Pixel density - can the playing field be leveled???

Started Jun 6, 2009 | Discussions thread
Malcolm Practice Contributing Member • Posts: 593
Re: A little discretion please!

Virvatulet wrote:

bushi wrote:

ejmartin wrote:

the issue is not the fill factor but other aspects of the layering of the chip.

So according to that picture by Sony:

So, either this picture is wrong , and you are right about microlenses allowing nearly all light to reach photosensitive area, or the picture is right, and I am right, stating that less MP on the otherwise same sensor (= less wiring that stops some light from reaching the photosensitive area) equals more light being captured. And all my findings and analogies were right, as for the general description what is going on under the hood.

Well, at the moment it seems that I was right.

And I would like to make a supplementary note that during past years Sony Semiconductors has several times referred to development that has helped them to increase the efficiency of microlens structure along with PD/charge well size increase (sometimes even absolute like ICX495 -> ICX624, though mostly relative). If the light gathering premise of 100% would be valid this development would not have been possible.

In fact there are very few things in real life where 100% efficiency would even be achievable under any conditions.

I think the real issue is not whether microlenses are 100% efficient, but whether microlenses now determine effectively the fill factor of a pixel. There are several indicators that this is so:

  1. The failure of the high fill factor/no microlens approach pioneered by FillFactory and used in the Kodak FF DSLRs

  2. The ability of progressive improvements in microlens design to yield better QE

  3. The lack of any clear evidence in practice for a dependence of QE on pixel size.

It is also likely that microlens design has been improving all the time that Sony (and the others) have been developing the back illumination concept, and that the gains of back illumination over a modern sensor may not be as great as were envisaged at the time of the start of the programme. Very likely, the marketing material comes from the case that was put forward then.

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