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08-10-2010, 08:02 AM   #1
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Is corner sharpness overrated?

I just finished a four day dance event at which I was the primary photographer, and have edited down my shots and the shots of another photographer into a slide show. In the process, I looked quite closely at the shots of the other photographer, who used a Rebel XTi and a Canon 18-135mm lens. (I used three Pentax digital bodies, mostly primes, plus the DA12-24, 17-70 and 55-300 ).

The Canon 18-135 was not a favorite of the Photozone crew, with rather bad corner sharpness results. However, I found that the very few times where lousy corner sharpness made a real difference in my choice not to include a shot in the show were balanced out by times when it actually enhanced the shot. The center sharpness of this lens was much more than adequate, even indoors.

This is an oft-asked question around here, but I wonder if we don't obsess just a bit too much about the corner pixels. Simple works pretty darn well.

08-10-2010, 08:14 AM   #2
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It all depends on the subject. If you are primarily taking pictures of small to medium size subjects -- i.e., people, critter, flowers, etc. -- corner sharps generally is not needed, and is often a flaw, since you want to isolate the subject. If you taking pictures of very large objects, such as buildings, or landscapes, corner sharpness may be highly desirable.
08-10-2010, 08:19 AM   #3
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QuoteOriginally posted by northcoastgreg Quote
It all depends on the subject. If you are primarily taking pictures of small to medium size subjects -- i.e., people, critter, flowers, etc. -- corner sharps generally is not needed, and is often a flaw, since you want to isolate the subject. If you taking pictures of very large objects, such as buildings, or landscapes, corner sharpness may be highly desirable.
Absolutely. Perhaps I should revise my question to say corner sharpness at wider apertures. Most of these lenses sharpen up very nicely at F8 and below, where landscapes usually live. Like the Pentax kit lens or the superzoom, the Canon snapped nicely across the field of view used outdoors at smaller apertures.
08-10-2010, 08:20 AM   #4
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It depends what you're shooting. Dance shots will typically have one main subject (the dancers) more or less centered. So corner sharpness is a non-issue.

For architecture, landscapes, sometimes for macro, and for anything using creative composition, corner sharpness becomes important.

08-10-2010, 08:23 AM   #5
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QuoteOriginally posted by bdery Quote
It depends what you're shooting. Dance shots will typically have one main subject (the dancers) more or less centered. So corner sharpness is a non-issue.

For architecture, landscapes, sometimes for macro, and for anything using creative composition, corner sharpness becomes important.
True. People shots in general (other than large groups) are probably the least challenging for corner-challenged lenses.
08-10-2010, 08:31 AM   #6
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It depends on what you shoot. At F2-F2.8 the extreme corners/borders will most likely be in the "bokeh" anyway. Sometimes "weak" corners can make the pic look sharper in the centre. I know that some people prefer center to border sharpness and weaken the borders in PP, but I think the result is better when it's done "naturally" by the lens itself.

I prefer to have two lenses for each FL: 1. A slow lens with even sharpness for landscapes and general purpose (such as the K 35mm F3.5). 2. A fast lens with high centre sharpness for low light bokeh-shots/portraits (such as the M 28mm F2).

Kind regards
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08-10-2010, 08:33 AM - 1 Like   #7
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QuoteOriginally posted by GeneV Quote
I wonder if we don't obsess just a bit too much about the corner pixels.
That, and everything else.
08-10-2010, 08:39 AM   #8
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I do wish someone would make a high-quality lens in this range for Pentax. I would fault Canon for making a lens without the range of the Pentax/Tamron 18-250, but with about the same size and performance. The same is true of the tests of the Sigma lens in this range. It seems to me that this FL range could be improved to be the superzoom for the pixel obsessed.

08-10-2010, 08:54 AM   #9
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QuoteOriginally posted by GeneV Quote
I do wish someone would make a high-quality lens in this range for Pentax. I would fault Canon for making a lens without the range of the Pentax/Tamron 18-250, but with about the same size and performance. The same is true of the tests of the Sigma lens in this range. It seems to me that this FL range could be improved to be the superzoom for the pixel obsessed.
Totally agree with you on this. A really good 18-135 would be a perfect one-lens solution for travel or other space-restricted situations. I would even be happy with a little less reach than that if that's what it took to get the IQ up to snuff.

As far as corner sharpness in general, I can't help but be reminded of the Sigma 30/1.4. It gets slammed for its corner sharpness all the time, but, aside from this being an exaggerated issue, that is an excellent lens for shooting people. In fact, it's one of the best for shooting people indoors with no flash. Horses for courses, as they say.
08-10-2010, 10:05 AM   #10
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QuoteOriginally posted by GeneV Quote
I do wish someone would make a high-quality lens in this range for Pentax. I would fault Canon for making a lens without the range of the Pentax/Tamron 18-250, but with about the same size and performance. The same is true of the tests of the Sigma lens in this range. It seems to me that this FL range could be improved to be the superzoom for the pixel obsessed.
You really hit the nail on the head. I gave my K10 and Tamron 18-250 to my nephew recently. Great guy and i'm glad i did it, but i miss the lens :-)

The long tele end of the lens was not very good, reportedly, but dang i've sold enough framed images from that super zoom lens, mostly in the range of 50 to 135 to pay for it twice over. These were ones i usually took on a tripod, but not always. I stopped using it much because of its slowness.

I have the Pentax 50-135 and love it, but if they came out with a 18-135 F4 or better tomorrow, i would buy it immediately.

Last edited by philbaum; 08-10-2010 at 10:19 AM.
08-10-2010, 10:46 AM   #11
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I'll shout that THE EDGES AND CORNERS DON'T K*CKING MATTER. If viewers are looking at edges and corners, then the subject isn't compelling enough... unless the subject EXTENDS to edges and corners. In which case, back up (or zoom out) a little, shoot, and crop.
08-10-2010, 11:59 AM   #12
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I find that a high-quality 17-70 gets the job done pretty well for travel. You can crop from 70 to "135" quite easily, and it's easier to make a good lens with a smaller range.

Sigma used to make a 18-125 but it was not a fantastic lens. None of the superzooms are.
08-10-2010, 05:12 PM   #13
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QuoteOriginally posted by bdery Quote
I find that a high-quality 17-70 gets the job done pretty well for travel. You can crop from 70 to "135" quite easily, and it's easier to make a good lens with a smaller range.

Sigma used to make a 18-125 but it was not a fantastic lens. None of the superzooms are.
I also use my DA17-70 as a one-lens solution, but its long end, while good, is not really up to heavy cropping at wide apertures.

I've looked at the Sigma, and its results are not up to the Canon (which Photozone is careful to say is not a "good" lens). I just don't see why a 7x zoom can't be made with significantly better IQ than a 14x zoom.
08-10-2010, 06:36 PM   #14
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I guess I don't see why you wouldn't want a lens that was sharp edge to edge. Sure, it probably isn't the most important part of the photo and you can always crop the corners out if it is too bad, but I guess I would still choose a lens that was sharp edge to edge and add vignetting in post processing if I thought it enhanced the photo.
08-10-2010, 08:47 PM   #15
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QuoteOriginally posted by Rondec Quote
I guess I don't see why you wouldn't want a lens that was sharp edge to edge. Sure, it probably isn't the most important part of the photo and you can always crop the corners out if it is too bad, but I guess I would still choose a lens that was sharp edge to edge and add vignetting in post processing if I thought it enhanced the photo.
All things being equal, sure, I'd rather have a lens capable of corner to corner sharpness. I titled the thread "overrated" not "undesirable." That's sort of what I had hoped to see in a 7x over a 14x zoom.

I was just a little surprised, as I was when I recently revisited the kit lens, at how seldom it does make a big difference.
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