Expodisk for calibrating color analyzer

Discussion in 'Darkroom Equipment' started by Michael Firstlight, Jan 2, 2018.

  1. Michael Firstlight

    Michael Firstlight Subscriber

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    I am looking for a fast and painless easy way to calibrate my color analyzer and get a starting color filtration pack quickly without needing to make multiple test strips. I think I read that one can simply shoot a test frame pointing at a standard photo color chart using an Expodisc, put that neg in the enlarger carrier and then zero out the RGB channels to get a pretty good starting pack that often works for that particular film/paper combination and do slight adjustments from there.. Do I understand this method correctly?

    Regards,
    Mike
     
  2. John Koehrer

    John Koehrer Subscriber

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    As I recall, an Expodisc is used to give an integrated reading similar to an incident reading through a camera with ttl metering, not darkroom.
    I have seen several iterations of printing aids, usually with a series of areas with different filter values. In any case, you're going to need to
    make a good test print to calibrate your system.
     
  3. pentaxuser

    pentaxuser Subscriber

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    There is an extensive thread on this subject that includes an advocacy of the Expodisc as just such a means of calibration. I can't remember the thread's name so do a search or with a bit of luck Mick Fagan from Downunder will respond. Right now he is probably having breakfast.

    pentaxuser
     
  4. wiltw

    wiltw Subscriber

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    The assumption is that the light falling upon the Expodisk can be interpreted as 'neutral'...which works well when it is source of the light falling upon the Expodisk to be integrated for a reading.

    If you put a negative/slide of an 18% gray card, projected that thru the lens to the Expodisk, the light passing thru the Expodisk could indeed be use for calibration of a color meter for enlarging, as the gray card photo is already an 'integration'.. In THEORY might be able to project a scene recorded on the neg/slide, but the challenge is that a lot of grass and trees in the recorded photo will make 'the average' tend toward greenish bias than a neutral gray card photo. Or a photo of a bright red Ferrarri with throw the balance toward red. ...and both in spite of the fact that it was neutral daylight sun which illuminated both shots.
     
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    Michael Firstlight

    Michael Firstlight Subscriber

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    I've acquired a Colorstar 3000 analyzer and read (somewhere) that creating a reference frame like you describe with an Expodisc is the easiest way and a quite precise method of calibrating the analyzer short of creating traditional test strips. I recall I read that creating test strips isn't even needed using this method and was looking for the process. You say just shoot the gray card, but somewhere I read to shoot the gray card along with the color scale (like the one I have in my old Kodak color print guide).

    MFL
     
  6. Mick Fagan

    Mick Fagan Subscriber

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    Hello all, I did a google search and found this; makes me tired just reading what I wrote almost a decade ago.

    https://www.photrio.com/forum/threads/colorstar-3000-calibration.39823/print

    There was another very recent thread, inside the last month or so also concerning printing and colour analysers, do your own search. But the thread from 2008 is pretty good, read it all.

    Mick.
     
  7. RalphLambrecht

    RalphLambrecht Subscriber

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    I used it and it worked for me.
     
  8. John Koehrer

    John Koehrer Subscriber

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    Memories fade just like C prints.
    In the 70's Beseler and Unicolor made calibration sets. It was a plastic card with filter sections and a "light integrator"
    The integrator was frosted plastic and set under the lens to make a test exposure.

    This seems to be what I'm remembering judging from the box but there's no mention of the gizmo on the left side of the picture
    that I think is what I'm going on about.
    https://www.ebay.com/itm/Unicolor-C...07&rk=1&rkt=1&&_trksid=p2045573.c100507.m3226

    The one below is exactly what I remembered.
    https://www.ebay.com/itm/Vintage-Mi...276775?hash=item361481ad27:g:7Z8AAOSw2gxYx2yQ
     
  9. Mick Fagan

    Mick Fagan Subscriber

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    I have one of those, complete. Including the clear plastic holder that keeps it all in one place. I believe this was a Bob Mitchell invention.

    Works reasonably well, but Bob Mitchell did better with his own product, the Colorbrator.

    Mick.
     
  10. rpavich

    rpavich Subscriber

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    You are correct but id only add that you do an expodisc shot in any new lighting condition. Each time i go out to shoot, i take an expodisc shot of the light source.

    Micks instructions won’t steer you wrong.

    I wouldnt print color if I couldn’t do this.
     
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    Michael Firstlight

    Michael Firstlight Subscriber

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    Thanks all for the advice - I'll give it a go.

    Mike
     
  12. Bill Burk

    Bill Burk Subscriber

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    Cool. So if I understand it, you make a special neutral gray negative best you can with the ExpoDisc (perhaps aimed at midsummer's midday sun on auto), and calibrate the analyzer with that special negative that you keep forever.

    Then later whenever you are out shooting, you make a color balance ExpoDisc exposure aimed at the light falling on the scene, and use that ExpoDisc negative to adjust color for a print of that scene.

    Right?
     
  13. rpavich

    rpavich Subscriber

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    OH...yes. I re-read what you wrote..yes you are correct.

    Some analyzers come with that special negative but in my experience, making your own works better, I don't know why I was never able to get true neutral grey while using the supplied reference neg but can do it using a homemade expodisc one.

    The only thing you need to do while you print is make a test strip for density. If I could figure out how to automate that I'd be in heaven.
     
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    Michael Firstlight

    Michael Firstlight Subscriber

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    I was wondering if some folks use a scanner to scan their images and make a digital reference proof for comparing color, and,if there was any (relative) information that could be attained from the scan, or from comparison to reference scans tp help with determining density - all other elements being equal?
     
  15. John Koehrer

    John Koehrer Subscriber

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    I'd wonder if the ink colors are consistent from batch to batch.
     
  16. wiltw

    wiltw Subscriber

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    So if you have your 'special gray card' photo and can put that into your enlarger to expose, and then process your paper...all to ensure that your 'entire process'. is well in control.

    But then the Expodisk is NOT appropriate to use with any other neg/transparency you may shoot! Take a shot in incandescent rather than daylight, or have it inclusive of any strongly colored object in the scene, and the Expodisk is not beneficial to use for that shot.
     
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    Michael Firstlight

    Michael Firstlight Subscriber

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    After nearly two decades of ink-jet printing, I'd say they are as long as they are OEM. Everything else in the chain must be consistent too through - lots of potential variables.
     
  18. Mick Fagan

    Mick Fagan Subscriber

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    Not quite right, close though.

    You must first take an Expodisc negative of the light falling onto the scene you are going to photograph, with the camera on automatic, this is a reference negative.

    You then photograph the scene with that light falling onto it.

    Then in the darkroom, you get the best possible colour rendition you can, including correct density (time of paper exposure). Once you have done this you then place the expodisc negative into the enlarger without changing anything on the enlarger. Place the Jobo (Lici) colorstar probe in the centre of the projected image and switch the enlarger on. At the same time switch all darkroom lights off and in complete darkness adjust the dials/levers/buttons on whichever Colorstar unit you have until all the lights are out; you now have correct colour.

    The last sequence is to get density (close enough only) you then adjust the time factor so that the analyser shows the exact same time as what you gave the paper in getting your perfect colour print. The time will be down to fractions of a second 1/10 of a second is as low as they go. Take note of all of these settings on the analyser and keep them with that box of paper.

    You go out into the wild world find something you wish to photograph and take a frame of said wonderful scene. Immediately after taking said wonderful scene, pop an Expodisc onto the front of the lens, face the direction of the light source and with the camera on automatic, take an exposure. (if you have a manual camera, align up your aperture and shutter combination until you have what the camera metering facility says is a perfect exposure).

    When back in the darkroom, take your wonderful scene negative and frame it as you would like it to be framed on the baseboard/easel. Then pull that negative out and replace it with the Expodisc negative taken immediately after. Switch off all darkroom lights, turn the enlarger on and adjust the Colorstar so that you have the settings as per your perfect original colour print. Now you will need to adjust the enlarger dials until all of the Colorstar lights go out; you will now have near perfect colour. The analyser will also give you an exposure setting, which in all probability will be different to your original perfect colour print.

    Now you just pop the negative you took out a minute or so before, compose, focus then expose.

    Within reason you will have an extremely good colour print and the density will probably be within ¼ to an 1/8 of a stop of what you like.

    If the print is a bit light, it may look slightly cool, if it is a bit dense it may be a tad warm. If this happens, it means you are really, really close to perfect colour and density. Adding exposure will make the print more red, reducing exposure will make the print more cyan. This is how the third colour is corrected and/or obtained in the colour negative printing process.

    Bill, with one exception that I know of, all colour analysers require you to obtain a perfect colour print before you actually start to use the colour analyser of your choice. The one exception that I know of and actually have and used, is Bob Mitchell's Colorbrator. Rather interestingly, it is an analogue unit, no electronics involved.

    So in general, there is no really easy route to printing colour negatives if you've never done it before. However, if you do chance upon a Colorstar analyser, once you have somehow gotten the perfect print with a matching Expodisc negative, you are off and running and will wonder just how easy it really is to print really good colour day in and day out.

    For what it is worth, I started serious colour printing in an industrial colour lab. The colour analysers they had were next to useless as they analysed one colour at a time; in short they took up too much time. As a result, everyone without exception, did colour by eye. Terrible waste of paper, but so quick compared to using the analysers we had. One day I brought in my Colorstar analyser and my own box of paper. We grabbed a roll of C41 and did some studio shots and with each lighting change, we took an Expodisc negative. I think we did about four scenes. We went into a darkroom and placed an Expodisc negative into the enlarger, fiddled, then exposed a frame. We ended up with a seriously good print from the get go.

    The big boss was very impressed and suggested we look further into this. We didn't get them, the industry supply gurus suggested that we would be better off with video colour correction. This was fine, but on a DeVere enlarger this added about $10,000 cost. We had around 9 DeVere enlargers, but could only afford one video unit; grrrrr.

    Mick.
     
    Last edited: Jan 5, 2018
  19. Bill Burk

    Bill Burk Subscriber

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    Look at what Mick wrote... he clarified a lot.

    In any case you point the camera with ExpoDisc at the light source as you would an incident meter, not at the scene.
     
  20. wiltw

    wiltw Subscriber

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    I do not disagree with shooting a photo to baseline White Balance for the rest of your photos.

    What I mentioned was pertaining to the darkroom, the calibration of enlargement printing color filters, useful for deriving initial color balance, but not necessarily to take a random photo you want to print, and quickly derive a filter pack value for that photo. The OP did explicitly state, "I am looking for a fast and painless easy way to calibrate my color analyzer and get a starting color filtration pack quickly without needing to make multiple test strips."
     
  21. Bill Burk

    Bill Burk Subscriber

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    It sounds to me as if the first pass calibrates the analyzer to your paper and enlarger. Then all subsequent photography can use that calibration, in conjunction with an ExpoDisc photo + a real photo in that light... to quickly determine color filter pack for any real photo in any light.
     
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    Michael Firstlight

    Michael Firstlight Subscriber

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    That's how I understand it.

    MFL