Movie Makers (Jan-Dec 1930)

JV%IWajy%RY 1930 KNOWING Your CAMERA'S EYE Final Data 0?t h,enses — Their Use With Artificial Light AFTER we have familiarized ourselves with the basic principles of the lens and know, thereby, what it can accomplish under various conditions, we should next turn to the proper care of the objective. This is a most important subject, for, no matter how fine a lens we may have, it will not give us the results of which it is really capable unless we keep it clean. The lens is a precision product, ground and polished to shape with great care. Not only must the surface of the lens remain clean but the polish itself must be maintained in order that the lens shall perform at its best. Many a lens is blamed for poor performance when its owner is at fault. It is impossible t o secure clean-cut images and sparkling definition with the lens coated with dust, or if its surface is marred by other foreign matter. Wherefore, keep your lens clean. A fuzzy, blurred picture — a picture that is gray and poorly defined, even though the focus is carefully set — these are the symptoms of a lens that is not clean. The best way to clean a lens is not to allow it to become dirty. The lens surface is not a magnet for attracting dust and dirt. If reasonable care were exercised in keeping the outer element of the lens covered when not in use, very little cleaning would be necessary. No professional owner of a fine lens would dream of allowing it to remain uncovered except when actually focusing or taking a picture. The lenses made for 16 mm. cine work are as fine a class of objectives as may be found anywhere; they deserve this fundamental good treatment and should have it. The lens cap is undoubtedly the best way to keep the front surface of the lens free from dust when not in use. That such a covering is effective is demonstrated by the fact that the rear By Russell C. Holslag element, being always encased or protected by the camera, very seldom requires cleaning. The objection is advanced that with the use of the lens cap comes the risk of shooting the picture with the cap on, in which case the THIS WOULD HAVE BROUGHT THE MOUNTAIN TO MAHOMET A Study Of A Telephoto Lens By Alexander de Canedo. resulting image would be somewhat underexposed! But, seriously, this is not a valid argument against the lens cap. By the same logic, one might argue that the dark slide in the plate holder should be abolished because one sometimes forgets to draw it when making an exposure! A recent form of lens cap is made with a projection that is apparent in the finder, so that one may be reminded that the lens protection is to be withdrawn while the scene is being recorded. You can make a lens cap of your own from the cover of a pill-box of the proper size. Line the inside carefully with black velvet and attach the cap to the camera by a string. As a reminder, you can fasten the string so that it passes in front of the finder when the cap is on. This makes an effective indicator and the idea is used on a popular 9.5 mm. camera. At any rate, it is not advisable to carry the camera around all day with the lens uncovered. This is an excellent means of causing a layer of dust and dirt to collect on it. If you have no lens cap, keep the camera in the case when not shooting. Keep your fingers away from the lens surface. Hold the camera so that the lens is protected as completely as possible. Next comes the use of the sunshade. This is a small tube, which is really in the form of an extension of the lens barrel, %" to 1/2" deep. Such an extension is very valuable in protecting the lens from side glare and in preventing the direct rays of a light source from reaching the lens. We are all familiar with the dictum that direct rays of sunlight should never be allowed to strike the surface of the lens. This rule is very easy to observe when the sun is at one's back, but very often excellent effects may be secured when the sun is in front of the camera or slightly to the side. We should have to eschew these excellent side, rim and backlighting effects if our lens were not protected with a hood, for we must never allow direct rays of the sun to touch the glass of the lens. But this principle is not only applicable to sunlight. It applies to artificial home lighting sources with even greater force. These are almost invariably in front of the camera and more apt to appear in the field of view. Therefore, the use of the lens hood is especially appropriate in interior set-ups. In the excitement of arranging the set and planning the action it is all too easy to forget the danger of flare. This appears in the finished picture as a brilliant haze, generally emanating from one side or corner of the frame. The lens hood or shield is an excellent specific for this particular malady. One may make an effective hood out of any small cardboard cylinder of suitable size to slip over the lens hood and hold by friction. The inside of such a cylinder should be lined with black velvet or painted with a dull finish black paint. (See the Clinic for March, 1929.) The extension of this hood beyond the lens should not be too great or part of the field of view will be cut off. The hoods supplied as standard equipment with most good lenses will answer every purpose and there is no valid reason why they should not be used all the time. In fact, the /:1.9 lens of a wellknown camera incorporates such a permanent hood or shield. Such a hood is valuable also as an actual protection against accidental damage or contact with the front element of the lens. All fast lenses are provided with this type of hood, either removable or permanent. (Continued on page 52) 42