kwalsh
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 p.2 #3 · Why isn't very low ISO available? | |
calemon wrote:
Most of the comments about "buckets" are correct, but most are tailored towards CCD sensors. Remember that Canon uses CMOS sensors, which means there is/can be processing on board the sensor (unlike CCD). This means that the sensor could "divide by 2/4/8/16" in realtime during the exposure acquisition to prevent blowing highlights if this feature was _chosen_ to be implemented.
While it is theoretically possible to put on electronics to reset or divide the well on a CMOS imager this would have a major impact on the sensor design and dramatically degrade the noise performance across all ISOs. CMOS sensor design involves extremely difficult trades in the number and size of transistors in each pixel cell, adding a entire extra transistor just for a low ISO option would be a very bad trade. Case in point, you can implement an electronic shutter easily onto a CMOS imager, no more mechanical shutters to break down, shutter speeds way up at 1/50,000, no flash-sync problems ever again. This would obviously be a huge feature improvement everyone would love, and it has been demonstrated numerous times over the past few years in R&D sensors, but no one has put it into a product because the addition of the one transistor per cell to implement the electronic shutter kills the sensor performance. A low ISO option on sensor would have a similar or worse impact. So yeah, it could be done, but it won't (or at least not anytime soon).
As someone else already suggested, take as many images as it takes and average them digitally (i.e. in Photoshop). Would work fine for things like waterfalls, but for some images the gaps in between the images would cause problems (i.e. moving lights, etc.). Otherwise, sadly, it means breaking out the ND filters.
Ken
P.S. Actually electronic shutters are used in imagers for machine vision systems all the time, just not in many megapixel photo quality sensors because of the noise impact.
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