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THE 10 MOST IMPORTANT THINGS TO KNOW ABOUT LENSES
1. When selecting a lens, make sure it fits your camera. Not all
lenses fit all cameras. Even if you change to a newer model of the
same manufacturer's camera, the old lens might not work. If the lens
has electric zoom, iris, and maybe focus, these functions may be
powered and controlled by a multi-wire cable that connects between the
lens and the camera. Getting the right signals and voltages from the
camera to the lens is a tricky matter. Make sure that your dealer
guarantees that the lens you've selected can be adapted to the camera
you are using.
Years ago most cameras and lenses had "C-mounts" having a
certain size hole and a certain size threads so that any lens would
fit any camera. Now there are several kinds of mounts, some of them
proprietary to certain manufacturers. Mounting one type of lens to
another type of camera is often possible with an adapter, if one is
available.
Lenses are designed to make a certain size picture. Cameras
have various sized sensor chips. The two must be matched so that
the diameter of the image equals the diagonal size of the active
pickup area. Since cameras now come with 1/4", 1/3", 1/2", and 2/3" chips,
the lenses need to be sized accordingly. If the lens' image is
smaller than the chip, you will see vignetting, a dark shadow around
the edges of the picture, especially in the corners. If the lens
makes a bigger picture than the camera needs, the lens will work but
the image will appear magnified. If you have a real nice lens that
you don't want to waste, you may find it possible to live with the latter
situation; just zoom your picture out more than you normally would,
and enjoy the fact that you can zoom in tighter than you ever could
before.
Most non-professional camcorders come with built-in lenses; you
have no choice but to accept what they give you. The Canon L1 and L2
are the most notable exceptions, as these cameras have a VL lens mount
which can accept other Canon lenses, even lenses from 35mm still
cameras. Canon makes a wide selection of lenses to meet even the
most unusual needs. Professional cameras, on the other hand, come
without lenses, (and their published prices don't include the lens)
and the lenses may cost from $1000 to several thousand
dollars each.
2. Buy a plain glass or UV (ultra violet), or skylight filter for
your lens. The filter barely changes the look of your image, but
protects the outside of your expensive camera lens from fingerprints,
dust, salt spray, water, sandblasts, flying watermelon seeds, and
other hazards. These attachments thread onto the outside of your
existing lens (perhaps you take your lens hood off first and reattach
it to the outside of the filter) and can be removed easily for
cleaning. Many videographers then furlough their lens cap (it's
usually dangling by a string, flopping in the breeze, or otherwise in
the way) allowing their UV filter to protect their lens. This also
saves ENG camera operators from taking extra time to uncap their lens.
Ambient light entering a chip camera lens while the camera is off will
not damage anything unless the camera is aimed directly at the sun or
some other bright light for a while.
3. For most ENG and EFP work, get a lens with a 10x zoom ratio or
more. The broad zoom ratio will permit you the flexibility of
shooting in caves or hotel rooms (where you need a super wide shot),
or zooming to supertelephoto to catch the raging bull from a
comfortable 100 meters away.
Lenses are described by focal length, usually telling you the
lens' widest image angle and the zoom ratio (ratio between the lens'
widest and narrowest angle). The focal length measured in
millimeters is number derived from a mathematical formula. The bigger
the number, the more telephoto the lens.
4. For motorized zooms, check the variable zoom rate. Some zooms
work at only one speed, usually not the speed you like. Others may
have two speeds, better but not stellar. The best lenses have
variable speed motors operated by rocker switchers that allow you to
nudge the picture slowly or to swoop it in quickly.
5. Try to get macro and telephoto extenders built-in. Lenses having
a macro feature are able to disengage their normal zoom and focus
functions, and become "close-up" lenses able to fill the screen with a
postage stamp.
Built-in lens extenders may allow you to multiply a zoom lens's
focal length by 1.5 or perhaps .8, making the entire lens act more
telephoto or more wide-angle than normal while still maintaining zoom
capability. For instance, with a 1.5X feature engaged, your 10 -
100mm zoom lens will act like a 15 - 150mm telescope, allowing you to
view birds, and sports action from afar. With the wide angle function
engaged, you can shoot more easily indoors or inside a vehicle.
6. The higher priced lenses generally will create less picture
distortion. High quality lenses correct chromatic abberations. Aim a
good lens at a distant point of light and you should see a white dot.
The dot should remain white even if it is in the corner of your
picture. Cheaper lenses have trouble in these corners allowing the
white dot to turn into a dot with a blue and red fringe.
Internal reflection is another problem with inexpensive lenses.
The light comes in, bounces around between the glass and ends up
creating multiple highlights. This is especially noticeable when you
are shooting bright objects with dark backgrounds.
Cheap lenses can make a sharp image in the center of your
picture, but it takes a high quality lens to maintain the sharp image
out to the corners of the picture.
Straight lines should always remain straight. Barrel
distortions in the lens would cause the image of a Tic Tac Toe board
to bulge outward in the middle. Pincushion distortions would cause
the board to squeeze inward. These distortions are most noticeable
when shooting wide angle shots of skyscrapers.
7. The faster the lens the better. The "speed" of a lens represents
how much light is allowed through it. The most efficient "faster"
lenses have low f numbers. Team a sensitive camera with a fast lens
and you will be able to shoot in minimal light.
8. If you shoot in humid climates, keep your camera and lens sealed
tightly in a box. Let the two warm up to outside temperatures
(preferably within a sealed plastic bag so that condensation
forms on the BAG, not on the LENS or CAMCORDER) before
you use them to avoid condensation forming on your gear. If dampness
gets inside your lens, fungus starts to grow and it nearly impossible
to remove.
9. The second most important lens attachment to buy is a polarizing
filter. This filter reduces glare and shine, darkens hazy blue skies,
allows you to shoot through glass windows or through a pond's surface.
A polarizing filter has to be rotated to the right position in order
to work correctly. If your lens turns while it focuses, the
attachment may also turn, messing up your polarization; you may need
to hold the polarizing filter still while the rest of the lens
rotates. Cokin and others sell polarizing filters that slip into a
holder that remains stationary even though the lens turns. These
holders (sometimes called matte boxes) also have other advantages:
you can buy numerous glass filters and drop them into the holder, even
teaming the filters up for special effects. Because each filter is
simply a square of glass that drops into the slot in your filter
holder, they are less expensive than the ones mounted in their own
threaded retaining rings.
10. Avoid zooming. Amateurs zoom a lot, thinking the motion in the
picture is intriguing. The pros know better; if they want motion,
they move the camera.