Image quality is affected by filters depending on the quality of the filter and on the surface area of the filter.
The larger the surface area of the filter, the greater the reduction in image quality. (You can see this with a softening filter--when your lens is stopped down, the effective diameter and surface area of the filter are reduced. When the surface area goes down, the image quality goes up, and hence there is less of a "softening" effect from the softening filter at smaller apertures (large f numbers).)
A filter with twice the diameter has four times the area. Large filters are bad in this way.
But ultimately, it is due to the expense--the larger the filter, the more expensive it is to make one the same quality as a smaller filter.
In fact, achieving that same level of filter quality isn't enough because even at the same level of filter quality the image quality will still be worse because of the larger area.
« Last Edit: February 04, 2013, 01:39:12 PM by helpful »
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