*sigh, I so rarely post on forums because I can never restrain myself and end up with dense, impossible-to-read posts... O well.
Mammy645, I would love to hear more about your experiences with calibrating ACR. Could you post some before/after examples? How does the calibration hold up under strongly tinted light such as tungsten or sunset light?
Couple of thoughts:
1) The medium format back with 16bit processing and higher dynamic range will pick up on subtle variation in color that a dSLR, or high-saturation slide film (i.e. velvia) would not. This will be especially true when comparing dark-and-saturated tones and pastel colors in highlights. Therefore you'll expect to see a blue-tint in shadows when balanced for warmer daylight. On a dSLR this blue-tint would be less obvious. If you want to emulate an existing camera, for instance to add to a continuing body of work, my suggestion would be a slight toe in the curve to reduce apparent dynamic range. Also you can experiment with easy-black, or easy-gray input ICC profiles in Capture One. These profiles push lightly saturated colors back towards neutral. This can be useful in a variety of instances. Easy-gray is more aggressive than easy-black.
2) The non plus and plus versions of the back have different IR-cut filters in front of the sensor. The result is that sometimes a P25 might
3) While ACR, especially when tweaked and calibrated, can do a fine job of processing the P1 files, any serious experimentation should include Capture One, especially 4.1. If you're looking for something to do on a rainy day Irrident Raw Developer can process phase one files as well. We have a comparison of various developers here:
http://www.captureintegration.com/tests/software/
4) The ability to control default settings is being included in 4.2 Pro due shortly after Photokina. It's not of much of a substitute, but there are some really slick ways to copy settings between images in Capture One 4.1. My favorite for this situation would be
copy adjustments [Shift-Apple-C]
select all [Apple-A]
paste adjustments [Shift-Apple-V]
If the first two things you do are set an input profile and a white balance then this combination of shortcuts will copy the profile and WB to all images in that folder very quickly. However, the ability to set a default would be better, and is slated for 4.2 Pro.
5) Often a dSLR will clip one channel but not the others, which will produce incorrect color in the highlights or shadows. The most common instance would be tungsten light or early daylight where the content of the light is biased towards red. In this case the red channel is over exposed and the blue channel is under exposed. When the white balance is applied there is an effective pull given to the red and a push to the blue. Without good dynamic range this means the red channel will be clipped and loose highlight-accuracy. This comes up all the time with skin tones under strongly warm light; the average exposure will be spot on, but the red channel is being pulled a stop or more and highlights on the face will become blotchy and produce unnatural red fringing.
By the way, what is an input profile you ask?
Different light sources have holes (or peaks) in parts of the visible spectrum. White Balance shifts the white point within the visible spectrum but does not take into account the variances specific parts of specific colors. By selecting the proper profile your colors should match even when changing between light sources. For instance, imagine you're shooting a model with a rainbow dress inside in industrial and incandescent lighting as well as outside. White balancing these shots would match neutral grays, but a specific color like red might be under-saturated or appear off in hue. By also using the proper input profile those reds would match as well. There are limits of course, because no two lights are the same, but it does a pretty snazzy job.
Dale, if you're having problems producing consistent accurate color then you should speak with your dealer. They should be able to help you; there is very little chance your back is defective, so more likely there are elements of your workflow that need tweaked to produce best quality. With a proper workflow these backs produce the most accurate and consistent color of any system I've ever used. It's also possible that you're accustomed to a certain look from another camera system which was not as technically-precise in color. If this is the case your dealer should be able to help you to create a profile using Color Editor that matches the color reproduction of whatever your used to. At Capture Integration we often produce a profile for a legacy digital back when a customer upgrades. For instance, a month ago we produced a P45+ profile to match the color reproduction of the P25 for a customer who had become used to the P25 and had to match upcoming P45+ shots with archived P25 shots. After all, "accuracy" (as measured in a lab scientifically against known consortium-established targets) is the least important part of a color-workflow unless the goal is matching specific colors (e.g. "Coke Red"). Otherwise the important part is that you find the colors pleasing, which is purely subjective.
Happy experimenting,
Doug