vendredi 10 décembre 2004

Softly, Softly... MTF... "More Touchy Feely" Some time ago I decided not to join the MTF Club. To the uninitiated, MTF or Modulation Transfer Function evaluates lens performance and is expressed in figures as line-pairs-per-millimetre for resolution and as a percentage of contrast. As far as I'm concerned though, a lens has either got it or it hasn't... and if one of mine hasn't then I get rid of it! Two I did keep for some time were for Canon EOS and Pentax 67 cameras... two quite different systems. The first is 35mm, autofocus, fast and light... the second medium-format, manual, heavy and slow. They are as different as chalk and cheese yet both systems include expensive "soft-focus" lenses in their line-up. To spend over $1,000 dollars on both the Canon EF 135mm f2.8 and Pentax 67 120mm f3.5 Soft lenses whose prime function is to produce images as fluffy as candy floss was a hard decision. But the answer was convenience... these lenses are simple in design yet specialised in use. They guarantee the predictable results that photographers look for when they want something different... and soft-focus images are different. The Canon EF lens for the EOS system uses a separate setting ring with three click-stop positions... "0" for normal with "1" and "2" for increasing degrees of softness. The Pentax 6x7 lens uses a common aperture and soft-control ring... although softness can be hand selected without taking the eye from the camera viewfinder the lens's working aperture also has to be taken into account. The image above of Trish my wife nearing her 60th birthday caught her softly despite MS affecting her. In general if any of these special lenses is used at the maximum or widest aperture the soft-focus effect will be maximised. But if the shooting aperture is around f/8, f/11 or smaller the soft-focus effect will disappear altogether and results will only show a slight degradation in resolution... which is not much of a desirable effect. Another thing that should be understood... "soft-focus" is not the same as "out-of-focus." Think about it and you'll see what I'm getting at... soft-focus is subtle and deliberate whereas out-of-focus is an unacceptable mistake. The above image of Montbretia or Crocosmia in our previous Welsh garden and the wine glasses below taken at a smaller aperture and therefore appearing "sharper than soft", but certainly not out of focus show this. Soft-focus has a long history and many old photographs demonstrate the effect wonderfully... although many of these were the result of equipment of the period. Nowadays, lens manufacturers have to consider sharpness before most things else in the battle for sales. So, apart from the few specialised lenses it is left to photographers to alter the optical characteristics of their lenses to produce the soft, dreamy and romantic images that can be applied to so many subjects including portraits, nudes, landscapes and still-life. The current trend towards soft-focus and romantic imagery is due in some measure to the "innocently adolescent" subject matter popularised by David Hamilton in his books, calendars and posters... as well as the nostalgic joie de vivre advertising photographs of fashion model turned photographer Sarah Moon. Their work has more than influenced photographers... it has become recognisable in poster form to the general public even if the creators are not household names. A Cheap Approach Soft-focus images can be produced in a variety of ways. You can spend several hundred dollars on a specialist lens or simply breathe on the front element of whatever lens you have. The results can be remakably similar at times, except that the first method accurately controls the effect for you whereas the latter usually produces it through sheer good luck. The one advantage of using your own breath on a lens is that it's an instant effect... and as the condensation slowly evaporates it offers several different soft-focus options. This makeshift technique can be applied to any lens - which saves on filters if you own lenses with different attachment sizes - but it is not so successful in hot, dry weather when you may run out of huff or puff! Another cheap soft-focus option is to dip into the household jar of Vaseline. A dab of petroleum jelly smeared onto a protective Skylight filter, not onto the lens element itself, will produce reasonable results - but leave a clear centre spot for some visual reality. Not much Vaseline is required either! Whilst on the search for household products look for bits cellophane or cling-film food wrapping which can be crumpled then stretched across the front of the lens to act as a softener. Rumour has it that Sarah Moon started her trend with the screwed-up wrappings from packets of her French Gauloises cigarettes. If fact there appears to be a strong "French Connection" with all soft-focus effects... Hamilton takes after the Impressionists by living and working in the French Mediterranean light. Sarah Moon is French and works in Paris, the "City of Light"... and there's master of filters Monsieur Cokin, who has explored every image manipulation possibility with neutral and coloured Centre Spot, Diffractor, Diffuser, Varnish and Vaseline, Dream, Fog and Pastel filters... and could peut-être eventually come up with spray cans of mist? What Monsieur Cokin has done is bring a multiplicity of visual effects to the enthusiast photographer, at minimal expense, via a simple modular filter system... which many other manufacturers have since copied but never quite emulated. Important Secrets Whether you're using a pair of cast-off nylons, a trick filter or a special soft-focus lens, there are two basic guide-lines to follow for the best soft-focus effects. First, the optimum lens aperture settings are the wide ones. Closing-down the lens aperture by two or three stops will make the main subject progressively sharper and the desired soft- focus effect may disappear completely at the middle to minimum apertures, especially with any lens wider than the 50mm standard, such as a 35mm or 28mm wide-angle. Secondly, the subject and lighting contrast should be fairly high. Backlit subjects lend themselves particularly well to the soft-focus treatment, especially when the rim lighting produced is diffused to create a halo around the subject. Because soft-focus attachments scatter light in all directions, cameras with built-in TTL exposure meters will tend to see too much light and give a false reading leading to under-exposure. In fact soft-focus images are best created with over-exposure by one or even two stops from the recommended meter reading... colour slides which normally look washed-out when exposed to too much light will benefit from slight over-exposure in these cases. Because the soft-focus effect can be achieved with as little as a puff of breath, a smear of Vaseline or a pair of laddered tights, it's easy to experiment without committing yourself to undue expense. The effect is personal in both rendition and appreciation. If you like what you see after your initial attempts you can invest in a proper set of Zeiss "Softar" lens attachments. Zeiss have an interesting page on "Expressing Emotion" describing the use of soft-focus lenses. Manufacturers currently making soft-focus auto-focus lenses for 35mm systems are Canon, Minolta and Pentax. For medium-format SLR users, there are examples from Mamiya and Pentax, whilst a new independent company has exploded on the scene with "Lensbabies" which can be adapted to fit most 35mm/digital SLR cameras. Although some of these specialist optics are very expensive and primarily for the domain of the studio portrait and advertising photographer, you can find some good alternatives in your kitchen cupboard or bedroom drawer to experiment with... all it takes is a little imagination and an acceptance of pictures that aren't as pin-sharp as you would normally expect them to be. As I hinted at the start... it's not necessary to join the so-called MTF Club... it may stop you taking the pictures you really like! 9:17:15 PM    comment []