Colorstar 3000 calibration
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:
Film: Kodak Portra 160 NC
Paper: Fuji Crystal Archive
Development method: Nova slot tank
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.
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.
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.
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.
Originally Posted by Mick Fagan
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 :o and I could never get things to work out. But with a working probe making a perfect grey print is fairly simple if boring.
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Nick, interesting, you learn something new every other minute.
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, 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:-