Phase One IQ4-150 Achromatic – High ISO or Push Process
We often field questions on best ISO use and cameras from various manufacturers have varying abilities to extend beyond their base exposure settings. While the more aged Phase One digital backs that held CCD sensor technology could run to 400 & 800 ISO’s, the resulting look would be much like high-speed color negative film, with poppy bright spots and a clear ‘grain’ pattern.
The CMOS sensor technology that has been the primary flagship sensor technology for Phase One for the last decade or so reaches higher ISO’s with more ease and latitude than the CCD backs, but with a different set of artifacts like all digital cameras inevitably do when you overdrive the sensors.
Let’s get this out at the very beginning, this is an exercise in pixel peeping as viewing the comparative quality of these files, even when viewed at 100%, can be somewhat difficult. Admittedly, even worse when trying to convey this information with anything less than the full 16-bit raw files in a darkened viewing environment on a good monitor.
The purpose of this endeavor was to find the limitations of preserving shutter speed while not giving up an operational depth of field within a demanding naturally lit underwater environment that our client Riccardo Ullio was shooting within, upon his upgrade from IQ3-100 Achromatic to IQ4-150 Achromatic.
I sought to determine what changes of quality would be met when combining the overdriving of the sensor through ISO expansion in comparison and in combination with the power Capture One’s exposure compensation abilities utilizing the Phase One 16-bit raw file to Push underexposed captures so that maximum reproduction sizes could still be maintained.
All of the test images here if clicked, will expand into a full screen version that represents the screen captures from my EIZO monitor. The images are keyed with Color Tags for the ISO they were shot with as well as Star-Ratings representing the amount of software push was utilized to maintain the same overall exposure in the purposefully underexposed shots.
Initially the results were somewhat surprising until I integrated what I already knew and understood about Phase One 16-bit captures with these test results.
Brad Kaye – Technical Services Manager, Capture Integration
The Camera:
The Scene:
The Exposure Matrix as shot:
5-star= No Push, 4-Star=+1 Push, 3-Star=+2 Push, 2-Star=+3 Push, 1-Star=+4 Push
ISO 200=Green, 400=Blue, 800=Pink, 1600=Purple, 3200=Yellow, 6400=Orange, 12,800=Red, 25,600=Grey
100% Crop @ each available Full Stop ISO increment
(I found myself staring at the wood grain a lot while reviewing these files)
We will primarily be addressing the top ISO 200 – ISO 3200 portion of this matrix that has the most relevancy within this specific test.
(shown as actually exposed from camera without software exposure push from Capture One)
Here’s what a 400% pixel peep looks like with a normal exposure across the ISO range:
Here’s the comparison matrix that will follow in the images below… Reference Frame @ ISO 200, compared to Base Exposure for ISO 3200 with camera underexposing and pushes to the ISO’s falling back to 200 to maintain the same exposure:
Here’s what I see from these files.. (have a look and compare with me)
Really difficult to come up with a clear-cut, definitive statement, but my quick conclusion (after staring at images for literally days as I bounced in and out of writing this) is I would have no problem running an ISO of 800 with a 2-stop underexposure if I needed to achieve ISO 3200 sort of shutter speeds and there’s certainly the math for even 3-stop and 4-stop pushes given the incredible amount of tonal bandwidth available in Phase One raw files. That’s the magic here… the fidelity of the 16-Bit capture here is phenomenal and the raw IIQ 16-Bit Extended format file really shines. I tend to like how the wood grain in these shots render with the ISO 800 +2 shots compared to the ISO 3200 shots even when applying 75% shadow recovery which is another additional Push.
I will likely repeat this test with the color unit at a future date, as the dance of color enabled pixels may change the dynamic. -bk
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