Reading through this thread has completely put me off getting the DP0 Quattro.
I noticed that Ffordes has just got in the DP0Q in the kit form with the loupe.
I actually do not need the DP0Q but I would have liked to have one to play with. But if the highlights issue is embedded in the sensor and processor then it really kills all interest for me.
Another issue now is the forthcoming Sony A7rII. I now have a pretty substantial Sony ILC kit and with the A7RIIs even higher resolution combined with killer lenses from Zeiss I think I may finally be at an end with the Merrills in my kit.
We'll see but as said I can't see investing money in a product with such obvious flaws - which would really show up in landscape photography imho.
Just my two cents.
LouisB
If you would have liked the DP0Q lens and likes the sample pictures, I would not discourage you from trying one. Why not? Because I think the highlight issue in itself is very much overblown
If one tries to shoot a Quattro just like a Merrill, it will surely clip the channels easier (and more simultaneously). Or if one trusts the metering system without minus compensation, the same will probably happen in pictures that have very light objects, like sun reflections in water, very light and glossy objects etc. And it is easy to attribute it to sensor flaws "embedded" in the sensor.
But if you adjust your shooting technique to the sensor characteristic this will not be that much of a problem. This link provides more information about the measured DR:
Sigma dp2 Quattro Review - Exposure
The conclusion was:
DR with high quality (low noise) was 6.25 f-stops
DR with med-high-quality was 8.85 f-stops
DR with medium quality was 9.91 f-stops
DR with low quality was 10.7 f-stops
DR detected (complete range) was 12.8 f-stops
And please note, this may have changed slightly (to the better) somewhat since that time, as it was software-dependant (noise reduction) to some degree. Some early tests with Kalpanika also shows that SPP doesn't always use all highlight-data available in the RAW-files, so there may be some more high-quality DR possible to achieve.
Anyway this was below the average compared to the best Bayer-sensors. Compared to Merrill? Hard to tell exactly as the same source didn't do a test of the DP Merrills in the same way. (The SD1 pre Merrill showed however more than one stop more high quality DR but 3 stops lower detected DR. That was also below average for its time. Another source says 12.2 maximum DR of the Merrills:
DP2 Merrill sensor read noise finally measured: Sigma Camera Talk Forum: Digital Photography Review
But if you adjust your shooting style to the Quattro I doubt that you will run into problems that often. If one does, it could be more of a metering problem IMHO. You may need to compensate on the minus-side with the Quattros, like -0.3 to -1.0, where the Merrills could do with +-0 or +0.7 (from what I have read, not tested myself). Or spot meter the bright areas to make sure they do not clip. The Quattros does not have the same highlight-headroom but instead better shadow recovery than the Merrills and a DR in the same ballpark. So adjust to it and it will work fine for most subjects. If you could get a Merrill to work (which also has limited high-quality-range compared to Bayers) you could most probably get a good shot from a Quattro as well, if you use it according to its characteristics.
I have some RAW files from the DP3Q if you want to try the characteristics of the Quattro files. I have a few test-pictures with clipped highlights but those could have been easy to save with some more minus-compensation to the metering system and compensation in SPP afterwards. In the beginning I used only -0.3 and that was too little for some high-contrast-scenes. I should have used -0.7 or -1.0 with the default Evaluative-metering settings, or changed to spot-metering.
I hope this either confirms your decision or makes you rethink