Originally Posted by bobof
I've not measured DI, but on my X7900 I get to the published spec easily for iris -15 native.
If what you say is correct re: DI behaviour, this would mean folk running at -15 would have no DI benefit... Is that the case?
I've seen more than one post here mentioning different DI behaviour in terms of how far the DI closes the lens iris down depending on input signal type ("SDR" vs "HDR"). I wonder if this is coming into play in your observations.
The DI behaviour isn't fundamentally different. Here is how it works:
- The on value is defined by the manual iris position. The DI can't open wider than the manual position set.
- The only possible gain with the DI is on the black value.
- Hence the biggest improvement with the DI is always iris fully open (the larger the multiplier). This also comes at the price of more visible gamma and pumping artifacts.
- The closer the manual iris, the closer the result will be to native (the smaller the multiplier), and the least pumping and gamma artifacts
- Native have always met the specs if measured at -15, long throw, uncalibrated (high bright)
- DI has usually met at least half the specs if measured at 0, long throw, uncalibrated (high bright). This is measured in an SDR calibration, to answer your question above.
- Auto1 and Auto2 measure the same re on/off contrast. They differ by gamma manipulation (and possibly speed, I haven't checked) only.
- Any difference between SDR and HDR have to be due to the manual iris position. HDR tends to have a more open iris position, hence the higher DI measurements in that mode.
- Gamma (PQ for HDR or Power Gamma for SDR) should make zero difference for on/off contrast, as unless there is a bug gamma never influence 0% and 100%, which are used for contrast measurements.
- So in the same calibration mode (same manual iris setting, same lamp, and filter, etc), you should be able to change the gamma curve between PQ and any power gamma value without having any impact on on/off measurements.
- There shouldn't be a significant difference between low lamp and high lamp re on/off contrast measurements, but there can be a minor one.
- The eshift models had a "-16" iris position that was much further closed down than -15, hence couldn't be reached with the manual iris.
- The new models don't have this "-16" iris position, well, they do but the difference with -15 is much smaller.
To give you an example, with my beloved X500 (rs49), the difference in black level between -15 and "-16" was as follow: black was 0.18 lux at -15, and 0.05 lux at "-16" with the DI enabled, irrespective of the manual iris position. This means that the native at D65 was from 26,000:1 fully open to 46,800:1 fully closed (short throw at the time), but the dynamic was 422,000:1 (fully open) to 229,000:1 (fully closed), with a max of 600,000:1 dynamic in bright mode.
With the rs2000, the black level (not comparable in absolute values, the meter-to-lens distance wasn't the same) was 0.06 lux at -15, and 0.04 at "-16". So almost the same at closest iris position, and as you open the iris, "-16" goes up to 0.06 at -10 and 0.07 at 0. The native at D65 goes from 31,000:1 to 56,600:1 (mid-throw), but the dynamic goes from 212,429:1 to 82,500:1, with a max of 235,000:1 in bright mode.
It is this difference that explains the low dynamic contrast in the new models:
- less difference between -15 and "-16"
- "-16" not as fully closed in the new models as in earlier models.
Again, all the detailed measurements are in the new calibration thread, so it's easy to observe how the DI behaves in relation to the manual iris.