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12-17-2013, 08:42 AM   #1
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Lens Sharpness -- the Ultimate Criterion

I am new at this hobby, and I have a couple of questions for the more experienced. I noticed that when looking for a lens, it seems that to many people, the ultimate criterion is obtaining a very sharp, or the sharpest lens. It appears that various other lens qualities or deficiencies, such as color rendition, bokeh, aberrations, focusing, contrast, etc. often take a backseat. For example, I will often see posts asking for recommendations for the sharpest lens in a particular focal range, with other lens qualities sometimes not even mentioned, or if they are mentioned, not being nearly as crucial.

Considering all of the qualities associated with a lens, the balance appears to tip clearly in favor of lens sharpness. Has the trend always been like this, or is this a more recent phenomenon? Is this something that is more characteristic of new photographers or amateurs, or is it characteristic of experienced photographers and pros alike? Just curious.

12-17-2013, 08:52 AM   #2
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Well, sharpness is very important. In my opinion it ranks right up there next to colour rendering. What's gone is gone, softness, artistic vignetting, or any other artsy vintage effects can be added in PP afterwards. (In the rare case that it is required.) But you can't add extra sharpness in PP from a soft image.

And yes, this is something that came together with the digital age. In the film days vignetting used to be a very desired feature of a lens. Softness too, you can still find some Pentax lenses around that are intentionally soft. Like the "FA 85 soft".
12-17-2013, 08:59 AM   #3
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Depends on the style or subject. Absolute sharpness is often desired in macro, but is often not desireable in a female facial protrait, for instance. Many will argue that the eyes should be perfectly sharp and facial imperfections (even visible clean pores) can be corrected in post.

I'm no expert but that looks to me the way the excess clarity in cleaned up then "corrected" digital audio sounds. I can't explain it, but I know it.
12-17-2013, 09:01 AM   #4
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Sharpness is easy to measure...the other parameters you mentioned are subjective. One person can say that they like the color or rendition of a lens, the person standing next to him can say he hates it.
Also, you can correct a aberrations, and add contrast in post processing (you can also change the color rendetion in post processing as well to a certain extent).

12-17-2013, 09:13 AM   #5
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As far as the 'sharpness' factor goes - my opinion is that many lenses have a huge difference in sharpness, or relative sharpness.

Eg. My Sigma 18-200mm DC f/3.5-6.3 is nowhere near the sharpest tool in the shed across the image (corners/borders are mush), but in the center its 'not bad'.

If I compare it to my Rokinon 85mm f/1.4 - its as dull as a butter knife. Its not seen at say - 50% - and decent for 5x7 or possibly 8x10.
The Rokinon is sharp on the corners/borders/center - however, using anything faster than say f/4 is very difficult w/o a tripod due to the manual focus.
12-17-2013, 09:13 AM   #6
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Aberrations are funny. Lightroom is so easy with normal CA's it's not an issue for me.

LIghtroom 3 couldn't correct PF so I hated PF. I think Lightroom's better at it now.

Bokeh can't really be fixed. 'Rendering' in theory can, in practice it's a pain in the butt. Sharpness can be improved but only somewhat.
12-17-2013, 09:30 AM   #7
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I genuinely don't think there's any way to really know whether a lens (or a lens design or whatever) is good until you try it yourself. As stated above, natural sharpness does add something to an image, and it's a simple metric by which to gauge a lens, even if it doesn't translate into how you actually like the image.

I think it's something like looking for a car with the biggest engine or the most horsepower or something. It genuinely is useful, to a point, and it's easy and quick to judge by, but realistically there are more important factors that are less noticeable and much more difficult to compare.

Everyone wants objectivity even if it isn't relevant to what they're actually looking for.
12-17-2013, 09:38 AM - 1 Like   #8
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Lenses are like automobiles, everyone thinks they want a Ferrari, but more often than not, the job requires a pickup truck, or a four door family car. Also, a great driver in a pickup can get around the track faster than a normal person in the Ferrari.

Rense Haverman is a skilled, nearly magically gifted photographer. He shot the Single In challenge a couple of months ago with the Holga 60mm f8. That lens is not even as sharp as a sponge, and vignettes something fierce. The absolute antithesis of what a "good" lens is. Yet almost every day, he managed to make a truly special image. You can see his work here. (I hope Rense doesn't mind me linking to his Holga photo collection!). I think his set really exemplifies that sharpness isn't everything.

Monet painted in a style that favored color over "sharpness" if you will, yet his pieces are master-works.

Sharpness is only one aspect of a lens' performance. It is up to the photographer to choose tools that express the right overall look for the image at hand. If you are reproducing flat artwork, then corner sharpness is absolutely paramount. Otherwise, other characteristics can be just as important.

All that said, I do love a sharp lens, but not above all else.

12-17-2013, 09:48 AM   #9
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Here's a nice sharp image for you. (Sigma 8-16)

Heres a not so sharp image. (Pentax 10-17)

They both have their place. I have bought my lenses mostly for sharpness, with the exception of the 10-17 fisheye.

Or this, taken with the Pentax 18-55.

The thing is, while you like sharpness in the first image, the second two images, they would be fine even softer. There isn't a one size fits all lens, you really need them all.
12-17-2013, 10:30 AM   #10
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Oh my - #2 is stunning! Pastoral. I want a hang-able print.
12-17-2013, 11:04 AM   #11

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I used to buy into the argument that sharpness is most important because it's the variable that can't be fixed in post; but years of experience trying to fix low contrast, flat color images in post has taught me otherwise. Since nowadays most lenses are plenty sharp; and since most people can't distinguish, in terms practical output, between a sharp lens and a very sharp lens; since, in short, greater sharpness rarely guarantees that actual images, in the manner in which they are viewed, will look significantly better: for these reasons I have come to regard concerns about sharpness and resolution as being, more often than not, grossly exaggerated. For many types of photography, for many focal ranges, sharpness is not as important as far too many photography enthusiasts make it out to be. (The one major exception to this is photography involving long focal lengths. In such photography, resolution may be more important because (1) many cheaper telephoto lenses aren't in fact "plenty" sharp; and (2) big cropping may be necessary at longer focal lengths for the simple reason that the photographer might not have a lens long enough to properly capture his subject.)

In terms of visual impact, I have found that microcontrast is the most important factor in determing the quality of printed images on visual perception. Microcontrast can be mimiced in PP up to a point (e.g., the clarity slider in Lightroom, adept use of curves, etc.), but only up to a point. A little bit of PP can often improve an image; cranking up contrast, clarity slider, saturation more often than not produces an over-processed mess. A lens with better microcontrast produces a higher quality raw file: and if you start out with a higher quality file, all things being equal, you'll end up with better overall output, particularly in prints. Mike Johnston, who introduced the term bokeh into the English language, explains the relation between resolution, contrast, and MTF charts as follows:

Technically speaking, MTF measures both contrast and resolution more or less simultaneously. In a photographer's reading of an MTF chart, however, generally the position of the topmost lines (typically 10 lp/mm, sometimes 5) will have the highest correlation to visible lens contrast. The lowest set of lines (30 or 40 lp/mm) will correspond best to actual resolving power. Personally, I pretty much ignore the lowest set or sets of lines when reading an MTF chart.
Johnston ignores the lowest set of lines because "resolution of very fine structures seldom helps pictorial photographs much, and, in my opinion, is an overrated property where lens quality is concerned."

Another important element of lens performance, perhaps the most under-rated, is color rendition. While you can make dramatic changes to color in post, making subtle changes that lead to more aesthetic pleasing results is much more difficult. Higher end lenses like the Pentax limiteds are specially designed to produce aesthetically pleasing colors in the camera. They capture subtleties of tone and hue that can rarely be matched in post. You'll never quite match the colors produced by a DA limited or DA* lens with a lens like the DA 18-55, because the raw files from the DA 18-55 don't record the same level of color information.
12-17-2013, 11:07 AM   #12

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After sharpness, what's next? These days I look for other qualities in lenses than sharpness and I'm starting to put that lower on the my priority list when I'm looking for a new lens. Sharp pictures are a dime a dozen these days.
12-17-2013, 12:09 PM   #13

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QuoteOriginally posted by monochrome Quote
Oh my - #2 is stunning! Pastoral. I want a hang-able print.
Ditto! Very nice, Norm. Love it.

Was this de-fished? I hear at the 17mm end, the 10-17 FE isn't terribly distorted, but this just looks plain "wide" and not "fishy" at all to my novice eyes.
12-17-2013, 05:30 PM   #14
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QuoteOriginally posted by filoxophy Quote
Ditto! Very nice, Norm. Love it.

Was this de-fished? I hear at the 17mm end, the 10-17 FE isn't terribly distorted, but this just looks plain "wide" and not "fishy" at all to my novice eyes.
I checked the exif…. 10mm. So here's the thing, some lakes, and this isn't the only one, look better with distortion, depending on the shape of the shore line. Everyone seems to assume that the distortion can ruin a picture, and sometimes it does. Other times it makes it look better. Distortion alters the photo. So it only makes sense that it doesn't always go one way. In this image, the shoreline looks natural, and my wife looks skinny, instead of short and squat like she would if I'd used the "corrected" 8-16. The 10-17 gives you two shots at a natural looking landscape used beside a more corrected lens. We have many images taken with the 10-17 taken in locations where it provided the best image possible for the occasion. We never defish, if I think an image is worth defishing I use the Sigma 8-16… I know people repeat that you can do anything in PP. But the only people I know who have the lenses to do it both ways say it's better off the lens, and PP can never quite match it, no matter what you do.
12-17-2013, 05:57 PM   #15
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The level of sharpness desired depends entirely on the desired image. Between the 1940's and early 1970's, soft lenses sold for a premium. The intended use was portraiture. I remember reading all sorts of articles and 'how-to' guides suggesting methods of artificially softening a lens that was too sharp.

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