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Old Apr 24, 2004, 5:12 PM   #1
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Default single element vs. doublet close-up lenses [text & pix]

People argued here and on other boards about a simple question: Do those doublets close-up lenses perform better than those cheap single element close-up lenses? The answer seems an obvious YES. However, the argument boils down to a simple fact that for daily casual shooting the single element close-up lenses suffice. As you can expect, many would disagree. So, a friend of mine asked me to see if I can show an obvious result to prove or disprove this claim. It is a difficult task because many images were shot and resized and image defects are also reduced. However, there is one way to magnify the defect of a close-up lens: the use of a high power monoscope. Even though this monoscope may not have very high resolution, its magnifying power will enlarge all sorts of problems of the close-up lenses.

Among a number of monoscopes, the EagleEye 5X is by far the sharpest. See my Coolpix 4500 user guide for some details. Hence, I mount a EagleEye on a Coolpix 4500. Then, I took two images, one with a cheap single element Tiffen +4 close-up lens and the other with a high quality Nikon #6T +2.9 close-up lens. The following image shows the result of the Tiffen's. Its coverage is approximately 8mm×10.7mm with a magnification about 0.66X, which is slightly larger than 4500's 0.43X.

The following image shows the result of Nikon #6T +2.9. The coverage is about 10.5mm×14mm with a magnification of 0.51X, which is smaller than that of the +4 Tiffen but is slightly larger than the 4500!

I tried to apply the same amount of level and USM to both to keep my comparison fair. It is clear that the Tiffen +4 single element close-up lens performs much worse than the high quality doublet Nikon #6T. To convince you, the following is the 100% crop of the left eye from the Tiffen +4 image. Note no in-camera sharpening was applied to the image.

And, this one is from the #6T lens:

The Tiffen +4 is soft, and chromatic aberration in the form of purple and green fringes (near the corners) are obvious. One may suggest that I should use a small aperture to reduce chromatic aberration. Yes, I did. Both images were take with aperture F9.1!

While the EagleEye 5X may have amplified the problems too much and/or introduce its own problems, that the image quality of the #6T is better than a single element Tiffen +4 is so obvious. in daily casual shooting, if you do not print large images, you may not see these deficiencies. However, once you print large images, the printing process will "enlarge" your image and all deficiencies of a poor single element close-up lenses. No, I am not promoting expensive doublet close-up lenses; but, I wish my experiment can tell you something.

If you are interested in the way of computing the magnification of a lens, check this page which will be online soon:

Nikon Coolpix 950/990/995/2500/4500/5700 User Guide
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