Why does Pentax FF have to truly be FF?

Started May 25, 2012 | Discussions thread
Joseph S Wisniewski Forum Pro • Posts: 34,130
Hexagons would maximize yield...

Mark Ransom wrote:

I've always thought that a square sensor would need to keep the same imaging circle as the APS-C sensor. That would result in a sensor of 4176x4176 pixels compared to the 4928x3264 of the K-5, 15% smaller on the long edge.

Your comment got me thinking though. Obviously it would be possible to make a cross that has 4928x3264 in both directions. Building on that you could make an octagon that fills in the diagonals of the cross, and it would still fit in the same image circle.

Octagons aren't a packing shape, so you end up using squares. They give you a slightly higher yield, because you can tolerate flaws in the corners.

The problem is that chip manufacturing really only works with rectangles and squares.

Ford Aerospace has (had) a neat process (and patent, obviously. It's Ford) for dicing up hexagons. Those are a packing shape. Regular hexagons are great for surrounding circles. You can also get some pretty good rectangular crops inside a hexagon: no more than a 10% reduction off the chord, if memory serves.

Same with raw files.

That shouldn't be hard to fix.

You might as well accept a 4928x4928 square and crop if you don't like the image quality in the corners.

Next comes the question of cost. I don't think sensor cost is proportional to the area of the silicon, it's probably closer to the square of the area.

There's usually a table, because a simple exponent doesn't work any more.

The K-5 sensor is 372 mm². My hypothetical square is 562 mm², or approximately 2.3 times more expensive. A FF sensor would be 843 mm², or approximately 5.1 times more expensive than the APS-C. Given that the square sensor is almost half the way to the cost of FF, and FF is a much easier sell, guess which one is more likely?

I'd say the FF is cheaper. You get Sony and Nikon's design money, and some of their line cost. Obviously, Pentax gets hit with the higher final costs, but it should keep the differential under the normal 30% decade that would make a Pentax FF cost twice as much as a Nikon or Canon.

Build the square, and Pentax pays for everything.

Besides, anything you can do with a 24mm square, you can do with a 24x36 rectangle. You pretty much never have to turn the camera, because you've got the resolution for a vertical crop from a horizontal image. Picture event shooting with a 24-70mm f2.8 and that 36mp sensor.

  • 24x36mm horizontal, so the lens is a nice "general purpose" normal zoom.

  • 19.2x24mm vertical, so you've got a 35-100mm equivalent from the 1.4x crop factor. If you have that 36mp sensor, you've got 19.2mp in that vertical.

Vertical grips are so 2011...

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Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph


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