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Lenses Better Than Cheapies?
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There is an understandable feeling of expectation on the part of consumers that the expensive lenses perform "better" than their cheaper counterparts. But that is a fallacy not well understood by many people. In our digital dark room today, the image quality of the optical lens is easily - and far more critically - scrutinized by a few clicks of zoom-in buttons. That's why the manufactures are forced to pay much more attention to the image quality of their camera systems in general, and their lenses in particular. This is one of the main reasons behind new lines of lenses specifically designed (or re-designed) for digital photography.
Here is an interesting article (from Digi-Came Watch) about two Nikkor zoom lenses, both of which are new digital-age lenses for their Nikon DX-format DSLR cameras. The article compares AF-S DX Zoom Nikkor ED 17～55mm F2.8G ($1400) and AF-S DX Zoom Nikkor ED 18～55mm F3.5～5.6G ($170). The latter is the newer lens, initially offered as the Nikon D50 lens kit. The lens quality comparison was done on these lenses using a 12 megapixel Nikon D2x camera. The test result shows that at F11 aperture the 18-55mm F3.5-5.6 lens performed better - appreciably better - than the 17-55mm F2.8 lens, in terms of various aberration corrections and general sharpness. Even the author of the article was somewhat surprised by his own finding. After all, the 17-55mm F2.8, besides being far bulkier and heavier, and looking much more impressive, is almost 10 times the 18-55mm F3.5-5.6 lens in price.
Nikon lens site with MTF chart: http://www.nikon-image.com/jpn/products/lens/dx/zoom/af-s_dx_ed_17-55mmf28g_if.htm in English
Nikon lens site with MTF chart: http://www.nikon-image.com/jpn/products/lens/dx/zoom/af-s_dx_ed_18-55mmf35-56g.htm in English
What is the difference between these two lenses? The lens speed. If you make a lens, let alone a zoom lens, having the same focal length, but with the increase of lens aperture from F5.6 to F2.8, obviously the lens gets much bulkier, heavier, and of course, more expensive. Everything is coming from the bright lens aperture.
When you test the lens quality of the lenses having different apertures, how do you compare? Our cheaper lens does not have a F2.8. We have to use the common denominators; say, F5.6, F8, F11, and so on. The test result may go either way. The more expensive lens may perform better, or the cheaper one can outperform the more costly lens at some apertures, as the case may be. But even if the faster speed lens costing many times more is defeated by the less expensive, slower speed lens, the result should not surprise you. The faster lens is more expensive because of its needing bigger glasses. Again, this will increase the size, weight, as well as manufacturing cost. You are paying for the speed of the lens. You brought a F2.8 lens because you needed one. The other lens has only F3.5 at 18mm and F5.6 at 55mm! You did not have any choice.
If you are planning to use the lens at F11, and if you have a choice between a faster speed lens (expensive) and a somewhat slower lens (cheaper), which lens would give you the better result? There is no general answer. It depends on the brand and the specific combination of the lenses you are comparing. However, you can make one general observation on this. Letís suppose the two design teams are competing against each other to make a zoom lens to see whose lens performs sharper at F11. The focal length range is the same 18-55mm. However, Team A was told to make the aperture F2.8 while Team B is allowed to make a slower F5.6 lens. Obviously Team A that received the tougher requirement of F2.8 is at a serious disadvantage, giving Team B a better chance of producing a lens that outperforms at F11.
There may be a different reason people buy a $1400 AF-S DX Zoom Nikkor ED 17～55mm F2.8G over a $170 AF-S DX Zoom Nikkor ED 18～55mm F3.5～5.6G. This may include 1) impressing other photographers. Or, 2) holding this heavy lens all day will certainly build your muscle. Or, 3) you may need a fast F2.8 aperture for a brighter viewfinder image or a faster auto-focus operation. Or, 4) you may even actually want to shoot at F2.8, like a pro.
So, as a concluding remark, if you bought an expensive F2.8 lens and it did not perform as well at F11 compared with a cheaper F5.6 lens, it should not surprise you; it should not disappoint you, either. Because, after all, you did get what you paid for Ė a bright F2.8 aperture!
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