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  1. #1
    Join Date
    Mar 2007
    Posts
    2,132

    Post 18-55 vs 18-200 Sharpness Test

    I took a little time the past couple of days to do some testing. My initial setup looked something like the author of this website's ISO tests, with various spices and jars with good, readable text in a well-lit kitchen. While that was good, it wasn't the best to test sharpness between lenses, so I came up with something better.

    A pure text test. I made a document in landscape orientation, filled with text in Justified alignment so all edges were evenly covered. This would be the perfect way to show the sharpness of a lens over the entire image, and will bring out the best (or worst, as we are about to see) in any lens.

    I did not have perfectly controlled lighting so White Balance and Exposure were corrected, otherwise no post processing was done. They were resized so I could fit them onto my Photobucket for sharing purposes (1Mb file limit) but were still kept large, at 1793x1200. They were resized using regular Bicubic - not sharper, or smoother as not to alter the image.

    The following images speak for themselves but I will provide an analysis at the end for those who don't wish to review them.


    18mm
    18-55 VR - http://i90.photobucket.com/albums/k2...8-55VR18mm.jpg
    18-200 VR - http://i90.photobucket.com/albums/k2...-200VR18mm.jpg

    24mm
    18-55 VR - http://i90.photobucket.com/albums/k2...8-55VR24mm.jpg
    18-200 VR - http://i90.photobucket.com/albums/k2...-200VR24mm.jpg

    35mm
    18-55 VR - http://i90.photobucket.com/albums/k2...8-55VR35mm.jpg
    18-200 VR - http://i90.photobucket.com/albums/k2...-200VR35mm.jpg

    55mm
    18-55 VR - http://i90.photobucket.com/albums/k2...8-55VR55mm.jpg
    18-200 VR - http://i90.photobucket.com/albums/k2...-200VR55mm.jpg

    105mm
    18-200 VR - http://i90.photobucket.com/albums/k2...200VR105mm.jpg

    170mm
    18-200 VR - http://i90.photobucket.com/albums/k2...200VR170mm.jpg

    200mm
    18-200 VR - http://i90.photobucket.com/albums/k2...200VR200mm.jpg

    Center sharpness is good to very good for both lenses. Color and contrast are equal.

    Aside from your expected barrel distortions at the wide end, the main problem that comes into play here is corner sharpness, or the lack thereof. More like, corner blurriness. As you can see especially at 35mm and 55mm for the 18-200 lens, the edges are completely unacceptable. The problem does seem to pretty much correct itself after 100mm though. The 18-55, often referred to as the "kit lens" clearly outperforms the much more expensive 18-200. The 18-55 VR is what I would call "sharp to the edges". Now it could be that I have a bad lens - I am not sure how to tell as its an otherwise excellent lens. I like everything about it:

    -Size, perfect to get your left hand under it for support
    -Manual focus ring that doesn't turn itself
    -Distance scale for focus
    -Much faster focusing than the 18-55 VR
    -Much quieter focusing compared to the 18-55 VR
    -Nothing protrudes or turns on the outside of the lens as everything except the zoom is internal
    -Rubber gasket on the body-end for sealing

    Now you could crop off the corners of all your pictures with this lens...but you shouldn't have to. Otherwise you'll have to live with the downfalls. Note that this was at the automatically selected "max aperture" for each focal length. I am now going to attempt to stop down the lens a bit to see if those blurry corners improve and will post those shortly.
    Last edited by Visual Reality; 04-20-2008 at 01:40 PM.
    Nikon D300 | Tamron 17-50mm f/2.8 | Nikkor AF-S 70-300mm VR | Nikkor AF 35mm f/2 D | SB-600 | Lowepro Voyager C | Lowepro Slingshot 300 AW

    For Sale:
    Nikkor AF 35mm f/2 D - Like New (FX compatible)

    Wish List
    Nikkor AF-S 17-55 f/2.8
    Nikkor AF-S 70-200 f/4 VRII
    Tokina AF 11-16 f/2.8
    SB-900 (2)
    Umbrellas
    New Tripod

  2. #2
    Join Date
    Jan 2006
    Location
    Delfgauw, The Netherlands
    Posts
    2,207
    The difference between the two is indeed pretty big. I don't think it is caused by a bat sample of the 18-200, as the center seems pretty sharp and corners on either side seem to be equally blurring (ruling out a decentering issue).

    I think what you see here may be caused by field curvature; in other words, the plane which is in focus is not flat, but curved. The result of this is that the corners will seem very blurry.
    Field curvature occurs mostly at shorter focal lengths and closer focussing distances (like in this test). In cheaper lenses or superzooms the phenomenom is more common.

    My guess is that if you were to do this test with, say, a brick wall shot at a larger distance, the performance of the 18-200 should improve drastically.

    You should remember, though, that it is a superzoom; compromises have been made too give it such a large zoom range. While it may be much more expensive than the 18-55 VR, this does not mean it will outperform it.
    Nikon D-50
    // Nikkor 70-300 f/4-5.6 VR // Nikkor 50 mm f/1.8
    // Sigma 17-70 f/2.8-4.5 ...// Nikon SB-600
    // Sigma 10-20 f/4-5.6......// Nikon Series E 135 mm f/2.8
    // Kiron 105 f/2.8 Macro....// Manfrotto 190XPROB + 488RC4
    // Nikkor 35 f/1.8..........// Sigma 500 mm f/8

    My website: http://www.dennisdolkens.nl

  3. #3
    Join Date
    Mar 2007
    Posts
    2,132

    Thumbs up

    There never was the expectation that it would outperform in IQ, so I am not overly disappointed. I am uploading the next batch now and my findings are good. The edges do improve when stopped down. Now with that in mind, and taking what you say about longer focus distances, photographs in which sharpness from edge to edge is critical should be fine - landscapes or any other long distance, large DoF stopped down aperture type of shot come to mind. Hopefully the problem is mostly isolated to close to medium range subjects. I have yet to test that and I don't have a great method of doing so, but the resolution tests online seem positive at 18-24mm at small apertures.

    Here are the results:

    18-200 VR

    35mm


    f/6.3 - http://i90.photobucket.com/albums/k2...0VR35mmf63.jpg
    f/7.1 - http://i90.photobucket.com/albums/k2...0VR35mmf71.jpg
    f/8 - http://i90.photobucket.com/albums/k2...00VR35mmf8.jpg
    f/9 - http://i90.photobucket.com/albums/k2...00VR35mmf9.jpg
    f/10 - http://i90.photobucket.com/albums/k2...0VR35mmf10.jpg

    55mm

    f/6.3 - http://i90.photobucket.com/albums/k2...0VR55mmf63.jpg
    f/7.1 - http://i90.photobucket.com/albums/k2...0VR55mmf71.jpg
    f/8 - http://i90.photobucket.com/albums/k2...00VR55mmf8.jpg
    f/9 - http://i90.photobucket.com/albums/k2...00VR55mmf9.jpg
    f/10 - http://i90.photobucket.com/albums/k2...0VR55mmf10.jpg

    This tells me two things, so far. First, the problems you will have with this lens are when shooting at max aperture when you need your picture sharp from corner to corner. It just isn't going to happen. Second, the OOF (out of focus) "bokeh" is average at best. It is definetely there after 100mm, but even at 200mm its still somewhat harsh.

    If you keep these things in mind, you will know how to avoid its weaknesses and exploit what it does best - get you two lenses in one nice package.
    Last edited by Visual Reality; 04-20-2008 at 02:56 PM.
    Nikon D300 | Tamron 17-50mm f/2.8 | Nikkor AF-S 70-300mm VR | Nikkor AF 35mm f/2 D | SB-600 | Lowepro Voyager C | Lowepro Slingshot 300 AW

    For Sale:
    Nikkor AF 35mm f/2 D - Like New (FX compatible)

    Wish List
    Nikkor AF-S 17-55 f/2.8
    Nikkor AF-S 70-200 f/4 VRII
    Tokina AF 11-16 f/2.8
    SB-900 (2)
    Umbrellas
    New Tripod

  4. #4
    Join Date
    Dec 2006
    Location
    God's Country - Australia
    Posts
    10,424
    excellent. thanks for taking the time.
    D800e l V3 l AW1 l 16-35 l 35 l 50 l 85 l 105 l EM1 l 7.5 l 12-40 l 14 l 17 l 25 l 45 l 60 l 75
    flickr

  5. #5
    Join Date
    Mar 2007
    Posts
    2,132
    http://www.vanwalree.com/optics/astigmatism.html

    Mostly the last paragraph applies:
    A trusty method to mitigate image impairment by astigmatism and field curvature is to stop down the lens. The curved S and T surfaces themselves are not affected by the F- number, but the proportions of the blur at the position of the sensor will decrease. Or, differently phrased, the increased depth of focus helps to mask the worse effects. Of course, the Planar 1.4/50 is not designed for use in the macro regime. A far more elegant solution to overcome field curvature is found in the use of a dedicated macro lens. Such lenses are aberration-corrected for use at close range, including astigmatism, field curvature and distortion to enable copying work. Yet another remedy is the use of floating elements in the lens design. Floating elements (the differential movement of one or more lens groups) expand the working range of a lens by controlling aberrations over an extended range of object distances. Short-focus lenses for SLR's with floating elements are more expensive than their unit-focus competitors, but the performance gain at close range can be truly remarkable. Just keep in mind that floating elements are only instrumental when the lens is focussed by means of its focussing ring. Elements do not float with added extensions.
    This is basically a detailed explanation of what Prospero was saying. You learn something new every day

    I now know that I absolutely hate Field Curvature...
    Last edited by Visual Reality; 04-21-2008 at 08:02 PM.
    Nikon D300 | Tamron 17-50mm f/2.8 | Nikkor AF-S 70-300mm VR | Nikkor AF 35mm f/2 D | SB-600 | Lowepro Voyager C | Lowepro Slingshot 300 AW

    For Sale:
    Nikkor AF 35mm f/2 D - Like New (FX compatible)

    Wish List
    Nikkor AF-S 17-55 f/2.8
    Nikkor AF-S 70-200 f/4 VRII
    Tokina AF 11-16 f/2.8
    SB-900 (2)
    Umbrellas
    New Tripod

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