Resolution & Megapixels, what actually matters? Can my camera beat up your camera?

In the last couple weeks no category has caused more of a stir than the discussions about megapixels and resolution with the new Sony A7 series.  Most of this controversy starts with lens discussions.  There’s some considerable distinctions between the A7s‘s, 12.2 megapixel sensor, the 24mp on the A7, and the monster 36.3 of the A7r.  The sensors in the three cameras are all considered Full Frame(24×36), each measuring just under the 864 sq. mm. mark.  So what’s the difference between the three, if the sensor is basically the same size?  It’s a great question that confuses lots of people including myself….

Larger sensors tend to have larger pixels, which can translate to lower noise levels, and an increase in dynamic range(Cambridge in Colour article on Sensor size).  More light can be gathered by the larger pixel.  That at least makes sense.  How does this relate to the A7s and why is it the new low light king?   It has 12 really big Megapixels!  The light gathering potential is huge!  It becomes a dream camera for those who want to take low light or fast pictures(action, indoor photography, nights, low lit streets) and astral photography.    Somehow Sony has managed to increase the A7s picture quality by utilizing the unique in-camera processor(Bionz X) combined with the new Exmor CMOS sensor.  Does it have more resolution and capture images as sharp as the higher MP cousins…. no.  What it does do is provide a much sharper picture than the typical 12 megapixel camera (Sony A7s William Brawley’s Shooter report) with much more ISO range.   DXO explains that while the A7s performs better than any other camera tested in low light ISO, it actually looses some Dynamic Range compared to it’s partners(DXO A7 series comparison) after camera applies processing.

FD lens interior-07175
Described by one person as a 36 megapixel digital back, the A7r has few full frame equivalents.

That gets us to the A7 and A7r argument and that megapixels don’t matter.    It’s a complicated process to get an image to the SD card,    As the image zooms through the camera, Sensor size, pixel size, pixel density, processor, sensor type….  range of light/dynamic range… OMG!  –all contribute… Nasim Mansurav,(great articles on sensors etc) and others, refer to segments of this interaction as the “Image Processing Pipeline”(IPP). With the shared Bionz X processor, it’s similar in all three A7 cameras.  Suffice it to say that the largest sensor, with the largest pixels and highest pixel density wins, when the IPP is the same.  It’s starting to make sense why each camera performs the way it does.   Both A7s and A7 have better low light performance in some ranges than the 7r.  The 7r crushes in image quality when used in it’s optimum range.  Some things to ponder when the playground bully says his camera can beat up your camera.

  • About 12,000,000 pixel difference between the A7 resolution, 6024 x 4024,  vs  A7r 7392 x 4920.
  • staggering disparity in pixel density
  • 14 bits of color per pixel vs 12, on A7s and A7.  I think that’s good.
  • NO Anti-Aliasing filter
Lens dust
Ultimate Resolution with the Native FE 55 lens and the A7r.

This information helps resolve why the lens performance on the A7, can seem radically different on the A7r.  Lessor optical quality isn’t realized until placed on the unforgiving 36.3 MP sensor.  On the “R” everything is magnified, good or bad.  It explains why people go to great lengths to defend how good some lenses are!  In the A7 world they are that good.  A bit of a paradox I suppose.

Those of us who live in 7r-ville can hope that the new Loxia lens line, the about to be officially announced FE 16-35 f4 and FE 85 1.8 are capable at 36.3 megapixel levels.

Another good resource for this discussion