On Jan 21, 2009, at 10:01 AM, Adam Maas wrote:
IQ is quite good, although it seems the ISO ratings are pessimistic
(I'm
getting exposures corresponding to ISO 160 when set to ISO 100, and
ISO 5000 when set to ISO 3200). It seems Panasonic didn't want to deal
with the hassle of people complaining about the base ISO being 160
instead of 100 so they just labelled it 100 instead and worked up from
there.
I shot a sequence of ISO/meter calibration tests using the E-1, L1 and
G1 bodies. I swapped the same lens, Olympus ZD 35mm f/3.5 Macro, to
each body for the testing so as not to have any variability based on
lens differences.
Test setup:
Open-shade sunlight, northern exposure, on the porch on a clear sunny
day with mid-afternoon sunlight. Reference meter showed light was
constant for all exposures. All exposures were made within about a 1
hour period. Checks were made with the reference meter to ensure that
the light stayed at a consistent level.
- Manual focus, manual exposure, AWB for all exposures; tripod mounted.
- f/6.3 lens opening throughout.
- ISO values stepped from minimum to maximum for each body, exposure
time adjusted from 1/4 to 1/125 second to compensate. Basically, the
same manual settings were used on all three bodies to isolate ISO
sensitivity from meter readings.
- Sekonic L328 incident meter reading was used as the reference target.
- Subject target included the Sekonic meter, a Kodak gray card plus
decamired grayscale wedges, and a notebook ruled paper page. This
latter does a good job of indicating whether you've saturated the
capture as the light blue rule lines are easy to blow out.
- RAW capture only was evaluated.
- All RAW files were imported into Lightroom 2.2 and processed at the
LR2 defaults. *
* note * :: The E-1's 1600 and 3200 files were given an Exposure
setting adjustment of +1 and +2 stops because the E-1 extended range
ISO settings are adjusted in software automatically only with Olympus
Studio 2. Lightroom and Camera Raw cannot apply the adjustment with
the Olympus' proprietary data format and scaling algorithms. However,
prior tests making the adjustment indicates the the results are par in
terms of noise/color quality with results using Olympus Studio 2. **
Observations:
- The L1 and G1 bodies' meters both indicated an overexposure
condition of +0.7EV for all exposures. The E-1 body's meter indicated
overexposure of +1EV.
- All files color correction on default settings as above is very
close to the same, and just a shade cool as expected given the shaded,
open sun lighting.
- Measurements were made of five reference points on the gray card in
Lightroom's Develop module. The L1 and E-1 images show values from
49-52% in all three component channels, the G1 images show values from
59-61% taken at the same points. This indicates that the G1's actual
ISO is more sensitive relative to the E-1 and L1 bodies by between
+0.3 to +0.5 EV, based upon prior gray scale tests to understand the
relationship between LR's percentage readings and in-camera EV-based
exposure settings.
- Considering the meter readings vs the actual data indicated values,
the E-1's meter calibration is most protective of highlight values,
the G1's the least, with the L1's in the middle of the range.
In a sense, the combination of the G1's slightly more sensitive than
the rated ISO performance and the G1 meter's indicated setting
compared to the reference meter, the G1's exposure system could be
considered the most accurate. "Most accurate" doesn't necessarily mean
that it produces the best exposures, remember: only that it will
indicate where saturation exposure will happen with the greatest
accuracy, at least for my use of RAW format capture.
Practical application of this observation means that in cases where
I'm using AE, if I set the E-1 to +.7-1 EV compensation, I'd set the
L1 to +.3-.7 EV and the G1 would fall in the range from -.3 to +.3 EV.
Another way of looking at it is that I'm more likely to get full,
correct RAW exposure without underexposure if I keep the G1 on 0EV
where I'd need +.3 and +.7 on the L1 and E-1 to achieve the same thing.
For a Pentax reference, metering for RAW capture with the *ist DS
usually meant +.3-.7 EV compensation and +0-.3 compensation for the
K10D in similar lighting conditions.
(As an aside, the *only* camera I've owned to date that actually
adjusted the metering calibration properly for RAW capture was the
Sony R1. Switching from JPEG to RAW capture with that camera
automatically re-evaluated the correct exposure setting and gave an
average boost of +.3-.7 EV over JPEG only readings for the same scene.)
---
I'm continuing to look at these files as a great deal of information
can be obtained from them. Particularly interesting are the noise and
detailing characteristics at ISO 800 and 1600 (and 3200 with the G1
and E-1) processed in several different standard ways using Lightroom
2's Tone Curve and Detail panel controls. I may shoot another sequence
with subject targets more specifically intended to exaggerate
detailing and noise characteristics in the image.
Godfrey
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