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October 24, 2007
[ FILTERS – WHO NEEDS THEM? ]
A FEW WEEKS AGO we took a look in the well-equipped camera bag to see what gadgets the complete photographer carries around. We rated a polarising filter as one essential item.
Unfortunately we misdescribed (as George W would say) the operation of a polarising filter, suggesting that it consists of two glass elements that can be rotated in relation to each other. Mike points out that if you did that you would finish up with an opaque filter.
Mike is right and what we should have said is that the polarising filter is mounted in two rings and the ring carrying the glass rotates insides the fixed ring screwed into the lens.
Mike used to work in the camera retail business. He says that he always encouraged customers buying single lens reflex cameras to invest in a polarising filter – partly to increase the profit on the sale and mainly because he knew that once a person gets the hang of polarised light her skies will be bluer, her clouds more dramatic and her shiny surfaces, such as the water of a placid lake, will have more transparency.
Makers of digital cameras insist that we use a circular, not a linear, polarising filter. This doesn’t really have anything to do with the difference between film and digital, it is to do with the operation of auto-focus lenses. The older style of linear filters, while arguably giving a better reflected glare cutting effect, interfere with the auto-focus operation, and a circular polariser is designed to work with the newest lenses.
Compact camera users can benefit from a polarising filter if the camera lens mount has a filter thread, because the effect of the flter can be seen on the LCD screen.
There was also some correspondence with Bob, who writes: “One glaring omission to your list of essential gadgets would have to be a UV or Skylight filter for each lens. Having one permanently attached to each lens can save the front glass element from physical damage, which is cheap insurance. As well it will enhance your images by cutting down on excess UV light...”
We consulted an expert for advice. On the matter of lens protection Bob is right. And a good filter of a well known brand won’t harm the optical quality of the lens, although care needs to be taken with putting filters onto wide angle lenses because if the mount ring is thick it will show up in photos. And in some conditions even a good filter can cause flare, spots of fairy lights in the picture.
However, on the beneficial haze-cutting effect of the UV filter we were told there is none. UV filters are useful with film because film is naturally over-sensitive to light at the ultraviolet end of the spectrum. Digital sensors, on the other hand, are excessively sensitive to infrared light.
The best advice seems to be to use the lens cap for protection in the bag, and a hood when the lens is in use, which will cut flare and guard the front element of the lens against a knock. However, in some conditions – where’s there’s a lot of dust or wind-blown salt spray in the air – there is still a good case for a filter. Better to get muck on a cheap filter than an expensive lens.
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Posted by terry at October 24, 2007 10:55 PM
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