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Nikon T-series close-up lenses
A lens that works like a filter
by justin 09:01PM Thursday Oct 20 2005 Tipped by climbers See Profile
Nikon T-series close-up lenses screw on to your camera like filters, and are an inexpensive, simple, and lightweight way to increase the close-up and macro capabilities of most camera systems.

If there is any camera gear near and dear to my heart, it's my Nikon close-up lenses. I used them with my first digital camera, the Olympus C-2100UZ, and use them with my current Minolta DiMAGE A1. I'm sure they'll be used with my next camera, too. They are the least expensive, easiest way to improve a fixed-lens camera's macro ability.

A good question you might have is, "My camera already has a built-in macro mode, why should I fool with these?" This, and a lot of other questions will be answered in the rest of this review.

They come in two thread sizes:
•52 mm for the Nikon 3T & 4T
•62 mm for the Nikon 5T & 6T

There are two strengths:
•+1.5 diopters for the 3T & 5T
•+2.9 diopters for the 4T & 6T

Sometimes you'll see the 4T and 6T listed as +3 diopters; that isn't correct according to Nikon's own literature. Some people just round-up to make computations easier.

At the time this review is being written, the 3T and 4T cost about $35 each; the 5T and 6T are around $50 each. Similar lenses offered by other companies are 2 to 3 times costlier.

Background information

This is a review, not a technical explanation of photographic optics, but a little background information will help show why they should be considered as an addition to any macrophotographer's bag. First, although this review is mostly about using these filter's with fixed-lens cameras, they are certainly not limited to those. Close-up lenses have no idea what kind of camera or sensor you are using! Screw-on, close-up supplementary lenses were originally designed for film cameras. They can be used with film cameras, digital SLRs, camcorders, or anything else that has a lens system.

Don't confuse the Nikon T-series with the $29.95 set of three you may have picked up when you bought your camera. If you bought a set of those--usually in powers of +1, +2, and +4 diopters in a handy storage case--you've probably retired them to the deepest recess, where you hide your useless photographic gear from your significant other. These cheap lenses are single-element ones which cause images to be sharpest in the center and progressively blurrier farther from it. They also create chromatic aberrations (color fringing) in an image. This is because light traveling through a curved piece of glass bends, much like it does through a prism, with light at either end of the spectrum--red and blue--being affected more:


(Image from Wikipedia)

The Nikon T-series are very different creatures; they are high-quality two-element (doublet), achromatic lenses which reduce the chromatic aberrations to very nearly zero, and keep images sharp from edge-to-edge. This happens because of their construction. One element is made of crown glass and the other of flint glass, each of which bends light differently and effectively cancel color abberation. This is what happens to light when it passes through a two-element achromatic lens:


(Image from Wikipedia)

These lenses also reduce spherical and coma aberrations, but those will not be discussed in any detail in this review.

Interestingly, the lenses of your eyes have chromatic aberration. This is reduced by a yellow pigment in the fovea called the macula lutea which absorbs blue light.

How to use them

If your camera's lens has the same size threads as the close-up lens, you just screw them on. If your camera lens has threads, but not in the right size, you'll need an adapter; either a step-up ring, or (not recommended, as will be explained later) a step-down ring. These are inexpensive--usually less than $10. If your camera lens has no threads, check with your manufacturer. Some companies offer special adapters that will let you use threaded lenses. Although not recommended due to potential camera damage, people have resorted to using tape, or even have constructed their own slip-on adapters out of things like toilet paper tubes!

Why bother?

Because fixed-lens cameras are weak on two counts: magnification and working distance. Rarely does a fixed-lens camera magnify more than .5x. True macro doesn't even begin until magnification reaches or exceeds life-size at 1x! Cameras which do exceed .5x require a very close working distance. For instance, the new Panasonic DMC-FZ30 can focus down to about 2 inches, giving reasonably good magnification, but this close focusing distance has a cost; the camera will block much natural light as well as the camera's built-in flash. One of the universal, basic rules of macrophotography is that the more magnification you use, the more light you need. There are some workarounds, such as using an external flash, but that's one more bulky, battery-eating piece of gear to carry.

Magnification

To calculate the magnification of a close-up lens paired with your camera's lens is simple--multiply the camera's 35 mm-equivalent focal length by the dioptric power of the close-up lens and divide by 1000.

***Math box***

Let's calculate the maximum magnification of a Panasonic DMC-FZ30 with a Nikon 6T: The maximum 35 mm-equivalent zoom of the Z30 is 420 mm, and the 6T is +2.9 diopters, so we have 420 x 2.9 / 1000 = 1.218--more than life-size. If we used the Z30 at 200 mm (35 mm-equivalent) zoom with a 5T, the calculation would be: 200 x 1.5 /1000 = 0.3, or about 1/3 of life-size.

**************

Working Distance

In general, the working distance of a close-up lens is its focal length. Focal length for a close-up lens, in inches, is equal to 1000 mm divided by the dioptric power of the lens, and then divided again by 25.4 to convert from millimeters to inches.

***Math box***

The focal length of a Nikon 6T is 1000 / 2.9 / 25.4 = 13.6 inches, or slightly over a foot. Similarly, for a 5T we have 1000 / 2.9 / 25.4 = 26.25, or a little more than 2 feet.

A working-distance graph of a wide range of dioptric powers:



**************

As you can see, a single Nikon 6T is a pretty good add-on for a Panasonic Z30--more than life-size magnification at a working distance of a foot, as well as giving a vast improvement in ease of lighting. We've turned a telephoto lens into a zoomable macro lens for about $50. Pretty handy for skittish bugs who don't want you too close!

Stacking

Nikon T-series lens may be stacked; that is, they are threaded on front and back so that one may be screwed onto another. This means you can use more than one at a time to get more magnification. To
calculate the new dioptric power of the combination, you add, not multiply. A 3T stacked on a 4T would be 1.5 diopters plus 2.9 diopters = 4.4 diopters. The order they're put together doesn't matter in terms of power, but Nikon advises users to put the highest power nearest the camera lens. This isn't a hard and fast rule, and some systems seem to work better the other way, and in some cases, reversing one of the lenses may offer a slight improvement. There's no limit to the number which can be stacked, but the more you use, the greater the problems mentioned in the next section will be.

Light loss & vignetting

Sometimes you'll read that close-up lenses like the T-series don't have light loss. This clearly isn't true--anytime light passes through glass, some of it is reflected, and some of it is absorbed. The better the glass, and the better the reflective coatings, the less this is prone to happen. The T-series is so good, that this loss is minimal, and that's probably why they are often considered, "lossless." It can be a more of a problem though with stacking. I've never used more than 3 4ts together because of this. For more power and less light loss, I use a reversed 50 mm camera lens which acts as a super-high-quality 20-diopter close-up lens. Since this is a review of the Nikon T-series, I'll give no more detail here.

Another problem with close-up lenses, including the Nikons, is vignetting--a darkening in the corners and edges of an image. This is typically not a problem if a single T-series lens is the same size as the camera's lens, or larger. This is why step-down rings aren't recommended. In any case, vignetting is less of a problem at full zoom. Vignetting becomes more of a possibilty as you stack lenses, since you are essentially looking through a tube. Cameras like my Minolta A1 have more of a problem with vignetting than most, since the beginning of their range is wide-angle: 28 mm. Because the A1 has 49 mm threads, I have to use a step-up ring to mount the 52 mm Nikon lens. This also increases the tube-like effect, and yields some vignetting. The cure was a rather extreme one--I kept filing down an already thin step-up ring until the vignetting disappeared.

DOF (Depth of field)

One of the facts of photographic life is that the greater the magnification, the thinner the part of the scene in focus is. The Nikon T-series isn't immune to this. The practical limit for field use is a combination that results in no more than 2x--twice life-size. Any greater than this, and the slightest movement of the camera or your tiny subject will throw the image out of focus. Tripods, and built-in image stabilization like both the cameras I've used these lenses with helps, but above 2x, getting a well-focused image is more luck than skill. This review is not the place for an in-depth presentation of the complexities of DOF, but fortunately, there's a lot of information in the DSLR.org Technical Topics FAQ section: »Digital Imaging

Finally, no review would be complete without an example. This full-frame photo was taken using 3 Nikon 4Ts stacked on my Minolta A1 at full zoom, giving almost a 2x magnification:


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