It’s true that there is a mind-bending assortment of high-quality lenses available to enhance the capabilities of Nikon cameras. You can use thousands of current and older lenses introduced by Nikon and third-party vendors since 1959, although lenses made before 1977 may need an inexpensive modification for use with cameras other than the Nikon D5000, D3100, D3000, D60, D40, and D40x. (More on this later.) These lenses can give you a wider view, bring distant subjects closer, let you focus closer, shoot under lower light conditions, or provide a more detailed, sharper image for critical work.
Other than the sensor itself, the lens you choose for your dSLR is the most important component in determining image quality and perspective of your images.
Sensor Sensibilities
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From time to time, you’ve heard the term crop factor, and you’ve probably also heard the term lens multiplier factor. Both are misleading and inaccurate terms used to describe the same phenomenon: the fact that cameras like the D3100 (and most other affordable digital SLRs) provide a field of view that’s smaller and narrower than that produced by certain other (usually much more expensive) cameras, when fitted with exactly the same lens.
Figure 1 quite clearly shows the phenomenon at work. The outer rectangle, marked 1X, shows the field of view you might expect with a 28mm lens mounted on one of Nikon’s “full-frame” (non-cropped) cameras, like the Nikon D700, D3, or D3x. The area marked 1.5X shows the field of view you’d get with that 28mm lens installed on a D3100. It’s easy to see from the illustration that the 1X rendition provides a wider, more expansive view, while the inner field of view is, in comparison, cropped.
The cropping effect is produced because the sensors of DX cameras like the Nikon D3100 are smaller than the sensors of the D700, D3, or D3x. The “full-frame” camera has a sensor that’s the size of the standard 35mm film frame, 24mm × 36mm.
Your D3100’s sensor does not measure 24mm X 36mm; instead, it specs out at 23.6 × 15.8 mm, or about 66.7 percent of the area of a full-frame sensor, as shown by the red boxes in the figure.
You can calculate the relative field of view by dividing the focal length of the lens by .667. Thus, a 100mm lens mounted on a D3100 has the same field of view as a 150mm lens on the Nikon D700.
We humans tend to perform multiplication operations in our heads more easily than division, so such field of view comparisons are usually calculated using the reciprocal of .667—1.5—so we can multiply instead. (100 / .667=150; 100 × 1.5=150.)
This translation is generally useful only if you’re accustomed to using full-frame cameras (usually of the film variety) and want to know how a familiar lens will perform on a digital camera.
I strongly prefer crop factor over lens multiplier, because nothing is being multiplied; a 100mm lens doesn’t “become” a 150mm lens—the depth-of-field and lens aperture remain the same. Only the field of view is cropped. But crop factor isn’t much better, as it implies that the 24 × 36mm frame is “full” and anything else is “less.”
If you’re accustomed to using full-frame film cameras, you might find it helpful to use the crop factor “multiplier” to translate a lens’s real focal length into the full-frame equivalent, even though, as I said, nothing is actually being multiplied.
Crop or Not?
------------------
There's a lot of debate over the "advantages" and "disadvantages" of using a camera with a ?"cropped" sensor, versus one with a ?"full-frame" sensor. The arguments go like these:
References:
-----------------------
Cengage David Buschs Nikon D3100 Guide to Digital SLR Photography 2011 ebook.
Other than the sensor itself, the lens you choose for your dSLR is the most important component in determining image quality and perspective of your images.
Sensor Sensibilities
------------------------
From time to time, you’ve heard the term crop factor, and you’ve probably also heard the term lens multiplier factor. Both are misleading and inaccurate terms used to describe the same phenomenon: the fact that cameras like the D3100 (and most other affordable digital SLRs) provide a field of view that’s smaller and narrower than that produced by certain other (usually much more expensive) cameras, when fitted with exactly the same lens.
Figure 1 quite clearly shows the phenomenon at work. The outer rectangle, marked 1X, shows the field of view you might expect with a 28mm lens mounted on one of Nikon’s “full-frame” (non-cropped) cameras, like the Nikon D700, D3, or D3x. The area marked 1.5X shows the field of view you’d get with that 28mm lens installed on a D3100. It’s easy to see from the illustration that the 1X rendition provides a wider, more expansive view, while the inner field of view is, in comparison, cropped.
 |
Figure 1: Nikon offers digital SLRs with full-frame (1X) crops, as well as 1.5X crops. |
The cropping effect is produced because the sensors of DX cameras like the Nikon D3100 are smaller than the sensors of the D700, D3, or D3x. The “full-frame” camera has a sensor that’s the size of the standard 35mm film frame, 24mm × 36mm.
Your D3100’s sensor does not measure 24mm X 36mm; instead, it specs out at 23.6 × 15.8 mm, or about 66.7 percent of the area of a full-frame sensor, as shown by the red boxes in the figure.
You can calculate the relative field of view by dividing the focal length of the lens by .667. Thus, a 100mm lens mounted on a D3100 has the same field of view as a 150mm lens on the Nikon D700.
We humans tend to perform multiplication operations in our heads more easily than division, so such field of view comparisons are usually calculated using the reciprocal of .667—1.5—so we can multiply instead. (100 / .667=150; 100 × 1.5=150.)
This translation is generally useful only if you’re accustomed to using full-frame cameras (usually of the film variety) and want to know how a familiar lens will perform on a digital camera.
I strongly prefer crop factor over lens multiplier, because nothing is being multiplied; a 100mm lens doesn’t “become” a 150mm lens—the depth-of-field and lens aperture remain the same. Only the field of view is cropped. But crop factor isn’t much better, as it implies that the 24 × 36mm frame is “full” and anything else is “less.”
If you’re accustomed to using full-frame film cameras, you might find it helpful to use the crop factor “multiplier” to translate a lens’s real focal length into the full-frame equivalent, even though, as I said, nothing is actually being multiplied.
Crop or Not?
------------------
There's a lot of debate over the "advantages" and "disadvantages" of using a camera with a ?"cropped" sensor, versus one with a ?"full-frame" sensor. The arguments go like these:
- "Free" 1.5X teleconverter.
The Nikon D3100 (and other cameras with the 1.5X crop factor) magically transforms any telephoto lens you have into a longer lens, which can be useful for sports, wildlife photography, and other endeavors that benefit from more reach. Yet, your f/stop remains the same (that is, a 300mm f/4 becomes a very fast 450mm f/4 lens). Some discount this advantage, pointing out that the exact same field of view can be had by taking a full-frame image, and trimming it to the 1.5X equivalent. While that is strictly true, it doesn't take into account a factor called pixel density. Nikon manufactures both full-frame and cropped sensor cameras with 12MP of resolution (the Nikon D700 and D5000, for example).
The cropped model packs all those pixels together much more tightly, into that 23.6 ?~ 15.8mm area. So, your 300mm f/4 lens delivers the same field of view as a 450mm optic at the camera's full 12MP resolution. When you crop the D700 image to get the same field of view, you're using only five megapixels worth of resolution. So, while both images will be framed the same, the cropped sensor version, with its higher pixel density, will be sharper.
- Dense pixels=more noise.
The other side of the pixel density coin is that the denser packing of pixels to achieve 14.2 megapixels in the D3100 sensor means that each pixel must be smaller, and will have less light-gathering capabilities. Larger pixels capture light more efficiently, reducing the need to amplify the signal when boosting ISO sensitivity, and, therefore, producing less noise. In an absolute sense, this is true, and cameras like the D700 and D3 do have sensational high-ISO performance. However, the D3100’s sensor is improved over earlier cameras (for one thing, it is a high-sensitivity CMOS sensor, rather than a noisier CCD sensor like that found in some earlier Nikon entry-level cameras), so you’ll find it performs very well at higher ISOs. Indeed, its ISO sensitivity is more or less comparable to that of the Nikon D3x, which also relies on high-density pixel-packing to achieve its 24.5MP resolution. You needn’t hesitate to use ISO 1600 (or even higher) with the Nikon D3100: just don’t expect the same results at H1 or H2 (ISO 6400 and 12800 equivalent) as D700 owners get from their cameras.
- Lack of wide-angle perspective.
Of course, the 1.5X “crop” factor applies to wide angle lenses, too, so your 20mm ultra-wide lens becomes a hum-drum 30mm near wide-angle and a 35mm focal length is transformed into what photographers call a “normal” lens. Zoom lenses, like the 18-105mm lens that is often purchased with the Nikon cameras in a kit, have less wide-angle perspective at their minimum focal length. The 18-105mm optic, for example, is the equivalent of a 27mm moderate wide angle when zoomed to its widest setting. Nikon has “fixed” this problem by providing several different extra-wide zooms specifically for the DX format, including the (relatively) affordable 12-24mm f/4 DX Nikkor. You’ll never really lack for wide-angle lenses, but some of us will need to buy wider optics to regain the expansive view we’re looking for.
- Mixed body mix-up.
The relatively small number of Nikon D3100 owners who also have a Nikon full-frame camera like the D700 can’t ignore the focal-length mix-up factor. If you own both FX and DX-format cameras (some D3100 owners use them as a backup to a D700, for example), it’s vexing to have to adjust to the different fields of view that the cameras provide. If you remove a given lens from one camera and put it on the other, the effective focal length/field of view changes. That 17-35mm f/2.8 zoom works as an ultra-wide to wide angle on a D700, but functions more as a moderate wide-angle to normal lens on a D3100. To get the “look” on both cameras, you’d need to use a 12-24mm zoom on the D3100, and the 17-35mm zoom on the D700. It’s possible to become accustomed to this field of view shake-up and, indeed, some photographers put it to work by mounting their longest telephoto lens on the D3100 and their wide-angle lenses on their full-frame camera. Even if you’ve never owned both an FX and DX camera, you should be aware of the possible confusion.
References:
-----------------------
Cengage David Buschs Nikon D3100 Guide to Digital SLR Photography 2011 ebook.
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