Colorstar 3000 calibration

Discussion in 'Color: Film, Paper, and Chemistry' started by Tom Kershaw, Jun 27, 2008.

  1. Tom Kershaw

    Tom Kershaw Subscriber

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    I've just been experimenting with a Colorstar 3000, and from reading the Frances Schultz article on the Colorstar I need to calibrate the machine with a colour negative of a gray card, not included with my example. So my question is: what are most appropriate methods to create the negative? My initial thoughts are to photograph a gray card under my 5000 K CRI 98 tubes (4 x 58W ceiling mounted in a small room) with a neutral film such as Kodak Portra 160 NC. However I'm sure there are other considerations that I should take into account...

    To show my chemicals are okay (freshly mixed Fuji RA-4 Xpress) I've included a very quick scan of an initial attempt:

    [​IMG]

    Film: Kodak Portra 160 NC
    Paper: Fuji Crystal Archive
    Development method: Nova slot tank

    Tom
     
  2. RobC

    RobC Member

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    I would photograph it in daylight. Just put it into a few test shots of various subjects. It should give a density of 0.7 when measured from the print if you have zeroed your densitometer on the paper base white.
     
  3. Nick Zentena

    Nick Zentena Member

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    I just picked my stock film at the time and shot the card in daylight.

    You want JUST the card in the frame. Fill the frame.
     
  4. Mick Fagan

    Mick Fagan Subscriber

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    Tom, the perfect way to get a genuinely neutral grey negative, is to use a Wallace Expo/Disc, period.

    They may have a shortened name now, but the Wallace Expo/Disc is a calibrated scientificly designed and manufactured, semi transparent unit, that slips on your lens, like a filter, except it slides on instead of screwing.

    When you receive one, you will get a calibration card showing the deviance from 18% (I think from memory). I have two sizes, 52mm and 72mm, which went onto all of my Nikkor lenses.

    Having used a myriad of different gadgets to obtain a correct grey, this is the absolute best. You can also check shutter speeds and/or lens f stops, by using different exposures.

    Bob Mitchell had a small grey card made out of laminex, designed to go on a key ring, it is very good, but not as good as the Expo/Disc.

    I've had mine since the very early nineties and did quite good to very, very good colour balance on my personal printing.

    I have the original Jobo Colorstar 1000, which is like comparing a sixties BMW motorcycle, to a naughties BMW motorcycle, they are the same, but completely different.

    To get a perfect grey negative for lab use for both colour balance and density, you slide the disc over the filter threads, turn the camera on to "A" for automatic aperture and/or shutter speed, point it at the light source, (generally), then trip the shutter.

    Even if the shutter speed was down to, say ½ a second and you had camera movement, it won't matter, you will still have a perfectly exposed neutral grey negative.

    You then take that negative and print a dead neutral grey tone, on colour paper, this is reasonably hard, actually.

    Bob Mitchell invented another colour system which was designed to eliminate that guesswork, allowing you to get a perfect grey tone on your colour paper, he called it the, "Colorbrator", note the American spelling.

    Basically this is an extension of the Unicube colour system, which I believe he also invented.

    I have all of these different systems, they all work to different degrees of colour accuracy, all are quite good and quite accurate, but the combination of the Wallace Expo/Disc in the field, combined the Bob Mitchell Colorbrator in the darkroom, is perfect!

    You can literally switch from daylight balanced film to tungsten, painlessly in the darkroom, provided you have exposed at least one frame from each film and lighting set-up first.

    Once you have set your Colorstar analyser to a genuine grey, it is so easy, just put the probe under, turn the lights out, the enlarger on, then change the enlarger dials until all the colours on the Colorstar go out. Bingo, you will have a genuine neutral grey, and I do mean neutral.

    Mick.
     
  5. Nick Zentena

    Nick Zentena Member

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    With the 3000 this isn't that hard. Hardest part is the intial guess on the filter pack. You make your grey test print. Cut a dry strip off. Insert it into the probe and measure. The unit takes a reading. You hit the buttons and it adjusts. You go back and make a new grey print.

    If the starting filter pack isn't too far off then it's not that hard. If it's way off you'll end up with an extra step or two.

    The first time I tried it my probe was busted :surprised: and I could never get things to work out. But with a working probe making a perfect grey print is fairly simple if boring.
     
  6. Mick Fagan

    Mick Fagan Subscriber

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    Nick, interesting, you learn something new every other minute.

    Mick.
     
  7. Tom Kershaw

    Tom Kershaw Subscriber

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    Mick,

    Thank you for the notes on grey cards. What light source would you recommend, the 5000K tubes (consistent) or sunlight (inconsistent but bright)? Now to find the Wallace Expo/Disc..


    Tom.
     
  8. Tom Kershaw

    Tom Kershaw Subscriber

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  9. Mick Fagan

    Mick Fagan Subscriber

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    Tom, yes that is the modern, or electronic version, which as I understand it, is virtually identical to my own units.

    The Expo/Disc has been around for about 35-40 years and has applications in scientific photography as the light transmission is so well controlled it can and does get used for scientific photographic applications.

    I know this from a photographer who did her Applied scientific photographic course from RMIT in Melbourne, became a forensic photographer, and is currently freelancing between various government and semi government scientific photographic assignments, that cannot be easily done, if at all, electronically.

    You may find this quite interesting:-

    http://expodisc.com/about/history.php

    Mick.
     
  10. eunkefer

    eunkefer Subscriber

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  11. RobC

    RobC Member

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    Unless the colorstar 3000 has built in recognition of 18% grey, then it really doesn't matter what calibration target you use. A Macbeth colour chart is probably a far better option to put in the image as you get a whole range colours as well as greys. A slight deviation from grey will show up more on its complimentary and opposite colours on a colour chart than it will on grey. Infact it doesn't have to be a macbeth chart. You can design and print your own. The actual colour values are not that critical. The name of the game is reproducing a colour in the print that is on your target. Every print you make will likely be tweaked for colour so it is a starting point only for the particular film you are using that you are looking for.
     
  12. Nick Zentena

    Nick Zentena Member

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    The calibration program does require a grey negative. It automatically adjusts the calibration. You'll never the thing to work using anything else.
     
  13. RobC

    RobC Member

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    Yes but a Macbeth colour chart does have grey swatches which can be put under the probe. So does the colour star require an 18% gray card and how does it know if the grey card was exposed correctly. It would need a known reference then and not a photograph of a known reference which could throw the reference off.

    Square 22 of the chart is 18% grey (density 0.7).

    http://usa.gretagmacbethstore.com/i...enuGroup/__Menu USA New/desc/ColorChecker.htm

    Bloody expensive:surprised:
     
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  15. Nick Zentena

    Nick Zentena Member

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    It needs a grey negative. The built in densitometer handles the rest. You could stick a 35mm negative into the probe and check exposure if you really wanted to.
     
  16. RobC

    RobC Member

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    Ok I misunderstood. You are saying the actual negative needs to be grey/neutral in colour as opposed to a colour negative which has a colour mask in it. Yes?
     
  17. Nick Zentena

    Nick Zentena Member

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    No it needs to be a photo of a grey card. C-41 for RA-4. E-6 for positives.

    Really doesn't need to be much more then a full frame shot.
     
  18. Mick Fagan

    Mick Fagan Subscriber

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    Tom, the light temperature of the first negative you should use to calibrate your analyser with, is easiest if you use mid morning or mid afternoon light on a clear day.

    Then you print a genuine neutral grey, presumably using the inbuilt programme as mentioned by Nick.

    Once you have these enlarger settings correct, you tell the analyser, with these filtration settings in place, this is a neutral grey with this paper.

    Obviously at this stage you will print a frame from that roll, at least I did.

    From then on, when you decide to take a set of colour pictures, you take a frame with the Expo/Disc attached as before, first up.

    When back in the darkroom you take that first grey Expo/Disc exposure, place it in the enlarger, place the probe under, set the analyser to the correct settings, then you change the enlarger settings until the analyser is happy.

    At this stage, without using any paper, you have analysed the light and corrected for a near exact light temperature from your previous testing.

    You then make a test print, within reason it should be virtually colour perfect. The only thing you really have to adjust for is density.

    Remember that Red and Cyan are obtained by density. A dark print will have a red cast and a light print will have a Cyan cast. This assumes all other colours have been corrected first.

    You normally use two of the three filters for colour negative printing, these are Magenta and Yellow. The Cyan filter is not used, the amount of correct Cyan or Red you have in your print, is generally determined by print density.

    Hope this helps.

    Mick.
     
  19. Ed Sukach

    Ed Sukach Member

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    Calibration of the Colorstar 3000 does NOT require an 18% gray negative. It would be helpful to either use a uniformly exposed frame or one where the same spot can be accurately accessed on each trial.

    A test exposure on the media in question is made, and the ColorStar will measure the deviation from a density of 0.55 on cyan, yellow, magenta - and overall integration - and utomatically compensate for these deviations. Another test is made - and the results further refined, until the ColorStar will be able to accurately determine the filtraiton necessary to produce an average "gray" from the TEST strip.

    Do you have a copy of the ColorStar 3000 manual?
     
  20. Tom Kershaw

    Tom Kershaw Subscriber

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    Ed,

    Yes I have a copy of the ColorStar 3000 manual, but I've been working from the Frances Schultz article which is based on using a grey negative to calibrate the machine. I was under the impression that the grey negative was to insure colour neutrality as a starting point.

    Mick,

    From your description of how to use the Expo/Disc, a new grey negative is made per film / lighting situation etc, and so a new set of calibrations are made per grey negative?

    Tom
     
  21. Mick Fagan

    Mick Fagan Subscriber

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    Tom, once you have your enlarger set for a perfect grey picture, you set the analyser.

    The next time you are out shooting, you take an Expo/Disc negative for every different light situation.

    You take a merry-go-round with tungsten and daylight, take a Expo/Disc frame with the camera pointing to the merry-go-round and if possible, some daylight as well. On your walk you take seascapes, take an Expo/Disc negative of the seascape, on the way home you take pictures of your friends in a restaurant, take an Expo/Disc negative.

    In the darkroom you decide to do the merry-go-round shots, put a neg in and compose the picture, replace it with the Expo/Disc negative and adjust the enlarger until the analyser is happy, change negs, focus and print, process and see just how good you and your technique are.

    Then you do the restaurant frames, put a neg in and compose, replace with the restaurant Expo/Disc negative, set the enlarger, change negs, focus and print.

    You should have virtually perfect colour balance, density is another issue, but you should be able to work out from a contact sheet the fine density changes required.

    I enlarge in 1/8 f stop increments, put a chart on the wall where you can glance for the changes.

    Kapish?

    Mick.
     
  22. Tom Kershaw

    Tom Kershaw Subscriber

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    Mick,

    Thanks, that makes the process very clear. The vast majority of my successful efforts have been in analogue black & white where one can guess a good starting exposure and contrast grade...

    Tom
     
  23. Tom Kershaw

    Tom Kershaw Subscriber

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    Thinking through the process of using the Expo/Disc it would seem that using a through the lens metering camera would be helpful, rather than placing the Expo/Disc over an external light meter.

    Tom.
     
  24. Richard Harris

    Richard Harris Member

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    It doesn't matter what you use as a grey negative you just need to measure an area and make that area grey when you print. I would suggest you photograph a white towel and fill the frame with it You will then have a negative with a total area of uniform colour and a textured surface to measure exposure. You could use a red towel, it would make no difference. You are setting the analyser to print a grey tone, not measuring the colour of the negative. Personaly I find skin tones and grass colour etc just as important as finding a grey So I use spot metering of these areas projected on the baseboard of the enlarger. Most negatives will not integrate to a perfect grey and so using integrated measurements is less use than using your normal filtration and adjusting the results, IMHO.
     
  25. RobC

    RobC Member

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    If you read what Mick has said carefully, his method suggests although I don't think he said it directly, or maybe he did, you make one grey negative to give your initial calibration of the colorstar and then for each subject in different lighting, you make another grey negative. Using that grey negative from each subject to set your filter pack for printing but not actually printing it, automatically corrects, near as damn it, for the colour temperature of each individual subject. That should save a lot of paper when printing as with a little experience, you should only need to make one density test for each print and it will be nailed for time and colour.
     
  26. Mike Wilde

    Mike Wilde Member

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    flogging the horse named colorstar 3000

    boy - what a discussion, and this is a device that makes color printing so much easier.

    The colorstar has either 8 or 99 channels, depending on its firmware. Mine has 8, so I keep a log of the numbers for way out there channel readings and dial the numbers to match the recorded settings into channel 7 or 8 when I need them. Things like blue sky, green grass, white clouds.

    Most of the time I use grey from a betty neg I made up to calibrate the system at the beginning of the session. Ths neg is even taped to its own matt board neg carrier. Channel 1 for ng, meter, dial the filters, aperture to be near 5s, and expose, process, hair dry, autocalibrate, and away we go, dialled in for the night. Chanel 2 I have set for spot neutral caucasian flesh, and channel 3 for spot, warm caucasian flesh. These 3 use 90% of the time.

    With the flesh channels, the need for me to shoot a grey each roll is almost never needed. Usually there is a snippet of flesh somewhere on the roll, or on another roll that I shot that day, so that the second print is bang on, if the first print is a bit off.