From: John Sheehy on
Scott W <biphoto(a)hotmail.com> wrote in
news:fbef99b9-2adc-429e-96bc-9f46ec665b7f(a)x41g2000hsb.googlegroups.com:

> Do we really need more cross posting?

I generally don't mind relevant cross-posting, but that comes from using
Agent. I am using XNews now, and the method of cross-post management in
XNews seems a bit inferior and dangerous, so I wind up seeing a lot of
things twice.



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John P Sheehy <JPS(a)no.komm>
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From: John Sheehy on
floyd(a)apaflo.com (Floyd L. Davidson) wrote in
news:87vdz6zora.fld(a)apaflo.com:

> That is just false.

> The two different sensors, mounted behind the same lense
> and getting identical processing (in camera as well as
> post camera) would be the way to make "all other things
> being equal" a valid statement.

Pay attention, Floyd. I clearly stated that the optics were unequal.
However, I also stated why it doesn't affect the comparison very much.
Even an aliased image of B&W edges from a 5.7 micron pixel pitch is going
to be softer than the 1.97 micron pixel-pitch, with 289% upsampling. How
much clearer about that could I have been?

> If you think Nikon, Canon, Sony, et al are not doing exactly
> that, I've got a bridge for sale that you'll enjoy testing.

What is "that"?

> And if you cannot do that, then you simply cannot expect
> your tests to be considered seriously.

Tell me how a 5.7 micron PP is going to competehere, with even the
sharpest lens? Anyway, my main point here is the noise. The higher
pixel density sensor clearly has far less noise per unit of area.

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John P Sheehy <JPS(a)no.komm>
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From: John Sheehy on
Juf´┐Ż <b0wser(a)h0me.c0m> wrote in news:Zhbfk.265$av4.11(a)trnddc04:

> John, nothing you've posted here is correct. If you want, I'll shoot
> pix using my G9 and 5D at ISO 1600, and post the 100% crops.
> Resolution of the sensors is very close, only the size of the pixels
> is very different. It will shot that smaller pixels simply cannot
> compete with larger pixels. Unless I'm totally missing your point
> here...

Yes, you are totally missing the point here. The demonstration is of PIXEL
DENSITY; not SENSOR SIZE; not PIXEL SIZE.

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John P Sheehy <JPS(a)no.komm>
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From: John Sheehy on
John Sheehy <JPS(a)no.komm> wrote in
news:Xns9ADCEBDB1EE43jpsnokomm(a)199.45.49.11:


> Yes, you are totally missing the point here. The demonstration is of
> PIXEL DENSITY; not SENSOR SIZE; not PIXEL SIZE.

Sorry; that last one should have been "PIXEL-LEVEL PERFORMANCE", not "PIXEL
SIZE".



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John P Sheehy <JPS(a)no.komm>
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From: Roger N. Clark (change username to rnclark) on
John P Sheehy wrote:
> I've made a direct comparison of RAW data per unit of area in the deep
> shadows of ISO 100 between the FZ50 (1.97 micron) and the 400D (5.7
> micron). Exposure is the same, same Av (f/4.5), same Tv (1/100), same real
> focal length (22mm), both shot at "ISO 100" pushed to ISO 13,500. Large
> crop is 100% for FZ50 (0.4MP), and small crop is 100% for 400D (0.05MP),
> and the other two are the other camera scaled to the 100% crop of each. As
> I already knew, the bigger pixels of the DSLR are inferior compared to the
> higher pixel density of the small sensor camera:
>
> http://www.pbase.com/jps_photo/image/100092629
>
Hello,
Someone asked me to comment, so...

John, here is why the test is not equal and biased in favor of the
small pixel camera: the gain and noise in the electronics. The FZ50
at ISO 100 is operating at about 2x unity gain. The 400D is operating
so far below unity gain so that noise from the A/D converter is the limiting
factor. Try your test again with the 400D at similar 2x unity gain
(ISO 1600 should do). That way the noise in both images will be
dominated by photon noise and sensor read noise, not post sensor electronics.

For others who have not visited, here are references to this
subject and a little on how things work:

General discussion on the effects of pixel size:
http://www.clarkvision.com/imagedetail/does.pixel.size.matter
With regard to lenses not matching such small sensors, see Figure 8
which shows MTF as a function of pixel pitch (note pixel pitch is
another way to express spatial frequency, so spatial frequency
is inversely proportional to pixel pitch. For John's f/4.5 test,
the diffraction limit (a perfect lens) has 0% MTF at about 3-micron
pixel pitch (varies a little with color).

Example images with large and small pixels for the same total
pixel count is shown at:
http://www.clarkvision.com/imagedetail/does.pixel.size.matter2
But that is not John's test (but was another question asked).
In that case, large pixels are clearly better, and that is basically
the choices we have today.

But John does have a point about more pixels can be better. As pixel
size drops, so does dynamic range. You can't have more dynamic range than
the total number of photons you collect per pixel. The FZ50, for example,
collects a max between 1,000 and 2,000 photons, whereas the 400D
over 40,000. That's 20 times the highlight room! (We do need better
A/D converters in these cameras, as they currently are the limiting factor
in dynamic range and low signals at low ISO).

Figure 9 at:
http://www.clarkvision.com/imagedetail/digital.sensor.performance.summary
shows the image quality as a function of pixel pitch (again, related to
spatial frequency) and for different sized sensors and thus different
megapixels. What we see is image quality increases as we first decrease
pixel size, but then image quality drops. (This decrease in image
quality is analogous to an image getting soft as you close
down the aperture.) It drops at different points depending
on f/ratio which limits detail, and it drops because dynamic range
decreases with decreasing pixel size. The sweet spot for f/8 diffraction
limited lenses is around 5-microns or 30 megapixels for a full 35mm frame
sensor. But are there any diffraction limited f/8 lenses that cover a
35 mm frame? There are telescopes, in particular a Wright design that
could do probably it, but not normal to wide angle camera lenses.

So, John, please redo your test with ISO 1600 on the 400D and use a
quality raw converter. What you should find is that the FZ50 image
will look noisier, with higher sampling. The 400D will show fainter
intensities and overall higher S/N and both images will resolve about
the same detail. The larger pixel gains because there is less noise
due to 1 read noise whereas in the smaller pixels there are square root
N more read noise where there are N small pixels per large pixel.
The larger pixel camera will detect fainter stars, for example.

The physics of larger pixels is a well-understood science, and why you
see large pixel sensors being used in scientific applications, from telescope
cameras, to spacecraft cameras, to Mars landers.

Roger