10 most important things to know about lenses

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10 most important things to know about lenses Pag

http://videoexpert.home.att.net/artic1/225blens.htm 09/11/2004 07:42:42 A

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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 thesame manufacturer's camera, the old lens might not work. If the lenshas electric zoom, iris, and maybe focus, these functions may be

powered and controlled by a multi-wire cable that connects between thelens and the camera. Getting the right signals and voltages from thecamera to the lens is a tricky matter. Make sure that your dealerguarantees that the lens you've selected can be adapted to the camerayou are using.

Years ago most cameras and lenses had "C-mounts" having acertain size hole and a certain size threads so that any lens wouldfit any camera. Now there are several kinds of mounts, some of them

proprietary to certain manufacturers. Mounting one type of lens toanother type of camera is often possible with an adapter, if one isavailable.

Lenses are designed to make a certain size picture. Camerashave various sized sensor chips. The two must be matched so thatthe 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 aroundthe edges of the picture, especially in the corners. If the lensmakes a bigger picture than the camera needs, the lens will work butthe image will appear magnified. If you have a real nice lens thatyou don't want to waste, you may find it possible to live with the lattersituation; 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.


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Most non-professional camcorders come with built-in lenses; youhave no choice but to accept what they give you. The Canon L1 and L2are the most notable exceptions, as these cameras have a VL lens mountwhich can accept other Canon lenses, even lenses from 35mm stillcameras. Canon makes a wide selection of lenses to meet even the

most unusual needs. Professional cameras, on the other hand, comewithout lenses, (and their published prices don't include the lens)and the lenses may cost from $1000 to several thousanddollars each.

2. Buy a plain glass or UV (ultra violet), or skylight filter foryour 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, andother hazards. These attachments thread onto the outside of your

existing lens (perhaps you take your lens hood off first and reattachit to the outside of the filter) and can be removed easily forcleaning. Many videographers then furlough their lens cap (it'susually dangling by a string, flopping in the breeze, or otherwise inthe way) allowing their UV filter to protect their lens. This alsosaves ENG camera operators from taking extra time to uncap their lens.Ambient light entering a chip camera lens while the camera is off willnot damage anything unless the camera is aimed directly at the sun orsome other bright light for a while.

3. For most ENG and EFP work, get a lens with a 10x zoom ratio ormore. The broad zoom ratio will permit you the flexibility ofshooting in caves or hotel rooms (where you need a super wide shot),or zooming to supertelephoto to catch the raging bull from acomfortable 100 meters away.

Lenses are described by focal length, usually telling you thelens' widest image angle and the zoom ratio (ratio between the lens'widest and narrowest angle). The focal length measured inmillimeters is number derived from a mathematical formula. The biggerthe number, the more telephoto the lens.

4. For motorized zooms, check the variable zoom rate. Some zoomswork at only one speed, usually not the speed you like. Others mayhave two speeds, better but not stellar. The best lenses havevariable speed motors operated by rocker switchers that allow you tonudge the picture slowly or to swoop it in quickly.

5. Try to get macro and telephoto extenders built-in. Lenses havinga macro feature are able to disengage their normal zoom and focus


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functions, and become "close-up" lenses able to fill the screen with apostage 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 moretelephoto or more wide-angle than normal while still maintaining zoomcapability. For instance, with a 1.5X feature engaged, your 10 -100mm zoom lens will act like a 15 - 150mm telescope, allowing you toview birds, and sports action from afar. With the wide angle functionengaged, you can shoot more easily indoors or inside a vehicle.

6. The higher priced lenses generally will create less picturedistortion. High quality lenses correct chromatic abberations. Aim agood 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 yourpicture. Cheaper lenses have trouble in these corners allowing thewhite 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 upcreating multiple highlights. This is especially noticeable when youare 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 imageout to the corners of the picture.

Straight lines should always remain straight. Barreldistortions in the lens would cause the image of a Tic Tac Toe boardto bulge outward in the middle. Pincushion distortions would causethe board to squeeze inward. These distortions are most noticeablewhen shooting wide angle shots of skyscrapers.

7. The faster the lens the better. The "speed" of a lens representshow much light is allowed through it. The most efficient "faster"lenses have low f numbers. Team a sensitive camera with a fast lensand you will be able to shoot in minimal light.

8. If you shoot in humid climates, keep your camera and lens sealedtightly in a box. Let the two warm up to outside temperatures(preferably within a sealed plastic bag so that condensationforms on the BAG, not on the LENS or CAMCORDER) beforeyou use them to avoid condensation forming on your gear. If dampnessgets inside your lens, fungus starts to grow and it nearly impossible


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to remove.

9. The second most important lens attachment to buy is a polarizingfilter. 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 orderto work correctly. If your lens turns while it focuses, theattachment may also turn, messing up your polarization; you may needto hold the polarizing filter still while the rest of the lensrotates. Cokin and others sell polarizing filters that slip into aholder that remains stationary even though the lens turns. Theseholders (sometimes called matte boxes) also have other advantages:you can buy numerous glass filters and drop them into the holder, eventeaming the filters up for special effects. Because each filter is

simply a square of glass that drops into the slot in your filterholder, they are less expensive than the ones mounted in their ownthreaded retaining rings.

10. Avoid zooming. Amateurs zoom a lot, thinking the motion in thepicture is intriguing. The pros know better; if they want motion,they move the camera.

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10 most important things to know about lenses