Just what is the ideal pixel density?

Started Sep 30, 2011 | Discussions thread
Iliah Borg
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Re: Just what is the ideal pixel density?
In reply to Tony Beach, Oct 1, 2011

To get a high grade 8-bit CMYK TIFF for printing one needs 10 bits useful information form raw. For that, about 4096 levels on ADC are needed. To shoot events, we often need ISO 800, 1600, 3200. 3200 adds 4 bits to the level count (given base ISO is 200), so the minimum well depth is about 60 to 70 thousand (and that not including latitude for exposure errors due to light or scene changing). (Well depth can't be always substituted with binning, by the way; and when it can - where is our resolution now?) Current sensor technology suggests that for 135 format sensor such well depth is achievable if the pixel count is about 18 megapixels.

The hope is that with really low noise sensors 9 bits of useful information from raw is enough, and that brings us to wells of about 30-40 thousand, which is now doable on 48 megapixel 135 format sensors. However here is where white balance kicks in. With 9 bits useful on the green channels we do not have the same in red and blue. Working with some sensors that have 120 thousand wells, the difference is really impressive compared even to D3s.

The question of landscape is - does increasing pixel density past some value really and visibly increases the amount of details captured in the scene? Or the better way is to use full colour pixels and stay at lower pixel densities?

The smaller is the pixel the shorter should be the shutter speed, to counteract different types of blur. Some shots, like a waterfall, need slower shutter speeds. The rule known from fine grain film is that even shooting with a tripod one needs to up his shutter speed 4 to 8 times to really benefit from higher resolution. Bye-bye 1/30, we now start from 1/125 or 1/250. For digital it means we are underexposing now in far too many situations, which brings us close to the scenario above.

You can try with a850 shooting the same scene using 1/30, 1/250, and 1/1000. Which shot is sharper? I do not see many folks realising that even with past generation pixel densities we are in the realm of high shutter speeds if we are after he resolution.

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