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The term "purple fringing" is commonly used in photography to describe chromatic abberations (CA). In optical design, chromatic aberration (CA) is caused by a lens having a different refractive index for different wavelengths of light (the dispersion of the lens). Longitudinal and lateral chromatic aberration of a lens is seen as "fringes" of color around the image, because each color in the optical spectrum cannot be focused at a single common point on the optical axis. The crops on the right are taken from our CA image sample test while viewed at 200%. |
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In this shot taken at full wide angle, looking at the highlight reflected area near the edges of the chimney, the Nikon AF-S DX 18-55mm exhibits a hint of "purple fringing" compared to the other three lenses, although this is something that would be hard to notice in a normal print. In general, we found that all the lenses performed well in our image sample tests with respect to controlling chromatic abberation. A compliment to Nikon's ED (Extra Low Dispersion) glass which is designed to correct for and minimize CA's and is incorporated in all of the Nikkor DX lenses that we tested. |
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After comparing and testing these Nikon DX wide angle zoom lenses over a period of a couple of weeks, we had the opportunity to see how well these lenses handled in terms of both ergonomics and performance.
With respect to the general feel and design, in our opinion the Nikkor AF-S DX 18-70mm and the AF-S DX VR 18-200mm deliver the best experience. Both feel very nice and solid (more metal) and this higher quality of construction contributes to the increased cost of these lenses compared to both the Nikon AF-S DX 18-55mm and the AF-S DX 18-135mm.
The Nikon AF-S DX 18-55mm and the Nikon AF-S DX 18-135mm zoom have the advantage of being lighter due to their polycarbonate body construction. The Nikkor AF-S DX 18-55mm zoom is also quite a bit smaller than the other lenses (52mm filter diameter).
All of the lenses that we tested focused quickly and quietly based on what we would expect from consumer oriented (non Pro) lenses. The AF-S DX 18-55mm f/3.5-5.6G ED II was a little louder than the others although as far as we are concerned nothing to complain about for an entry level lens.
If you like to occasionally manually focus your lens, we found that the Nikkor AF-S DX 18-70mm f/3.5-4.5G IF-ED offered the best solution with its larger and more comfortably placed focus ring.
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Sharpness
We were actually quite surprised to see from our sample image comparison tests how close these four lenses performed in terms of sharpness. We found it difficult to distinguish a big difference in sharpness between the lenses that we tested when looking at 8" x 10" prints from a normal viewing distance. The AF-S DX 18-70mm and the AF-S DX VR 18-200mm lens offered very good results however, both the entry level AF-S DX 18-55mm and AF-S DX 18-135mm IF-ED zoom impressed us considering the value for the dollar that they deliver.
As we have already said, you have to print quite large prints to really notice the difference between these lenses. If you need to be able to produce 16" x 20" prints and beyond on a regular basis then you might want to consider the AF-S DX 18-70mm f/3.5-4.5G IF-ED zoom and complement with the Nikon AF-S 70-300mm VR to get the extra telephoto range.
One thing to take into consideration when looking at our image sample comparison tests is that with digital photography it is easy to enlarge the image on screen once it has been downloaded to your computer. This can magnify small errors in Auto Focus that would otherwise not be as noticeable when viewed at a more traditional print size.
For example, imagine looking at an image taken with 6 megapixel digital SLR on a 17 inch SXGA monitor (1280x1024) from a distance of 16-20 inches away. Under these conditions, the size of the image displayed on the monitor is approximately equivalent to a 32 in. x 21 in. print size viewed at the same distance. In this case any slight errors in AF are magnified many times over on the monitor when in reality they are less likely to be visible when the image is printed.
Distortion
With both the Nikon AF-S DX 18-135mm f3.5-5.6G IF-ED and the Nikon AF-S DX VR 18-200mm f/3.5-5.6G IF-ED zoom we noticed slight pincushion distortion at the upper telephoto end, and minor barrel distortion at the wider end. The Nikon AF-S DX 18-55mm f/3.5-5.6G showed slightly greater barrel distortion at the wide end and some minor effects at the tele end. All in all though, we feel that our four Nikon test lenses handled distortion quite well.
Vignetting (Darker Corners)
Most lenses exhibit vignetting to some degree (unintended darkening of the corners in an image). The effect is usually most noticeable when the lens is shot wide open and gradually disappears as the lens is stopped down.
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We found that all four of the lenses performed well in terms of keeping vignetting to a minimum in our sample tests. We did notice that the AF-S DX VR 18-200mm zoom and AF-S DX 18-55mm ED II showed more vignetting compared to the other lenses when shooting at wide angle with the lens set wide open at f/3.5. An example of this can be seen in the image on the right (illuminated light table as the subject). By the time we stopped down the lens to an aperture of f/8 however, we found that the effect was pretty much gone. |
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Aspect ratio
Even if you end up wih an image that shows some vignetting, if you print an 8"x10" or 11"x14" enlargement any light fall off will not be as visable since the darker corners are cropped out in the final print.
One thing to remember is that your digital negative is recorded in a 2 x 3 ratio format. Generally when printing enlargements most users tend to go with standard available print sizes like 5"x7", 8"x10" and 11"x14". What this means is that at many typical print sizes a part of your image area will be cropped, and image inperfections in the corners will not be as likely to be seen in the final print.
The illustrations below
show how much of the area will be lost (bounded in grey), with the green
tinted area reflecting the actual portion of the image that will be seen
in the photo once printed.
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Actual
Image Area
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When
printed as a 5 "x 7" (Green area)
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8" x 10" or a 11" x 14" print aspect size
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Likewise, were we saw that both the Nikon AF-S DX 18-135mm f/3.5-5.6G and the AF-S DX VR 18-200mm f/3.5-5.6G exhibited greater corner softness when shooting at wide angle with a near or wide open aperture, the soft corner effect will be less noticeable in the final image when it is cropped to fit one of these print sizes.
Zoom Creep (Barrel Drop)
Some users have reported that when shooting with the Nikon AF-S DX VR 18-200mm f/3.5-5.6G IF-ED zoom lens pointing in a downwards position, the lens will sometimes "creep" (slide) from its set focal length position if you are not holding the barrel.
We understand from Nikon that with the weight and number of glass elements in this lens, some potential zoom creep is unavoidable without having to design an even larger and heavier (more costly) lens.
From our experience with our test lens we found the issue related more to the 24mm - 70mm focal range. Set at 18mm or 200mm the lens did not seem to move. When set to 24mm and while sitting on a tripod the lens barrel started to slowely slide when we pointed the camera and lens towards the floor.
If you are out there all day taking close up pictures of flowers from above you might want to consider one of the other Nikon DX zoom lens options. For most photographers, when you consider the many other benefits of this lens, this is probably not as much an issue.
Recommendations
For many customers buying into a digital SLR camera, a standard kit lens like the AF-S DX 18-55mm f/3.5-5.6G ED II is an attractive option based on price point. In family oriented picture taking situations this is also often all that is really needed.
If you are a more avid photographer, the AF-S DX 18-135mm f/3.5-5.6G is a nice solution that offers considerably greater telephoto zoom power than the basic 18-55mm kit lens. It is also considerably less expensive than the AF-S DX VR 18-200mm IF-ED zoom, and still serves as an effective all in one lens solution for most applications.
For those wanting durability and the best overall consistency of image quality we would recommend the AF-S DX 18-70mm f/3.5-4.5G IF-ED zoom. The thing to consider if you buy this lens is that you would probably want to complement it with a longer zoom lens like the AF-S VR 70-300mm f/4-5.6G IF-ED or the Nikon AF-S VR 70-200mm f/2.8G IF-ED.
The AF-S DX VR 18-200mm f/3.5-5.6G IF-ED zoom is an ideal all in one lens solution, and offers solid construction with very good image quality considering the extreme focal range covered.
The Vibration Reduction II technology works well and will allow you to hand hold the lens while shooting at up to 4 stops slower than would be possible with a regular non VR lens. A great travel companion that will save you from being burdened with having to carry two lenses around to cover the same focal range.
See
related products:
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Nikon
DX Wide Angle Zoom Lens Comparison Test: Nikkor
DX Zooms
Versus 50mm f/1.8D Prime Lens |
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Nikon
DX Wide Angle Zoom
Test Optical Characteristics and Conclusion |
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