Sony Alpha DSLR-A700 Review
Dynamic Range (contd.)
Create Style options
The graph below shows the dynamic range response from each of the A700's fourteen Creative Styles. As you can se each has a very slightly different curve mostly due to changes in contrast and brightness for each. The important point to note here is that no single Creative Style delivers more dynamic range than the 'Standard' mode and of course because of more contrasty responses some actually deliver less.
ISO Sensitivity and Dynamic Range
Due to engineering and design constraints some sensors optimum base sensitivity isn't ISO 100, we have seen this many times on various digital SLRs with base sensitivities of ISO 200. In our normal evaluation of dynamic range we discovered that in actual fact the A700's optimum base sensitivity is actually ISO 200, that using ISO 100 will lead to less highlight range (by 0.7 EV; two thirds of a stop).
What's more concerning is that the only reference to this fact in the A700 user manual is hidden in the following sentence: "The larger the number from the standard (ISO 200), the higher the sensitivity". The other hint being that if you factory reset the camera it defaults to ISO 200. There is also no indication on the camera display that sensitivities lower than ISO 200 (ISO 100, 125 and 160) are not optimum, however it does indicate this (with borders around the numbers) for ISO 4000, 5000 and 6400.
Understanding that ISO 200 is optimum we can see that at this sensitivity the A700 delivers almost nine stops of dynamic range, more importantly that almost four stops of this are highlight range (compared to the more typical three and a half stops for most DSLRs).
|Sensitivity||Shadow range||Highlight range||Usable range|
|ISO 100||-5.1 EV||3.2 EV||8.3 EV|
|ISO 200||-4.9 EV||3.9 EV||8.8 EV|
|ISO 400||-4.9 EV||3.9 EV||8.8 EV|
|ISO 800||-4.9 EV||3.9 EV||8.8 EV|
|ISO 1600||-4.3 EV||3.9 EV||8.2 EV|
|ISO 3200||-3.7 EV||3.9 EV||7.6 EV|
|ISO 6400||-3.4 EV||3.9 EV||7.3 EV|
Dynamic Range compared
Despite ISO 100 not being the A700's optimum it still manages to deliver about the same highlight range as the Canon EOS 40D and Nikon D200. At ISO 200 the A700's highlight range extends about half a stop further than the EOS 40D and two thirds of a stop further than the D200.
|Sony DSLR-A700 (ISO 100)||-5.1 EV||3.2 EV||8.3 EV|
|Sony DSLR-A700 (ISO 200)||-4.9 EV||3.9 EV||8.8 EV|
|Canon EOS 40D (ISO 100)||-5.7 EV||3.4 EV||9.1 EV|
|Nikon D200 (ISO 100)||-5.0 EV||3.2 EV||8.2 EV|
The wedges below are created by our measurement system from the values read from the step wedge, the red lines indicate approximate shadow and highlight range (the dotted line indicating middle gray).
Experience has told us that there is typically around 1 EV (one stop) of extra information available at the highlight end in RAW files and that a negative digital exposure compensation when converting such files can recover detail lost to over-exposure. As with previous reviews we settled on Adobe Camera RAW for conversion to retrieve the maximum dynamic range from our test shots.
As you can see the default Adobe Camera RAW conversion delivers less dynamic range than JPEG from the camera (a more contrasty tone curve and less noise reduction in shadows). The best we could achieve was just over ten stops (10 EV) of total dynamic range - at the optimum ISO 200, more importantly almost a stop of that is in highlights (although with no guarantee of color accuracy).
- ACR Default: Exp. 0.0 EV, Blacks 5, Contrast +25, Curve Medium
- ACR Best: Exp. -2.5 EV, Blacks 1, Brightness + 50, Contrast -50, Curve Linear
WARNING: Although ACR was able to retrieve the 'luminance' (brightness) of wedge steps which were previously clipped there's no guarantee of color accuracy as individual channels may clip before others. This can be seen fairly clearly in the examples below, on the right the negative digital exposure compensation has revealed some more detail in the background but this soon turns into gray as one or more of the color channels clips.
|Adobe Camera RAW default conversion||Adobe Camera RAW with -2.5 EV digital comp.|
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