"Paul Renfree" <> wrote:
>I want to be able to take close ups of spider webs, insects, leaves etc. Can
>I use a non-macro telephoto lens such as a Nikon 70-300 to do this, or does
>the telephoto lens need to have a macro setting?
In general, zoom lenses are not as good as fixed focal length
lenses when used with devices to allow closer focusing. To get
a zoom to zoom there have to be a lot of compromises made; one
effect of that is that with a zoom lense the closest focusing
distance more likely to be a performance design point, where it
simply doesn't produce sharp images at closer distances (rather
than being a matter of what is convenient to engineer in the way
of a focusing mechanism, even though the lense would still be
sharp if focused closer).
The effect is that if you buy, for example, a set of extension
tubes or a closeup lense, either of which will allow closer
focusing, they will work better with fixed focal length lenses
than with zooms.
>What about using a close up lens that screws on to a regular lens ?
Closeup lenses come in a variety of powers (such as +1, +2, and
+3 diopter lenses). They can be stacked, so all of those together
would be a +7 diopter lense.
They also come in two basic designs, one is a single element
lense and the other is a multi-element lense that is achromatic,
which is both a significant improvement and a significantly
higher cost. Also, closeup lenses work best when used with
longer focal length regular lenses. Hence the effect of a
+3 diopter closeup lense when used on a 35mm lense is small, and
is fairly great when used on a 100mm lense.
Extension tubes and bellows are another way to get a particular
lense to focus closer than it does with normal mounting. In
some cases the results are quite sharp, and in others it causes
degradation of the image.
A third method is to use a telextender. A 2x telextender, for
example, has the effect of doubling the focal length but does
not change the minimum focusing distance.
Now, to really make life complicated, consider that a standard
50mm lense can be reverse mounted in front of another lense, say
a 100mm focal length, and will perform as an *excellent* +20 diopter
achromatic closeup lense! And, when used with extension tubes or
on a bellows it is sometimes a significant improvement to reverse
mount a regular lense (typically, a "normal" 50mm lense will be
sharper for closeups when reverse mounted). And, if you use a
bellows there are many very inexpensive macro lenses to choose
from because old 50 to 150mm enlarging lenses are excellent macro
lenses.
You'll need to do some research. Use google and search on the
term "photomacrography".
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska)