From: Pat on
On Mar 7, 7:03 am, "ipy2006" <ipyasa...(a)gmail.com> wrote:
> I have to shoot action photos in low light conditions. What is the
> best DSLR for this purpose?
> Thanks,
> Yip

At the risk of pissing off all of the "purists" out there, you might
want to consider the original Canon Digital Rebel (the good old 300).
That would get you a useable body for not much money. Then add the
Russian operating system to get to ISO of 3200. It's a bit grainy but
sometimes grainy is better than nothing.

Then, with your "extra" money get a Canon 580 flash (or two) and a
"wedding bracket" to avoid red eye and limit shadow. Skip the kit
lens and get the Tokina F2 (or f2.8) zoom. it is something like a 28
to 70mm.

That would get you a servicable package within you price range.

There are lots of situation where this wouldn't be the right setup,
but for what you are describing it will work just fine.

Good luck with it.

From: Roger N. Clark (change username to rnclark) on
John Sheehy wrote:
> "Roger N. Clark (change username to rnclark)" <username(a)qwest.net> wrote
> in news:45F577C0.9020706(a)qwest.net:
>
>>I and other astrophotographers tend to ignore fixed pattern noise
>>because we can calibrate most of it out of our images.
>
> I'm not sure where "fixed pattern noise" came into play here; the issue
> was read noise and one of it's components, 1-D noise. There is, for all
> intents and purposes, zero fixed pattern noise in my 20D. Subtracting a
> stack of black frames from a short exposure results in nothing but
> slightly higher noise.

Fixed pattern noise occurs in different ways with different
sensors. All sensors have fixed pattern noise, even your
20D unless you have a magical one. For example, see:
http://www.astrosurf.org/buil/5d/test.htm
It is in French, but the pictures are labeled well enough
with 30D, 5D etc, that you can see the effects. Common
is vertical striping and amplifier glow. There is no camera,
CCD or CMOS that doesn't have fixed pattern noise.

Figure 10 at this page:
http://www.clarkvision.com/photoinfo/night.and.low.light.photography
shows that the Canon 1D Mark II has a low level background offset.
That too is fixed pattern noise. So is the line striping
you see in the images on this page. All cameras have these
effects.

A good example of amplifier glow creating an offset near the
edge of the frame is at:
http://www.clarkvision.com/imagedetail/long-exposure-comparisons
e.g. see Figure 2b.

>> If that is an
>>issue for other people, then I suggest they learn how to take
>>dark frames, average them, and subtract them from their images.
>
> What about the read noise in short exposures?

Read noise produces a random signal added to all
other signals, regardless of exposure. It is a property of
reading the sensor, not a property of the exposure time.
Examples on the above two web pages show read noise in both
short and long exposures.

>>It is really pretty easy, but for best results, it needs to be
>>done on linear data.
>
> And in the case of Canons which have "negative noise" at the blackpoint,
> it needs to be done without any clipping at the black level.

Sensors collect photons, which are converted to electrons.
The signal is always positive or zero, not negative.
The readout electronics add a negative offset
so that the signals do not go negative. Of course,
if noise is too high, then the output signal could hit
zero. Very few pixels are zero in most cameras, even
at the shortest exposure times in the dark.
(I know you know this; I'm adding information to provide
a complete story for others reading, so please don't take
offense; I know you have studied sensors in detail and you have
provided great information to us for years.)
So, I don't know what you mean by negative noise.

>>Another calibration that can improve images is
>>flat field calibration, which not only corrects for pixel to pixel
>>variations, but corrects for light fall-off from lenses.
>>But if someone wants to pay me to run more tests......
>
> I don't feel like financing anything right now, but I might suggest that
> when you have the time, you do a "gap" test of large vs small pixels.
> Your 1DmkII vs S70 page seems to be about pixel size, but it is really
> about sensor size. Do a test with a small-pixel camera, and the 1DmkII,
> both using the same real focal length, the same Av value, the same Tv
> value, the same ISO setting, of the same detailed subject from the same
> distance. I guarantee that your big pixels will fall to the ground like
> Goliath, when viewing the subject at any magnification, from both
> downsampled to both upsampled, or printed large. This is the real test
> of pixel size. What you seem to overlook in your analyses is the fact
> that standard deviation is only *one* factor in the noise equation;
> magnification is another, and the low noise of big pixels is visually
> magnified when the pixels are magnified along with the subject.
>
> I am quite certain that the only benefits of big pixels are:
>
> 1) quicker readout time and less storage requirements, and
>
> 2) slight benefit in photons collection rate per unit of sensor area due
> to less wasted space on the sensor (not always realized, however; my
> 1.97u FZ50, for example, collects about the same number of photons per
> unit of area as the 1DmkII, at RAW saturation for the same ISO).

Here is the fundamental fallacy of your assertion that the
only benefit is better fill factor (that is what you describe in
#2 above): The physics of lenses, and not directly related
to sensors at all.

Every lens at a given f/ratio delivers, for a given light source,
the same surface brightness in th4e focal plane. Another
way to put this is the photons per square micron is constant
at a given f/ratio regardless of the lens focal length.
So an f/4 lens of 20mm focal length looking at a gray
card in sunlight delivers the same number of photons per
square micron to its focal plane as does a 500 mm f/4 lens
looking at the same gray card. It is a simple deduction,
that given two sensors, identical in every way including
quantum efficiency, read noise, and fill factor, that
the sensor with larger pixels collects more photons
simply due to lens physics.

An 8 micron pixel collects 16 times the photons as a
pixel 2 microns in size (8*8/(2*2) = 16), and that is exactly
what we observe with today's digital cameras. For example,
see:
Digital Cameras: Does Pixel Size Matter?
Part 2: Example Images using Different Pixel Sizes
http://www.clarkvision.com/imagedetail/does.pixel.size.matter2

> Here is one of my tests; it needs to be redone, because I realized after
> doing it that ISO 1600 on the FZ50 is crippled by a very bad amplifier,
> that is worse than pushing 100 to 1600. Here is the original, however:
>
> http://www.pbase.com/jps_photo/image/74020772
>
> Don't forget that the 10D images would need to be sharpened more,
> sharpening the noise as well.

Your test is biased in that the two images from the two cameras
are not comparable. By using two different sized sensors
with the same focal length, of course the sensor with
smaller pixels sees finer detail. But the large sensor
shows a larger field of view that is not covered by the
smaller sensor at all. So depending on who wanted the
image, one could draw different conclusions: the person who
wanted a wide field of view would choose the large sensor;
one who wanted a telephoto image would choose the small
pixels. But in either case, the pixels from the small
sensor would be noisier in proportion to the square root
ratio of the areas of each pixel.

Roger

From: David J. Littleboy on

"Roger N. Clark (change username to rnclark)" <username(a)qwest.net> wrote:
> John Sheehy wrote:
>>
>> I don't feel like financing anything right now, but I might suggest that
>> when you have the time, you do a "gap" test of large vs small pixels.
>> Your 1DmkII vs S70 page seems to be about pixel size, but it is really
>> about sensor size. Do a test with a small-pixel camera, and the 1DmkII,
>> both using the same real focal length, the same Av value, the same Tv
>> value, the same ISO setting, of the same detailed subject from the same
>> distance. I guarantee that your big pixels will fall to the ground like
>> Goliath, when viewing the subject at any magnification, from both
>> downsampled to both upsampled, or printed large. This is the real test
>> of pixel size. What you seem to overlook in your analyses is the fact
>> that standard deviation is only *one* factor in the noise equation;
>> magnification is another, and the low noise of big pixels is visually
>> magnified when the pixels are magnified along with the subject.
>>
>> I am quite certain that the only benefits of big pixels are:
>>
>> 1) quicker readout time and less storage requirements, and
>>
>> 2) slight benefit in photons collection rate per unit of sensor area due
>> to less wasted space on the sensor (not always realized, however; my
>> 1.97u FZ50, for example, collects about the same number of photons per
>> unit of area as the 1DmkII, at RAW saturation for the same ISO).
>
> Here is the fundamental fallacy of your assertion that the
> only benefit is better fill factor (that is what you describe in
> #2 above): The physics of lenses, and not directly related
> to sensors at all.
>
> Every lens at a given f/ratio delivers, for a given light source,
> the same surface brightness in th4e focal plane. Another
> way to put this is the photons per square micron is constant
> at a given f/ratio regardless of the lens focal length.
> So an f/4 lens of 20mm focal length looking at a gray
> card in sunlight delivers the same number of photons per
> square micron to its focal plane as does a 500 mm f/4 lens
> looking at the same gray card. It is a simple deduction,
> that given two sensors, identical in every way including
> quantum efficiency, read noise, and fill factor, that
> the sensor with larger pixels collects more photons
> simply due to lens physics.

I think you guys are talking past each other here.

I think John is arguing that _for a sensor of a given size_, larger pixels
aren't any better.

David J. Littleboy
Tokyo, Japan


From: Roger N. Clark (change username to rnclark) on
David J. Littleboy wrote:

> I think you guys are talking past each other here.
>
> I think John is arguing that _for a sensor of a given size_, larger pixels
> aren't any better.

1) Well, his example used 2 different sized sensors.

2) There is a difference. The signal you record has added
read noise. A larger pixel collects more photons
so the signal is larger compared to the read noise.
Thus you can detect fainter things, or have better high
ISO performance. If you sum the signal from a smaller
pixels to equal the area of a larger pixel size,
you are also adding read noise, so you don't gain
as much as having the larger pixel with one read noise.

Roger
From: acl on
On Mar 16, 6:29 am, "David J. Littleboy" <davi...(a)gol.com> wrote:

> I think you guys are talking past each other here.
>
> I think John is arguing that _for a sensor of a given size_, larger pixels
> aren't any better.
>

But doesn't this make him a "crop fan" for you? Or does your attitude
depend on who you're replying to?