More megapixels, better photos: Fact or fiction?

Started Feb 7, 2008 | Discussions thread
Jay Turberville Forum Pro • Posts: 12,917
Re: I agree it depends

In the example given the size of the aperture area of the photo
diodes have increased by 7% compared to the earlier (10 Mp?) sensor.
This does not necessarily lead to an increase in amount of collected
light of 7% as microlenses are used to focus the majority of the
light hitting a sensor on the aperture areas of the pixels.

Right. But if you read the Sony papers, they also do things to improve the efficiency of the microlenses. Though I suspect there is less room to improve there. So you may suffer lower native ISO sensitivity with smaller pixels. For instance, my Coolpix 8400 has ISO 50 as its lowest ISO while the Coolpix 8400 is at ISO 100.

If as you say the number of pixels have roughly doubled (an increase
by 100%) compared to the older 7.1 Mp sensor, there is now 50% less
area for the microlense of each pixel. Now, unless the efficiency of
the microlenses of the 7.1 Mp sensor was only 50% (which is extremely
unlikely) and is 100% now (which is virtually impossible), I can not
see how performance could be similar.

Like I said above, you may lose some sensitivity. Take a look at this chart I put together some time ago for Sony sensors. Sensitivities do tend to drop, but not always. And when they do, it often isn't as dramatic as people might thing based on what they think they know about "pixel size."

If they keep the photodiode roughly the same size as the pixel pitch is reduced in size, then your you don't lose in per-pixel dynamic range and noise - at least you don't for having made the pixel pitch smaller. But the photodiode area is not the only place where improvements are being made.

So the summary is that even if you don't improve the per pixel performance, there is a good argument that overall sensor performance actually improves with smaller pixels by virtue of the increased number. It reminds me of the comment supposedly made by Stalin that, "quantity has a quality all its own."

But the reality is that many aspects of per pixel performance are actually maintained as the pixel pitch is decreased. The total amount of light sensitive silicon tends to increase with the newer finer pixel pitch sensors. So we actually get a double win. That is evident in the example I posted where an 8Mp 2/3" CCD soundly thrashes the older 5Mp 2/3" CCD in almost all areas of image quality performance. So you really don't know what to expect in overall performance from a sensor unless you have some good technical information or have access to images taken with it. And if people want to be upset about a trend in compact sensors, be upset that the larger 2/3" and even 1/1.8" sensors are less and less common. The shrinking format sizes is more of an issue IMO.

If you want to read more on Sony sensors, look through the back issues of CX news that are published by Sony.

http://www.sony.net/Products/SC-HP/cx_news/backnumber.html

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