Q4kntmare said:
I just purchased a D7200 and while watching videos on camera operation... I heard a comment in which I wanted to get more information about.
The comment was that most camera lenses (kit to be specific) only have the ability to capture 9 megapixels even though the sensor has the ability of 20+. Is this true?
If so, my kit lens from my D80 (AF-S DX Zoom-Nikkor 18-135mm f/3.5-5.6G IF-ED) is useless.
Any thoughts?
Well, that's the way the DxO Mark laboratories test and rank lenses, based on the ability of the lens to transfer a certain pixel count, let's say 24 million pixels, into visibly, usable information. The better the lens, the higher the megapixel rating the lens delivers. For example, take a realllllly good, very expensive lens, like Nikon's 200mm f/2 VR-II Nikkor: the DxO Mark "score" for that lens on the Nikon D800e is 44, and their sharpness measurement is a 34 on their P-MP or Perceptual Megapixel system. I own verison 1 of this lens..it is the best lens I have ever shot. Period. It is the top-ranking lens they tested on the D800e in that lens category. If you have any doubts about how good this lens is, or how extraordinary its performance, rent one, or drop the almost $6k on one. It is
stellar. It is an
extraordinary lens. Nikon's 400/2.8 and 300/2.8 are numbers two and three. I have a Nikon 300/2.8...its optics are stellar. (Another
almost perfect lens is the new Zeiss 135mm f/2 APO).
See the list of lenses for Sports and Wildlife use on the D800e here:
Best telephoto primes and zooms for wildlife | DxOMark
Now let's look at a "similar" lens, in focal length and aperture, the older Nikkor 180mm f/2.8 ED~IF lens, in 14th place: Score is 24, P-MP is 14 megapixels. I own this lens, have had two copies of it, this is about right. It's good, but in no way "stellar", in no way is it "extraordinary". It's good, but nothing remarkable.
Let's go down to the 70-300 VR Nikkor...23 and 13 P-MP...I'd say this is about right. I own this lens. It's okay, but it is in no way "stellar" or "extraordinary.
Generally speaking, the top-level primes (supertelephotos, Zeiss high-dollar primes, a couple of Sigma's newest ART series primes)have very high scores, and have very high Perceptual megapixel ratings. They are damned fine lenses, designed in the modern era, AND they cost a lot of money; these lenses were not designed to be light, small, and affordable; they were instead designed to be GREAT optics, with HIGH performance.
Generally speaking $99 and $109 and $149 kit zooms are low-ranking performers, and they typically deliver only 50 to 70 percent of the sensor's theoretical information delivery because these lenses are low-cost, and designed to be made affordably, and as we move into higher and higher megapixel counts and denser and denser pixel-packing (smaller pixels, very densely packed on the sensor) it becomes imperative that the lens be able to deliver excruciatingly fine detail at very high contrast levels..the MTF or modulation transfer function of a $99 to $149 or even a $299 kit zoom lens is simply NOT good enough to make a dense, 24-MP APS-C sensor show its maximum imaging potential.
We also run into diffraction at very wide f/stops, like f/4.5, on high-MP count sensors. Because diffraction kicks in sooner as sensor MP levels rise, and it hurts resolving power quite a bit, MOST of the kit zooms are already diffraction limited wide-open on high MP-count modern sensors, and
at f/5.6, these lenses are already into diffraction territory. Contrast that with something like the 200 f/2 VR, which is critically sharp wide-open, improves at f/2.2, improves more at f/2.5, and at f/2.8 is so sharp its images look extraordinarily detailed--even on the ancient Nikon D2x. As far as it goes, an extraordinary lens shot on a 12MP sensor looks exceptional, because the lens is delivering almost the absolute theoretical performance potential, with high sharpness, and high contrast, and exceptional micro-contrast. You can NOT test an 18-55mm f/3.5~5.6 lens at f/2 or f/2.2 or f/2.8, like you can the 200/2 VR, where its wide aperture and extreme optical prowess can inflate the resolving ability.
Another way of looking at diffraction is the way I look at it: because of diffraction, and because more in-focus fools the human eye into thinking things are "sharp", almost ANY lens is indistinguisable by normal people when it is shot at f/8. 24-70 AF-S looks like my pet 28-80-D with the plastic mount. At f/8, a $299 lens is as sharp as a $4,999 lens. (Pretty much, to most people, most of the time).
The simple fact is that a LOT of fine pictures can be made with almost any decent, modern lens on a good camera. However, at the extremes of picture-making, such as when you need to crop in and throw away 50% of a frame, the super-performers have a LOT of information in those pixels, while the average to low-grade lenses reveal lens flaws, and poor detail, and only average performance. Additionally, are lens "flaws" chromatic aberration of multiple types, field curvature, coma, poorly corrected spherical aberration, focus shift, and so on--these types of lens imaging faults are well-corrected in the most expensive lenses. The ability to focus the primary wavelengths of light to the same focus point, in a APO or apochromatic lens, leads to much,much sharper images, and this becomes a HUGE issue as the focal lengths approach 200mm, and at 300mm it's critical. Software can mitigate chromatic aberration, and low contrast an be 'fixed' somewhat in software, but the fact is, if the lens has NONE of these bad faults, an image from something like a 200/2 VR is significantly better in every way, than the 55-200 VR zoom is...when compared side-by-side it's noticeable. But that's the thing--pictures are shot with one lens, and shown with whatever they were shot! There is no A/B on a portrait...it will be shot with whatever lens it was shot with, and shown very often alone. So...don't fret. But also--realize that there are poor,average,good,fine,excellent, and superb lenses. Six different levels of performance.
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