sharpness - Are superzoom lenses really so bad?

I have read comments in multiple places, both on photo.SE and elsewhere, that superzoom lenses are not good and that most people will be better served by buying two zoom lenses, each spanning a smaller zoom range.

Specifically, I own the Sony NEX-5R, with the 35mm Sony F1.8 and the 19mm Sigma F2.8. I'm trying to decide whether to buy a superzoom lens, specifically, the Sony 18-200, as opposed to a non-superzoom lens like the Sony 16-50 or the Sony 18-105.

From DXOMark, the 18-200 has a perceptual megapixel score of 5 megapixels, while the 16-50 has a score of 7 megapixels. This seems like a small difference. Why do superzooms have a bad reputation? For comparison, the 35mm prime has a score of 11 megapixels.

Even 5 megapixels is not a significantly higher resolution than my 15-inch Retina Macbook Pro (5.05 megapixels) or my 30 inch monitor (3.9 megapixels). So it looks like I'm not going to notice the supposedly worse performance of the superzoom. I don't pixel-peep or print out my photos.

Note that I'm not looking for the Nth degree of optical performance here. I wouldn't pay hundreds of dollars for a small difference in performance (F1.4 vs F1.8, for example), or inconvenience myself by carrying and changing between two zoom lenses instead of one superzoom lens, if the differences were not visible to most people.

Is this analysis and conclusion correct?

Answer

I'm going to go all contrarian here. That is, against the protestations of photographic craftsmen, and against my own nature, I have to say that the value of a lens, any lens, lies not in its absolute, measurable qualities, but in what it does for your photography. And that means that the ends and aims of the photographer matter when deciding whether or not a particular lens is "good enough".

That 5MP sounds horrible to a lot of us. (So does the 7MP of the 16-50.) But it's enough for a good 6" x 9" print or a very acceptable 7-1/2" x 11-1/4" by anybody's standards. You can get away with a larger print if it's going to be viewed from anything more than arms' length. It' certainly good enough for a 1080P screen, and you'd need to pay close attention to notice anything amiss on a 4K screen. And those are pretty hard limits — the option to print large on glossy or lustre paper and examine your work close-up, filling your insides with a warm sense of pride in a job well done isn't quite there. For most of the people wrapped up in photography as a serious hobby (or, often, as a business), that sours things quite a bit.

The fact remains, though, that these "horrible" lenses can be perfectly adequate for a lot of people's ordinary use cases. You can shoot for the screen; you can shoot for the book-sized print (six by nines on twelve-inch-square pages is a lovely format); you can shoot for the larger canvas print (where minute detail is going to be lost in the texture of the ground anyway). And, you know, that's sometimes good enough. (Unless things have changed in the last couple of weeks, National Geographic still has a 6MP minimum standard. It's not that they don't want larger files, but that 6MP is good enough for a double gatefold at their format, provided that there are no other problems with the picture.)

So, yes — the lens is a horrible one. It causes you to "waste" precious pixels. And that matters if you had any plans to use all of those pixels. But if you're shooting to share online, shooting for the web, shooting for an album — basically, if you're not shooting for gallery prints or display ads and have no plans to expose yourself to gearheads online — and the lens allows you to go places and take pictures, then it's probably good enough. And coupled with the NEX 6, it's a lot better than the compact superzoom alternative.