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11-22-2010, 08:58 AM   #1
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Please explain "Sensor is Outresolving Some Lenses"

I am having trouble understanding how the better sensor of the K5 can produce an image that is inferior to one produced by the same lens on a lessor sensor. confused2
I don't doubt that it is happening; I just don't understand the physics involved.
(Film was so much simpler. sigh..........)

11-22-2010, 09:06 AM   #2
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Roughly, the image won't be inferior if printed at an equal size, it's just that if you pixel-peep at 100% the apparent details might be less sharp for a given "inferior" lens.

If you prefer, a lens should reach a certain resolution on given conditions. Now it's possible that the sensor's resolution on the K-5 be superior to the one of some lenses. 16Mp are far more demanding than 10Mp.... But I'm sure you already know that
11-22-2010, 09:18 AM   #3
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Couldn't you just dial down the resolution on the K-5 like you can on a Nikon FF shooting with DX lenses instead of FX lenses?
11-22-2010, 09:20 AM   #4
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Is it not true that higher resolution will reveal lens flaws, such as chromatic aberration? I cannot see how it would make for less sharp images, but maybe I'm missing something.

Rob

11-22-2010, 09:21 AM   #5
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the idea is that the resolution of the sensor, or more importantly the pixel pitch is getting to be a smaller and smaller number, considering an ASP-C sensor and approximately the 16 x 24mm format, as the image goes from 6MP to 10MP to 14MP to 16 MP (considering the *istD, K10D, K7D and now K5D)

if you consider these sensors you have had an approximate change in pixel pitch from 8 microns on the *istD to 6.2 on the K10D to 5.24 on the K7D to 4.9 on the K5D.

WHat people are saying is that as the pixel pitch has reduced in distance, it is possible now to resolve more than previously, and this may mean that some lenses are now at their limit relitive to the sensor. While this may be true when moving from the *istD to any other camera, the difference in resolution of any of the cameras in the 10-16mp range is so slight that I doubt that you would notice. This would be especially true in stepping up, for example, from a K20 or K7 to a K5. The increase in pixel pitch is so slight, (roughly 5%) that I would think any difference noticed here would be in the fariability shot to shot of your technique.
11-22-2010, 09:23 AM   #6
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A higher resolution sensor will never produce an image inferior to a lower resolution sensor, all else equal.

Here's a graph I made, where the perceived sharpness is the intersection of the 3 curves:



For those interested, there is some good discussion on the comments of the first two answers here.
11-22-2010, 09:28 AM   #7
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QuoteOriginally posted by Kikool_CH Quote
..............it's just that if you pixel-peep at 100% the apparent details might be less sharp for a given "inferior" lens.
That's the part I'm hoping to have explained.
Let me try to explain my confusion another way.
Let's make a comparison situation to a lens producing a better image on a K20D than it does on a K5:
Let's say I had really sharp eyesight and owned a pair of cheap binoculars. When I look through the binoculars, I see an image of a given quality, i.e. resolution, contrast, etc.
Now let's say I develop macular degeneration. I wouldn't expect to see a better quality image through those same binoculars due to a sensor (retina) of lesser capability. An equal one maybe, if the binoculars were really crappy; but certainly not a better quality image.
I'm not trying to make a comparison between they eye and a sensor, I'm just trying to clarify the question.
11-22-2010, 09:33 AM   #8
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Parallax, by pixel peeping on a K-5 vs a K20D, you are effectively using a larger magnification on the same image, and thus will see more image degradation. It's like looking at a print and using different intensity magnifying glasses.

When you make print or view them at the same overall normalized physical size, they will appear the same, because the aberrations are optically based and independent of the medium they are projected on, ignoring any sampling boundary issues.

11-22-2010, 09:49 AM   #9
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QuoteOriginally posted by Lowell Goudge Quote
....................
WHat people are saying is that as the pixel pitch has reduced in distance, it is possible now to resolve more than previously, and this may mean that some lenses are now at their limit relitive to the sensor. While this may be true when moving from the *istD to any other camera, the difference in resolution of any of the cameras in the 10-16mp range is so slight that I doubt that you would notice. This would be especially true in stepping up, for example, from a K20 or K7 to a K5. The increase in pixel pitch is so slight, (roughly 5%) that I would think any difference noticed here would be in the variability shot to shot of your technique.
Okay, I can understand how the part I put in bold would preclude a particular lens from looking better on the K5. In other words a picture form a K5 taken with a DA 40 Ltd may look better than the one from the K20D, but one taken with the kit lens may be indistinguishable from the K20D picture. But how can improving the resolution capability of the sensor degrade the performance of one lens, but enhance that of another?

I have one possible explanation, but it may be a stretch. Is it possible that if the resolving capability of the sensor and lens are equal, or very nearly so, that it causes problems. (something like the principal that moire pattern can be created from equal sized lines, but not from dissimilar). Could there be a threshold there that when either crossed or stayed shy of is not an issue, but if stood on causes problems?

QuoteOriginally posted by Eruditass Quote
Parallax, by pixel peeping on a K-5 vs a K20D, you are effectively using a larger magnification on the same image, and thus will see more image degradation. It's like looking at a print and using different intensity magnifying glasses.

When you make print or view them at the same overall normalized physical size, they will appear the same, because the aberrations are optically based and independent of the medium they are projected on, ignoring any sampling boundary issues.
That also makes sense.
11-22-2010, 10:23 AM   #10
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QuoteOriginally posted by Parallax Quote
(Film was so much simpler. sigh..........)

Indeed. IMO, all that ends on the same old question: how much light do I need to get a properly exposed photography. Film was far more forgivable on this issues.
11-22-2010, 10:55 AM - 1 Like   #11
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QuoteOriginally posted by Parallax Quote
That also makes sense.
That's the one answer to start from. Smaller pixels make you "microscope" the defects without degrading the image as a whole.

Pixel quality and image quality are two different things. Btw, that's a common source of misunderstanding when discussing depth of field as well.


So, the initial assumption (that a higher resolution sensor may deliver worse images) doesn't hold true. Actually, it may hold true if the fill factor degrades. But that's not currently the case with dSLRs, except maybe in corners below f/1.8.


After this has been clarified somehow, you may want to have a look at LumoLabs Article -- Understanding Image Sharpness

It explains how a better sensor may even help a lens which is already "outresolved". Think of lens and sensor both having a filter layer which adds fuzzyness. What you see is the combined (added) effect from looking through both layers. And a higher resolving sensor is like a thinner filter layer, helping (a little bit) even if the other layer is thicker already.

---------- Post added 11-22-10 at 07:09 PM ----------

QuoteOriginally posted by Eruditass Quote
A higher resolution sensor will never produce an image inferior to a lower resolution sensor, all else equal.

Here's a graph I made, where the perceived sharpness is the intersection of the 3 curves:
Eruditass, nice graph.

However, the overall perceived sharpness depends on all three factors in a more complex way. The correct treatment would be the multiplication of all three MTF curves describing each effect. Of course, that's rather complicated. In my paper (cited above) I try to provide simplifications.

Probably the best simplification would be to introduce a blur (the inverse of resolution) or fuzzyness (the square of blur or surface of a blurred point).

The statement then simplifies to saying that the overall fuzzyness is the sum of fuzzyness due to missing lens quality, finite sensor pixel size and diffraction. If you replace fuzzyness by blur, then this is a rule aka Kodak formula. However, I found fuzzyness allows a better treatment for digital devices which can sharpen.

And as being a sum, reducing the finite sensor pixel size will always reduce overall fuzzyness. And overall fuzzyness can never become smaller than the finite sensor pixel size.

This statement isn't mathematically exact but as I tried to show, the best possible simplification.

Last edited by falconeye; 11-22-2010 at 11:15 AM.
11-22-2010, 11:19 AM   #12
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Thanks, everyone. Falk, that was the icing on the cake that cleared it up completely for me.
11-22-2010, 04:25 PM   #13
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QuoteOriginally posted by Mortox Quote
Couldn't you just dial down the resolution on the K-5 like you can on a Nikon FF shooting with DX lenses instead of FX lenses?
No.

null characters.
11-23-2010, 10:32 AM   #14
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If this is a real issue, I wonder what would happen if Pentax was to build a FF camera?
That would be a real letdown for those who recurrently are complaining about that "weakness". Perhaps that's why Pentax don't have plans for that to happen in the near future. lol

Last edited by Manel Brand; 11-23-2010 at 10:34 AM. Reason: typo
11-23-2010, 03:01 PM   #15
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QuoteOriginally posted by Manel Brand Quote
If this is a real issue, I wonder what would happen if Pentax was to build a FF camera?
That would be a real letdown for those who recurrently are complaining about that "weakness". Perhaps that's why Pentax don't have plans for that to happen in the near future. lol
FF decreases rather than increases the issue. Because FF tends to have larger pixels. Actually, that's a much stronger argument pro FF than DoF or high iso noise. It's just not well understood by many.
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