Some dumb questions I have been wondering about

Started Mar 28, 2013 | Discussions thread
mike703
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Re: Some dumb questions I have been wondering about
In reply to Wellington100, Mar 28, 2013

Interesting questions.  Some entirely subjective responses...

1) Why are camera sensors not square? Surely a square sensor is the most efficient way to get the best out of a lens?

You'd think so (or even better, round to match the image circle).  but most people seem to prefer rectangles... the golden ratio of about 1.6:1 is supposed to be the most aesthetically pleasing proportion and crops up in paintings a lot for that reasons. A square somehow looks too symmetrical.  So it's just an aesthetic thing, not a technical one.

2) Does using a Polarising filter reduce the Dynamic Range of an image taken in sunlight with a digital camera?

Sort of.  First there is the underlying neutral-density-filter effect which just costs a couple of stops of light.  That contribution affects the whole image equally so doesn't alter the DR.

The additional polarising effect selectively reduces in intensity specular refections (off surfaces such as glass, leaves, metal, snow, rock or a shiny forehead).  So on that basis it would reduce the DR.... except that other bright areas (direct sunlight, bright clouds) are not affected in the same way.  In an 'average' scene, whatever that is, some - maybe even most - of the highlights will be brought down in intensity, but not all of them.  So strictly speaking the DR of the scene is the same, even though the proportion of highlights is less.  if you shot a scene where basically all the bright areas were specular reflections (e.g. a rock face with the sun behind you) then all of the bright areas would be reduced in intensity and the DR of the scene would decrease.

3) Why do most cameras have IQ reducing AA filters when the few cameras that don't have them jump in IQ and moire is nowhere to be seen in 99.99% of the images?

There's a can of worms.  Maybe moire used to be a major problem in some far-off age and we've over-compensated ever since.  Apparently it's now quite easy to get rid of - it used not to be and was a major hassle if you got it.  Maybe that's the answer and we will now see more and more cameras with no AA filters as the benefits become apparent.

4) What is the optimum resolution for small camera sensors? High resolution sensors seem to add significant file size for little discernible improvement in resolution, so what is the cut off for a functional and well rounded small sensor?

You will never lose detail by having more and more pixels, and (as long as you print at the same size) noise effects cancel out, more or less.  but as you imply there is a point beyond which your lens quality and technique need to be immaculate to capture any more detail.  Unless you are shooting with top-drawer lenses under very controlled conditions using a tripod and mirror lock up my impression is that we already have enough resolution and pixel count is not the limiting factor in the technical quality of most pics.  But there are a few people with demanding requirements who do shoot like that and will make the most of higher resolution.

Best wishes

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