[Leica] PIXEL PITCH SIZE/large prints

[steve.barbour at gmail.com (Steve Barbour)]

On Mar 1, 2010, at 9:09 AM, Bryan Willman wrote:

>> From astronomy refering to telescopes - aperture wins.   (A cheapish 16"
> reflector will put the wump on even very high end 12" refractors for all
> but special cases.)
> 
> For terrestrial imaging (what we call photography) "imaging plane size
> wins, mostly".
> 
> Footnotes - historically, a good lens on a 4x5 view camera could make an
> image that was superior to any image made by a smaller camera, if you
> could manage to capture it with 4x5.
> 
> But of late, I find images from 1st rate 35mm FF cameras (5dM2 and of
> course the M9) to be very competitive with samples from medium format
> back cameras (I don't own one.)   Well scanned film from large format
> seems to be the only thing with an obvious advantage and even that is
> narrowing.
> 
> So our old notions of how large an image we can make from a 35mm frame
> seem to be changing in the digital era.

how large are the prints that people are now making ? people like us, who 
are not decorating the side of buses...?
20x30 " ?   bigger  ? or  8x10" or maybe not at all  ?  maybe mostly 
internet 800 pixel jpegs ? 
one gets an impression that as people talk bigger, less prints of any size 
are now being  made...
of course some few are making huge prints, how many ?....less than a 
majority...?
> 
> I'm sure cameras like the S2, or the coming full frame 645 cameras, will
> have advantages in quality - whether you can see them in prints smaller
> than, say, 20x30 or even 40x60 will likely determine the fate of those
> formats.


good point...


Steve


> 
> 
> -----Original Message-----
> From: lug-bounces+bryanwi=bryanwi.com at leica-users.org
> [mailto:lug-bounces+bryanwi=bryanwi.com at leica-users.org] On Behalf Of
> Jean Louchet
> Sent: Monday, 01 March, 2010 04:50 AM
> To: lug at leica-users.org
> Subject: Re: [Leica] PIXEL PITCH SIZE
> 
> George,
> 
> You are right to point out the fact that on most serious cameras the
> pixel
> size is somewhere between 5 and 10 microns. There is a physical
> explanation
> to this.
> 
> ZVisible light wavelength is spread between (roughly) 0.4 and 0.7
> microns.
> Lenses do have both geometrical optical aberrations and diffraction that
> limit their resolution.
> 
> 
> Again in very rough terms, geometrical aberrations are greater at large
> apertures, inversely proportional to the inverse of the f-number.
> Technology
> may help reduce them (better glass with higher refractive indexes and
> less
> dispersion, more complex designs, aspheric elements etc.) to a certain
> extent - we all know Leica are very good at this.
> On the other hand, diffraction can't be avoided, it is a physical law.
> Parallel light coming through a hole (here, the diaphragm) in a
> "perfect"
> lens will draw on the film or sensor, not a single point as we woulod
> like
> it, but a "diffraction pattern" that looks a bit like the circles when
> one
> drops a stone into a lake. The main spot, the central diffraction
> pattern
> has a diameter equal to 1.22*f*lambda/d where f is the focal length,
> lambda
> the wavelength and d the diaphragm diameter. As the f-number "n" equals
> f/d,
> the diffraction diameter is 1.22*n*lambda.
> 
> As lambda is not a single value but is spread between 0.4 and 0.7
> microns,
> the diffraction pattern is really ugly with colour fringes on its sides
> and
> the effects of diffraction are still visible and annoying inside a
> circle
> with diameter approx. 2*n*lambda. As lambda is around 0.5 microns, this
> means the diffraction pattern diameter will be about 2 microns at f:2l;
> 4
> microns at f:4,  etc.
> 
> As the actual blur pattern is the addition of the effects of diffraction
> to
> those of geometrical aberrations, and as it is very expensive to correct
> geometrical aberrations,in most lenses the blur diameter is a convex
> (parabola-like) curve with its minimum (= best sharpness) a couple of
> f-stops above full aperture- the good old Nikon 1.4/50 had its optimum
> at
> the centre of the image, at about f:5.6. Top lenses like the recent
> Leica
> ones have their optimum very close to full aperture (and this is at a
> cost!). All in all, one can safely say that the best blur circle
> diameter of
> a given lens, measured in microns/micrometers, is equal to about twice
> its
> maximum aperture.
> 
> This is why with a top-of-the-range lens with aperture 2.8 it is wise to
> choose a pixel size around 6 microns. Quid erat demonstrandum :-)
> 
> By the way, some P&S cameras are sold as 12 Megapix. Their sensors are
> often
> about 4.5 x 6 mm large . This means the pixel size is 1.5 microns, which
> is
> totally ridiculous - even worse since most of them use high-factor zooms
> that go with even more aberrations and low maximum aperture. Actually
> there
> can't be more than 0.7 MPix useful in these cameras! All the rest is
> just
> redundent data.
> 
> On the other hand, a pocket camera like the D-lux 4 uses a lens with a
> very
> small zoom factor (hence low aberrations) , a high max aperture (hence
> low
> diffraction) and ... I don't remember its sensor size but here
> advertising
> 10 MPix looks like it makes sense.
> 
> If I had to draw a conclusion, it is that what matters most of all is
> the
> sensor size. Megapixels don't mean anything if the sensor is too small.
> 
> Jean
> 
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