Digital BW, The Print

This article does a good job of dealing with the issues of pixel size that I
had in mind:

http://www.outbackphoto.com/dp_essentials/dp_essentials_02/essay.html .

But, it does not suggest any specific limit.

The article does note that at 125 lp/mm, a 4 micron pixel is enough.  The
Canon 20D and XT/350D sensors use 6.4 micron pixels.  This suggests an 80
lp/mm limit.

In my lens testing with film cameras, hitting 80 lp/mm was very good, and
what I expected of a good lens on film.  True, I was able to see over 100 on
film in some cases, but it was inconsistent.  With a grain focuser, I was
often able to see over 300 lp/mm in the aerial image, but the low contrast
of the fine detail was apparently such that the film and paper could not
record it.  I suspect this low contrast was caused by the diffraction of the
light and would not be avoided by better lenses.   

Hitting 80 lp/mm even with Tech Pan was, as a practical matter, what I
expected of a good lens in terms of on-film resolution.  Actually, 50 lp/mm
was a more realistic target for the field, where focusing errors, DOF, etc.
played a major role.  If this holds true with digital, then progress may be
more along the lines of dynamic range and other issues than increasing pixel
count.  If that is the case, we may not be far from stable image sensor
sizes for serious shooters.  (And tiny sensors in cell phones for snapshots
may dominate the low end.)

Paul
www.PaulRoark.com 





> -----Original Message-----
> From: DigitalBlackandWhiteThePrint@yahoogroups.com
> [mailto:DigitalBlackandWhiteThePrint@yahoogroups.com] On Behalf Of Paul
> Roark
> Sent: Wednesday, April 27, 2005 10:36 AM
> To: DigitalBlackandWhiteThePrint@yahoogroups.com
> Subject: [Digital BW] Optimum sensor size (was www.OpenRAW.org ...)
> 
> 
> Steve,
> 
> 
> > There is a discussion here about the optimal pixel size under digital
> > image sensors:
> >
> > http://www.normankoren.com/Tutorials/MTF7.html
> >
> 
> Yes, that site has a lot of good information.  However, I was wondering
> more
> about what fundamental limits might exist on the technology.
> 
> I suspect that companies like Canon have looked at fundamental limits in
> making their long term plans.  So, aside from the factors that affect
> one's
> choice given today's technology, it would be interesting to see an
> analysis
> of where a practical end point of sensor shrinkage is.
> 
> Canon fabricates its own semiconductors, I believe.  As such they probably
> are, in at least the fab division, up to their eyeballs in these problems.
> I don't think any other camera manufacturer has a fab.
> 
> The diffraction limit of light is one obvious problem.  The semiconductor
> industry has fought this battle for years, but they have been able to
> avoid
> the limits imposed by the wave length of visible light by going to UV
> light
> and even non-glass optics.  The camera manufacturers will not have these
> options.  So, I'd guess this imposes a practical limit on how small a
> sensor
> of a given resolution can be.
> 
> There is also what I think is referred to as "shot noise."  The particle
> nature of light causes, among other things, the sensors to detect not a
> smooth ramp of increasing exposure, but the steps caused by the quantum of
> each photon hitting the sensor. The quantum nature of light appears to
> result in significant problems, including noise, as the cell size
> decreases.
> This in combination with optical diffraction, will probably put a lower
> limit on the cell size.  Of course, it may be so small that it will have
> no
> impact on any living photographer.
> 
> Probably a more practical current factor will simply be the economics of
> making a full system of lenses and accessories for any particular sensor
> size.  This will probably cause there to be discrete plateaus.  I would
> guess Sigma and Tamron will follow Canon.  If they see Canon making
> specific
> lenses for a sensor size, they may assume it will be a significant enough
> standard to invest in making third party lenses.  Then again, Canon might
> predatorily sucker the third party manufacturers into wasting lots of
> development money on what turns out to be a very fleeting, "false"
> standard.
> It would be fun to be a fly on the wall of the decision making bodies
> here.
> I sense there is a lot of gaming that could be going on.
> 
> Paul
> www.PaulRoark.com
> 
> 
> 
> 
> 
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