Archived posting to the Leica Users Group, 2002/11/21

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Subject: RE: [Leica] Digital back for Leica lenses
From: "Austin Franklin" <darkroom@ix.netcom.com>
Date: Thu, 21 Nov 2002 10:56:32 -0500

Hi Sam,

> Does that mean that we are nearing a threshold in CCD development as
> it
> relates to size, using today's format benchmarks? At what resolution
> would the laws of physics start working against the 35mm format?

They already DO work against it.  It's a matter of balancing a number of
things.  First and foremost is you pretty much need %100 sensor yield.  In
other words, all the sensor elements in the array have to be good.  The
larger the sensor (as in number of sensor elements) the higher the chance
that some of them will be bad.  Second is balancing sensor element size with
noise.  The smaller the sensor elements, the higher the noise.  You can get
a lot more sensor elements per unit area, but you get noise images.  For
video, that is fine, but for one shot imaging like photography, it's not so
good.

> Are we ever going to see
> 40
> megapixel CCDs based on the 35mm format?

That's an easy thing to calculate.  Assume a 24mm x 36mm (864 sq mm) sensor
array size:

5u (25u sq) sensor elements given an array of: 34M
7u (49u sq) sensor elements given an array of: 17M
9u (81u sq) sensor elements given an array of: 11M
12u (144u sq) sensor elements given an array of: 6M

And 5u sensors aren't going to be that great, at least in current
technology...but it certainly is possible.  Processes for making CCDs are
getting better....but along with the physical individual sensor size as an
issue, it's getting the wires to/from the sensor elements that becomes an
issue...

> I once read that digital had
> to
> get to 40 megapixel to equal some of the finer grained 35mm films,

Well, that seems about right, but film grains and sensor elements are really
different animals.  One is random in both size and position, and the other
is fixed in both size and position.  Apples and oranges.  Plus, digital
imaging sensors, with the exception of Foveon, don't have three planes of
color...only one plane, with %50 Green sensors, %25 Blue and %25 Red.  So,
don't confuse number of sensor elements with pixels, they are NOT the same,
except in the Foveon, which uses a tri-sensor element.

> BTW: How do you know so much about digital?

I have been designing digital imaging systems for over 25 years ;-)

> Any good websites for
> someone to learn the basics, something like a CCD Design 101?

Funny enough, Kodak.  They have a couple of papers on CCD imagers.  Try
poking around their web site in the digital imaging sensor area, and if you
can't find them let me know, and I'll email them to you.

Regards,

Austin

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