LENS CARE

By Jeff Griffin CEng MIMechE.

The best advice regarding the care of optics will always be: "Don`t keep cleaning your lens-keep your lens clean", In other words keep the lens capped when it isn`t in use. Many people fit an ultra violet filter to each of their lenses as protection for the front element but discretion is needed. A filter is certainly worthwhile in gritty envioroments or when near the coast (salt in the air) but it should not be fitted when shooting into light. Hoods are designed to keep stray light away from the front element of the lens rather than something placed in front of it.

It`s apparent that a UV filter has some role to play in lens care. However, owners of rangefinder cameras, which have focal plane shutters with fabric blinds, must`nt consider a filter as an alternative to a lens cap in all respects. A lens is a device for focusing light rays onto film and shutter blinds run ahead of the lens plane. Should an uncapped lens catch the direct rays from the sun a neat hole can be quickly burned in a shutter curtain. As a final word on UV filters, it should not be thought that a permanent fitting will necessarily give improved colour redention as a bonus. A modern LEICA lens has UV filters incorporated by virtue at the patented ABSORBAN process. Fitting a filter to the lens is only beneficial at altitudes in excess of 3,500 meters.

Inevitably, a lens will need cleaning from time to time and this is an operation approached with great anxiety by many owners. Certainly caution is needed. The worst consequences of careless cleaning is the production of a multitude of very fine scratches. A large number of such abrasions is far more serious than a single deep scratch.

Dirty lenses fall into two catagories, i.e. those with dust, dirt etc. only and those that also have grease or fingerprints (it happens!). To remove dust etc. an air blower and soft brush are needed and used thus:-

1. Turn the lens so that the surface to be cleaned is facing the floor; removed dust then falls away from, instead of back onto the lens. Use the blower to remove loose particles.

2. Remove any remaining particles (lens still facing downwards) with the soft brush. With blower-brushes check before use that the bristles aren`t dust-laden otherwise particles may be added rather than removed. Such tools are best regarded as brushes with built-in-bristle cleaning arrangements and a seperate blower obtained. Brushes of the retracting and capped type are preferable. If the bristles are anchored into a metal sleeve the latter should be taped to eliminate one possible source of scratches. When the bristles become dust-laden they can be emptied by flicking with a (clean) finger. Should they come into contact with grease, then clean them with spirit (see later), or replace the brush. Common sense suggests the use of two brushes with one reserved exclusively for optical surfaces and the the other used to clean any other surface. If there are fingerprints or grease on the lens surface additional treatment is necessary but the two previous steps are still required. The objective is to remove all abrasive material before rubbing is done so that there is no possibility of producing scratches. Care is needed when rubbing the lens surface but there is no need to become neurotic about it. Modern LEICA lenses have comparitively hard coatings on the front and rear external surfaces so that they will withstand sensible treatment. A soft no-fluffing cloth and some cleaning fluid are required. Use Kodak lens cleaner or spirit such as pure ether or alcohol. Do not use impregnated cloths or tissues such as those sold by optitians for cleaning spectacles as their effect on coating is unknown. A good cloth is that known as "Selvyt" and sold by photo dealers. A linen handkerchief is satisfactory provided that all the dressing has been washed out (this takes very many washes using toilet soap, not detergent). White toilet tissue may be used but this sheds fibres which must be blown away afterwards.

3. Turn the lens so that the surface to be cleaned is facing up. Bunch up the cloth or tissue, place over the open bottle of fluid and up-end. Do not pour fluid onto the lens as it is easy to overdo this with the result that some seeps into the lens and may cause a cement failure because of the solvent action.

4. Gently rub the lens with a light circular motion starting at the centre and gradually working outwards. Then using a dry portion of the cloth (also bunched up) repeat the polishing action. The grease spots may have only been partially removed and some may have been spread over the surface. If so, repeat using more fluid on the cloth and polish dry. Finally breath on the lens and polish to remove any residual smears.

The wish to take care of expensive lenses is natural enough, but it is by no means necessary to remove every speck the instant it lands on the lens. An enormous amount of dust etc. must accumulate before the image quality is impaired to any detectable extent.