibration Wedges and Reflection Plates to go with them. Their Reflection Calibration Standard Plate sells for $71.00. I'm not sure of your calibration process but with my 810 I just read the plates three different densities and tune the densitometer to what X-Rite says the plate should read. I hope some of this helps.
     
  3. Stephen Benskin

    Stephen Benskin Member

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    I got mine from Macbeth a few years back. It cost me around $150.00.
     
  4. Helen B

    Helen B Member

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    The TR-927 gets calibrated using the green channel for reflection (ortho for transmission), and the calibration reference should be marked accordingly. Call Macbeth on 845 565 7660. I think that the current price is around $160.

    Best,
    Helen
     
  5. Claire Senft

    Claire Senft Member

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    Helen where have you been and what have you been doing? Never mind it is probably too exciting for an old man to hear.
     
  6. Silverpixels5

    Silverpixels5 Member

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    Dang, the target is gonna cost more than the unit itself...lol. Oh well...time to start saving again. Thanks everyone!
     
  7. Jorge

    Jorge Inactive

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    Ron, you dont need to buy a manufacturer's calibration plate, all you need is a calibrated reflection step tablet. Stouffers has them for $30.
     
  8. clay

    clay Subscriber

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    I've got the calibration plaques for my Heiland if you want to drop by and borrow them sometimes. Let me know. 713-725-7924
     
  9. Silverpixels5

    Silverpixels5 Member

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    Thanks Jorge! I completely forgot about Stouffer. I have a 4x5 step tablet around here somewhere, but its uncalibrated. Thanks for the offer Clay, but I think I'll go ahead and buy the stouffer ones(transmission & reflection), since the prices are so attractive. Somehow I won this unit for a whopping $20 and it arrived today. To my suprise, it measures UV density too! I tested a few negatives, and everything seems to be in working order, but I wanted to check something of a known density so that I knew for sure. The calibration sticker says that it was last calibrated about this time last year.
     
  10. resummerfield

    resummerfield Subscriber

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    Just a thought---

    Why don't you take your uncalibraed step tablet to someone (a friend or even a local one-hour lab) and have them calibrate it? Cheaper than buying another one.
     
  11. Helen B

    Helen B Member

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    A $20 price tag puts a different perspective on things and makes my reply about the Macbeth calibration reference look rather silly, but it all depends on what you want to use it for...

    The standard filters in the TR-927 read Status T RGB (wide band gelatin filters: Wratten 25, 61 and 47), ortho and UV (Wratten 18A). Depending on your intended use, it may not be necessary to use a calibrated step wedge. If you did want the highest accuracy you may need to bear in mind that a narrow band instrument (eg TR-924 with Status A and M dichroic filters, and visual) might give a different reading from a wide band instrument, depending on the ‘neutrality’ of the target – so there’s a possible twist to ‘calibrated step wedge’. But it probably doesn’t matter, just something to be wary of if you wanted to measure colour and correlate the readings with another instrument to the second dp.

    With the TR-927 the green filter is normally used for reflection calibration, and the ortho for transmission, however there’s no point in using the green filter for calibration if that isn’t a channel you are interested in. The 61 green filter is usually the fastest to fade, and differential fade could throw the other readings off.

    As far as the frequency of calibration goes, I thought that it was normal practice to zero every channel every session, for which you need a reflection reference but not a transmission reference, and calibrate every few days. If the instrument has changed hands, the calibration pots may have tempted idle fingers. I calibrate every session because it is so easy, though I suspect that I’ll soon fall to the charms of a modern, low cost spectrophotometer – the reason that there are all these cheap densitometers on the market?

    Best,
    Helen
    PS Claire – Me? I ain’t been up to nothin’, honest.
     
  12. Silverpixels5

    Silverpixels5 Member

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    Thanks for the info Helen! I plan on using the unit for B&W film and paper testing for use with silver gelatin and Pt/Pd. I would also be calibrating every session. It has been my experience that older units seem to stray from their set point more often than one would think. :smile: