From: Paul Furman on
John Sheehy wrote:
> Paul Furman wrote:
>> John Sheehy wrote:
>>> Paul Furman wrote:
>>>
>>>> Of course, the DSLR image is enlarged [approx] 3x!
>>>>
>>>> 7.18 x 5.32 mm
>>>> 24 x 18 mm
>>> That's the point, or at least part of it.
>>
>> For stacked astronomy data capture that may be useful, I'm not sure
>> about normal daylight hand held still photos though. Or high contrast
>> scenes needing dynamic range.
>
> I'm not sure what you're trying to say here. What is "that"? My "that"
> was the upscaling factor. If you're talking about stacking images with
> sub-original-pixel alignment, yes, that is useful.

I'm saying more dense pixels might be useful for astronomy where you can
stack them to overcome the noise & DR limitations and take advantage of
the higher resolution/magnification through the same telescope. I'm not
even sure about this, so I said 'may be useful'.


> You get higher
> resolution detail, albeit at a low contrast, and if your SNR is low
> enough, and you have the bit depth, you can sharpen it to good effect.
> However, that is not why I upscaled the 400D here. It was to show how
> the two different pixel densities compared, resolving the same area of a
> focal plane, not only in resolution, but in noise. The 400D has one of
> the lowest read noises in the industry at ISO 100, just behind the D3 and
> the 1-series Canons by about 1/3 to 1/2 stop; much better than anything
> fom Nikon/Sony CCD, the D2X, or any other MFR's DSLR except the
> exceptional Pentax K10D. Yet, it can't touch the tiny 2 micron pixels of
> the FZ50 here, which have almost exactly the same read noise relative to
> absolute signal at ISO 100 as the 400D, at the pixel level. With 8.35x
> as many pixels per unit of area, the effective read noise factors down by
> the square root of that, to about 35% the read noise of the 400D.

Yeah, OK but the 400D goes up to ISO 1600 in fine form so this is pretty
much irrelevant isn't it?

--
Paul Furman
www.edgehill.net
www.baynatives.com

all google groups messages filtered due to spam
From: Scott W on
On Jul 17, 8:12 am, Paul Furman <pa...@-edgehill.net> wrote:
> John Sheehy wrote:
>
> > What I am demonstrating needs to be demonstrated.  There is too much
> > nonsense out there circulating as fact, suggesting that the more pixels
> > you "stuff" into a given sensor size, the noisier the images get, the
> > less DR they have, etc, etc.  This clearly shows that this is not true,
> > that pixels covering less of the focal plane each can currently do much
> > better than big pixels, at representing the area that they are
> > responsible for.
>
> > This test, however, is not about DR, per se, as the 400D still has some
> > more headroom than the FZ50 here.  It is more about absolute sensitivity
> > in this case, although the usable DR should still be better with the
> > smaller pixels.
>
> 'Usable DR'?

I had a thought about this whole DR thing, you would not expect
smaller pixels to give more DR because the over all well size does not
change for a given area. But there is one advantage to the smaller
pixels in that it effectively adds more bits to the A/D converter.
Say I have a sensor with 4 times the pixels for the same area, this
would be like added one bit on the A/D.

But a bit more though shows this really not to be an advantage what
works, by going to 4 time the number of pixels you slow the capture
time way down, it would be far less painful to simple put in a 14 bit
converter in place of the normal 12 bit one.

Scott


From: John Sheehy on
Paul Furman <paul-@-edgehill.net> wrote in
news:t1Mfk.8546$L_.5832(a)flpi150.ffdc.sbc.com:

> I'm saying more dense pixels might be useful for astronomy where you
> can stack them to overcome the noise & DR limitations and take
> advantage of the higher resolution/magnification through the same
> telescope. I'm not even sure about this, so I said 'may be useful'.

The higher pixel density does not have more noise and DR limitations to
overcome; that is my main point. Higher pixel densities generally give
higher DR at base ISOs. Only a *very* small number of DSLRs have lower
area-based read noise than P&S pixels like the FZ50's do, and not by
much.

The 400D here, clearly has more noise at the same level of illumination.

> Yeah, OK but the 400D goes up to ISO 1600 in fine form so this is
> pretty much irrelevant isn't it?

Not at all. Low signals can be deep shadows at low ISOs; not just
midtones at high ISOs.



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John P Sheehy <JPS(a)no.komm>
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From: John Sheehy on
Juf� <b0wser(a)h0me.c0m> wrote in news:1MFfk.371$av4.294(a)trnddc04:

> Since you can't acquire cameras with sensors of the same physical size
> that produce raw data, and can only compare grossly different cameras
> and sensors, what's the point of this excercise? Even if it did prove
> something, what good is the info is you can't possibly make use of it?

This is all about awareness of the fact that small pixels are not poor
imagers per unit of area, as they are often made out to be.

--

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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:Xns9ADE17B816Fjpsnokomm@
199.45.49.11:

> Anyone with any amount of experience in these matters would recognize
> that even a magic lens with no softness of any kind

Sorry, I hit send before I finished that post. It should have read "Anyone
with any amount of experience in these matters would recognize that even a
magic lens with no softness of any kind would pale next to the FZ50 lens
and pixel density here, using the 400D and scaling 289%.

--

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John P Sheehy <JPS(a)no.komm>
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