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Author Topic: Why I need MPs  (Read 6351 times)

Denabears

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Re: Why I need MPs
« Reply #15 on: December 10, 2011, 11:29:17 AM »

Perhaps you read in haste.


I don't believe so.  But I certainly don't want to get into an endless argument either as I doubt it would help anyone. 

I look forward to perhaps 10 years from now when 100+Mpixel cameras will be available, fast and cheap,until then we can but dream (or stitch, but not so much for sports photographs). 

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Re: Why I need MPs
« Reply #15 on: December 10, 2011, 11:29:17 AM »

ferdi

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Re: Why I need MPs
« Reply #16 on: December 10, 2011, 12:33:42 PM »
Firstly remember what is expected of you. Practice composition in camera so you don't have to crop in post because this takes forever for a few thousand pictures. If the client wants to publish any pictures he will crop them anyway, and usually not very artistically.

For your own portfolio, pick a few of the best and edit these more thorougly, including crop, angle, spot removal, vignette, etcetera. 10 MP should still be enough for a web portfolio and smaller prints (up to A4). If not then your upcoming 7D might be the right solution for you; I would have suggested renting it otherwise.
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Re: Why I need MPs
« Reply #17 on: December 10, 2011, 12:48:28 PM »
Best if everyone makes up their own mind on this based on looking at large prints, but second best is evidence from some of the lens testing sites.

The first error people make is bringing diffraction into discussions like this (particularly along with misuse of the word "limit").  Diffraction is not a function of pixel size - as a property of the lens how could it possibly be so?


Do use a camera without a lens??  The diffraction properties of a lens are part of the camera system, and affect the final result.  There is not a "Limit", its a gradual effect. 

You can have a 100mp sensor and get 100mp files, but the resolution will be limited by the lens and lens aperture.


distant.star

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Re: Why I need MPs
« Reply #18 on: December 10, 2011, 01:30:05 PM »

I second this emotion.

I like looking at your finished pictures. Good work.


Nice shots. Love the crop on the first image.
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Re: Why I need MPs
« Reply #19 on: December 10, 2011, 01:38:06 PM »
The original question here is not about cropping.

The question is whether increased megapixels increase the ability to crop without losing detail.

I've read the responses and now I'm more confused.

neuroanatomist

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Re: Why I need MPs
« Reply #20 on: December 10, 2011, 02:35:38 PM »
But I certainly don't want to get into an endless argument either as I doubt it would help anyone. 

Well, if you believe that the sensor characteristics play no role in determining the effect of diffraction on an image, it definitely would be endless...   Can you provide some documentation or evidence that the pixel density of the sensor has no effect on the aperture at which diffraction affects image sharpness?
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Re: Why I need MPs
« Reply #21 on: December 10, 2011, 03:48:11 PM »

Well, if you believe that the sensor characteristics play no role in determining the effect of diffraction on an image, it definitely would be endless...   Can you provide some documentation or evidence that the pixel density of the sensor has no effect on the aperture at which diffraction affects image sharpness?

of course he can not.
but some people would even argue that they can build a spaceship that´s faster then light.

i mean what is so complicated to understand?
everyone with some school education that includes math can look at the wikipedia link and see that what is written there it´s correct.

Quote
Cameras
 
If two objects imaged by a camera are separated by an angle small enough that their Airy disks on the camera detector start overlapping, the objects can not be clearly separated any more in the image, and they start blurring together. Two objects are said to be just resolved when the maximum of the first Airy pattern falls on top of the first minimum of the second Airy pattern (the Rayleigh criterion).
Therefore the smallest angular separation two objects can have before they significantly blur together is given as stated above by
 

Thus, the ability of the system to resolve detail is limited by the ratio of λ/d. The larger the aperture for a given wavelength, the finer the detail which can be distinguished in the image.
Since θ is small we can approximate this by
 

where x is the separation of the images of the two objects on the film and f is the distance from the lens to the film. If we take the distance from the lens to the film to be approximately equal to the focal length of the lens, we find
   
but f/d is the f-number of a lens. A typical setting for use on an overcast day would be f/8.[8] For blue visible light, the wavelength λ is about 420 nanometers.[9] This gives a value for x of about 4 µm. In a digital camera, making the pixels of the image sensor smaller than this would not actually increase image resolution.

« Last Edit: December 10, 2011, 03:55:49 PM by Canon-F1 »
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Re: Why I need MPs
« Reply #21 on: December 10, 2011, 03:48:11 PM »

Canon-F1

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Re: Why I need MPs
« Reply #22 on: December 10, 2011, 04:00:33 PM »
Quote
Perhaps you wrote in haste. 

The diffraction from the lens does, of course, produce a slightly fuzzy (unsharp) representation of the image on the sensor.  This fuzziness in the focal plane does, by no means depend on anything to do with the sensor.

well you don´t know what we are talking about.
 
the fuzziness does not depend on the sensor sure.... nobody said it does.
but the RESOLUTION is limited when the airy disc is bigger then the photosites.
and the photosites depend on the sensor. :)

the bad thing is he gave you TWO links to get some infos.... but you seem to ignore it.

the lens (the lens design) has nothing to do with the resolution limit on sensor level.
it depends on the aperture and the wavelength of the light ONLY.
for this we assume a PERFECT lens.... so no negative effects by lens design (imperfections).

so even in 100 years you will still be bound by this simple rule of physics.
because you can´t build a better lens then a PERFECT lens.

the only thing a REAL lens does it to make the diffraction effect WORSE.
but ultimately at some photosite size you can´t resolve more details even with a physical and mathematical PERFECT lens.

to resolve more details you have to go to smaller wavelengths (smaller then visible light).

when you look at at this link: http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

you should see why smaller photosites can not resolve more information then the size of the airy disc.

Quote
In fact the fuzziness is exactly the same whether there is a sensor there or not e.g. if film were used.

that´s correct but you have to think it through!
no matter if FILM or a DIGITAL SENSOR, when aperture and wavelength combination create an airy disc that´s bigger then a photosite or a grain on film, then you can´t resolve more then that size of the airy disc. because there is not more INFORMATION.

ergo... at some point, independend from lens quality, more megapixel (smaller photosites) on a sensor will not result in better resolution.

Quote
Note that you will never see an Airy disk in a real photograph unless you photograph point sources.

you should read the articles again.  ::) 
this one sentence shows your lack of understanding.
the first sentences in the wikipedia article should give you an hint:

Quote
"In optics, the Airy disk (or Airy disc) and Airy pattern are descriptions of the best focused spot of light that a perfect lens with a circular aperture can make, limited by the diffraction of light.

The most important application of this concept is in cameras and telescopes. Owing to diffraction, the smallest point to which a lens or mirror can focus a beam of light is the size of the Airy disk. Even if one were able to make a perfect lens, there is still a limit to the resolution of an image created by this lens. An optical system in which the resolution is no longer limited by imperfections in the lenses but only by diffraction is said to be diffraction limited."
 
« Last Edit: December 10, 2011, 06:02:23 PM by Canon-F1 »
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Denabears

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Re: Why I need MPs
« Reply #23 on: December 10, 2011, 04:57:07 PM »
Can you provide some documentation or evidence that the pixel density of the sensor has no effect on the aperture at which diffraction affects image sharpness?

Let me try this argument, which I hope is based on assumptions that we can agree on.   3 points make the argument (which is by no means original):

1) The sharpness, more precisely the MTF, of the system (camera+lens) can be expressed as the product of exactly 3 factors:
a) MTF curve describing lens aberration excluding diffraction,
b) MTF curve diffraction (not quite a simple as the correct formulae kindly given by Canon-F1 would suggest)
c) sensor MTF. 
Note: as usual for MTF curves a, b and c are all functions of spatial frequency (normally declining with frequency).

2) a and b are functions of the aperture (as well as spatial frequency).  We all know that factor a usualy improves as the lens is stopped down quite quickly at first, then more slowly (from f/4 or so for most decent lenses).
We also all know that factor b follows the inverse relationship hinted at by Canon-F1's Rayleigh criterion - but that is only one point on the curve.  I suspect the most important point is that some (perhaps little) contrast remains to much higher spatial frequencies (and yes, there are nulls where there is no contrast at all, for one color of light at a time).

All I claim is that factor c does not depend on the f/no. (which seems self-evident to me)

3) The product of a x b x c therefore has a maximum determined by max(a x b) and is scaled overall by c.  A "perfect" sensor will have c = 1 at all spatial frequencies, and so the MTF is just a x b any lower pixel count sensor (with a smaller value of c independent of f/no.) gives a smaller product at any f/no.  (QED)

I believe that anyone who thinks I'm mistaken has to disagree with one of the 3 points (and it would be good to know which), or we have a purely semantic disagreement (most likely due to the 100% viewing when the image gets bigger as the pixels get smaller - that is not the situation I'm describing!).


ps. Seeing another post by Canon-F1. The pixel / Airy disk illustration given by Sean McHugh is seriously misleading I know that many many people have been misled by it. Sampling theory tells quite a different story.  It is best to calculate using MTF in the spatial frequency domain, as suggested above.

pps. not even neutrinos go faster than light  ;) never mind spaceships.

ppps. there seems to be a bug that prevents me from italicizing one of the "c"s.

Gothmoth

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Re: Why I need MPs
« Reply #24 on: December 10, 2011, 05:00:48 PM »
1) The sharpness, more precisely the MTF, of the system (camera+lens) can be expressed as the product of exactly 3 factors:
a) MTF curve describing lens aberration excluding diffraction,
b) MTF curve diffraction (not quite a simple as the correct formulae kindly given by Canon-F1 would suggest)
c) sensor MTF. 

you can forget that argumentation because we already assume a perfect lens.  ;)
again, the LENS has NO influence on the SMALLEST POSSIBLE SIZE of an Airy Disc.

a perfect lens can achive this SMALLEST size, a less then perfect lens can only achive a BIGGER airy disc size.

you can´t do better then the physical minimum.

if you go under this minimum with the size of the photosites you will not resolve more detail.
once you are under this minimum you can make the photosites smaller and smaller but you will not get more details. it´s simply not there.

Quote
All I claim is that factor c does not depend on the f/no. (which seems self-evident to me

and all i say is that at some point the resolution can not be increased by better lens design nor smaller photosites (because of diffraction).  ;)

of course you can resolve more details with smaller photosites when you go to shorter wavelengths. because the size of the airy disc will be smaller with smaller wavelenght.
but that is no real solution for most photographers as we like to photograph visible light not ultraviolett and shorter.
« Last Edit: December 10, 2011, 05:28:05 PM by Gothmoth »

Denabears

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Re: Why I need MPs
« Reply #25 on: December 10, 2011, 05:13:31 PM »
Oh dear, as I feared we are all getting at cross-purposes here, because the assumptions and question are not clear enough (that is even more evident from Gothmoth's perfect lens post that has just popped up).


Quote
"In optics, the Airy disk (or Airy disc) and Airy pattern are descriptions of the best focused spot of light that a perfect lens with a circular aperture can make, limited by the diffraction of light.

The most important application of this concept is in cameras and telescopes. Owing to diffraction, the smallest point to which a lens or mirror can focus a beam of light is the size of the Airy disk. Even if one were able to make a perfect lens, there is still a limit to the resolution of an image created by this lens. An optical system in which the resolution is no longer limited by imperfections in the lenses but only by diffraction is said to be diffraction limited."
 

That's absolutely correct, of course.  I did not claim there was no diffraction limit for lenses! - I'm sorry if something I wrote it made you think so. 

My claim is that there is no diffraction limit for sensors, so that a higher resolution sensor always gives a better result (however slightly).

Thanks for the links I am already extremely familiar with them (but you were not to know that). Sean McHugh is not, however, the best source as he ignores sampling theory.

If you look carefully at my first post you should see that I effectively say that we need 3 blue pixels to resolve the "Airy disk" not just 1.  (If you read between the lines and think what produces the 80 lp/mm figure.)

I am being much more subtle than you give me credit for (but that's cool).

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Re: Why I need MPs
« Reply #26 on: December 10, 2011, 05:19:38 PM »
What about post-processing?

Do increased megapixels give greater ability to process images?

It seems like people are discussing too many variables here.

PLEASE PEOPLE...

Is there an "all other things equal" way to compare different megapixel counts ???

All these formulas and extra variables mean 90% of people viewing this thread probably don't understand the discussion.

Gothmoth

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Re: Why I need MPs
« Reply #27 on: December 10, 2011, 05:20:06 PM »
so that a higher resolution sensor always gives a better result (however slightly).

and this is only correct if you can make the wavelength of the rays you collect smaller and smaller.

i repeat again:

Quote
In a digital camera, making the pixels of the image sensor smaller than this would not actually increase image resolution.

the resolution will not get worse when we ignore noise and other effects... but it will be stagnating at some point.

« Last Edit: December 10, 2011, 05:22:47 PM by Gothmoth »

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Re: Why I need MPs
« Reply #27 on: December 10, 2011, 05:20:06 PM »

Denabears

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Re: Why I need MPs
« Reply #28 on: December 10, 2011, 05:20:50 PM »
but that is no real solution for most photographers.

Yes absolutely, perfect lenses are very expensive.  That's why I started this whole string of threads off with the 80 lp/mm figure from DXOmark: not theoretical, not nearly the best that can be done, but it still justifies of order 200Mpixels. Diffraction imperfect lens and all.

After all many of us have an 85/1.8 (or an even better lens) and we'd see (a litte) benefit with 200Mpixels at f/5.6.

P.s. another point - compacts with 2 micron pixels are reasonably sharp at f/5.6.  That is also about 200Mpixels on full frame (decide yourself).

Denabears

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Re: Why I need MPs
« Reply #29 on: December 10, 2011, 05:23:13 PM »
so that a higher resolution sensor always gives a better result (however slightly).

and this is only correct if you can make the wavelength of the rays you collect smaller and smaller.

i repeat again:

Quote
In a digital camera, making the pixels of the image sensor smaller than this would not actually increase image resolution.
No, the wavelength is of course assumed constant  in the 3 point argument.  Which step don't you agree with?

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Re: Why I need MPs
« Reply #29 on: December 10, 2011, 05:23:13 PM »