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10-18-2014, 05:54 PM   #226
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QuoteOriginally posted by Kunzite Quote
You are not the "mechanical engineers", but the "theoretical physicists" of the photographic world.
Which do you prefer?





10-18-2014, 06:08 PM   #227
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QuoteOriginally posted by jsherman999 Quote
You never are really required to learn beyond the bare scaffolding of facts needed to bring you A) basic sustenance, B) some measure of material surplus beyond A, and C) internet service.
Knowledge is not the same as understanding.
10-19-2014, 05:15 AM   #228
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And understanding is not wisdom

jsherman999:
11-29-2014, 02:07 PM   #229
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QuoteOriginally posted by PJ1 Quote
The focal length of the lens does not change and nor does the aperture. If I put my FA 135/f2.8 on my K-01 it tells me that it is a 135mm lens and - wide open - it gives the appropriate exposure for f2.8. The "crop factor" crops the area that the light falls on. It does not reduce the intensity of light coming through the lens (as it would if it reduced the aperture). To put it another way, every lens produces an image circle and the brightness of the image is determined by the size of the aperture. A larger aperture gives a brighter image. But the brightness of the image is usually the same across the entire image circle (the exception is where there is vignetting if the image circle is too small for the format). You can crop that image circle to any size you want. If the lens if f2.8, any section of it will still be f2.8. That is the physics of it. No smoke and mirrors.
This is the correct interpretation not that of the first poster. There is a depth of field difference that is conferred by the crop factor, but F1.8 is F1.8. even if the first poster was correct (which he's not) once the aperture got small enough to fit inside the sensor size the difference would go away, f8, 16 etc are way smaller than the sensor on APSC or 4/3rds.

---------- Post added 11-29-2014 at 05:19 PM ----------

QuoteOriginally posted by Aku Ankka Quote
Assuming that the sensor related noises (which are minute and irrelevant outside of deep shadows) are the same, then he is right. The amount of noise (ie. standad deviation) in light itself is equal to the square root of the number of photons. 10000 photons captured means standard deviation of 100 and SNR of 100.


Didn't you just disagree with that?


While the exposure is maintained, the effect of exposure will be different. An f/2.8 image on an iPhone will have vastly lower signal-to-noise ration than an f/2.8 image on a medium format camera.

If you disagree what I wrote in bold, would you explain why it would be wrong.

If you want to have the same SNR on a smaller sensor, you will either need to increase the aperture (ie. reduce the aperture number), or increase the exposure time. Just like you said: it's abut the total light.

---------- Post added 18-10-14 at 14:12 ----------



If you use the same exposure parameters on FF and C2 (Full frame and crop 2) and have the same field of view (ie. 50mm on FF, 25mm on C2):
  1. FF DOF will be more shallow
  2. FF wil capture four times more light
  3. The above two are a tradeoff - to capture more light over fixed unit of time you need to reduce the DOF. There are no ways around this.
  4. FF has four times the signal, thus twice the SNR
  5. Thus the images of FF and C2 will be different using the same exposure parameters.
In order to create an identical omage on different formats you need to use different exposure parameters.

---------- Post added 18-10-14 at 14:33 ----------



Equivalency as a tool for comparing different formats. Nothing more nothing less. It is based on solid science. You may not like it, but it that doesn't make it into religion.

Here is a small example:
  1. FF sensor (full frame) and C2 (crop factor 2) are to be considered
  2. They are idealized - identical quantum efficiency, same pixel count, same colour filters, same read noise etc.
  3. The above is just to make isse as clear as possible - the real world cameras don't change the results much and the principle at all
  4. 25mm lens for the C2, 50mm lens for the FF
  5. Same field of view for both due to point 4
  6. Exposure time 1 seconds
  7. Aperture number of f/2 is considered
  8. The FF aperture if thus 25mm, while the C2 aperture is 12.5mm
  9. The area of the apertures differ by factor of 4 (four) - area = pi*r^2
  10. Four (4) times more light goes through the bigger aperture even though the aperture number is the same
  11. Standard deviation (ie. noise) of light is the square root of the number of photons captured (poisson distribution)
  12. FF has four times more light, thus four times more signal.
  13. FF has two times more noise (!)
  14. FF has two times higher signal-to-noise-ratio (SNR)
  15. FF also has more shallow DOF - this is the tradeoff that is needed for higher SNR with fixed exposure time and light
  1. If we change the FF aperture number to f/4:
  2. Same aperture diameter
  3. Same amount of light captured
  4. Same noise
  5. Same DOF
  6. Identical image information (ie. apart from the inherit randomness of the light and sensor noise the images are identical)
  7. The FF could be exposud for up to four (4) times longer to get better SNR unless for example movement prevents this


---------- Post added 18-10-14 at 14:45 ----------



Pixel size is almost irrelevant.
It's the total light that is captured which is relevant, not the light a single pixel captures. The image is made from all the pixels, not one.

The QE (quantum efficiency - the percent of photons entering the sensor (after the color filters etc.) turned into signal) of K5 is about twice that of 5D which means that in spite of the sensor is about 2.25 times smaller it still captures a similar amount of photons with the same exposure parameters.

The deep shadows of the Pentax will be much regardless and actually have signal long after the Canon hasn't any.

Now, if we're not contrained by the exposure parameters, then K5 can capture images with higher SNR all over the place because it has slightly higher sum of pixel's full well capacity. If we saturate both sensors with ETTR, then the K5 has about 8-9% higher SNR over the upper end and middle parts of the tonal range, while in the shadow range it's SNR is even better and infinitely better for the last three stops or so once the Canon loses signal alltogether (at the base ISO).
If you are going to use that type of logic, no matter how many numbers and theoretical equations you throw at it. If you use a FF lens on a crop factor camera then all will be equal because the F stop argument of F2 not being F2 goes out the window since the apertures will be the same size. This will only hold water if you are trying to tells us that crop factor lens has difference sized openings for F1.8 than a FF lens I can't say for sure but I highly doubt that is the case.

11-30-2014, 09:09 AM   #230
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QuoteOriginally posted by kh1234567890 Quote
Knowledge is not the same as understanding.
QuoteOriginally posted by Kunzite Quote
And understanding is not wisdom

jsherman999:


Why do so many of these threads come to this? Not denying for a moment the truth (or wit) of the two quotations.
11-30-2014, 09:23 AM   #231
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QuoteOriginally posted by Mikesul Quote
Why do so many of these threads come to this? Not denying for a moment the truth (or wit) of the two quotations.
Because threads like this are pointless. The equivalence believers won't accept that to get a similar image with the same lens on two different size sensors they have to change the subject distance which changes just about everything else.
11-30-2014, 01:29 PM   #232
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There is a definite need for comparative measures that will allow customers to compare one camera format to another. Many enthusiasts buy cameras or advise other purchasers from time to time. So as a practical matter, there is a real need to for useful information that would allow customers to compare one product to another.

I liked Tony Northrup's explanation because it confirms what we empirically observe, for example, we all know, i think, that smaller sensors have less low light capability than larger sensors. With Tony's explanation of how to apply crop factors to ISO, than its easy to see what sensor formats excel in low light.

I'd much rather have a comparative system that helps me differentiate one camera from another, rather than spend time parsing definitions. Its the comparative system that i value, not the debate. If you think you've got a better system of comparing one camera to the other, than describe the complete comparative process, not just one part of it.

The old saw about "If you don't know where you are going, than any route is good enough to get you there" may apply here

Last edited by philbaum; 11-30-2014 at 02:14 PM.
11-30-2014, 02:02 PM   #233
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QuoteOriginally posted by philbaum Quote
There is a definite need for comparative measures that will allow customers to compare one camera format to another. Many enthusiasts buy cameras or advise other purchasers from time to time. So as a practical matter, there is a real need to for useful information that would allow customers to compare one product to another.

I liked Tony Northrup's explanation because it confirms what we empirically observe, for example, we all know, i think, that smaller sensors have less low light capability than larger sensors. With Tony's explanation of how to apply crop factors to ISO, than its easy to see what sensor formats excel in low light.

I'd much rather have a comparative system that helps me differentiate one camera from another, rather than spend time parsing definitions. Its the comparative system that i value, not the debate. If you think you've got a better system of comparing one camera to the other, than describe the complete comparative process, not just one part of it.

The old saw about "If you don't know where you are going, than any route is good enough" may apply here
Thank you for your thoughts on this. The comparisons do seem to be mainly one feature at a time. I wish I had a suggestion for a system but I do not. Perhaps a more technically and artistic member can come up with a way to compare the systems. As it is now, for me, I still do not see much advantage to the FF. I understand the discrete items but looking at photographs it is hard to separate camera from photographer from light from opportunity etc.

11-30-2014, 02:21 PM   #234
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QuoteOriginally posted by Mikesul Quote
Thank you for your thoughts on this. The comparisons do seem to be mainly one feature at a time. I wish I had a suggestion for a system but I do not. Perhaps a more technically and artistic member can come up with a way to compare the systems. As it is now, for me, I still do not see much advantage to the FF. I understand the discrete items but looking at photographs it is hard to separate camera from photographer from light from opportunity etc.
I'm not convinced to spend money yet, either. If i did jump into the FF pool, the A7S attracts me most. But we don't know what Canon, Nikon, Pentax and even Samsung are up to, yet. 2015 will be an interesting year.
11-30-2014, 02:25 PM   #235
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QuoteOriginally posted by philbaum Quote
I'm not convinced to spend money yet, either. If i did jump into the FF pool, the A7S attracts me most. But we don't know what Canon, Nikon, Pentax and even Samsung are up to, yet. 2015 will be an interesting year.
Isn't it funny that the most interesting FF for many of us is the one with the least megapixels? We really do need a reasonable standard of quality.
12-01-2014, 09:08 AM   #236
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you're not following the narrative

QuoteOriginally posted by MikeD Quote

If you are going to use that type of logic, no matter how many numbers and theoretical equations you throw at it. If you use a FF lens on a crop factor camera then all will be equal because the F stop argument of F2 not being F2 goes out the window since the apertures will be the same size. This will only hold water if you are trying to tells us that crop factor lens has difference sized openings for F1.8 than a FF lens I can't say for sure but I highly doubt that is the case.
Everything Aku Ankka posted there that you quoted is essentially correct, and I encourage you (and others) to read/understand it.

To your specific statement:

QuoteOriginally posted by MikeD:
..This will only hold water if you are trying to tells us that crop factor lens has difference sized openings for F1.8 than a FF lens I can't say for sure but I highly doubt that is the case.
There are different size openings if FOV is being held constant - ie if you are taking the 'same shot' on both formats. What's being assumed there is the same FOV between both formats from the same position, at the same exposure (same shutter speed and f-stop).

If you have the same FOV from the same position, that requires a different focal length.

Very simply - for example, same FOV, f-stop + shutter speed (exposure) and distance:

aps-c: 33mm f/2.8 --> 33 / 2.8 == 11.8mm physical aperture
FF: 50mm f/2.8 --> 50 / 2.8 == 17.8mm physical aperture

Same f-stop, same exposure, same FOV, but the FF image has more total light due to the larger physical aperture, and if the sensor gens are similar, will have about a stop better noise/DR performance and 1.3 stops less DOF.


.

Last edited by jsherman999; 12-01-2014 at 09:16 AM.
12-01-2014, 05:55 PM   #237
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QuoteOriginally posted by Mikesul Quote
Isn't it funny that the most interesting FF for many of us is the one with the least megapixels? We really do need a reasonable standard of quality.
For whatever reason, manufacturers have persistently increased the pixel density on sensors for some time now. And the selling phrase to consumers is: this camera will have higher resolution. What isn't discussed as much is that higher pixel density often leads to higher noise levels, example, several posters have commented that the K5 has less noise at 1600 iso than the K3, which some folks prefer to shoot at 800 iso.

I have a friend who has both the A7R and the A7S, and he far prefers to shoot with the A7S. He says he likes the look of the 12mp sensor better than the 36MP, and claims he isn't the only one that likes the A7S better.

The interest that some of us have indicated for the A7S is perhaps pushback on constantly increasing MP/resolution, at the cost of more noise. With its large photosites, the A7S seems designed for one goal: to increase the SNR in low light situations. At least some people think that a higher SNR also results in more attractive images. BTW, the friend i mentioned shoots only single photographs - no video. The A7S is such a high profile camera, it will be interesting in 2015 as to whether Canikon follows with a similar model - not sure who they would buy the sensor from, as Sony says its for their own camras only.
12-01-2014, 06:02 PM   #238
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QuoteOriginally posted by philbaum Quote
For whatever reason, manufacturers have persistently increased the pixel density on sensors for some time now. And the selling phrase to consumers is: this camera will have higher resolution. What isn't discussed as much is that higher pixel density often leads to higher noise levels, example, several posters have commented that the K5 has less noise at 1600 iso than the K3, which some folks prefer to shoot at 800 iso.

I have a friend who has both the A7R and the A7S, and he far prefers to shoot with the A7S. He says he likes the look of the 12mp sensor better than the 36MP, and claims he isn't the only one that likes the A7S better.

The interest that some of us have indicated for the A7S is perhaps pushback on constantly increasing MP/resolution, at the cost of more noise. With its large photosites, the A7S seems designed for one goal: to increase the SNR in low light situations. At least some people think that a higher SNR also results in more attractive images. BTW, the friend i mentioned shoots only single photographs - no video. The A7S is such a high profile camera, it will be interesting in 2015 as to whether Canikon follows with a similar model - not sure who they would buy the sensor from, as Sony says its for their own camras only.
Interesting thoughts, Phil. I hope, expect, Pentax to take these ideas into consideration if, when, they do FF.
12-04-2014, 10:39 AM   #239
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QuoteOriginally posted by kh1234567890 Quote
Because threads like this are pointless. The equivalence believers won't accept that to get a similar image with the same lens on two different size sensors they have to change the subject distance which changes just about everything else.
Can I get a similar image with different lenses on two different size sensors without changing subject distance?
12-04-2014, 10:49 AM   #240
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QuoteOriginally posted by carpents Quote
Can I get a similar image with different lenses on two different size sensors without changing subject distance?
Depends on what you mean by similar. Once you get into standard lenses like comparing a 50mm image with a 35 mm image, the differences in DoF are magnified to the point that if you're shooting for narrow DoF you'd want to be shooting Full Frame, but if you're shooting for wide DoF, you have more chance of getting the DOF you want, in the sweetest spot of the lens, if you're shooting APS-c. Shooting longer lenses, I'm not convinced it makes as much difference.

So in terms of subject size and magnification, they may be similar, but DoF and quality of out of focus areas may be different depending on your shooting style, or they may not even be noticeable.

Last edited by normhead; 12-04-2014 at 10:54 AM.
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