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Does f/2=f/2?

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ewelch said:
All cats are mortal.
Socrates died.
Therefore, Socrates was a cat.
Click to expand...
But at least I understand why you think that. : )
ewelch said:
But that once again ignores the physical characteristics of light.
You could also state that a football field gathers more light than an
APS sensor, but that has nothing to do with the image on the sensor.
An area of the football field the size of the sensor is getting the
same amount of light as the sensor. All the rest would be non-imaging
light.
Click to expand...
We are talking about the light that the sensor gathers. A larger sensor gathers more light for the same f-ratio than a smaller sensor for the same scene and perspective.
ewelch said:
The reality of it is the intensity of the light is what counts.
Click to expand...
No. What would even make you think that? Consider that fast lenses of compact digicams. What do their images have in common with images at the same f-ratio from larger sensor systems for the same framing?
ewelch said:
A bigger pixel is impacted more efficiently than a smaller pixel (just
like film), thus the Nikon D3 has better noise performance than a
D2X, even though the file size in the end is about the same.
Click to expand...
No. For the same output size, sensors with the same design and efficiency will have the same noise. The D3 sensor is more efficient than the D2X sensor. However, the primary reason the D3 has less noise for the same f-ratio is that is collects 2.25 times as much light.
ewelch said:
The bottom line is that "more light" gathered by a "bigger sensor" is a
canard. The efficiency is in the pixels' size, not in the sensor's size.
Click to expand...
Wrong.
ewelch said:
F/2 is f/2 is f/2.
Click to expand...
But it produces wildly different results on sensors of different sizes, just as 50mm produces wildly different results on sensors of different sizes.

For those who don't mind reading (and/or looking at images that demonstrate the principles):

http://www.josephjamesphotography.com/equivalence/

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/
 
ewelch said:
But that once again ignores the physical characteristics of light.
Click to expand...
Not at all.
ewelch said:
You could also state that a football field gathers more light than an
APS sensor, but that has nothing to do with the image on the sensor.
An area of the football field the size of the sensor is getting the
same amount of light as the sensor. All the rest would be non-imaging
light.
Click to expand...
Not if the football field and the APS sensor both are exposed to lenses with appropriately large image circles operated at the same f-number. This follows directly from the definition of an f-numberand the most basic principles of optics.

Note that if it were otherwise the entire system used to determine exposure for photography for the past century or so would collapse.
ewelch said:
The reality of it is the intensity of the light is what counts.
Click to expand...
Intensity is certainly important. That's why people typically compare at the same f-number. They want to compare how sensors perform with light at the same intensity.
ewelch said:
A
bigger pixel is impacted more efficiently than a smaller pixel (just
like film), thus the Nikon D3 has better noise performance than a
D2X, even though the file size in the end is about the same.
Click to expand...
For some sensor types, large pixels can have somewhat higher quantum efficiency than smaller pixels, but this isn't where most of the advantage of larger pixels is coming from. At constant f-stop, a larger pixel is hit with more light.

At the same f-stop, each D3 pixel is getting hit with over 2X more light than each D2X pixel.
ewelch said:
The
bottom line is that "more light" gathered by a "bigger sensor" is a
canard.
Click to expand...
Far from a canard, it's a inescapable logical consequence that follows from the most basic definitions of the terms involved.
ewelch said:
The efficiency is in the pixels' size, not in the sensor's
size.
Click to expand...
Big pixels gather more light than small ones. If we keep the number of pixels constant, then bigger pixels imply bigger sensors. Since each pixel is gathering more light, then the whole sensor must be gathering more light too.
ewelch said:
F/2 is f/2 is f/2.
Click to expand...
And this is precisely why a larger sensor is hit with more light. The f-number determines the intensity of the light. The same intensity over a larger area implies more total light.

--
Ron Parr
Digital Photography FAQ: http://www.cs.duke.edu/~parr/photography/faq.html
Gallery: http://www.pbase.com/parr/
 
I tested three cameras: Oly 5050(5mp), Canon XTI(10mp) and Fuji 6000FD(6mp). All cameras used ISO 200 and F/5.6. The exposure times turned out to be 1/13, 1/13 and 1/10 respectively. The exposures (picture brightness) were the same despite the much greater area of the APS (XTI) sensor. It is remarkable that a small sensor like the Fuji can be competitive in terms of image quality with only 1/8 the total light of the XTI (1/20 compared with a full frame camera like the 5D).

I now realize, after being dead wrong, that f-stop corresponds to light intensity which is the same regardless of sensor size for a given f stop. Previously I thought that a small sensor camera had greater light intensity focused on a smaller sensor. I wish I could delete my erroneous post.

Total light is different, so a non-Aps lens on an XTI will have less total light than the same lens on a full frame, i.e., some light and image is lost.
 
Humphrey Nash said:
I tested three cameras: Oly 5050(5mp), Canon XTI(10mp) and Fuji
6000FD(6mp). All cameras used ISO 200 and F/5.6. The exposure times
turned out to be 1/13, 1/13 and 1/10 respectively. The exposures
(picture brightness) were the same despite the much greater area of
the APS (XTI) sensor.
Click to expand...
The entire purpose of the f-ratio is to normalize exposure for lenses and across systems.
Humphrey Nash said:
It is remarkable that a small sensor like the Fuji can be competitive in terms
of image quality with only 1/8 the total light of the XTI (1/20 compared with
a full frame camera like the 5D).
Click to expand...
You'll have to be far more specific with the term "competetive".
Humphrey Nash said:
I now realize, after being dead wrong, that f-stop corresponds to
light intensity which is the same regardless of sensor size for a
given f stop.
Click to expand...
Yes.
Humphrey Nash said:
Previously I thought that a small sensor camera had greater light intensity
focused on a smaller sensor. I wish I could delete my erroneous post.
Click to expand...
No worries.
Humphrey Nash said:
Total light is different, so a non-Aps lens on an XTI will have less
total light than the same lens on a full frame, i.e., some light and
image is lost.
Click to expand...
I'm not sure exactly what you mean here. Let's work through it by example. Consider a 50mm lens on a 35mm FF sensor and a 30mm lens on a 1.6x sensor (each lens on each system will give the same AOV). It is irrelevant whether the 30mm lens is FF glass or cropped glass. As long as the image circle covers the sensor, it will work the same.

Now, if the 50mm lens on FF and the 30mm lens on 1.6x are at the same f-ratio, then a lot more light (specifically, 2.56x as much light) will fall on the FF sensor than on the 1.6x sensor, but the two images will also have very different DOFs and the FF image will also have softer edges and more vignetting.

However, if we up the f-ratio on the FF system to get the same DOF (1 1/3 stops), and up the ISO to get the same shutter speed and apparent exposure (also 1 1/3 stops), then the same amount of light will fall on each sensor, and the two images will be equivalent. As a consequence, have the same edge sharpness, vignetting, and noise (given sensors of the same design and efficiency).

Here's more (a lot more) on that subject:

http://www.josephjamesphotography.com/equivalence/

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/
 
for the excellent reference. I read it previously and I can't believe I didn't understand the basic science.
joe mama said:
It is remarkable that a small sensor like the Fuji can be competitive in terms
of image quality with only 1/8 the total light of the XTI (1/20 compared with
a full frame camera like the 5D).
Click to expand...
Joe wrote "You'll have to be far more specific with the term "competetive". "

I will specify what I mean by competitive. For my applications (full screen views and prints up to 8X10) I see no image quality advantage to the XTI over the Fuji. The dynamic range is similar, the sharpness of detail similar and the color just as pleasing. Fuji images are essentially noise free though ISO 400 and I doubt that an 8X10 ISO 800 print image would be noticeably different at ISO 800. AT ISO 1600 the XTI looks noticeably better. The Fuji has ISO 3200 which the XTI doesn't have. Even very large images up 100% Fuji (3 feet wide screen display) are not inferior to the XTI

I often use my XTI for macros (using the 60mm lens) and to increase apparent magnification I can crop and still have sharp detail. I can't do much cropping of the 6 megapixel Fuji image.

From a prior post:

"I have the Canon XTI with super-sharp 60mm macro lens. I also have the Fuji 6000FD which is a DSLR-like P&S. It compares very well with the XTI up to ISO 400 and is competitive at ISO 800. I have run my own comparisons and have posted some.

For a more independent comparison download both ISO 400 test pictures from DPreview. Alternatively, side by side comparison are available from
  1. http://www.imaging-resource.com/IMCOMP/left.htm (delete #)
The Fuji compares surprisingly well with the XTI, 30D, 40D and even the 5D. Part of this is due to some built-in P&S sharpening, part to the excellent Fuji 6 megapixel sensor, part due to the fantastic Fuji lens, part due to DOF. part due to the difficulty larger format sensors and lenses have at the edge of the sensor.

The Fuji 6000FD, IMO, is a real gem. DPreview also thinks so since they gave it a highly recommended (quite a feat for a 6 megapixel sensor)!"

Joe, you may be surprised how well it (the Fuji) compares in such screen tests.
 
Humphrey Nash said:
Humphrey Nash said:
Humphrey Nash said:
It is remarkable that a small sensor like the Fuji can be competitive in terms
of image quality with only 1/8 the total light of the XTI (1/20 compared
with a full frame camera like the 5D).
Click to expand...
Click to expand...
Click to expand...
Humphrey Nash said:
Humphrey Nash said:
"You'll have to be far more specific with the term "competetive".
Click to expand...
Click to expand...
Humphrey Nash said:
I will specify what I mean by competitive. For my applications (full
screen views and prints up to 8X10) I see no image quality advantage
to the XTI over the Fuji. The dynamic range is similar, the
sharpness of detail similar and the color just as pleasing. Fuji
images are essentially noise free though ISO 400 and I doubt that an
8X10 ISO 800 print image would be noticeably different at ISO 800.
AT ISO 1600 the XTI looks noticeably better. The Fuji has ISO 3200
which the XTI doesn't have. Even very large images up 100% Fuji (3
feet wide screen display) are not inferior to the XTI
Click to expand...
That's exactly what I mean when I say the following in the conclusion of the essay:

http://www.josephjamesphotography.com/equivalence/#conclusion

"To that end, each person has their own 'quality threshold' -- that is, a level of quality beyond which any improvements are inconsequential. One of the most important considerations in this regard is the output size of the image. Depending upon the individual's quality threshold, it may well be that the differences at, say, 8x12 are completely insignificant between modern DSLRs, and even at 20x30, all are 'good enough'; at least, for low ISOs and higher DOFs."
Humphrey Nash said:
The Fuji compares surprisingly well with the XTI, 30D, 40D and even
the 5D. Part of this is due to some built-in P&S sharpening, part to
the excellent Fuji 6 megapixel sensor, part due to the fantastic Fuji
lens, part due to DOF. part due to the difficulty larger format
sensors and lenses have at the edge of the sensor.

The Fuji 6000FD, IMO, is a real gem. DPreview also thinks so since
they gave it a highly recommended (quite a feat for a 6 megapixel
sensor)!"

Joe, you may be surprised how well it (the Fuji) compares in such
screen tests.
Click to expand...
Surprise me. : )

Most of my photography is high ISO shallow DOF, so a compact is completely out of the question. I do, however, have a Sony P150 (that I only use for video), but it puts out quite a decent show at ISO 100:

http://www.pbase.com/joemama/sony_p150

You may also be interested in a few pics I took with 3 & 4 MP compact digicams, some of which I have printed at 11x14 and they look stellar:

http://forums.dpreview.com/forums/read.asp?forum=1010&message=24929197

Like I say, it depends on the image, the photographer, the print size, and the "quality threshold" of the viewer. For deeper DOF, lower ISOs, and smaller print sizes, I think most people are best served with modern compacts.

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/
 
ewelch said:
The reality of it is the intensity of the light is what counts. A
bigger pixel is impacted more efficiently than a smaller pixel (just
like film), thus the Nikon D3 has better noise performance than a
D2X, even though the file size in the end is about the same.
Click to expand...
So you want to focus on the pixels? Fair enough. But you'll have to deal with two facts:
  • The ratio of sensor area to pixel area is the pixel count. So for cameras with the same pixel count, it's a moot point whether it is pixel size or sensor size that matters.
  • If you consider different-sized sensors with the same pixel pitch and design, then you'll get the same quality in 100% crops. But the larger sensor will still have an advantage in equal-sized prints, because its higher pixel count provides more pixels per inch.
The relevance of total light, then, is that it is the product of light per pixel and pixel count.

But the fact that you can explain everything in terms of pixels does not contradict other explanations based on total light, or light intensity, as I said in more detail here:
http://forums.dpreview.com/forums/read.asp?forum=1018&message=25564422

--
Alan Martin
 
That's all a load of nonsense. A Canon S3 at ISO 80 is going to give you the same shutter speed as a Mamiya RZ at ISO 80 for a given aperture (f/5.6). And that's the bottom line. Depth of field will be different, etc. But when you're in a certain light, and you set the camera at ISO 80, the given shutter speed is tied to the given aperture and ISO. Nothing else matters. You deal with different numbers to get the depth of field you want. But a pixel is a pixel is a pixel. It may be bigger or smaller, more efficient or less efficient. But in the end, a pixel sees a specific intensity of light and sends a signal to the camera. It doesn't care how many other pixels are on the sensor.
joe mama said:
For those who don't mind reading (and/or looking at images that
demonstrate the principles):

http://www.josephjamesphotography.com/equivalence/

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/
Click to expand...
--
Eric

All cats are mortal.
Socrates died.
Therefore, Socrates was a cat.
 
Which is heaviest:

a, a 2 pound MF camera with lenses,

b, a 2 pound 35 mm camera with lenses,

c, a 2 pound dSLR with lenses?

Which programme is longest on our TV

a, a 15 minute film about MF,

b, a 15 minute film about 25 mm cameras,

c, a 15 minute film about digital?

Who is talest:

a, a 6 ft Welshman,

b, a 6 ft Frenchman and

c, a 6 ft photographer?

Answers tomorrow (to give some of you a chance to work it out... ).

Regards, David

And for bonus points: Was this the silliest thread ever?
 
ewelch said:
That's all a load of nonsense. A Canon S3 at ISO 80 is going to give
you the same shutter speed as a Mamiya RZ at ISO 80 for a given
aperture (f/5.6).
Click to expand...
Who said otherwise?
ewelch said:
And that's the bottom line.
Click to expand...
Interesting philosophy, that the bottom line is exposure, and only exposure.
ewelch said:
Depth of field will be different, etc.
Click to expand...
Yeah, there is that.
ewelch said:
But when you're in a certain light, and you set the
camera at ISO 80, the given shutter speed is tied to the given
aperture and ISO. Nothing else matters.
Click to expand...
Well, more power to you. Good luck with that.
ewelch said:
You deal with different numbers to get the depth of field you want. But a
pixel is a pixel is a pixel. It may be bigger or smaller, more efficient or less
efficient. But in the end, a pixel sees a specific intensity of light
and sends a signal to the camera. It doesn't care how many other
pixels are on the sensor.
Click to expand...
Well, I gotta say that's a real compelling argument and difficult to argue with. Yes, a "pixel is a pixel is a pixel" and "it may be bigger or smaller, more efficient, or less efficient" -- I'd look like a fool arguing against that.

But for some of us who care about DOF and noise, there's a little more to the equation than exposure.

Still, don't keep me from stopping you from doing what works for you!

--
--joe

http://www.josephjamesphotography.com
http://www.pbase.com/joemama/
 
I believe "gather more light" here has more to do with the "quality" of the light signal (vs. noise signal) because the pixel is larger. Otherwise f/2=f/2.
 
my wong said:
I believe "gather more light" here has more to do with the "quality"
of the light signal (vs. noise signal) because the pixel is larger.
Click to expand...
"gather more light" means "gather more light".

--
Seen in a fortune cookie:
Fear is the darkroom where negatives are developed
 
nickleback said:
"gather more light" means "gather more light".
Click to expand...
You are right, but finally I think the decisive factor is the pixel size.

If we have an APS-C sensor (eg 12Mp) and a FF 35mm sensor (again 12Mp), but with the APS sensor we step slightly back, so that both show exactly the same view (so the frame is the same), then:

(a) the analysis of the photograph will be the same in both cases, since both pictures will have 12Mpixels;

(b) but the colour accuracy and smoothness of the larger sensor will be better, because the size of its pixels is larger (of course, this is a consequence of the sensor being larger).

So, finally, the decisive factor is the size of the pixels, which if they are larger will gather more light, and so will produce more electrons per pixel. It will also be possible to quantize in much more levels (since we have much more electrons), and so produce a smoother transition from one encoding level to the next.
Don't you agree?
best regards,
George
 
Perhaps we're confusing why we use larger sensor with larger pixels that can "gather more light"

The amount of light has not changed whether we use a camera with tiny image sensor with tiny pixels or a camera with large image sensor with larger pixels. No matter what size image sensor we use, the exposure is the same.

"gather more light" per pixel does not affect exposure, only the quality of the light signal we are able to extract from it, which results in better dynamic range, less noise at high ISOs, etc.

:)
 
George said:
nickleback said:
"gather more light" means "gather more light".
Click to expand...
You are right, but finally I think the decisive factor is the pixel
size.
If we have an APS-C sensor (eg 12Mp) and a FF 35mm sensor (again
12Mp), but with the APS sensor we step slightly back, so that both
show exactly the same view (so the frame is the same), then:
Click to expand...
Just a minor clarification: If you step back, then both sensors can't have the same view because perspective changes. The only way for both sensors to have the same view is to use different lenses.

--
Ron Parr
Digital Photography FAQ: http://www.cs.duke.edu/~parr/photography/faq.html
Gallery: http://www.pbase.com/parr/
 
my wong said:
Perhaps we're confusing why we use larger sensor with larger pixels
that can "gather more light"

The amount of light has not changed whether we use a camera with tiny
image sensor with tiny pixels or a camera with large image sensor
with larger pixels. No matter what size image sensor we use, the
exposure is the same.
Click to expand...
The exposure is the same because the amount of light per unit area is the same. The total amount of light is larger on the larger sensor.
my wong said:
"gather more light" per pixel does not affect exposure, only the
quality of the light signal we are able to extract from it, which
results in better dynamic range, less noise at high ISOs, etc.
Click to expand...
The "quality of the light signal" is higher because more light is involved.

--
Ron Parr
Digital Photography FAQ: http://www.cs.duke.edu/~parr/photography/faq.html
Gallery: http://www.pbase.com/parr/
 
Ron Parr said:
The "quality of the light signal" is higher because more light is involved.
Click to expand...
Just to clarify this, we're talking about "more light" in the sense of "more photons", rather than the more familiar sense of "brighter illumination".

Or in SI units, "more lumen-seconds" rather than "more lux".

--
Alan Martin
 
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