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Why do you need a macro lens?

To demonstrate the direct advantages of a macro lens over a regular lens, I will show what macro lenses can do, that others cannot, and that is get close.  I'll do this by using various other non-macro lenses at their respective minimum focusing distances.  You will see the effects that focusing distance and picture angle have on the magnification factor.

This standard U.S. dime was photographed with the 200mm macro lens at 1:1 reproduction ratio.  A regular dime is only 0.705 inches (17.9mm) in diameter.   This is the full-frame (uncropped) picture.  At the closest focusing distance, the dime actually spilled out of the top and bottom of the frame.	Click to enlarge.
Compare to this photograph of the same dime, taken with my 70-200mm lens, set at 200mm.  This picture was taken at the closest focusing distance of this particular lens, which is 4.9 feet.  (Compare to 19.4 inches for the macro).   This lens has a maximum reproduction ratio of 1:6.1, or roughly 16.4% life-size.   Both lenses (at 200mm) have a picture angle of 12° 20'.  This is the full-frame (uncropped) picture.	Click to enlarge.
This picture of the same dime was taken with a 70mm lens.  It has a much closer minimum focusing distance of approximately 15 inches.  However, the gain in a closer focusing distance is almost exactly offset by its larger picture angle of 22° 50'.  This gives it a maximum reproduction ratio of 1:6.2.  This is the full-frame (uncropped) picture.	Click to enlarge.
This final picture was taken with a 24mm lens at its minimum focusing distance of only 11.8 inches.  Its much larger picture angle of 61° gives it a magnification factor of only 1:8.3 (12% life-size).  Even though the camera was 5 times closer to the dime than with the 200mm non-macro lens, the dime appears smaller in the photograph.  This is the full-frame (uncropped) picture.	Click to enlarge.

None of these lenses even come close to the capability of the macro lens for close-up work.  Need I say more about what a macro lens can do?  The pictures speak for themselves.

As you focus further out from the minimum focusing distance, the reproduction ratio drops accordingly, but the 200mm macro lens will still focus out to infinity, so I also have a very nice 200mm fixed-focal-length telephoto lens.

Here's another macro example using my watch.  Because the watch face is bigger than the dime, I had to photograph it from slightly further away, in order to get the entire watch face within the frame.  This resulted in a reproduction ratio of 1:2.5 (40% life-size).  This is the full-frame (uncropped) picture.	Click to enlarge.
Here's a side-by-side size comparison of the dime and the watch.	Click to enlarge.

Why might a longer-focal-length macro lens be better?

I use Nikon's 200mm macro lens, and I prefer it over the 105mm for several reasons, although they are both 1:1 macro lenses.  This is not a sales pitch for the Nikon lens, but these are all factors to consider when looking at any macro lens.

The 200mm's narrower picture angle allows for greater flexibility in taking pictures.   The 105mm lens requires you to be extremely close to your subject at full reproduction ratio (1:1).  On the other hand, the 200mm lens has a greater minimum focusing distance of 19.4 inches.  Minimum focusing distance is not the same as the minimum working distance.  Focus distance is measured from the subject to the focal plane of the camera.  Working distance is measured from the subject to the outer lens element (the end of the lens).  My lens is over 7 inches in length, plus the focal plane is still a couple inches behind the lens mounting flange on the camera.  This means that I have a minimum working distance of about 10 inches, from the subject to the outer lens element, at 1:1 reproduction ratio.  The dime, in the first photograph above, was about 10 inches from the lens when the picture was taken at 1:1.  [Compare to the smaller 105mm lens:  It has a minimum focusing distance of 12 inches, but a minimum working distance of only slightly over 5 inches from the end of the lens.   You have half the working distance, and double the picture angle.]

This image shows the focal plane mark, as indicated on the camera, for determining such distances.

Click to enlarge.

A greater working distance is nice to have when you're photographing live creatures that might be frightened away, if you approached them too closely.  It also allows for more creative lighting effects.  If you wanted to use a diffuser, reflectors, or external flashes, you have more room to work with them.  Also, with a very small working distance, you run the risk of causing your own shadow to fall on your subject.   Being able to stay a little further away helps to avoid this problem.

A more narrow picture angle means that you can get the entire subject in the frame, with less "area" of the background appearing behind it.  See Topic 4 for a demonstration of this using telephoto lenses.  The narrow picture angle, with a shallow depth of field, allows you to blur the background to really get your subject to stand out in the photograph.

Because of the shallow depth of field, you will need to stop down the aperture in order to get more of the subject's depth to be in sharper focus.  This will require longer exposure times.   Longer exposure time means that some type of camera support is required.  The center column of my tripod can be removed, and the legs can be spread flat, so that ground level shots can be taken with the tripod.  The longer focal length of the 200mm lens is good to have in this situation, as well.  If you're photographing something that is very near, or on, the ground, keep in mind that your tripod and tripod head can only get your camera so close to the ground.  With a shorter focal length lens, and therefore a smaller working distance, you will need to physically get the camera and lens closer to the subject.  The closer the camera is to it, the steeper of a downward angle it will need to be at, in order to photograph the subject.  The lens with a greater minimum focusing distance can stay further back, therefore visually coming in from a shallower angle.  This may be very advantageous at times.

Since tripods are so important, here is an example of a tripod that can get very close to the ground.  By removing the center column and extending the legs straight out, you can get very near-ground-level shots.  This photo shows a 200-400mm telephoto zoom lens being used.  This is not a macro lens, but a macro lens might be used in this configuration, and is where a longer focal length could be desireable.	Click to enlarge.
This picture shows the tripod in a "macro" configuration.   The center column has been turned horizontal, and the legs have been configured to support the camera pointing straight down at the ground, in order to photograph something directly from above.  Just about any configuration is possible.  This lens is the 200mm macro lens, and this type of configuration was used to photograph the dime and the watch in the pictures above.  Sometimes I find it necessary to place a counterweight on the rear leg, otherwise the tripod may tip forward under the weight of the camera and lens.	Click to enlarge.

Not all tripods have these functionalities, but they are features you may find useful, and should be taken into consideration when you are choosing a tripod.