is a ZOOM lens?
the focal length of some lenses
is fixed, zoom lens allow the photographer to shift the
focal length and consequently frame the image more tightly
by zooming in or zoom out to gain a wider angle on the scene
being photographed without moving the camera position. Rather
than carrying a whole stash of lenses in their kit, this
also means the photographer has a variety of lenses in one
unit. However because the lens is designed to do a variety
of tasks it is often never quite a sharp as a fixed focal
However because the optics of a zoom lens are adapted to project light from a range of perspectives for critical work many photographers will use a fixed focal length lens.
lens set on 100mm
lens set on 200mm
In many compact digital cameras this is done by pushing
a button - but in SLR designs this is done by either extending
or contracting the barrel of the lens( through pushing or
pulling) - or by rotating the lens.
Zoom lenses have become the standard on every digital compact, pocket, prosumer camera on the market.
on this camera zooms from 5.8 to 17.4 mm - the aperture when the focal length is 5.8mm is f2.8 and at 17.4
it is f4.9
So as the focal length of the lens increases the relative
aperture becomes smaller.
However - when the focal length of the lens is altered the perspective is changed and the
maximum aperture in many lenses is altered.
zoom lens on this SLR can zoom from 35mm to 70mm by
sliding the front of the lens backwards
over to view roll over image
Zooming during the exposure.
A technique that can be interesting with a zoom lens is to use a relatively long exposure of about 2 second - use a flash and zoom during the exposure. This depends upon the subject and you will have to experiment with this to get the right effect, but it gives a great sense of movement.
Try zooming in and then try zooming out.
is a macro lens?