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01-07-2014, 10:35 AM   #1
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Lens definition vs sensor limitation


I did some reading about how a lens can limit the amount of pixels used in a sensor.

Does any kind of information exist regarding pentax lenses and at how many pixels they will be optimal ?

ie: will a 35mm f2.4 model X lens show more detais on a k3-24mp or aK5iis with 16mp.

Just curious as to at what point the amount of pixels really is an advantage..... 16, 24, 40, 64........ ?

Last edited by devouges; 01-07-2014 at 10:43 AM.
01-07-2014, 11:08 AM   #2
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The lenses don't act directly on the pixels, but some lenses are not able to produce sharp enough an image to show a difference once you reach a certain level of sensor quality. Even with a better sensor you would get the same quality image after that point for the most part.

Someone is doing some interesting experiments on this topic in another thread:

For the most part we are already to the point where a good lens produces a better image than a bad lens on current sensors, so the lens is the limiting factor. But we are not at the point where a good lens is limiting the quality of images from the current sensors.
There is no "list" or guide to which is which and no set number for sensor size or MP count.
01-07-2014, 11:15 AM   #3

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The lens/sensor relationship will vary with aperture, focal distance, position within the frame, and with zoom lenses, the focal length. Also, movement in both subject and camera can be the limiting factor.
01-07-2014, 12:26 PM   #4
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Well now you have it.
A lens has a certain maximum amount of detail it can resolve. And a sensor has a certain maximum detail it can detect and record. Which one is the limiting factor? Hard to say, because both are improving. But when the D800 came out, with its 36MP sensor, a lot of people were afraid the sensor would outresolve their lens and record all the little "faults" (thus making the lens suddenly seem bad)
With the K-3 specifically, and this is my unscientific understanding, the current Pentax primes should still outresolve the sensor, and the K-3 will be a noticeable improvement over the 16MP cameras.
Of course, there are other things to consider, like all the other lens and camera features that might affect the "quality"

01-07-2014, 12:49 PM   #5
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Technically the D800's pixel size (?) is about the same as the k-5/D7000 etc. So the k-3 has even smaller pixels. If I remember correctly, there were a few sites that declared the lens resolving limit on APS-C was something like 36 or 45 megapixels.
01-07-2014, 03:01 PM   #6
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QuoteOriginally posted by devouges Quote
I did some reading about how a lens can limit the amount of pixels used in a sensor. Does any kind of information exist regarding pentax lenses and at how many pixels they will be optimal ?
Be aware that a lens' resolving power depends upon the f-number: The larger the f-number (the more the lens is stopped down), the lower the resolution.

For ideal, diffraction-limited lenses the relationship will be:

Resolution on sensor = 2.44 * (wavelength of light) * (f-number).

For example, the wavelength of yellow-green light is some 0,000555 milimeters and any lens at f/2 (f-number = 2) will at best be able just and barely to separate two points of an image formed on the sensor that are separated by 0.0027 mm. At f/4 the points will have to be separated by 0.0054 mm - which is just a bit above the pixel pitches that we see on APS-C sensors today.

Now, as said, this assumes ideal lenses, and no real lenses are only diffraction limited. Further, the two points must have an adequate difference in contrast for the sensor to detect that there is actually a difference. So, indirectly the sensor characteristics come into play as well. And there are more complications involved as well......

Although the following article in Luminous Landscape is nearly 6 years old, I believe (I am NOT an expert) that this is still an accurate description of the situation:

Do Sensors “Outresolve” Lenses?
01-07-2014, 03:37 PM - 2 Likes   #7
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Before everyone goes off on discussions about FF vs APS-c and resolution. I suggest everyone go to the pentax Q forum and legacy lenses on the Q. With a roughly 5.5 crop factor and 10 mp it is a good way to test at least center resolution as the sensor would be equal to a 250MP full frame sensor in its pixel size

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